Revised report of findings, residual shear strength research, Horseleg Mountain, west Rome by-pass, Rome, Floyd County, Georgia / prepared for state of Georgia, Department of Transportation ; prepared by Willmer Engineerin

'REVISED REPORT OF FINDINGS RESIDUAL SHEAR STRENGTH RESEARCH
Horseleg Mountain West Rome By-Pass Rome, Floyd County, Georgia
WILLMER ENGINEERING INC. WEI Proj~ct No. ATL-171-2465
Prepared for STATE OF GEORGIA DEPARTMENT OF TRANSPORTATION
Atlanta, Georgia
Prepared By WILLMER ENGINEERING INC.
3772 Pleasantdale Road Suite 165
Atlanta, Georgia 30340 770-939-0089

WEi~ WlllMER ENGINEERING INC. ; ; ENVIRONMENTAL & GEOTECHNICAL

SERVICES

February 20, 2003

VIA U.S. MAIL

Ms. Georgene Malone Geary, P.E. State of Georgia Department of Transportation Office of Materials and Research 15 Kennedy Drive Forest Park, Georgia 30297

SUBJECT:

Revised Report of Findings - Residual Shear Strength Research Horseleg Mountain West Rome By-Pass Rome, Floyd County, Georgia Willmer Project No. ATL-171-2465

Dear Ms. Geary:

Willmer Engineering Inc. (Willmer) is pleased to present this revised report of residual shear strength testing on soil samples recovered during the Horseleg Mountain Slope Stability evaluation (Willmer Project No. 171-2171 D dated June 25, 2002) in Rome, Floyd County, Georgia. This testing work was performed in accordance with Willmer Proposal No. P02-318 dated September 6, 2002 and your' notice to proceed (NTP) dated September 9, 2002. Revisions have been made based on comments received from Georgia Department of' Transportation (GDOT).

Background
Willmer performed a slope stability analysis for a high 2H:1V proposed slope on the Horseleg Mountain route (report dated June 25, 2002). The overburden soils in the proposed cut area appear to be weathered from shale of the Middle Ordovician Age Murfreesboro Limestone Formation (OWM). Historically, GDOT has used unconsolidated-undrained (UU) triaxial shear strength test data to characterize soils strength for long-term slope stability analyses. Several of these tests were performed on select undisturbed samples obtained from the Horseleg Mountain geotechnical exploration. The stability analyses indicated the proposed 2H:1V slope was unsafe under earthquake loading conditions with residual shear strengths in the soils based on UU triaxial shear strength tests. A 3H:1V slope was safe with the exception of one loading condition.

3772 PLEASANTDALE RD . SUITE 165 ATLANTA, GA 30340-4270 (770) 939-0089 FAX (770) 939-4299

Revised Report of Findings - Residual Shear Strength Research Horseleg Mountain - West Rome By-Pass Willmer Project No. ATL-171-2465 Page 2
During subsequent discussion of the results with GOOT personnel, the use of UU strength data was discussed. Use of the UU data may lead to overestimating slope stability factors of safety. A literature search of shear strength for similar soils indicated that torsional shear testing may be more appropriate to represent shear strengths for clays derived from shales and mudstones, similar to .the subsurface conditions found in the Valley and Ridge Geologic Province of Northwest Georgia. Compelling evidence and interpretation have accumulated over the past three decades to suggest that residual shear conditions may also be present on part of the slip surface of first-time natural or excavated slope failures in stiff clays and clay shales. A torsional ring shear testing program was proposed to GOOT and approved.
Testing Program
Torsional ring shear tests were performed on five selected samples at the University of Illinois (U of I) at Champaign-Urbana under the direction of Professor Tim Stark. Professor Stark has conducted extensive research on residual shear strengths using the torsional ring shear device and has published considerable information on the subject. The tests were performed in accordance with ASTM 0 6467. A more descriptive narrative of the test procedure can be found in the United States Bureau of Reclamation Procedure for Performing Rotational Shear Testing of Soils, USBR 5730-89, Earth Manual, Part 2, 1990 (copy attached to this report).
The test procedure consists of air drying the soil sample, passing the soil through the No. 200 sieve to remove sand particles, then processing the minus No. 200 soil in a ball mill crusher. Water is added to the pulverized soil to form a paste with a consistency close to the liquid limit. The amount of water added to form this consistency varied with the plasticity of the material. This paste is allowed to "cure" in a humidity controlled room for about seven days so that all the soil particles become fully hydrated. The paste is then placed in the annular ringed groove of the test apparatus and a normal load is applied to consolidate the sample. After consolidation, the sample is sheared torsionally until a residual state of failure has been achieved. The next confining pressure is then applied and the sample allowed to consolidate again before shearing. Three confining pressures (100, 400, and 700 kPa) were used in all the tests for each soil sample. Photographs of test specimens and testing apparatus are included in the Appendix.
The Horseleg Mountain samples tested are summarized below and in the attached Table A of test results:

B-3 8-8 B-9 B-9 B-10

Environmental Exploration Sampler Shelby Tube Auger Cuttings Auger Cuttings Composite Auger Cuttings

A boring location plan and the boring logs for the materials selected above are attached for reference purposes in the Appendix.

Revised Report of Findings - Residual Shear Strength Research Horseleg Mountain - West Rome By-Pass Willmer Project No. ATL-171-2465 Page 3
Test Results
Results of the soil classification tests and the residual shear strength tests are summarized on the attached table. The individual stress strain curves are attached as part of the figures.
Predicted residual phi angles using the Stark and Eid (1994, copy attached) database and the test sample liquid limit and clay fraction percentage are shown in the table with the actual test data. The Stark and Eid (1994) database is based on 32-ring shear tests of clay stone, mudstone, and clay shale samples from the continental U".S., Alaska, England, Canada, and the Panama Canal where test sample liquid limits range from 28 to as high as 288 and clay size fractions from 10 to 88 percent. The Horseleg Mountain samples had liquid limits that range from 35 to 59 and clay size fractions from 22 to 71 percent. The results of the current tests are also plotted as a comparison with the 1994 data and are shown on Figure 1. The individual test results are shown on Figures 2 to 6."

Discussion of Test Results

Comparison of the Horseleg Mountain torsional ring shear test results to the values of secant residual friction angles predicted from the Stark and Eid plot of drained residual friction angle versus liquid limits do not indicate expected correlation (see Figure 1 and Table A). The friction angles for samples 8-3 at 104 to105 feet, 8-9 at 90 feet, and 8-9 at 110 feet were higher than predicted from their respective liquid limit and clay fraction values. However, the results from 8-8 at 40 to 42.5 feet and 8-10 at 60 to 70 feet were lower than predicted.

The lower correlation with the Stark and Eid chart may be explained by consideration of

difference in geology and material deposition. The chart is based on test results from around the

world on samples of marine deposited clay stones, clay shales, and mud stones, while Horseleg

Mountain samples are the product of varying degrees of weathering of Valley and Ridge

residual shale. Residual soils typically exhibit less weathering than marine deposited clay

shales; hence the clay minerals would not be as broken down, resulting in larger clay particles

and higher residual friction angles.

"

Further understanding can be provided by relative evaluation of the HorselegMountain data. In a typical weathering profile in the Valley and Ridge Province, weathering effects should decrease with depth. The shallower samples should exhibit more clay particles, hence lower friction angles. This trend is supported by the data. Samples 8-8 and 8-10 are more shallow in the weathered soil profile, exhibiting lower friction angles ranging from 9.4 to 11. Deeper samples produced friction angles ranging from 20.5 to 33.3. This trend is also supported by comparison of results of the two samples from 8-9. With the same liquid limit (35), and similar clay fractions, the friction angle is higher in the deeper sample, suggesting less weathering in the deeper sample.

Another phenomenon to consider is the activity of the clay defined as the ratio of the plasticity index (PI) and the percent clay fraction (CF). Research has shown that the higher the activity of the clay minerals, the lower the friction angles. 8-8 exhibited the highest activity (0.64) and the lowest friction angles, while 8-10 had the next highest activity (0.39) and slightly lower friction angles, as expected.

Revised Report of Findings - Residual Shear Strength Research Horseleg Mountain - West Rome By-Pass Will mer Project No. ATL-171-2465 Page 4

Comparing friction angles achieved versus those predicted from the Stark and Eid curves, the 8-10 (60 to 70 feet) sample is the only one with a MH Unified Soil Classification, suggesting more active clay particles than other samples. The percent clay is also highest at 71 percent. This sample could be a pocket of expansive clay. 8-8 (40 to 42.5 feet) has a higher activity value than 8-10, and it falls further below the predicted curves, as w~uld be expected.
Comparing 8-9 and 8-3 which plot above the predicted curves, the activity value is about the . same, but the 8-3 sample has almost twice the clay fraction in the test sample. Hence, 8-9
should be expected to have higher friction angles due to less weathering (less clay), as it does.
8-8 has a higher activity than 8-10, but this is somewhat compensated for by the higher clay fraction in 8-10 (71 percent) relating to more clay particles to influence the friction angles. This explains why 8-10 is further below the predicted curves than 8-8 is below its corresponding predicted curves. The 8-10 clay minerals may also be more platy, leading to lower friction angles.

Conclusions

The torsional ring shear test results presented in this study can form an initial database for GOOT to use when evaluating the long term stability of slopes in the northwest part of Georgia. As other projects develop, we suggest that additional testing be performed on critical projects to allow development of a new set of curves for residual soils weathered from Valley and Ridge shales and mudstones of Northwest Georgia and provide site-specific information for long term stability analysis.

If you have any questions, please contact the undersigned.

Sincerely,

WILLMER ENGINEERI INC.
cl1
Edmond Leo, P.E Senior Geotechnical Engineer

Zil~~r,~ Vice President/Principal Consultant

EUJLW: cld

Attachments 80ring Records Laboratory Test Data

c:

Mr. Tom Scruggs - GOOT

171-24estRopomIRevIsecI Residual Sheor RpI.doc

References

ASTM 06467-99, Standard Test Method for Torsional Ring Shear Test to Determine Drained Residual Shear Strength of Cohesive Soils

Lupini, J. F., Skinner, A. E., and Vaughan, P. R. (1981). liThe Drained Residual Strength of
Cohesive Soils", Geotechnique, 31, 181-213

Mesri, G. and Shahein, M. (2003), Residual Shear Strength Mobilized in First-Time Slope
Failures, J. Geotech. Geoenviron. Eng., 129 (1), 12-31

Mesri, G., and Cepeda-Diaz, A. F. (1986). "Residual Shear Strength of Clays and Shales." Geotechnique, 36, 269-274

Stark, TO., and Eid, H. T. (1992). "Comparison of Field and Laboratory Residual Strengths." Proc., ASCE Spec. Cont. On Stability and Performance of Slopes and Embankments-II, A 25-Year Perspective, Geotechnical, Special Publication No. 31, (1), 876-889.

Stark T. D., and Eid, H. T (1994). "Drained Residual Strength of Cohesive Soils." J. Geotech. Eng., 120(5),856-871.

Stark T D., and Eid, H. T. (1997). "Slope Stability Analyses in Stiff Fissured Clays." J. Geotech.

Geoenviron. Eng., 123(4),335-343.

.

Terzaghi, K., Peck, R. B., and Mesri, G. (1996). Soil Mechanics in Engineering Practice, 3rd
Ed., Wiley, New York, 129, 158-160.

United States Department of the Interior, Bureau of Reclamation, "USBR 5730-89 Procedures for Performing Rotational Shear Testing of Soils, Earth Manual (1990), Part 2, 724-736 .

Voight, B. (1973). "Correlation between Atterberg Plasticity Limits and Residual Shear Strength of Natural Soils." Geotechnique, 23, 265-267.

TABLES

Table A Summary of Test Results Residual Shear Strength Tests, Willmer Project No. 171-2465

8-3

104 -105

E2 Sampler

49 30 19

51

8-8

40-42.5

Shelby Tube

49 33 16

25

8-9

90

Auger Cutting 35 28 7

27

8-9

110

Auger Cutting 35 27 8

22

8-10 (Composite)

60nO

Auger Cutting 59 31 28

71

All tests performed in general accordance with ASTM 06467. Note: E2 Sampler - Environmental Exploration Large Diameter Sampler

0.37 0.64 0.26 . 0.36
0.39

9.4 -12.2 27.4 - 29.4 30.7 - 33.3

MH

9.7-11

20.5 - 22 24 - 25 24 - 25
12.5 -16

Table 8
Index properties

Boring
B-3 B-8 B-9 (90') B-9 (110') B-I0 (combined)

Liquid Limit
(%)
49 49 35 35 59

Plastic Limit
(%)
30 33 28 27 31

Plasticity Index
(%)
19 16 7 8 28

Clay-size fraction (% <21l) 51 25 27 22 71

Photos of sedimentation analyses after approximately two weeks

FIGURES

Drained Residual Friction Angle v. Liquid Lim it

-Q)
en

l36
32

.c 28

-.-c

..0

24

..U-.. tn

... LL

Q) Q)

20

as en

.- -::I Q) 16
'a C tn

...Q)
~

12

cuas

8

Q)

tn

4

0 0

Horseleg Mountain Samples
0810,60'-70'

l?, 83, 104'-105'

A 88,40'-42.5'

:1C 89, 90'

+89,110'

I

~J

I
I

~ I I I

40 80 120 160 200 240 280
Liquid Limit (%)

~ I 320

Effective normal stress of 100,400, and 700 kPa used.

Reference: Stark & Eid, 1994

DAN BY: ERL
CHK BY: a

DATE: 12117102 DATE: 12/17102

FIGURE I

WILLMER ENG INEERING INC. REsiDUAL SHEAR STRENGTH RESEARCH

a ENVIRONMENTAL GEOTECHNICAL SERVICES
3n2 PLEASANTDALE ROAD - SUITE 165
ATLANTA, GA 30340-4270

HORSB.EG MCUlTAIN ROME. FLOYD COlHrY. GEORGIA WEI PROJECT No. ATL-171-2465

Effective normal Residual shear Residual friction

.stress (kPa)

stress (kPa) angle (degrees)

100

52.7

27.8

400

175.1

23.6

700

262.1

20.5

Index Properties
Liquid Limit 49 % Plastic Limit 30 % Plasticity Index 29 % Clay Fraction 51 %

,..... 250

a..

'~
'-"

200

eewnn

0:::
eln-

150

0:::
w
e::nI:

100

50

_ _- d - _ - _ . L . . -_ _ _ _ O~-_--I.-_-_.l.....-

......b.~-~..L---

--L.-",,"-~

o

200

400

600

800

EFFECTIVE NORMAL STRESS (KPA)

DRAINED RESIDUAL FAILURE ENVELOPE FOR HORSELEG MOUNTAIN BORING B-3, DEPTH 104-105 FEET

DRN BY: ERL CHK BY: EL

DATE: 12116/02 DATE: 12/16/02

.

FIGURE 2

WILLMER ENG INEERING INC. RESIDUAL SHEAR STRENGTH RESEARCH

a ENVIRONMENTAl GEOTECHNiCAl SERVICES

HORSELEG MOUNTAIN

3772 PLEASANTDALE ROAD - SUITE 165

ROME, FLOYD COUNTY, GEORGIA

ATLANTA, GA 30340-4270

WEI PROJECT No. ATL-171-2465

300

- - ~

l

.... J. J.

