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International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
Proceedings of the 18
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International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
the values obtained for effective normal stresses up to 250 kPa
(Table 5). The relatively low difference (7.7%) in P2-S1 soil is
attributed to the not so pronounced curvature of its failure
envelope. Xeidakis (1993) has reported that the residual friction
angle decreases as the moisture content of swelling soils
increases. This effect of moisture content on