250

-J.

..J....

----- -- 200

......
0...

(A --- = -....

-....

_lie:

\oj

~ 150 ~

e.~.n..

A~

a:

e~n 100

50 :.... ........ .... .... ....

....

J..
a
-....
....

..J.....

J..

J.

"'" A-'>.

---+- 100 kP
J. ~400kP
A-'>.
-A:-700 kP

--- - .. - _ .... .... ........ ............... .... .... .......

.... .-

o f 1---_.._-- .------. --.-,-'._."

o

5

10

-

15

20

_ . _ . _ - - - - , - - _....._'._----_.

25

30

35

SHEAR DISPLACEMENT (MM).
SHEAR STRESS-SHEAR DISPLACEMENT RELATIONSHIPS AFTER PRESHEARING FOR HORSELEG MOUNTAIN BORING B-3, DEPTH 104-105 FEET.

DRN BY: ERL CHK BY: EL

DATE: 12/16/02 DATE: 12/16/02

FIGURE 2A

WILLMER ENGINEERING INC. RESIDUAL SHEAR STRENGTH RESEARCH

ENVIRONMENTAL Ii GEOTECHNICAL SERVICES 3772 PLEASANTDALE ROAD - SUITE 165 ATLANTA, GA 30340-4270

HORSELEG MOUNTAIN ROME, FLOYD COUNTY,.GEORGIA
WEI PROJECT No. ATL-171-2465

Effective normal Residual shear Residual friction

stress (kPa)

stress (kPa) angle (degrees)

100

21.7

12.2

400

77.7

11.0

700

115.9

9.4

Index Properties
Liquid Limit 49 % Plastic Limit 33 %
\
Plasticity Index 16 % Clay Fraction 25 %

150 ..-----r----....------r"----.----r---.,...~--__r---...,

,......

a4...

"~
"-'"

100

eewnn

e.0..n:.:.

0::

w4
:::I:

50

(J)

o "--__---'-

-I.-

o

200

L...--_ _-.J..
400

...L-_ _---II..---_ _- ' -_ _- - '

600

800

EFFECTIVE NORMAL STRESS (KPA)

DRAINED RESIDUAL FAILURE ENVELOPE FOR HORSELEG MOUNTAIN BORING 8-8, DEPTH 40-42.5 FEET

DRN BY: ERL CHK BY: EL .

DATE: 12116/02 DATE: 12/16/02

FIGURE 3

WILLMER ENG INEERiNG INC. RESIDUAL SHEAR STRENGTH RESEARCH

ENVIRONMENTAL 6 GEOTECHNICAL SERVICES
~772 PlEASANTDALE ROAD - SUITE 165 ATLANTA, GA ~0340-4270

HORSELEG MOUNTAIN ROME, FLOYD COUNTY, GEORGIA
WEI PROJECT No. ATL-171-2465

140

120

t -All

A Al:.

100

,....
a.. 80
."..~.,"

rrawnn:: eln-

60

eaxwn:: 40

-~ --..
,
I

.... ....
--

.......

....... .......

-

-.-100 kPa

.......

...,.... ..A.. ___ 400 kPa

-&-700 kPa

-

- -- - - - .,.,

.,

20 ........
Ii
o o

........ ....... ................ ...
5

....

....

.::!:

------
10

....

....

15

--

...

20

25

I
i
i
I
i
_._----~
30

SHEAR DISPLACEMENT (MM)
SHEAR STRESS-SHEAR DISPLACEMENT RELATIONSHIPS AFTER PRESHEARING FOR HORSELEG MOUNTAIN BORING 8-8, DEPTH 40-42.5 FEET

DRN BY: ERL CHK BY: EL

DATE: 12/16/02 DATE: 12/16/02

FIGURE 3A

WILLMER ENGINEERING INC. RESIDUAL SHEAR STRENGTH RESEARCH

ENVIRONMENTAL a GEOTECHNIcAL. SERVICES
3712 PLEASANTDALE ROAD - SUITE 165
ATLANTA, GA 30340-.4270

HORSELEG MOUNTAIN
ROME, FLOYD COUNTY, GEORGIA
WEI PROJECT NO.ATL-171-2465

.J

-J

Effective normal Residual shear Residual friction

stress (kPa)

stress (kPa) angle (degrees)

100

56.3

29.4

400

216.2

28.4

700

363.3

27.4

Index Properties
Liquid Limit 35 % Plastic Limit 38 %
Plasticity Index 7 % Clay Fraction 27 %

425 r-----,----.,.------r-----r-----r--~.,__--__r--_.

375

,-....

IL

~
'-'"

300

neewnn:: e~n

225

nw:: eIn

150

75

_ _ O~

_L..

o

..L...__ ____L..
200

..L..._.._ __.L......:_.._ _....L.__ __..L.._ _~

400

600

800 .

EFFECTIVE NORMAL STRESS (KPA)

DRAINED RESIDUAL FAILURE ENVELOPE FOR HORSELEG MOUNTAIN BORING 8-9, DEPTH 90 FEET

DRN BY: ERL CHK BY: EL

DATE: 12/16/02 DATE: 12/16/02

FIGURE 4

WILLMER ENG INEERING INC. RESIDUAL SHEAR STRENGTH RESEARCH

ENVIRONMENTAL a. GEOTECHNICAl SERVICES
~772 PLEASANTDALE ROAD - SUITE 165
ATLANTA, GA ~034~270

HORSELEG MOUNTAIN
ROME. FLOYD COUNTY. GEORGIA
WEI PROJECT No. ATL-171-2465

400

350

r ..A.. .....

f

300

I

~

__ 250

<.:(

a..

lIl:::
'"e'n"
e.~n- 200
0:::
<.:(

;r-....
f---
t

.-...

w
e:nt:

150

-

-- --

..a
-.... ..,.....

....

.: ...

'""" ... -=

-.-100 kPa -s--400 kPa -b-700 kPa f-

-
"""

-....

-....

."'."....... -.... .-...

100

50 .L......... .. .......

.__.

~_.

.

~T

__=-T

_'_T

T

-~-_._----~-----------'

I

o V1f------------ "--_. -,-----.--.--- - - ._..-. _

o

5

'--'._'-

__. -.- -.. ---- -.- ~-._---- .._---------..-..--.-.-.~ ..--..- -

10

15

----,,-

----.. ---..--.. -- .. ----.,----.-.-.----~.-.--~--. ------ --

20

25

--- ._- -----.--~
30

SHEAR DISPLACEMENT (MM)
SHEAR STRESS-SHEAR DISPLACEMENT RELATIONSHIPS AFTER PRESHEARING FOR HORSELEG MOUNTAIN BORING 8-9, DEPTH 90 FEET

DRN BY: ERL CHK BY: EL

DATE: 12/16/02 DATE: 12/16/02

FIGURE 4A

WILLMER ENGINEERING INC. RESIDUAL SHEAR STRENGTH RESEARCH

ENVIRONMENTAL Ii GEOTECHNICAL SERViCES 3772 PLEASANTDALE ROAD - SUITE 165 ATLANTA, GA 30340-4270

HORSELEG MOUNTAIN
ROME, FLOYD COUNTY, GEORGIA
WEI PROJECT No. ATL-171-2465

Effective normal Residual shear Residual friction

stress (kPa)

stress. (kPa) angle (degrees)

100 400
700

65.7 247.7 416.1

33.3 31.8 30.7

Index Properties
Liquid Limit 35 % Plastic Limit 27 % Plasticity Index 8 % Clay Fraction 22 %

425

,,-....
.. ~ ..........
eewnn
~
Ie-n-
ew~ ::n:c

375 300 225 150
75

_ _ O ~ - _ - - - L . _ - _ . . . . b . . . . ~ _ . . . . . . . . l l -

.....L.._-_.&......._ _- I . . _ - _ - l -_ _----J

o

200

400

600

800

EFFECTIVE NORMAL STRESS (KPA)

DRAINED RESIDUAL FAILURE ENVELOPE FOR HORSELEG MOUNTAIN BORING 8-9, DEPTH 110 FEET

DRN BY: ERL CHK BY: EL

DATE: 12/16/02 DATE: 12/16/02

FIGURE 5

WILLMER ENG INEERING INC. RESIDUAL SHEAR STRENGTH RESEARCH

a ENVIRONMENTAL GEOTECHNICAL SERVICES
3772 PLEASANTDALE ROAD - SUITE 165
ATLANTA, GA 30340-4270

. HORSELEG MOUNTAIN ROME. FLOYD COUNTY, GEORGIA
WEI PROJECT No. ATL-171-2465

450

A

400

r/

-

350

,..... 300
a..
.lII::

I
I

';;; 250

.. -

ecw:n::
~
~:cwr:::: 200

7
. ~j

en 150

....J. -J..

100 kPa

III 400 kPa -

A 700 kPa

---

- -- - -- ....

.... ....

.... -.

-V

100 , - - - - - - - - - - - - - - - - . _ . _ - - - - - - - _ . _ - - - - - - - - - - - - - - _ . _ - - - - - - - - - - - - - - - - - - - -

1

.=--_._.-_ .. ..----.- --.----------------------------------'"'". - .........
50 J[::..----=~

--~------~--

....
- - - - - - - - - - - - _...._._------....;

o 1.11--------:-------------------- -- -'" -----..----------------------------------------.---.------..- - - - - . - ..--..--..------~

o

5

10

15

20

25

30

35

40

SHEAR DISPLACEMENT (MM)

SHEAR STRESS-SHEAR DISPLACEMENT RELATIONSHIPS AFTER PRESHEARING FOR HORSELEG MOUNTAIN BORING 8-9. DEPTH 110 FEET

DRN BY: ERL CHK BY: EL

DATE: 12116/02 DATE: 12/16/02

WILLMER ENGINEERING
ENVIRONMENTAL & GEOTECHNICAL SERVICES 3772 PlEASANTDALE ROAD - SUITE 165 ATLANTA, GA 30340-4270

INC.

FIGURE 5A
RESIDUAL SHEAR STRENGTH RESEARCH HORSELEG MOUNTAIN ROME, FLOYD COUNTY, GEORGIA
WEI PROJECT No. ATL-171-2465

Effective normal Residual shear Residual friction

stre.ss (kPa)

stress (kPa) angle (degrees)

100

19.4

11.0

400

73.9

10.5

700

119.5

9.7

125

,...... 100 a...
~
'-"
eewnn 75

0::
le-n

0w::

50

e::nI:

25

Index Properties
Liquid Limit 59 % Plastic Limit 31 % Plasticity Index 28 % Clay Fraction 71 %

o 200 400 600 800 O~---"'-----"'-----"'------'------'------'------'-------'
. EFFECTIVE NORMAL STRESS (KPA)
DRAINED RESIDUAL FAILURE ENVELOPE FOR HORSELEG MOUNTAIN BORING 8-10, DEPTH 60-70 FEET

DRN BY: ERL CHK BY: EL

DATE: 12/16/02 DATE: 12/16/02

WILLMER ENG INEERING
a ENVIRONMENTAl.. GEOTECHNICAL SERVICES
3772 PLEASANTDALE ROAD - SUITE 165
ATLANTA, GA 30340-4270

INC.

FIGURE 6
RESIDUAL SHEAR STRENGTH RESEARCH HORSELEG MOUNTAIN ROME, FLOYD COUNTY, GEORGIA
WEI PROJECT No. ATL-171-2465

140 -_.

120

AAA

J.
100

A

~

~

-

..>&

~

100 kPa

III

400 kPa
-

A- 700 kPa

-
D..

80

~

'-'

~.~
,

eenn

e~..n.. 60 k' ,

0:: .:ew:nI:

i

40



20

fL ....
,...~

-..... .-...

...-...

--

..:

"'"

"'"

....

...
~

o! 1~~-----_.. _---_---------.------.--------.-.---.---.-----------.----- -.---..-

o

5

10

15

20

SHEAR DISPLACEMENT (MM)

-.- --- ----j 25

SHEAR STRESS-SHEAR DISPLACEMENT RELATIONSHIPS AFTER PRESHEARING FOR HORSELEG MOUNTAIN BORING 8-10, DEPTH 60-70 FEET

DRN BY: ERL CHK BY: EL

DATE: 12/16/02 DATE: 12116/02

FIGURE 6A

WILLMER ENGINEERING INC. RESIDUAL SHEAR STRENGTH RESEARCH

e. ENVIRONMENTAL GEOTECHNICAL SERVICES

HORSELEG MOUNTAIN

3772 PLEASANTDALE ROAD - SUITE 165 ATLANTA, GA 30340-4270

ROME, FLOYD COUNTY, GEORGIA
WEI PROJECT No. ATL-171-2465

APPENDIX

BORING LOCATION PLANs/BoRINGS
WEI PROJECT No. 171-2171 D

SCALE: I~ = 100'

DRN BY:AMD CHK BY:.EL

DATE: 09/27/02 0 DATE: 09/27102

WILLMER ENG INEERING, INC.
eNlRONMENTAI.. s. GEOTECHNICAL. SERVICES
~m Pl.EASANTDALE ROAD - SUITE 165
ATLANTA." GA ~O

FIGURE I BORING LOCATION PLAN WEST ROME BV-PASS HORSELEG MOUNTAIN WEI PROJECT No. ATL-171-2465

ii2I WILlMER. ENGINEERING INCORPoaATED
ENV1RONMel'TAL GEOTECHNICAL SERV1CE5

Project: West Rome By-pass Location: Rome, Floyd County

HOLE No. B-3
Sheet 1 of 2

Project Number: ATL 171-21710

Location:

Azimuth:

Angle from Horizontal: 90

Surface Elevation: 810.00 Station: Sta 128+00, 390'Rt. of CL

Drilling Equipment: CME 550X

Drilling Method: HSA

Core Boxes:

Samples:

Overburden:

Rock:

Total Depth: 125.0

Logged By: Murthy Kotha

Date Logged: 5/21/02

UJ

..J::I:
01-
if=fifou
>

:t<!l
C ~.l..oJ
<!l

Cl. ~
I-
UJ ..J Cl.
:e:inE

:0>e :0>e
00
a: a0:

MATERIAL DESCRIPTION

1 --
5-

~ 10-

~ 15-

20-

~~ 25-

30-

35-

~~ 40-

1==
r--

SPT

~ 45- ;:;.:: SPT

~~ 50-

-=- SPT'

55-

E: SPT

60-

SH

- -\ RESIDUUM: Light Brown, Fine, Sandy,

ML

Claygy~ILT _ _ _ _ _ _ _ _ _ ~H

Hard to Very Stiff, Brown, Gray, Purple,

Silty CLAY

.

Boring Augered To 38.5 Feet Before Start of SPT Sampling

z
0
.~ ~ c 11
UJ..J UJ
810.0

.UJ

STANDARD PENETRATION TEST DATA (blows/foot)

:J
>..J

Z

10 20

40 60 80

805

800

i95

.790

785

780
775 .
770 765 760 755 750

..

.f

35 29

31

""\

26

~65-

SPT

70-

;:8: SPT

75-

:s:: SPT

745 740 735

8085

- - - - - - - - - - - - - SH
SPT

-

SPT

- - - f-Very Hard to Hard, Brown, Gray, Purple,

CL .

Black, Silty CLAY

730 725

90

SPT

720

95

SPT

715

32

31.

\
..I -r - r - 1-1. .. V"'v

31
36 83

54

V

36

100

SPT

NDI~T

710

"

51

105

SPT

110

115

SPT

705

J

49

700

695

..

37

120

SPT

690

37

125-

Boring Terminated @ 125 Feet Below

685

41

The Ground Surface'

No Groundwater Encountered @ The

Continued Next Page

SAMPLER TYPE

SS - Split Spoon

NX - Rock Core, 2-118'

ST - Shelby Tube

CU - Cuttings

..

:

-

,

NQ
...... ... ,.~_

--..-R..ock

Core,

1-7/8"

CT - Continuous Tube

DRILUNG METHOD

HSA Hollow Stem Auger

RW - Rotary Wash

CFA - Continuous Flight Augers

RC - Rock Core

,DC - Driving Casing

Hole No.
B-3

iifi(

W1LlMER. ENGINEElUNG
INCOIPOI.ATED ENVIRONMENTAl. .. CEO'nCHNICA!. 5ERVICES

Project: West Rome By-pass Location: Rome, Floyd County

-

HOLE No. B3

Sheet 2 of 2

Project Number: ATL 171-21710

Location:

UJ

...J :I: Q~
fi=fifou
>

Q
:Cc:l
~C.l...OJ
c:l

Cl.

~

;,g
0

UJ 0

...J Q

Cl. a:

~

;,g
0
0
a0:

CIJ

MATERIAL DESCRIPTION
(Continued)

z

0

UJ

~C" Q)
>.l!!
UJ...J

STANDARD PENETRATION TEST DATA (blows/foot)

::>
...J
> Z

UJ

10 20

40 60 80

Time of Boring

,

SAMPLER TYPE

SS Split Spoon

NX - Rock Core, 2-1/8"

ST - Shelby Tube

CU - Cuttings

NO - Rock Core, 1-7/8

CT - Continuous Tube

DRILLING METHOD

HSA - Hollow Stem Auger

RW - Rotary Wash

CFA - Continuous Flight Augers

RC - Rock Core

DC - Driving Casing

....'

_.

Hole No.
8-3

..... -..... _.-

Project: West Rome By-pass Location: Rome, Floyd County Project Number: ATL-171-2171D

W1LLMBt ENCiINEEIIINCi
INcoa'OIATED eNVIRONMENTAL. GEOTECHNICAL SERVlCI!ll
..

HOLE No. 8- 8
Sheet 1 of 1
Location:

Azimuth:

Angle from Horizontal: 90

Drilling Equipment: CME 550X

Surface Elevation: 691.00

Station: Sta 131+00,80' Rt of CL

Drilling Method: HSA

Core Boxes:

Samples:

Overburden:

Rock:

Total Depth: 75.0

Logged By: MK

Date Logged: 8/12102

w

2 t ..J J:
f- w
ffi Cl
>

'-' :Eo
0~... .0J 0

0>.-.
fW ..J
e:0:n.a.

:c:e
Cl
c'-:'

:c:e
Cl
c0:

MATERIAL DESCRIPTION

RESIDUUM: Light Brown, Fine, Sandy,

ML

5-

Clayey, SILT

10-~
15

- - - f- - - - f - - " - - - - - - - - - - - Very Stiff to Stiff, Tan, Brown, Medium to CL Fine Sandy, Silty, CLAY

z

0

w

j:

:

-:
Q)

w > .!-!!

STANDARD PENETRATION TEST DATA (blows/foot)

>.=.>J

.w.J

Z

10 20 40 60 80

6%198-

685-

680-

675-

20

670-

25

665-

30

660-

35

655-

40

SPT

ST


650-

26

45

645-

50

- - - -f- - - - - - - - - - - - - ---
Very Stiff to Stiff, Tan, Brown, Medium to CL

640-

55

Fine Sandy, Silty, CLAY (Highly Weathered Shale)

635-

60

630-

65

625-

70

",..,..,.

PARTIALLY WEATHERED ROCK:

PWR

620-

50/4

75

Samoled as Black . SHALE

Boring Terminated @ 75 Feet Below The

Ground Surface

No Groundwater Encountered @ The Time of Boring

SAMPLER TYPE

SS Split Spoon

NX~ Rock Core, 2-1/8'

ST - Shelby Tube

CU - Cuttings

....NQ Rock Core. 1-7/8'

CT - Continuous Tube

DRILLING METHOD

HSA- Hollow Stem Auger

RW - Rotary Wash

CFA - Continuous Flight Augers

RC - Rock Core

DC - Driving Casing

Hole No.
8-8

Project: West Rome By-pass

Location: Rome, Floyd County

Project Number: ATL17121710

Azimuth:

Angle from Horizontal: _ 90

Drilling Equipment: CME 550X

iii1 W1UMER ENGINEERING INCORPORATED
ENVlKONMENTAL ... CEOTECHNICAL SEIlVICES

-

-

HOLE No. 8-9
Sheef 1 of 1
;-
Location:

_ Surface Elevation: 744.00 Station: Sta 129+00, 220' Rt of CL

Drilling Method: HSA

Core Boxes:

Samples:

Overburden:

Rock:

Total Depth: 110.0

Logged By: MK

Date Logged: 8/14/02

S:2t ..J
od;

:c

fI-fioW

>

()
:I:<!l
0~...0J
<!l

wa.

>-

I- ?fi

W0

.a..J
<~

()
0:

?fi 0 0
0:

CfJ

MATERIAL DESCRIPTION

RESIDUUM: Brown, Fine Sandy, Clayey,

5-

SILT with some Rock Fragments

z
0
<w i >=~~Q-l
.w.J

w

STANDARD PENETRATION TEST DATA (blows/foot)

::l
<>..J
Z

ML 744.0

10 20 40 60 80

740-

10-

735-

15-

730-

20-

725-

25-

720-

30-

715-

35-

710-

40-

705-

45-

700-

- - 50-~ ~

-

%

55

60

SPT

ST

65

- - ~ Ve- ry- Ha- rd, - Tan- , B- row- n,- Gr- ay,- Fin- e ---C- L
Sandy, Silty, CLAY (Highly Weathered Shale)

695690685680-

""'0/3 I 100

70

SPT

675-

50/6

75

670-

80-

665-

85-

660-

90

SPT

655-

100

95

650-

%

100- %

645-

8 105

::L _ -

-

r-

-

-P-ART-IA-LLY-W-EA-TH-ER-ED-RO-CK-:

-

-

-PWR

640-

Sampled as Black, Gray, SHALE

110

Boring Terminated @ 110 Feet Below

635-

~0/5

The Ground Surface

No Groundwater Encountered @ The

,,

Time of Boring

J

SAMPLER TYPE

SS - Split Spoon

NX - Rock Core, 2"1/8'

ST - Shelby Tube

CU - Cuttings

NO Rock.9ore, 17/8"

CT - Continuous Tube

DRILUNG METHOD

HSA - Hollow Stem Auger

RW - Rotary Wash

CFA - Continuous Right Augers

RC - Rock Core

DC Driving Casing

Hole No.
8-9

iIi'ii W1LlMEIl. ENGINEERING INCOal"OIATED
ENVIRONMENTAL CEOTECHNICAL SERVICES

Project: West Rome By-pass Location: Rome, Floyd County

HOLE No. 8-10
Sheet 1 of 1

Project Number: ATL-171-2171D

Location:

Azimuth:

Angle from Horizontal: 90

Surface Elevation: 815.00 Station: Sta 129+00, 395' Rt of CL

Drilling Equipment: CME 550X

Drilling Method: HSA

Core Boxes:

Samples:

Overburden:

Rock:

Total Depth: 95.0

Logged By: MK

Date Logged: 8/12102

w

2 t ..J :r

()
I(!l

ff-fiow 0~.....0J

>

<!l

0..
>-
fW ...J 0..
::iE

:0:e
0
()
a:

;,!!"
0
aa0:

C/)

MATERIAL DESCRIPTION

RESIDUUM: Reddish Brown to Light

5-

Brown, Fine, Sandy, Clayey, SILT

z

0

i=

c
Q)

w > .S-1

STANDARD PENETRATION TEST DATA (blows/foot)

w :::>
>..J

w...J

Z

ML 815.0

10 20

40 60 80

810

10-

805

1520-

::S::SPT

800

795

I.

12

25-

790

30-

785

.35-

780

40-

n5

45-

no

50-

- - - - '-

IH- ard-to-V- ery- St- iff,- Br- ow~ n, - Gra- y,- Pu- rpl- e, --C- L 765

55

Silty, CLAY(Highly Weathered Shale)

760

60

755

65

750

70

745

75

740

1::; 80-

COT

PARTIALLY WEATHERED ROCK:

PWR

i35

81

~ 85-

Sampled as Black, Gray, Clayey, SHALE

730

=~ 90-

725

95

Boring Terminated @ 95 Feet Below The

720

Ground Surface

No Groundwater Encountered @ The Time of Boring

SAMPLER TYPE

SS Split Spoon

NX - Rock Core, 2-1/8"

ST - Shelby Tube

CU - Cuttings

NO - Rock Core, 1-7/8'

CT - Continuous Tube

DRILUNG METHOD

HSA Hollow Stem Auger

RW - Rotary Wash

CFA Continuous Right Augers

RC - Rock Core

DC Driving Casing

Hole No.
8-10

PHOTOGRAPHS

",

': ..~"

" ''

I,.

PROCEDURE FOR PERFORMING ROTATIONAL SHEAR TESTING OF SOILS

UNITED STATES DEPARTMENT OF THE INTERIOR
BUREAU OF RECLAMATION

PROCEDURE FOR

USBR 5730-89

PERFORMING "ROTATIONAL SHEAR TESTING OF SOILS

INTRODUCTION

This procedure is under the juriSdiction of the Geotechnical Services Branch, code D-3760, Research and Laboratory Services Division, Denver Office, Denver, Colorado. The procedure is issued under the fixed designation USBR 5730. The number immediately following the designadon indicates the year of acceptance or the year of last revision.

1. Scope

1. 1 This designation outlines the procedure for

determining the residual shear strength of clay and clay-
a shale using" rotational (torsional) shear apparatuS.

"1.2 Slurried specimens of soil which pass the No. 200.

(75 m.tIl) sieve should be used for this procedure.

1.3 Analyses of results from this test are made assum-

ing that no significant pore pressures develop during

application of shear stress. Therefore, it is essential that

test specimens be sheared slowly enough to allow dissi-

pationof excess pore pressure.

."

Thil procedure was written based on equipment used

in the Geotechnical Services Branch Laboratory at the

Denver Office. Although this- procedure may be applicable

for other devices, specific operating instructions, as

furnished by the manufaeturer, should be observed.

2. Auxiliary Tests
2.1 The test specimen used in this procedure is initially prepared as a slurry and is air~dried to a consistency such that the resulting soil, when placed in a liquid limit device, requires 30 to 35 drops of the liquid limit cup to close the groove for 1/2 inch (13 mm). Refer to USBR 5350 for guidelines on using the liquid limit device.

3. Applicable Documents

3.1 USER Procedures:

USBR 1000 Standards for Linear Measurement Devices

USBR 1008 Calibrating Linear Variable Differential

Transformers

USBR 1012 Calibrating Balances or Scales

USBR 1045 Calibrating Force Transducers (Load Cells)

USBR 3900 Standard Definitions of Terms and Symbols

Relating to Soil Mechanics

USBR 5300 Determining Moisture Content of Soil and

Rock by the Oven M e t h o d "

USBR 5320 Determining Specific Gravity of Soils

USBR 5330 Performing Gradation Analysis of Fines and

Sand Size Fraction of Soils, Including Hydrometer Analysis

USBR 5350 Determining the Liquid Limit of Soils by

. the One-Point Method

.

USBR 5360 Determining the Plastic Limit and Plasticity

Index of Soils

USBR 5365 Determining Shrinkage Limit and Shrinkage

Ratio of Soils

USBR 5700 Determining the One-Dimensional Consoli-

dation Properties of Soil (Incremental Stress)

3.2 ASTM Srandards:

D 422 Particle. Size Analysis ofSoils

.

D 4318 Liquid Limit, Plastic Limit, and Plasticity Index

of Soils

E 11 Specification for Wire-Oath Sieves for Testing

Purposes

4. Summary of Method
4.1 A ring-shaped specimen of slurried clay or clay shale is consolidated at a given normal stress and is sheared by rotation. The force resisting rotation is measured. This force and the normal stress are used to determine the residual shear strength of soil. The vertical displacement is measured to monitor- specimen volume change.
5. Significance and Use
5.1 Residual shear strength is a property of a clay that is used to evaluate the potential for progressive (gradual loss of strength) slope failure.
5.2 Residual shear strength represents the resistance to shear along a fully developed failure surface.
5.3 In some cases, the residual shear strength value rather than the laboratory peak strength value of a material is used for design of a strueture.
6. Terminology
6.1 DefinitionS are in accordance with U8BR 3900. 6.2 Terms not included in USBR 3900 specific to this designation are:
6.2.1 Nominal Shear Srress.-The shear stress computed using the cross-sectional area of the shear box.
"6.2.2 Residual Shear Srress, Tr.-The shear stress a material can sUstain while undergoing continuous deformation at a constant normal stress.
6.2.3 Residual Angle of Inrernsl Friction, q,r.-The
slope of the line relating nominal residual shear streSS to normal stress. expressed in degrees.

U.':S.tSK :> / jU
1

.......- 4
"'=----5
18

oo

15

~---~,,::1=9~..-:...-_~~--~r----""20

1. Data acquisition center 2. LVDTcore -3. LVDT body 4. Load cell 5. Large diameter nuts
6.. Top plate 7. Load cell thrust arm
8. Shearing unit turntable 9. Consolidation LVDT arm 10. Adjustable horizontal restraining arm

11. -Yoke adjustment screw 12. Top bar of loading yoke 13. Loading yoke 14. _ Loading yoke pivot 15. Lever loading arm 16. Load hanger 17. Masses 18. Gear change lever 19. .Control panel 20. - Beam jack
.: Figure 1. - Rotational shearing unit.

725

16 1 7 r--ll---,...",.....

USBR 5730

6.2.4 Residual Cohesion, cr.-The nominal shear

stress intercept at zero normal stress of a line relating

aominal residual shear stress to normal stress, expressed

inlbf/in2;

.

6.2.5 Residual Srrength Scate.-The state of a soil

<'lhen the shear stress has decreased to a constant value

and is independent of displacement under a given normal

stress.

6.2.6 Couple.-A pair of equal, parallel forces acting

in opposite direCtions and tending to produce rotation.

6.2.7 Couple Distance.-The perpendicular distance

between the forces of a. couple. o

6.2.8 Seating Pressure.-A pressure, usually about

1./2 to 2 lbf/in2 (2 to 7 kPa), placed on a specimen to

firmly seat all parts of the testing apparatuS.

7. ApparatuS

7.1 General Appararus:

7. Lo l Balance or Sca1e.-Typical balances or scales

used for this designation are:

AppJieaoon

Reada.ble to Approximate eapadry

Moismre concent..

0.1 g

1000 g

Initial dry unit weight

1g

4000 g

7.1.2 Stirring Appararus .":El~Ctric .lnixing maChine with a special dispersion cup conforming to the requirementS of ASTM D 422.
7.1.3 Liqw'c/ Limit Devke.-Casagrande type, with a groving tool conforming to the requirements of ASTM
"D4318.
7.1.4 Sleve.-US.A. Standard series No. 200 (75 mm) sieve conforming to the requiremehts of ASTM E 11.
7.1.5 Force Measuring Devkes.-Load cells, used to
measure normal forces or couple forces, must be accurate to at least 0.25 percent of full scale.
7.1.6 Automatk DatB Acqw'sition and Reduction
System.-Any automatic data acquisition and/or reduction
must be performed using a system (computer) capable of maintaining the accuracy of the measuring device(s).
7.1.7 Time Measurement.-Timing devices readable to 1 second are to be used to measured elapsed time.
7.1.8 Miscellaneous EquJpment.",:,Equipment for
remolding the specimens, including distilled water. spatula,
grooving tools, knives, and straightedge. 7.2 Eqw'pment Unique to This Procedu.i:e: 7.2.1 Shearing Unit.-The shearing unit (fig. 1)
consists of a turntable (fig. 2, part 1), lower platen (fig. 2, part 2), inner confining disk (fig. 2, part 5), outer
confining ring (fig. 2, part 4), upper platen (fig. 3, part
3), thrust bearing (fig. 3,part 6); moment transfer plate (fig. 3, part 4), and top plate (fig. 4, part 3).
7.2.1.1 The soil specimen is sheared by_ rot~ting the turntable which is attached to the lower platen. The upper platen and moment transfer plate are held fixed.
The moment transfer plate contains a thrust bearing (fig:
3, part 6) which allows the wings of the moment transfer
plate to activate two load cells (fig. 4. part 4). The load
cells are clamped in place by carefully tightening large diameter nuts (fig. 4, .parr 5). The top Jilateis prevented

Degrees per minute

A

60.0 45.0 30.0 20.0 15.0

B

12.0

9.00 6.00 4.00 3.00

C

2.40 1.80 1.20 0.800 0.600

D

.0.480 0.360 0.240 0.160 0.120

E

0.096 0.072 0.048 0.0~2 0.024

~;~5

I

I

I,

II

I I

,

2

I

I

.: 3~->t~~i

4

I

I

I

I

I

I

2

1

1. . Shearing unit turntable with Plexiglas colIar in place
2. Lower platen 3. Porous disk 4. Outer confining disk 5. Inner confining disk '6. Height adjustment .screws
Figure 2. - Exploded view of shearing unit.
7.2.4 VertiaIl Deformation Measure.ment.-Changes in height of the specimen are determined using a dial gage or LVDT (linear variable differential transducer), accurate to 0.001 inch (0.025 mm).
8. Reagents and Materials
8.1 Distilled water is to be used whenever .water is required in this procedure.
9. Precautions
9.1 TechniaIlprecautions.-Unless the porous disks are
.cleaned frequently they may become clogged by soil particles and impede water flow into or our the specimen.
10. Sampling, Test Specimens, and Test Units
.10.1 Specimen Preparation: 10.1.1 Put about 500 mL of distilled water in a
porcelain dish.

1. Shearing unit turntable 2. Oamp nuts for securing lower platen 3. Upper platen with porous disk 4. Moment transfer plate 5. Thrust plate 6. Thrust bearing
Figure 3. - Exploded view of moment transfer plare.
10.1.2 Mix 300 to500 grams of soil into the distilled water, and let the soil-water mixture stand for a minimum of 24 hours.
10.1.3 Place the mixture of soil and water in the special dispersion cup of the stirring device (ASTM D 422).
10.1.4 Stir the mixture for 10 minutes. Attach a No. 200 (75 mm) sieve to a pan and pour the slurry through the sieve.
10.1.5 Air-dry the minus No. 200 sieve size material' retained in the pan so that the resulting soil, when placed in the liquid limit device (USBR 5350), requires 30 to 35 drops of the liquid limit cup to close the groove cut by the grooving tool for a distance of 1/2 inch (13 mm).
10.2 Specimen Placement: 10.2.1 Measure and record to the nearest 0.001 inch
the inner' diameter of the outer cQnfining. ring and the outer diameter of the inner coiJfining disk (fig. 7). These measurements are the outer and inner diameters of the specimen, respectively. Measure and record to the neareSt 0.001 inch the couple distance (distance between the load cells). Determine and record the mass of the top plate to the nearest O.llbm.

727"

USBR 5730

1. Shearing unit turntable 2. Moment transfer plate . 3. Top plate 4. Load cell 5. Large diameter nut
Figure 4. - Top plate placement ont~ the sh.earing unit turntable.

Figure 6. - The gears can be changed and the gear lever (top of picture) can be moved to produce several different roration mces.

1. Shearing unit turntable 2.. Top plate
3. Load cell 4. Adjustable horizontal
restraining arm 5. Loading yoke

6. Top bar of loading yoke 7. Yoke adjustment screw 8. Horizontal suPPOrt screw 9. Consolidation LVDT arm 10. LVDT

Figure 5. - Assembled shearing appararas.

10.2.2 Adjust the height of the inner confining disk

three to 0.190 inch (4.83 mm) above the porous disk in the

lower platen by turning the

horIzontal screws so

the three Teflon legs move in or out as required (fig. 8).

This adjustment determines the specimen thickness.

Figure 7. - The outer conftning ring, lower plateD, and inner confining disk from left to dght.
10.2.3 Adjust the height of the outer confining ring (fig. 9) to 0.130 inch (3.30 rom) above the porous disk in the lower platen by moving the three beveled horizontal screws (the three support pins that support the outer confining ring rest on the horizontal beveled screws) in the turntable in or out as required.
10.2.4 Moisten the porous disk in the lower platen with distilled water.
10.2.5 Place the specimen (as prepared in .subpar. 10.1) in the space between the inner confining disk and the outer confining ring (fig. 10). To place the specimen,
it is best to use a flexible instrument, suCh asa spatula,

Figure 8. - Height of the inner ccinfining disk is controlled by turning the three screws in it.

that will fit between the disk and ring. Special care must

be taken to ensure that voids do not exist anywhere in

the specimen.

10.2.6 Level the top ,surface of the specimen with

a stiff straightedge (fig. 11) using the top of the outer

confining ring as a guide.

10.2.7 Oean the surface of the outer confining ring

(fig. 12).

'

10.2.8 Oean the top of the inner confining disk while

being careful not to disturb the specimen.

10.2.9 Remove the three screws from the inner

confining disk.

11. Calibration and Standardization
iu Verify that equipment is currendy calibrated in
acc:ordance with the applicable calibration procedure. If the calibration is not current, perform the calibration before usiDg the equipment for this procedure. USBR 1000 Standards for Linear Measurement Devices USBR 1008 Calibrating Linear Variable Differential Transformers USBR 1012 CalibratingBalances or Scales USBR 1040 Calibrating Pressure Gauges USBR 1045 Calibrating FO,rce Transducers (Load Cells)
11.2 Cahbrate the normal loading device annually by loading a cahbrated load cell placed in the shear box.
11.2.1 If a lever loading yoke is used, the vertical force recorded by the load cell is:

Figure 9. - The height of the outer confining ring is controlled by three screws in the lower platen, The heads of twO (arrows) are visible in this view,

W = Cnm+mp

(1)

where:

W = vertical force; lbf (assume 1 Ibm = lIb)

C. =,.lever loading arm constant, usually 10.0*

I11 = hanger mass, Ibm

Inp '= top plate mass, ibm

.. If C. is not equal to 10.0, calculate a new constant

byth' e

relat'lon

r.....W , =

-

m m

p

a

fter

ensurm. g

that

th'e

load cell is properly calibrated.

11.2.2 If a pneumatic loading device is used, W'is, '

the vertical force which correspon<is 'to the reading'(>n

a calibrated pressure gauge:(fig. 13).

'.

11.2.2.1 If the force recorded by the load cell does

not equal the force determined by the pressure gauge plus

the tOP plate mass then either the load cell or the pressure

gauge, or both, may need recalibratiotL

12. Preparation of Apparatus

12.1 .Set the apparatus to the spe.cified turntable rotation rate by using the appropriate gears and gear lever position (table 1).
12.2 Place the Plexiglas collar in position and push it down over the O-ring in the turntable.

-729

USBR 5730

Figure 10. - Notehed spatula used to place specimen.

Figure 11.- A stiff straightedge (putty knife) may be used co level the

surface of the specimen.

12.3 Place the .lower plat~n containing the soil speci-

men over the lubricated centering pin. (A small amoUi1t' ......,

.of lightweight oil is sufficient for luPrication.) .Fix the

turntable in place by tightening the" nuts on the clamp ......

screws (fig. 14).

12.4 Moisten the porous disk. contained in the upper

platen with distilled water. Car~fully place the upper platen (fig. 15) and the moment t~a:nsferplate (containing the

thrust bearing) on the spead1en (fig. 16). Place the thrust

plate over the thrust bearwgs.

~

12.5 Align the-wings' of the momem/transfer plate

parallel to the horizo~ restraining arms.

12.6 Slide' the tOP plate mto position -over the wings

of the moment ttllt.nsfer plate so that the top plate is seated on the thrust b~'ring of the moment transfer plate and

the pointer 9.n/the moment transfer plate lines up with

. the line engi-aved in the top plate. Adjust the horizontal

restrainiiig arms to hold the top plate in position.

12.7 Swing the loading yoke (fig. 5, part 5) into position

and ensure that the top bar (fig. 5, part 6) of the loading

yoke is level. It can be leveled by adjusting the nuts at

the base of the loading yoke.

-

12.8 Place a seating stress on the specimen by placing

0a ; I-leIbssmthpalante10o nIbtfh/einl2oaisd

hanger unless required, then

a normal stress place a D.1-Ibm

plate on the hanger.

I ....

.. 12.9 Adjust the.load cells in the top plate so that both are 'jUSt tOllcbingthe. moment transfe~ plate. wings.

Figure 12 - The surface of the OUter confming ring being cleaned with .

. a moistened cottOn swab.

-,

USBR 5730

20.,...------------------..,-'-----------, Equation of best filline: y = -0.0378 + 0.0357x

Machine No. 10 Conbpi No. 501GR2000

Specimen Aree 3.18 in2

Hebu Mass 10.2 Ibm

I 15
QD
.5
'0 ttl
QJ
0:: 10

til

C

"E
:2
~ ~

ticl
;
".I

::G;

c

."
~
+
~ a :ll
~

til C

.=:0 ~
',~"

", S- o
:2 ~ ~

~ aD
:C:=:

~

."

~

..Gs ..~ .~.

QJ QD ;:::l (tl
~
.Q.J. 5
;ee::nn:l
.Q..)
0..

10.2 3.2 0

102.6 32.3 1

190.1 59.6 2

276.6 67.6 3

355.7 111.9 4

442.7 139.2 5

529.6 166.6 6

616.5 194.5 7

705.1 221.7 6

790.4 246.6 9

862.5 277.5 10

969.3 304.8 11

1055.2 331.6 12

1145.0 360.4 13

1228.3 386.3 14

50

100

150

200

250

300 350

400

450

1310.5 412.1 15
500 1400.5 440.5 16

1488.9 498.2 17

Load - Ibf/in2

Figure 13. - Calibration of pneumatic loading device - example.

Figure 14. - Lower plaren secured by clamp nurs (nurs to the left and

righr of the ouret confining ring).

.

12.10 Tighten the large diameter nuts on the load cell bolts, ensuring that load is not imposed on the load cells and that they are fixed in position.
12.10.1 If normal stresses are to be monitored, place 'a load cell in the recess in the top of the top plate.
12.11. Turn the yoke adjustment screw (fig. 5, part 7) until it is tight against the recessed nut (or load cell) in the. top plate and the lever loading arm (fig. 1, part 15) is approximately level. ' .. 12.12 Ensure that the beam jack (fig. 1, part 20) is
far enough away from the lever arm so that as the specimen

: Figure 15. - Upper platen in place over. rhe soil specimen.

consolidates, the lever arm will not come in contact with

the beam jack.

..

12.13 Mount an LVDT or dial gauge so that it bears

on the yoke adjustment screw (fig. 5, part 7) and adjust

it so an initial reading is obtained.

NOTE l.-H a computer is used to read LVDT values, execute the necessary keystrokes to display the LVDT values and posicion the LVDT body so that a zero reading is obtained.

12.i4 Read and record the specimen height on the .''Direct Shear Testing Specimen Information" form (fig. 17,

731

USBR 5730

Figure 16. - Moment transfer plate parlillel to horizontal resrrainingarms.

data sheet 1). This may be performed manually or with the computer.

NOTE. 2.-If a computer is used., initialize it. This entails ensuring that the storage registers are empey. If they are not,
old data should be pu;-ged. However, make sure a permanent copy of the old data is available before purging.

12.15 Remove the screws in the .Plexiglas reservoir. Insert a screwdriver through a hole and turn a horizontal
support screw (fig. 5, part 8) about one-fourth turn so that. the outer confining ring (fig. 2,part 4) is in its
uppermost position (fig. 18). Repeat the process for all the horizontal support screws. Replace the screws. .
12.16 Fill the Plexiglas reservoir with distilled water and keep it full for the remainder of the procedure.

NOTE 3.-If a computer is uSed, execute the necessary keystrokes to enter specimen physical properties and other specimen data as required.

13. Conditioning

13.1 Prior to testing, the sample is to be 'st9r~~ to prevent contamination with (a) other matter, (b) loss of
. soil, (c) loss of moisture, or (d) loss of identification.

14. Procedure

14.1 All data are to be recorded on the "Direct Shear

Testing (Rotational Shear)" form (fig.. 19, data sheet 2b).

14.2 Consolidation:

.

14.2.1 Calculate, record, and place the required mass

on the load hanger to apply the specified normal stress

on the specimen. If a pneumatic loading device is used,

increase the pressure to the appropriate gauge reading.

Always start wi~ the lowest stress and proceed to the

highest.

14.2.2 .Allow the specimen to drain and consolidate

until a well~defined stage of secondary consolidation has

been established. A computer can be used co automatically

indicate and record time and vertical displacement readings;

otherwise, observe readings and record by hand on the

"Direct Shear Testing (Rotational Shear)" form (fig. 19,

data sheet 2b). .

14.2.2.1 Refer to USBR 5700 for guidelines on

determining stages of primary consolidation and secondary

consolidation. Figure 20 shows a plot of vertical displace-

ment versus square root of time that is one plot that may

be used to determine the end of primary consolidation.

14.3 Shearing: .

14.3.1 Initialize the computer if it is to be used to

.take consolidation readings (see note 2).

14.3.2 Start the apparatus so that shearing begins.

14.3.3 Begin taking readings either manually

(fig. 19) or automatically if a computer is used. Record

the reading number, date, time, vertical displacement, and

load cell readings.

.

14.3.4 As shearing proceeds, the nominal shear

stress versus the average rotational displacement (%)

relationship should be determined and plotted (fig. 21).

14.3.4.1 Compute and record on data sheet 2b the

elapsed time, the average rotational displacement (%), the

average force, the moment, and the nominal shear stress.

. 14.3.4.2 When the slope of the line defining

nominal shear stress versus average rotational displacement

(%) is fairly horizontal, sufficient displacement has

occurred to form a fully developed failure surface; the soil

is in the residual state.

.14.3.5 After the soil is in the residual state. or as'

instruCted by the responsible engineer, stop shearing the'

specimen.

14.3.6 Apply the next required normal stress.

14.3.7 . Repeat the' consolidation and shearing pro-

cedures (subpars. 14.2 and 14.3) for each required normal

stress..

14.4 Conduding the Test Program:

. 14.4.1 Turn off the motor after the specified normal

stresses have been applied and all readings have been

recorded. .

....

14.4.2 Remove the normal stress from the specimen. 14.4.3 Dismantle the shearing apparatus andunless otherwise instructed-discard the soil specimen. 14.4.4 Thoroughly clean all surfaces that came into contact with the test -specimen. ..

15. ~a1cu1ations

15;1 Required calculations follow. . 15.1.1 The normal stress, Un, acting on the ring shaped specimen is calculated.
(2)
where:
Un = normal stress, lbfjin2 W = normal force, lbf (Add the mass of the hanger.
the mass on the hanger, the mass of the tOP

7.2356 (8.86) Bureau of Reclamation

DIRECT SHEAR TESTING - DATA SHEET 1 SPECIMEN INFORMATION

Designation USBR .2nQ:.!l2.

SAMPL.E NO. DRIL.L. HOL.E

Example DH-143

PROJECT Example
LOCATION

FEATURE Example DEPTH 3.8- 5.8

[KJ It 0 m

TEST TYPE:

0 DIRECT SHEAR

0 REPEATED DIRECT SHEAR

fK1 ROTATIONAL. SHEAR

TESTED BY

DATE

COMPUTED BY

DATE _ _ _ CHECKED BY

DATE _ _ _

SPECIMEN DATA

SPECIMEN NO. Example

SPECIMEN TYPE:

0 COMPACTED 0 _LJNDISTURBED 1XI SLURRIED

SPECIMEN DIMENSIONS 2.794<0.01 1.948 { tOJ IXIln Dmm

SLIDING SURFACE:

0 INTACT 0 PRECUT
f&J OTHER SLURRY

SOIL CLASSIFICATION SYMBOL PERCENT GRAVEL PERCENT SAND PERCENT FINES

CL 0
100

LIQUID LIMIT

36

('Ko)

PLASTICITY INDEX 16

1'Ko)

SPECIFIC GRAVITY 2.67

SOl L. CONSISTENCY (NO. OF BLOWS) 26

MOISTURE CONTENT DETERMINATION

INITIAL (TRIMMINGS)

CONTAINER NO.

MASS OF CONTAINER AND WET SPECIMEN

g

MASS OF CONTAINER AND ORY SPECIMEN

g

MASS OF CONTAINER

g

MASS OF WATER

g

MASS OF DRY SPECIMEN

g

MOISTURE CONTENT

'l(,

INITIAL DRY UNIT WEIGHT DETERMINATION

MASS OF SHEAR BOX + COVER PLATES MASS OF SHEAR BOX + COVER PLATES + WET SOl L MASS OF WET SOIL MASS OF DRY SOILa (MASS OF WET SOl Ll/ll + INITIAL MOISTURE CONTENTI100) INSIDE AREA OF SHEAR BOX HEIGHT OF SPECIMEN VOLUME - (AREA x HEIGHT OF SPECIMEN) INITIAL DRY UNIT WEIGHT a IC x MASS OF DRY 'SOI LNOLUME)
"For SI metric application, C- .009B07, wl1lch converts g/mm3 to kN/m3 For Inch-l3ound application, C-3 .81 0, which converts g/ln3 to IbfJtt3.

FINAL. (SPEC.)

g g g g g
'l(,

g
g
g
g
0 mm2
0 mm '0 mm3 0 kN/m3

-.-
0 ln2 0 In 0 1,,3
0 Ibf/tt3

REMARKS: SLURRY SPEelMAN TAKEN FROM DIRECT SHEAR TRIMMINGS.

-

Figure 17. - Direct shearresting - data sheet 1 - specimen information - example.
733

USBR 5730

where:
= Ad average rotational displacement, % = Adr angular displacement rate, cis
r = elapsed time, s F = factor to convert from degrees to radians, equals
( 1r/180)C
-n-+2r2- = average radius af soil speCl.ffien, 1.0

+ (d1
1r .

2d2)

--

average

o.rcumference

0

f

soil

speo.men,

.
10

100 = convert from decimal to percent

16. Report

Figure 18: - Turning the horizontal suppOrt screws eo center the oueer . confining ring on the specimen.

plate and convert the total to force by

changing Ibm to lbf, assume 1 Ibm = llbf.)

1"2 = outside radius of specimen, in

rl = inside radius of specimen, in

= 1r 3.14 .

(r; - 1r

r~) = area of specimen, in2

. 15.1.2 The residual. shear. stress, Tr, acting on the

ring-shaped specimen when the soil is in the residual state

is calculated.

3M

(3)

where:
= Tr .residual shear stress, lbf/in2
M = moment aCting on the specimen
= M o d(fl; 12) , in-lbf
= d couple distance, in 00
fl, 12 = forces of a couple, lbf

15.1.3 The residual angle of internal. friction, r, is 0
determined from. the slope of the best-fit line relating residual shear stress to normal stress. It can also be determined for specific values of residual shear stress and normal stress.

.A.,...,r = tan-1 ( -Tr)

(4)

. aD

o where:
= r = Tr = aD

residual. angle of internal friction, degree residual shear stress, lbf/in2 normal stress, lbfjin2

= tan-1 arc tangent

15.1.4 The residual cohesion, Cr (lbfjin2), is the shear Stress intercept of thehest-fit 'line relating residual shear Stress to normal stress (figs. 22 and 23).

16.1 Typical resultS are shown on figures 17, and 19

through 23.

16.2 The report is to include the following:

Machine number and tOP plate mass of apparatUS

(fig. 19).

Identification and description of the sample (fig. 17).

Initial height and area of the specimen (fig. 19).

Normal stress on the specimen (fig. 19).

Perpendicular couple distance (fig. 19).

Soil. consistency, expressed as number of blows

(fig. 19).

.

All basic test data including displacements, normal.

and shear loads, and specimen thickness changes (fig.

17 and 19).

Vertical displacement verus square root of time

(fig. 20).

Ploc' of nominal shear stress versus average rotational

displacement (%) (fig. 21).

.0 Plot of residual shear stress versus normal stress,

and the corresponding residual angle of internal friction

and residual cohesion (figs. 22 and 23).

16.3 Any abnormalities, such as loss of material,

"gritty" soil texture, etc., are to be documented (fig 17).

16.4 Any departures from the procedure shall be

documented (fig. 17 or an attached sheet).

16.5 All data are to show a checkmark and all plotting

must be checked.

NOI'E 4.-Informacion concerning the computer program and instructions for its use are available from the Denver Office Soil
and Rock Testing Section, Code D-3761.

17. 0 Background References

La Gatta, D. P., Residual Strength of Clsy a.nd Clsy-Shales 0 byRotation Shear Tests, Contract RePOrt 5-70-5, U.S: Army Corps of Engineers Waterways Experiment Station,
Vicksburg, Mississippi,]une 1970.

Townsend, Frank c., and Paul A. Gilbert, Eng.w.eer.w.g

Properties of Clsy Shales, Report 2: Residual Shear

.....

"

." _ . " ...~ __ .'fT'_ :1

.... L ".r__ C'L..-.I_,..T.T ~

1.unAUO..61 Burna of RedalDlUoa

I

DIRECT SHEAR TESTING DATA SHEET 2b ROTATiONAL SHEAR

ID'''....II USSR "'O-ft9

BA....LE NO. Example

SPECIMEN NO Example

'NITlAl SPECIMEN HEIGHT 0.130

OOInOmm

LOAD CELL FACTOR

I

' Ibl/V

MACHINE NO.

I

NOMINAL NORMAL STRESS

25.0

SPEC,MEN OIMENSIO~ 10.OJ 2..794

oo'n Oem

LVOTFACTOR

I

00 0 In/V mm/V

00 0 Ib'lln2

kP.

TOP PLATE MASS 9.3

11.0.1 1.948 COUPLE DisTANCE 4.32.7

OOInOcm OO .. Omm

00_ 0"" SOIL CONSISTENCY INa. 01 blowd~

SPECIMEN AREA 3.151

00, O,m'

ROTATIONAL RATE 0.00028 det/mln

TUTEDBY

Ae"DING NO.

DATE.

...

I 8/31 II

TIMe mIn
40

.
27'

DATE

COMPUTED BY

ELAPSED TIUe min

AVERAGE ROTATION DISPLACEMENT
"

VERTICAL DISPLACEMENT

READING

DISPLACEMEtlT

V

00 .. Omm

O'

0.00

0.0126

0.012!i

DATe

CHECKED BY

DATE

frlORMA\. FORC&

nEADING

FoRce

V

00 lb' ON

READING 1 V

SHEAR FORCE

FORCE 1

READING 2

PORCE 2

"H,\1~gc

MOMENT

NOMIN ....t SHeAR STRESS

OO'bl D ..

V

00 0 00 0 ,P. OO'bl ON lZl'b' ON

In_lbl

mm-N

Ibflln'

78.B

7B.B

13.2.

13.2

13.4

13.4

13.3

57.55

15.25

2' 'B/31 14 41 10' 3 8/31 17 41 10

IB07 360.7

0.01 0.03

0.Oi28 0.0124

0.0128 0.0124

78.8 7B.B

78.8 78.B

12.5

12.5

12.0

12.0

14.0

14.0

13.3

13.9

13.9

13.0

57.33 5603

15.19 14.B4

4 B/31 2.0 41 10 5 BI3I 2.3 41 10

540.7 72.07

0.04 0.06

O.OIlB 0.0114

O.OIlB 0.0114

7B.8

7B.8

11.9

11.9

14.1

14.1

13.0

5625

7B.B 78.B

11.7

11.7

13.9

13.9

12.8

55.39

14.90 14.67

6 9/1 02. 42. 10

901.7

0.07

7 9/1 05 42 \I 8 9/1 08 42. 41

IOBI.7 1262.2

O.OB 0.10

9 9/1 II 42 41

1442.2

0.11

10 9/1 14 42. 41

1622.2

0.13

II 9/1 17 42 41

IB02. 2.

0.\4

12 9/1 20 42 41

1982.2

0.15

13 9/1 23 42 41

2162..2.

0.17

14 9/2 02 43 \I

2342.7

0.18

15 9/2 05 43 II

252.2.7

0.2.0

16 9/2 08 43 II

2702..7

0.21

17 9/2 II 43 42 2883.3

0.22

IB 9/2 14 43 42 3063.3

0.24

19 9/2 17 43 42 3243.3

025

20 9/2 20 43 42 3423.3
tdulUpty Ihar ar-. bot 108 10 CDn'ftft NImrn2 to kh .
REMARKS: CONSOLIDATION DATA NOT SHOWN

0.27

0.0112 09111 0.0113 0.0114 00119 0.0122 0.0129 0.0130 0.0135 0.0166 0.0170
0.0186 0.0190 0.019B 0.0196

0.0112 0.0111 0.0113 0.0114 0.0119 0.0122 0.012.9 0.0130 0.0135 0.0166 0.0170 0.0186
0.0190 0.0198 0.0196

7B.B 7B.8 78.8 7B.8 7B.B 78.B 7B.8 7B.8 . 7B.8 78.8 788 78.E! 78.8 78B 78.8

78.B 78.B 78.8 78.B 7B.B 7B.8 78.8 7B.8 78.B 7B.8 7B.8 78.8 78.8 7B.8
7B.8

Il7 11.2 11.8 12.0 12.2 12.2 12.2 12.2 12..5 13.2. 13.2 13.3 134 13.7 12.9

11.7

13.3

11.2

13.7

11.8

13.5

12.0

13.4

122

13.4

12.2

13.2

12.2

131

12.2

13.3

12.5

13.2

13.2

13.2

13.2

13.1

13.3

130

13.4

129

13.7

10.9

12.9 I 11.5

13.3 13.7 13.5 13.4 13.4 13.2 13.1 13..3 13.2 132 13.1 13.0 12.9 10.9 11.5

12.5 12.5 12.7 12.7 12.8 12.7 12.7 12..8 12.9 13.2 13.2 13.2 13.2 12.3 12.2

54.09 53.87 54.74 54.95 55.39 54.97 54.74 55.17 55.60 57.12 56.90 56.90 5690 53.22 5279

14.33 14.27 14.50 14.56 14.67 14.56 14.50 14.61 14.73 15.13 15.07. 15.07 15.07 14.10 13.98

Figure 19. - Direct shear testing - data sheet 2b - rotational shear - example.

- Cp Olli In

USBR 5730

0.000 ....- - - - - - - - - - - - - - - - - - - - - - - - - , Ccnsohdallon of the Roletionel Shear Tesl Specimen
Normal $lr.u 2~.O Ibtlln2
c:
-0.002

~
c:
"E -0.Q04
."".
Q.

Ul
.i5
"::;:;;
>

-0.008
\
.------- -0.008 '-..-

0 - -_ _ 00

<.----.

-0.010.1---+---+---+---+---+---+---..,....--1

o

e

12

16

20

204

28

32

Square Root of Time -vrni;-

Figure 20. - Verrical displacement versus square root of time plor (norm.al stress = 25 Ibf/inl ) - exllmple.

so .,....----------:;..~"'::p,.,.,.".O:-;:.~."'::.,.,."-:D:::":::-".".H."'I.'"'D:::-H--:,"""-:.".".""h'"'J."'"'--:':-':.~""'"

LIquid umlt 3& PI..tIC'llF Ind.. II clIi,,'lcauan CL

C\l

FlO,. 100:: Sand 0:': ,sp.c-lIIe erl"lt, 2.1l'7

C
S

40

~ . _ ....._ . . . . ._ . . . _ . . . . ._ . . . - ....... - . _ . . . -. . - - -. .6 . _ . ....... _ .... _ .

.l:J

_ _.__ _- ..-...-...- ....-... ...- ...-....-.....-....

..

~ 10

E

0-1) DO'U/mJM6rm1lllr1d a-a $oa ..'/llla"......IIU'_

zo

a-a UIOOlll/l"Z"ormaJllral
o +----+------l----+---_-----l~-__1

0.0

O. I

0.2

0.3

0.4

0.5

0.6

AveJ"(ll~e Rotational Displacement - ~

17,45 Inch f"ominel CIr'C'ulnle~ence'

Figure 21. - Nominal shellr stress versus average rorotionlll displacemenr (%) plor - example.

100.,------------------.

80

rrnn
llJ

80

I-,

ronJ

I-,

ll:l

III

40

.l::

(JJ

'iii

::J

"0
Vi

20

tl

~.

Sample No. Example

Drill Hole No. Example

Liquid Umll 36 PI8Sticily Index 16

Fines 100';

Send 0 lI:

ClesslnceOon CL Specltlc Gravlly 2.67

Specimen Height 0.125 in

Outside Dlemeler 2.794 in

Inside Dlamelar l.946

Rolation

0.096 deg/min

RolaUon Rale 0.00026 in/min Tesl Dale: 6-31-69

Normal Stress (lbl/ln2)
25 50 100

Residual Sheer Slrass (lbf/in2)
13.4 22.9 41.3

o-r----f----+----!----I------{

o

20

40

60

80

100

Normal Stress - Ibf/in2

Reslduel Shear Sl...nglh . Coheaion (c) 4.2 Ibl/in2 Angle 01 Inlernal
Friction ('r) a 20.4

Figure 22. - Residual sheu stress (average) ve~us normal stress plor (Feature: rorsional shear) - example

100 ~------------------,
o Low RlduaJ Shear SLr~"lLh

1Io Avera" R.;lduat Shear SLrenllh

C\l l::
S 80

... Klab RuJdual Shoar SLren.Lh

~

I

rn

~

60

I-,
-en'

I-,
III
~ 40
en

i

::l

''C1:ili

20

cQ::l

0+----+---1----+----+-----1

o

20

40

80

ao

100

Normal Stress Ibf/in2

Sample No. Example

Drill Hole No. Exampla

Uquld Umll 36 PlasUclly Index l6

. Fines 100';

Sand 0 lI:

Classltlcallon CL SpecWc Gravity 2.67

Specimen Height 0.125 in

OUlslCie Diameter 2.794 In

Inside Dlamater 1.946

ROlation

0.096 deg/min

Rotallon Rate 0.00026 in/min

Tesl Date: 6-31-69

Normal Strass (lbl/1n2 )

Low Residual . Shear Stress (lbllln2)

Average Residual Shear Slress (lbf/ln2 )

High. Residual Shear Stress (lbf/1n2 )

25

13.4

14.2

15.3

50

22.9

24.4

26.4

100

41.3

42.9

44.3

Residual Shear Strength
Cohesion (c) -lbf/ln2 Angle of Internal
FricUon ('r) - degrees

Low 4.2
20.4

Average 4.9
20.9

High 6.3
21.0

Figure 23. - Residual shear srress (average, low, high) versus normal stress plot (Feature: rorsional shear) -:.. example.

STARK & EID 1994 PAPER
DRAINED RESIDUAL STRENGTH OF COHESIVE SOILS

DRAINED REsIDUAL STRENGTH OF COHESIVE SOILS
By Timothy D. Stark" Associate Member, ASCR, and Hisham T. Rid,l Student Member, ASCR
ABSTRACT:- Results of torsional ring shear tests on cohesive soils reveal that the drained residual strength is related to the type of clay mineral and quantity of c1aysize particles. The liquid limit is used as an indicator of clay mineralogy, and the clay-size fraction indicates quantity of particles smaUer than 0_{)()2 -mm. Therefore, increasing the liquid limit and clay-size fraction decreases the drained residual strength. The ring shear tests also reveal that the drained residual failure envelope is nonlinear, and the nonlinenrity is significant for cohesive soils with a c1ay-sizefraction greater than 50% and a liquid limit between 60% and 220%. This nonlinearity should be incorpqrated into stability analyses. An empirical correlation for -residual mction angle is described that is a function of liquid limit, clay-size fraction, and effective normal stress. Previous residual strength correlations are based on only one soil index property and provide a residual friction angle that is independent of effective normal stress. For slope stability analyses,_ it is recommended_that the residual strength be modeled using the entire nonlinear residual strength envelope oOnr athreessildipuaslufrrfiaccteio.n angle that corresponds to the average effective normal stress
INTRODUCTION

The drained residual shear strength of cohesive soils is a crucial parameter - in evaluating the stability of preexisting slip surfaces in new and. existing slopes and the design of remedial measures. At present, the reversal direct shear test is widely used to measure the drained residual strength of clays and clayshales even though it has several limitations. The primary limitation is that the soil is sheared forward and then backward until a minimum shear resistance is measured. Each reversal of the shear box results in a horizontal displacement that is usually less than 0.5 em. As a result, the specimen is
not subjected to continuous shear deformation in one direction, and thus a
fnuollLboerieonbttaatiinoend.of- the clay particles para-llel to the direction of s_hear may

The main advantage of the torsional ring shear apparatus is that it shears

the specimen continuously in one direction for any magnitude of displace-

ment. This allows clay particles to be oriented parallel to the direction of

shear and a residual strength condition to develop. Other advantages of the

ring shear apparatus include a constant cross-sectional area of the shear

surface during shear, minimal laboratory supervision during shear, and tile

possible use of data acquisition techniques.

_

The results of torsional ring shear tests on 32 clays and shales revealed that the drained residual failure envelope is nonlinear. The 32 clays and
clayshalesare listed in Table 1- by increasing liquid limit. This stress-dependent behavior of the drained residual failure envelope has also been observed by a number of other researchers, including Kenney (1967), Lupini

IAsst. Prof. of Civ. Engrg., Univ. of Illinois, Newmark Civ. Engrg. Lab. MC250,205 N. Mathews Ave., Urbana, IL 61801-2352.
2Grad. Res. Asst. of Civ. Engrg., Univ. of Illinois, Urbana, IL 61801. Note. Discussion open until October I, 1994. To extend tbe closing date One month, a written request must be filed with the ASCE Ml;mager of Journals. The manuscript for this paper was submitted for review and possible publication on November 13, 1990. This paper is part of the Journal of Geotechnical Engineering, _
pVeorl.pa1g2e0., PNaop.e5r,NMo.ay9,091.994. @ASCE, ISSN 0733-9410/94/0005-0856/$2.00 + $.25

856

J

at

6i 1
D) -E

1

-

-

-

-

1

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-_

_-:-1

i_It:
I:

:I:E"-
!0fi"-iIjjJz)!E!!-'

ll~8.c~n~ :--_1--------------
~

1

.I !t:

aE.
1II

:i~il22c81~--~-

(J)
.;

I.5~---I-----------------------I

.c

(J)

'0 I: III

fa
(3

..:

857

et al. (1981), Bromhead and Curtis (1983), Hawkins and Privett (1984;

1985), Lambe (1985), Skempton (1985), Anayi et al. (1988; 1989), and

Maksimovic (1989). Therefore, a disadvantage of existing drained residual

strength correlations is that a single value of drained residual friction angle

does not accurately model the nonlinear residual failure envelope. The main

objectives of this study were to gain an understanding of the nonlinearity

of the drained residual failure envelope, investigate the importance of the

nonlinearity in stability analyses, and develop a.new correlation that de-

scribes the nonlinear residual failure envelope.

.

SOIL DESCRIPTION AND TEST PROCEDURE

A modified Bromhead ring shear apparatus (Stark and Eid 1993) was

used for testing the 32 clays and clayshales. The original ring shear apparatus.
is described by Bromhead (1979). The ring shear specimen is annular with: an inside diameter of 7 cm and an outside diameter of 10 cm. Drainage is . provided by annular bronze porous stones secured to the bottom of the
specimen container and to the loading platen. The specimen is confined ' radially by the specimen container, which is 0.5 cm deep.

The specimen preparation procedure for the ring shear apparatus was , adapted from that used by Mesriand Cepeda-Diaz (1986) for the direct. ' shear apparatus. Remolded shale specimens are obtained by air drying a ' representati'(e sample of each shale. The air-dried shale is ball-milled until all of the representative sample passes the U.S. Standard sieve #200, Re--

molded silt and clay specimens (soil numbers I, 2, 3, 13, and 14 in Table 1) are obtained by air drying a representative sample, crushing it with a mortar and pestle, and processing it through the #40 sieve. Ball-milling is not used for these specimens, because it would change the texture and gradation of the soil. In both cases, distilled water is added to the processed soil until a liquidity index of about 1.5 is obtained. The sample is then
allowed to rehydrate for at least one week in a moist room. A spatula is

used to place the remolded soil paste into the annular specimen container. ' , The top of the specimen is planed flush with the top of the specimen con-
tainer using a 15.2-em-long surgical razor blade. It should be noted that the liquid limit, plastic limit; and clay size fraction of the specimens were measured using the ball-milled or sieved soil samples.
The mo<;lified ~romhead ring shear apparatus allows a remolded specimen to be overconsohdated and precut, which simulates the field conditions that lead to the development of a residual strength condition in overconsolidated , clays and clayshales. ,A consolidation stress of 700 kPa was chosen to rep-
resent the maximum effective stress that could be encountered in slope and

embankment field case histories. The specimens were sheared at effective

normal stresses between 50 and 700 kPa or an overconsolidation ratio of '

14 to 1, respectively.

'

The specimen is precut prior to shear by exposing the top of the specimen , after c:,nsolidat.ion at 700 kPa. The specimen is exposed by lowering the

outer nng and lOner core that surround the annular specimen. The inner core of the annular specimen container is lowered by threading it out of the bottom of the specimen container such that the top of the core is approximately 0.05 cm below the top surface of the specimen. The specimen COntainer is then placed on a horizontal surface and the outer ring is pushed

down until it becomes flush with the horizontal surface and center core.
The lowering of the center Core and outer ring exposes approximately 0.05 cm of the annular specimen above the top of the container.

858

A shear surface is created in the overconsolidated soil by slowly rotating

the top platen in the direction of shear. Th~s also allo~s the top platen and

porous stone to be separated from the specImen cont~mer. A IS.2-cm-long

surgical razor blade is used to precut the exposed specImen. The razor .blade

is placed on the upper surface of the sp.ecimen cont~iner a~d moved'm the

direction of shear until a smooth and pohshed surface IS obtal~ed. Theref?re,

the precut specimen is flush with the top surface of the speclmen.contamer

prior to shearing. When the top platen separated from the !ipeclmen con-

tainer, a layer of soil 0.01-0.03 c.m thick remains attached to the k,:,~rled

porous stone. This soil was prevIOusly presheared and usually exhIbits a

smooth surface.

After precutting, the top platen and specimen container are rea~sembled

and loaded to an effective normal stress of 50 or 60, kPa. All nng sh~ar

specimens were sheared at a drained displacement r~te of 0.018 m~/~m.

This displacement rate is based on values of coeffiCIent of cons?hdatlOn

evaluated from oedometer tests and during consolidation of the nng shear

specimen to 700 kPa. The procedure described by Gibson ~nd Henkel (I?S4)

and a degree of consolidati~n of 99.?~ were used to estl,mate the dramed

displacement rate for the high plastICIty shales. Faster dIsplacement rat~s

could have been used for some of the clays and silts. Hov.:ever, to aVOId

any possible rate effects, a di~placem~nt rate of 0.018 m~/.mm. was use.d for

all 32 specimens. After a dram~d r~sldual strength conditIon IS esta~hshed

at approximately SO kPa, sheanng IS stopped ~nd t~e normal stre~s IS d?u-

bled. After consolidation at 100 kPa, the specImen. IS sheared a~am untIl a

drained residual strength condition is obtained: ThIS procedur.e IS repeated

fora number of effective normal stresses and IS called a m~ltlst~ge test.

Fig. 1 presents shear stress-horizont~l displace~.ent relatlO~shlps from a

multistage ring shear test on the AUamlra bentomtlc. tuff obtamed f~~m the

Portuguese Bend landslide near Los Angeles, Calif. The bentom~lc tuff

sample was obtained from the sl.ip ~urface. at the toe of the landshde ap-

proximately. 150 m east. of Insp~r~tlOn Pomt. Th~ remolded tu~. sampl~

classifies as 'a clay of high plastiCIty, CH, accordmg to the U.mfled ~Oll

Classification System. The liquid limit, plasticity index, and clay-Size fr~ctlOn

of the remolded bentonitic tuff sample are 98, 61, and 68%, respectIvely.

It can be seen from Fig. 1 that during the first stage of shearing at an

effective normal stress ()":,) of 60 kPa the specimen exhibited a ~~all peak

strength. The peak strength of approximately 20. kPa was moblhz~d at a

horizontal displacemcent of about 0.02 cm. The reSidual strength of ~pprox

imately 15 kPa was reached at a horizontal displacement of. ap~roxlm~tely 2.0 cm. The small peak strength observed for an overcon~ohdatl?n ratIo of

12 is caused by the effectiveness of the precutting process 10 for~mg a shear

surface. Since the maximum effective normal stress on the shp surf~ce at

Portuguese Bend is approximately 640 kPa, the last stage of the mllltlst~ge

test had to be conducted at a normal stress greater than 480 kPa. Doubhng

the normal stress from 480 kPa would require a normal stress of 960 kPa.

Hthoewmeavxeir ~iut mwaesffdeecctiidveedntoormusael

only 850 kPa stress on the

because it significantly exceeds slip surface of 640 kPa..

It can also be seen from Fig. 1 that the specimen underw.e~t. a ve~tlcal

displacement of approximately 0:008 cm (i.~., 1.~% of the m.ltml heIght)

during the first stage of shear. ~lllS.small ~ertlcal dIsplacement IS. due to the

specimen having an overconsohdatlon ratl? of 12 an~ the prec~ttmg process

reducing the horizontal displacement reqUIred to achIeve ~ resldu~l strength

condition. For comparison purposes, a normally consohdated, mtact, re-

859

100 ,...-. U~= 850 kPa
80

I
(a)

60

480 kPa

40 rjr"

20

ilr'
L

240 kPa 120 kPa

60 kPa

o o

-E

0

-0

~!z -0.008

~-O:W W2 -0.016

~~a.. -0.024

CJ)

0 -0.032 0

1

2

3

HORIZONTAL DISPLACEMENT (cm)

(6)
--..;::::::::;~::::~-.........- - - - - - - - a~ .. 60 kPa 120 kPa

123
HORIZONTAL DISPLACEMENT (cm)

FiG. 1. Drained MUltistage Ring Shear Test on Altamlra Bentonitic Tuff

molded specimen required 9.9 em of horizontal displacement and underwent

0.043 em of vertical displacement before achieving a residual strength con-

dition. The second stage of this ring shear test was conducted at an effective

no~a.l stress of 120 kPa ane;t is also s~own in Fig. 1. Since a residual strength'

condItIon was reached durmg the fIrst stage of the test, the specimen did

not. exhibit .a peak strength. IIi .addition, only approximately 1.2 em of

honzontal dIsplacement was reqUIred to obtain a residual strength of about

26 kPa. A similar behavior was observed during the remaining three phases

of the multistage test.

.

NONLINEARITY OF DRAINED RESIDUAL STRENGTH ENVELOPE Ring shear tests on 32 clays and clayshales (Table l)were used to establish
the effect of clay ~ineral~gy on t~e drained residual failure envelope. Fig. 2 presents the dram~d resl.dual faIlure envelopes for seven of the clays and c1a~shales t~sted dunng thIS study. It can be seen that the magnitude of the dramed reSIdual s~rength e;tecreases with increasing liquid limit. It also appears t~a~ the dra!ned reSIdual strength. d.ecr~ases w~t~ increasing activity. The actIVIty (A c) IS defined as the plastICIty mdex dIVIded by the clay-size
860

400

SOIL NUMBER (TABLE 1)

3 a 19

.o.. n9

e 28 m32

012

LL Ac 35 039
t:
~

~a
:J

52

0.5\

CI
I 62 0.44

0 68 0.86 ~ 98 090
. 184 154

288 2.77

FIG. 2. Effect of Clay Mineralogy on Drained Residual Failure Envelopes

2.2

2.0
-:e.......~.. 18
'-...... 16
.......I.i:
~ 14


25%~ CF~ 45%

12

10 0

50

100

150

200

250

300

LIQUID LIMIT (!Xl)

FIG. 3. Reduction In Secant Residual Friction Angle from Effective Normfll Stresses of 50 kPa to 700 kPa

fraction. Both the liquid limit and activity provide an indication of clay mineralogy, and thus particle size and shape. In general, the plasticity increases as the platyness of the clay particles increases. Increasing the platyness of the particles results in a greater tendency' for face-to-face interaction, and thus a lower drained residual strength.
Fig. 2 also shows that the drained residual failure envelope can be nonlinear. This nonlinearity appears to be significant for cohesive soils with moderate to high liquid limit and activity. Fig. 3 presents the ratio of the secant residual friction angle at 50 kPa, (<1>:)50, and 700 kPa, (<1>:)700, for'
the 32 cohesive soils listed in Table 1. The secant residual friction angle corresponds to a linear failure envelope passing through. the origin and the residual shear stress at a particular effective normal stress. It can be seen
that the ratio of (<1>:)50 to (<I>:hoo is less than 1.3 for clay-size fractions (CF)
less than 45%. For clay size fractions greater than 50%, the ratio of (<1>:)50
to (<I>:hoo reaches a maximum of 1.85 to 1.9 at a liquid limit of approximately
100 and decreases to about 1.1 at a liquid limit of 288. Therefore, it may be concluded that the nonlinearity of the residual failure envelope is sig-
nificant, i.e., (<I> ;)501(<1> :)700 is greater than 1.3, for cohesive soils with a liquid
limit between 60 and 220 and a clay-size fraction greater than 50%. In this .
861

range of liquid limit and clay-size fraction, the residual frictioh angle under-

goes a reduction of 25-45% for effective normal stresses increasing from

50 to 700 kPa.

The nonlinearity of the drained residual failure envelope can be explained

in terms of particle size and platyness. For soils of low clay-size fraction

(CF less than 45%), and soils with a liquid limit less than 60 and a clay-size

fraction greater than 50%, the relatively rotund particles and/or stiff clay

plates dominate the shear behavior. These particles are able to establish

edge-to-face interaction even at the drained residual condition. Conse-

quently, the initial contact area and the increase in contact area during shear

are smaIl under any range of effective normal stresses. This leads to an

approximately linear drained residual failure envelope. A linear failure en-

velope also occurs.in soils with high clay-size fraction (CF greater than 50%)

and plasticity (LL greater than 220) but by a different mechanis~. The

highly flexible and platy particles of these soils establish face-to-face inter-

action even under low effective normal stresses. Consequently, the initial

contact area is large and the increase in contact area during shear is small

under any range ofeffective normal stress. This also results in a linear failure

.envelope.

.

.

Soils with a clay-size fraction greater than 50% and a liquid limit between

60 and 220 initiaIly have a combination of edge-to-face and face-to-face

interaction. At low effective normal stresses edge-to-face interactions can

exist and then' shearing converts some edge-to-face interactions to face-to-

face. This increases the contact area during shear and decreases the mea-

sured strength ~ntil a residual value is obtained. As the effective normal
are stress increases, initial edge-to-face interactions compressed to form a

face-to-face orientation and increases the contact area prior to shear. As a

result, the contact area at the residual condition is substantially greater at

high effective normal stresses than at low effective normal stresses for this

group of soils. This difference in contact area results in a nonlinear residual

failure envelope.

NEW DRAINED RESIDUAL STRENGTH CORRELATION
Fig. 4 presents a correlation of drained residual friction angle and soil index properties, at effective normal stress of 100, 400, and 700 kPa. It can be seen that there is a relationship b~tween the secant residual friction angle and both liquid limit and clay-size fraction. The higher the liquid limit and clay-size fraction the lower the secant residual friction angle. The liquid limit appears to be a suitable indicator of clay mineralogy, and thus drained residnal strength. However, clay-size fraction remains an important predictive parameter because it indicates the quantity of particles smaller than 0.002 mm. The proposed correlation differs from existing correlations because the drained residual friction angle is a function of liquid limit, c1aysize fraction, and effective normal stress.
Fig. 4 also illustrates the nonlinearity of the drained residual failure envelope in terms of the decrease in secant residual friction angle with increasing effective normal stress. It confirms that the nonlinearity is significant for cohesive soils with a clay-size fraction greater than 50% and liquid limit between 60 and 220. For example, at a liquid Iimit.of 100 and a claysize fraction greater than 50% in Fig. 4, the secant residual friction angle decreases from 9S at an effective normal stress of 100 kPa to 6.20 (or 35%) at lin effective normal stress of 700 kPa. For clay-size fractions less than
862

EFFECTIVE NORMAL STRESS
..lkPal 100 A 4QO II 700
...0 100 4QO
..a 700 100
400 700

CLoW SIZE FRACTION ('III
$20
25$CF$4S
~50

40

80

120 .160 200 240 280' 320

LIQUID LIMIT (%)

FIG. 4. Relationship between Drained Residual Friction Angle and Liquid Limit

45% and liquid limits less than 120, the reduction in secant residual friction

angle from 100 to 700 kPa is less than 1-20 (Fig. 4)..

..

The secant residual friction angle for a cohesive sad can be estimated for

a particular effective normal stress using the liq';lid I.imit, clay-size. f.raction,

and interpolation between the curves presented In FIg. 4. For sta~dlty anal-

yses it is shown in a subsequent sectIon that the averag~ effective no.rmal stress acting on the slip surface should be used to eShm~te the r~sldual

friction angle in Fig. 4. The effective normal stress can eaSIly be estImated

because the location of the critical slip surface is weIl defined ~y the p~eex isting shear surface. Fig. 4 can also be used to estimate the.nonhnear resl~ual

failure envelope by plotting the shear stress correspondmg to the dramed

residual friction angle at effective normal stresses of 100, 400, and 700 kPa.

A smooth curve can be drawn through the three points and the origin to

estimate the nonlinear failure envelope. For day-size fractions between 20%

and 25% and 45% and 50%, the residual friction angle can be estimated

for a particular effective normal stress by interpolation between the clay

size fraction groups.

(f(\ ~ 2. I) &.4 lif.7

EFFECT OF NONLINEAR RESiDUAL FAILURE ENVELOPE ON STABILITY ANALYSES

J
Ih;'

It is clear from the previous section that the drainf;:d residual fail~te envelope for cohesive soils with a liquid lim!t less tha~ 120 .and.a clay-~t.ze fraction less than 45% can be modeled uSlOg a straIght hne 10 stabthty analyses. However, cohesive soils with a c1a~-~ize fra~tion gr~ater than 50% .and a liquid limit between 60 and. 220 e~hlblt. a reSIdual. ~atlure envelope that is nonlinear. The effect of thIS nonhneanty on stablhty analyses was
investigated using a number of field case histories. Two of these case his-
tories are described in the folIowing. The Portuguese Bend landslide is a reactivated part of a 5.2 km2 1andslide
on the south flank of the Palos Verdes Peninsula, near Los Angeles, Calif.

863

EAST-eENTllAL SUBSUDE
:=
160 30 o
dl---...,15O;F,"' '---300~--'4"'50'---';;600;'------'7;F,50"'---";sOo;'---.n.!105o HORIZONTAL DISTANCE (METERS)
FIG. 5. Typical Cross Section through Portuguese Bend Landslide [after Ehllg (1987))

200 ,.--,---,---,---,--,.---,---,--,---,---, I AlTAMIRA BENTONmc ruFF
I I RING SHEAR TEST RESULTS
100
~----~-
O......,=-:=----J'-----L----J'------'----'----'-~--'----'
o 100 200 390 400 500 600 700 800 900
EFFECTIVE NORMAL STRESS (kPa)
FIG. 6: Drained Residual Failure Envelope for Altamlra Bentonitic Tuff

Recent movement of tbe lan'dslide began in 1956 when 1.052 km2 slid during

a surge in subdivision development. However, the Portuguese Bend land-

slide has long been recognized as a large slowly moving landslide on tbe

south slope of the Palos Verdes Hills (Woodring et al. 1946). Recent move-

ment bas continued from 1956 to 1976 at anaverage rate of 1 cm per'day.

From 1976 to 1986, the displacement rate increased to 2:5 cm per day, which

is attributed to wave erosion removing slide material at the toe and an

increase in ground-water levels. The slide movement appears to be con-

trolled by the coastal subslides (Fig. 5), and field observations show that,

if tbe coastal subslide moves, the remainder of the slide also moves (Ehlig

1992). It can be seen that the depth of the slip surface in the subslides ranges

from 30 to 45 m, which corresponds to an effective normal stress of 300-

640 kPa. The mean effective normal stress on the slip surface in the frrst

subslide is estimated to be 500 kPa.

...

.Sliding is occurring along thin bentonitic tuffaceous beds in the Altamira

shale member of tbe middle Miocene Monterey Formation. Thetuffaceous

beds consist of bentonite that is predominantly calcium-~ontmori1lonite.

The liquid limit, plasticity index, and clay-size fraction of the remolded

bentonitic tuff sample are 96, 61, and 68%, respectively. The slope has been

moving since the initial Pleistocene landslide; as a result the shear strength

of the bentonitic tuff in this area is probably at the residual value.

Fig. 6 shows the nonlinear residual failure envelope measured for the

bentonitic tuff and two linear approximations of the failure envelope. A

linear failure envelope passing through tbe origin and the test data in the

effective normal stress range of 300-640 kPa yields a residual friction angle

of approximately 6.5. Another linear failure envelope inclined at 6.9 cor-

responds to tbe secant residual friction angle estimated from Fig. 4 using

the average effective normal stress of 500 kPa.

Table 2 presents the factors of safety calculated using the cross section

864

TABLE 2. calcuiated Factors of Safety for Portuguese Bend Landslide

Effective cohesion (kPa)
(1 )
nonlinear
o o

Effective friction angle (degrees) (2)
nonlinear 6.5 6,9

Faclor of safely (3)
1.02 1.00 1.04

(j) 80

0:

-1~ 60

(6

iO~=:~wu

40 20

~

TENSION CRACK
------.;

ASSUMED PIEZOMETRIC lEVEL J!lJ=-~ONl
~~

_ - - - - - : - - - - - - - ..... fIIVERS EDGE

- --- - ~ --;~;;;;~~--- 'C;;;;N~

~~~ _--'7=-=:::..::t.

is oOL-----:5,J-:0-------:1~00::------:1:=50=---~2=0::0----;:'.250

HORIZONTAL DISTANCE (METERS) FIG. 7. Cross Section through Gardiner Dam Slide [after Jasper and Peters (1979))

in Fig. 5, Spencer's (1967) stability method, and the three failure. envelopes in Fig. 6. The nonlinear residual failure envelope was ~odel7d us~ng 19 data points in UTEXAS2 (Wright 1986). The average mOIst umt weIght of the slide mass was measured to be 17.5 kN/m3
It can be seen tha~ the three failure envelopes yield factors of safety that are in good 'agreement with field observations. Each e~velope pr.ovides the stability analysis with the residual strengt~ correspondmg to typIcal .val~es of effective normal stress acting on the shp surface. It can ,be seen ID FIg. 6 that other envelopes could be drawn through the data points, many of, which would not provide good agreement with field observations. In con-
clusion test data and correlations must evaluate the residual strength over the appropriate range of effective normal.stress. ~~is can b~ accom'plis~ed by modeling the entire nonlinear envelope ID a stabIlIty analysIs or estlmatmg
the residual friction angle (from test data or Fig. 4) that corresponds to the
average effective normal stress on the critical slip surface. The second case history involves a landslide that occurred in an excavated
slope near the tunnel inlet area at Gardiner Dam (Jasper a~d Pe~ers 1979). Gardiner Dam is located on the South Saskatchewan RIver, m western Canada, and is underlain. by the Bearpaw Formati0!1' The Be~rpaw F?rmation at this location consists of two sandstone umts and an mtervemng clay shale unit, which contains bentonite or b~nto~itic zones. The shal~ is a highly overconsolidated marine clay deposIted m ,late ~retaceous t1m.e (Jasper and Peters 1979; Peterson et aJ. 1960). The greemsh-gray shale IS
noncalcareous with a liquid limit, plasticity index, and clay-size fraction of 128, 101, and 43%, respectively. The remolded shale classifies as a clayeysand, SC, according to the Unified Soil Classification System.. The sh~le contained preexisting shear surfaces that led to a number of shdes dunng trench excavations and abutment slope trimming throughout construction
of Gardiner Dam. As a result, major design modifications consisting of
extensive upstream and downstream slope flattening (12, horizontal to 1
vertical instead of 8 horizontal to 1 vertical) and a 250-m downstream toe

865

berm with aslope of 85 horizontal to 1 vertical were required to compensate for the preexisting shear surfaces in the Bearpaw shale (Peck 1988). The average unit weight of the Bearpaw shale and overburden (Fig. 7) were measured to be 19.0 kN/m3 and 18.7 kN/m3 , respectively (Ringheim 1964). Fig. 8 shows the slightly nonlinear drained residual failure envelope obtained from a multistage ring shear test on Bearpaw shale. The measured residual failure envelope (Fig. 8) for the Bearpaw shale at Gardiner Dam yielded a factor of safety of 1.01 for the cross section shown in Fig. 7. The slightly nonlinear failure envelope was modeled using 19 data points in UTEXAS2.
The average effective normal stress on the slip surface was estimated to be 95 kPa. Fig. 4, the liquid limit, clay-size fraction, and average effective normal stress on the slip'surface of 95 kPa were used to estimate a residual friction angle of 9.8. The estimated residual friction angle of 9.80 yielded a factor of safety of 1.02. Fig. 8 provides a comparison of the measured and estimated residual failure envelopes for the Bearpaw shale. It can be seen that the estimated residual friction angle of 9.8 is in excellent agreement
with the measured envelope at effective normal stresses less than 200 kPa.
Therefore, the estimated residual friction angle is in excellent agreement with field observations because the average effective normal stress on the
slip surface is 95 kPa. However, if the average effective normal stress on the base of the slip surface was liigher, for example 400 kPa, the proposed correlation~ould have predicted a residual friction angle of 8.80 , which is. in good agreement with the measured failure envelope near 400 kPa (Fig.
8). Therefore, the proposed correlation in Fig. 4 can provide an excellent .
estimate of the nonlinear residual failure envelope, and thus field observations, by using a residual friction angle that corresponds to the average effective normal stress on the critical slip surface.

COMPARISON OF EMPIRICAL CORRELATIONS FOR DRAINED RESIDUAL STRENGTH

To illustrate the importance of using both liquid limit and clay size fraction together in estimating the drained residual friction angle, the proposed and existing correlations are compared using the Gardiner Dam and Portuguese Bend field case histories. The trend line or average residual friction angle was used from the existing correlations except for Mesri and Cepeda-Diaz (1986) and Voight (1973), where the data point corresponding to Bearpaw shale from Gardiner Dam was used. Table 3 provides a comparison of the proposed and existing empirical correlations for drained residual strength. It can be seen from Table 3 that most of the previous residual strength correlations based on clay-size fraction overestimate the factor of safety for

I I 200 r-----r---.---,--,----r---,-----,-----,

BEARPAW SHALE GARDINER DAM

RING SHEAR lEST RESULTS

'"

8.8 DEGREES
__

100

-----9.8 oE~-:::::::::::::::- .

---==-~--=-;:..::::-:,;;..-~

.

100 200 300 400 500 600 700 800 EFFECTIVE NORMAL STRESS (kPa)
FIG. 8. Drained Residual Failure Envelope for Bearpaw Shale from Saskatchewan, Canada
866

TABLE 3. Comparison 01 Empirical Correlations lor Drained Residual Strength Using Field Case Histories

Soil Index property
(1 )

Reference (2)

. Gardiner Dam

Portuguese Bend

(LL = 128;

(LL = 98; PI = 61;

PI = 101; CF = 43)

CF = 68)

Residual friction angle
(3)

Factor of
safety (4)

Residual friction angle
(5)

Factor of
safety (6)

. Liquid limit and clay fraction Current study

9.8

1.02

6.9

1.04

Clay fraction

Skempton (1964) Borowicka (1965)

18.0

1.91

12.3

1.67

7.5

0.77

7.5

1.12 .

Binnie et al. (1967)

15.2

1.61

11.5

1.58

Blondeau and 10sseaume 12.6

1.31

7.0

1.06

(1976)

Lupini et al. (1981)

13.4

1.41

4.9

0.81

Skempton (1985)

-"

-"

11.1

1.53

Collotta et al. (1989)

11.8

1.23

7.8

1.15

Plasticity index

Fleischer (1972) Voight (1973) Kanji (1974) Bucher (1975) Mitchell (1976) Seycek (1978) Vaughan et al. (1978) Lambe (1985) Clemente (1992)

9.1

0.94

9.1

1.30

6.3

0.65

9.8

1.38

6.0

0.61

7.5

1.12

.-"

-"

-"

-"

10.9

1.13

11.6

1.59

7.8

0.81

9.6

1.36

-"

_a

-"

-"

-a

-"

-"

-"

11.6

1.21

11.6

1.59

Liquid limit

Haefeli (1951)

-"

-"

-"

-"

Mitchell (1976)

13.0

1.36

13.0

1.75

Mesri and Cepeda (1986)

9.4

0.97

8.0

1.18

aNot applicable.

the Gardiner Dam case history. The Bearpaw shale has a high liquid limit (128) but a relatively low clay-size fraction (43%). The high liquid limit results in a measured secant residual friction angle at an effective normal stress equal to 700 kPa of approximately 8,5 (Fig. 8). However, existing correlations based on clay-size fraction predict a residual friction angle of approximately 120 -18. It was anticipated that existing correlations would not provide an accurate estimate of this residual friction angle, because of the high liquid limit (128) and low clay-size fraction (43%), of the Bearpaw shale. Typically a high liquid limit corresponds to a high clay-size fraction. However, this relation need not be general, as is illustrated by a number of the clays and clayshales tested during this study. It should be noted that the correlation proposed by Borowicka (1965) yielded a conservative estimate of the residual friction angle (7S) forthe Bearpaw shale at Gardiner Dam. The correlation presented by Skempton (1985) is also based on clay-
867

size fraction but it is limited to soils with an activity between 0.5 and 0.9, .and thus is not applicable to Bearpaw shale, which has an activity of 2.35.
Existing correlations based on clay-size fraction produced conflicting factors of safety for the Portuguese Bend case history (Table 3). Most of these c9rrelations overestimated the Portuguese Bend factor of safety, while the correlation proposed by Lupini et al. (1981) underestimated the factor of safety. The correlation proposed by Blondeau and Josseaume (1976) provided the best agreement with Portuguese Bend field observations. In summary, existing correlations based on only clay-size fraction tend to overestimate the drained residual friction angle. It is imperative that drained residual strength" correlations incorporate both liquid limit and clay-size fraction to provide an accurate estimate of clay mineralogy and'the quantity of clay-size particles, respectively. In addition, neglecting the nonlinearity" of the residual failure envelope, i.e., the average effective normal stress acting on the slip surface, probably aided the poor estimate of the factor of safety for the Portuguese Bend case history.
Existing correlations that utilize plasticity index or liquid limit also yielded conflicting factors of safety for the Gardiner Dam case history. Four of the correlations underestimated the .residual friction angle, and thus the factor of safety, for the Gardiner Dam case history. However, Mitchell (1976) and Oemente (1992) overestimated the residual fraction angle, and Fleischer (1972) provided the best agreement with field observations. Mesri 'and Cepeda-Dia~ (1986) data point for the Bearpa~ shale at Gardiner Dam cor- " responds to a reSidual friction angle of 9.4 and a factor of safety equal to 0.97. All existing correlations based oil plasticity index or liquid limit overestimated the residual friction angle, and thus the factor of safety, for the Portuguese Bend landslide. This is caused by the Altamira bentonitic tuff . exhibiting a plasticity index of 61 and a clay-size fraction of 68.
In conclusion, the drained residual strength is controlled by the type of clay mineral and quantity of clay-size particles. The liquid limit and claysize fraction in general provide an accurate estimate of the type of clay mineral and the quantity of clay-size particles, respectively. Therefore, existing correlations based on either clay-size fraction or clay plasticity do not provide a consistent estimate of the drained residual friction angle. In addition, the residual failure envelope can be approximated by a straight line for cohesive soils that have a clay size fraction less than 45%. For cohesive soils with clay size fraction greater than 50% and a liquid limit between 60 and 220, the nonlinearity of the drained residual failure envelope is significant. Existing drained residual strength correlations do not provide an estimate of this nonlinearity. Since the residual strength is usually small, small changes in the residual friction angle result in significant changes in the calculated factor of safety. Therefore, the stress-dependent nature of the residual strength is important in slopestability analyses. A new correlation is proposed to overcome the limitations of existing correlations and "provide better agreement with field case histories.
CONCLUSIONS
The following conclusions are based on the results of torsional ring shear tests on 32 clays and clayshales.
1. The magnitude of the drained residual strength is controlled by the type of clay mineral and quantity of clay-size particles.
868

2. The liquid limit provides an indication of clay mineralogy and the clay-

size fraction indicates the quantity of particles smaller than 0.002 mm. T.here-

fore, both the liquid limit and clay-size fraction should be used to estimate

the drained residual friction angle. 3. The drained residual strength

. failure

envelop~

. IS

.non" l~near.

The

non-

li~earity is significant for cohesive soils with a clay.size fr~ctJO~ greater than

50% and a liquid limit between 60 and 220. ThiS nonlmeanty should be

incorporated into stability analyses. . 4. A new drained residual strength

correlatI.On,Isd~scn.'bed

that

. IS

a

func-

tion of the liquid limit, clay-size fraction, an~ effectl~e norma~ stress..The

correlation can be used to estimate the entire nonlInear reSidual failure envelope or a secant residual fri~tion angle that corresponds to the average

effective normal stress on the slIp surface. .

.

5. It is recommended that the nonlinear reSidual failure env~lope or a

secant residual friction angle corresponding to the average effective nor?al

stress on the slip surface be used' in a stability analysis to model the effective

stress dependent behavior of the residual strength.

ACKNOWLEDGMENTS

This study w~ performed as a part of National Science Foundation Grant
?! BCS-91-96074. The support of this agency is gratefully ackno~led~ed. Paul
V. Lade and Stephen M. Watry of the l..!niversity Cahforma at Los

of Angeles provided the sample of the Altamlra bentomtlc shale. Serge Ler-
oueil Laval University provided the sample of B~ow'n London Clay. E. Karl Sauer of the University of Saskatchewan prOVided the ~ampl~ of the

Lea Park bentonitic shale. The writers acknowledge G. Mesn for hiS many

valuable suggestions during this study.

"

APPENDIX. REFERENCES

A :!

:h.oJdST~f

Boyce J. R. and Rodgers, C. D. measu'ring the residual strength of

(~19c8la8y)..""CTroamnsppa.riRsoesn.

of alternative Record 1192,

Transportation Research Board (TRB), Washmgton, D.C. " . . "Anayi, J. T., Boyce, J. R., and Rodgers, C. D. F. (1989). Modified rmg shear

apparjltus" ASTM GeoteclJ. J., 12(2), 171-173.'

.

BInD.le)

M A' Clark

..,

J

JFF '

and

continuities in clay bedrock on the

dSekseigmnpotofn~J aAms..Wm .th(1e9~6a7)~. g"I eT hp. eroejef" fcet.ct

of dls-
~
ra/IS.

9th Inl. Congress on Large Dams, InternatIOnal CommisSion on Large Dams

(ICOLD), Paris, France, Vol. I, 165-183.

.

..

BIroensdideuaeul,leFe.,n alnabdoJroastsoeiraeu.m" eB,ulH/e.ti(n19d7e6L).ia"isMonesduerseL dae lob ararelo'slirsteasn.dcees Pauonctls.s"eatIlClehmaeunst-

sees; Siabili/e de lalus I; versants na/llrels, Paris, France (numero speCial II), 90-

"

BOo1r0foW6clI{aCiy~.a "FrP~nrco,(ch.;,.9665t.h) In"tT.

he influence of the colloidal content on the

Con!.

Soil

Mech.

an d

'" d
IOlln.

Engrg.,

Mon

shear trea,l

strength Canada,

BrVomol.he1a,d1,7E5.-1N7.8.(1979). "A simple ring shear appara.tus. " Gr~lIndEngrg., 12(5)",

Br4oo0fm-mh4ee4a~sdu,rEin.gNth.,eanreds"idCuuartliss,trRe.n. gDth.

(1983). "A of London

comparison of alternative methods cIay. "GrOllndE ng'/g., 16(4) , 39-

Bu~~er, F. (i975). "Die Restscherfestigkeit natiirlicher Bi)den, ihre,~influssgrossen
und Beziehungen als Ergebnis experimente~ler ~nter~u~hungen. R~p. No. 103, Institutes fiir Grundbau und Bodenmechamk Eldgenosslsche Techmsche Hochschule, Ziirich, Switzerland (in German).

869

Clemente, J. L. (1992). "Strength parameters for cut slope stability in 'Marine'

Sediments." Proc., ASCE Specialty Conf. on Stability and Performance of Slopes

and Embankments~Il. ASCE, New York, N.Y., Vol. I, 865-875.

_

Collotta, T., Cantoni, R., Pavesi, V., Ruberl, E., and Moretti, P. C. (1989). "A

correlation between residual friction angle, gradation and the index properties of

cohesive soils." Geotechnique, London, England, 39(2), 343-346.

Ehlig, P. L. (1987). "The Portuguese Bend landslide stabilization project." Geology

of Palos Verdes Peninsula and San Pedro Bay. P. J. Fishcher, ed., Society of

Economic Paleontologists and Mineralogists and American Association of Petro-

leum Geologists, Los Angeles, Calif., Part 2, 17-24.

Ehlig, P. L. (1992). "Evolution, mechanics and mitigation of the Portuguese Bend

landslide, Palos Verdes Peninsula, California." Engineering geology practice in

southern California, B. W. Pipkin and R. J. Proctor, eds., Star Publishing Co.,

Belmont, Calif., pp. 531-553.

Fleischer, S. (1972). "Scherbruch- und Schergleitfestigkeit von Bindigen Erdstoffen."

Neue Bergballtechnik, Freiburg, Germany, 2(2), 98-99 (in German).

Gibson, R. E., and Henkel, D.J. (1954). "Influence of duration of tests at constant

rate of strain on measured 'Drained' strength." Geoteclmique, London, England,

4(1), 6-15.

Haefeli, R. (1951); "Investigation and measurements of the shear strength of satu-

rated cohesive soils." Geotechnique, London, England, 2(3), 186-207.

Hawkins, A. B., and Privett, K. D. (1984). "Residual strength: Does BS 5930 help

or hinder?" Proc., 20th Conf. of the Engrg. Group Geological Soc., Site IlIv~ti

gation Prqctice: Assessing BS 5390, The Geological SocietY,"London, England,

Vol. 1,274-280.

Hawkins, A. B., and Privett, K. D. (1985). "Measurement and use ofresidual shear -

strength of cohesive soils." GroundEngrg., 18(8),22-29;

Jaspar, J. L., and Peters, N. (1979). "Foundation performance of Gardiner Dam."

Calt. Geotech. J., Vol. 16, 758-788.

Kanji, M. A. (1974). "The relationship between drained friction angles and Atterberg

limits of natural soils." Geotechnique, London, England, 24(4), 671-674.

"

Kenney, T. C. (1967). "The influence of mineral composition on the residual strength

of natural soils." Proc., Geotech. Conf., Vol. 1, Norwegian Geotechnical Institute,

Oslo, Norway, 123-129.

Lambe, T. W. (1985). '.'Amuay landslides." Proc., Xl Int. Conf. Soil Mech. and

Found. Engrg., A. A. Balkema Publishing Co., Rotherdam, The Netherlands,

137-158.

Lupini, J. F., Skinner, A. E., and Vaughan, P. R. (1981). "The drained residual

strength of cohesive soils." Geoteclmique, London, England, 31(2), 181-213.

Maksimovic, M. (1989). "On the residual shearing strength of clays." Geotechnique,

london, England, 39(2),347-351.

Mesri, G., and Cepeda-Diaz, A. F. (1986). "Residual shear strength of clays and

shales." Geotechnique, London, England, 36(2), 269-274.

Mitchell, J. K. (1976). Fundamentals of soil behavior. John Wiley and Sons, New

.York, N.Y'-

.

Peck, R. B. (1988). "The place of stability calculations in evaluating the safety of

existing embankment dams." Civ. Engrg. Practice, Boston Society of Civil Engi-

neers, (Fall), 67-80.

Peterson; R., Jaspar, J. L., Rirard, P. J., and Iverson, N. L. (1960). "Limitations

of laboratory shear strength in evaluating stability of highly plastic clays." Proc.,

Conf. Oil Shear Strength of Cohesive Clays, ASCE, New York, N.Y., 765-791.

Ringheim, A. S. (1964). "Experiences with the Bearpaw shale at the South Sas-

katchewan River Dam." Pi'oc., 8th Int. Congress on Large Dams, Voi. I, Inter-

national Commission on Large Dams, Paris, France, 529-550.

Seyfek, J. (1978). "Residual shear strength of soils." Bull. Int. Assoc.ElIgrg: Ge-

ologists, Germany, Vol. 17,73-75.

Skempton, A. W. (1964). "Long-term stability of clay slopes." Geotechnique, Lon-

don, England, 14(2),75-101.

870

Skempton, A. W. (1985). "Residual strength of clays in landslides folded strata and

the laboratory." Geotechnique, London, England, 35(1), 3-18.' .

Spencer, E. (1967). "A method of analysis of the stability of embankments assuming

parallel inter-slice .forces." Geotechnique, London, England, 17(1), lr...26.

Stark, T. D., and EJd, H. T. (1993). "Modified Bromhead ring shear apparatus."

ASTM Geotech. J., 16(1),100-107.

.

Vaughan, P. R., Hight, D. W., Sodha, V. G., and Walbancke, H. J. (1978). "Factors

controlling the stability of clay fills in Britain." Clay fills Institution 'of Civil

. Engineers (ICE), London, England, 203-217.

'.

_

Voight, B. (1973). "Correlation between Atterberg plasticity limits and residual shear stren~th of natural soils." Geoteclmique, London, England, 23(2), 265-267.

Woodring, W. P., Bramlette, M. N., and Kew, W. S. W. (1946). "Geology and

. Np.aDl.eo2n0t7o,loVg.yS.oGf ePoalloogsicValerSduersveHyi,llWs, aCshailnifgotronni,a.D" .CU..S. Geological Survey Paper
Wr.lght;,~. G. (198~). "VT~XA~2: a c~mputer program for slope stability calcula-

tions: _Geo!echn,/cal Engmeermg Software GS86-1, Department of Civil Engineenng, Vmverslty of Texas, Austin, Tex.

871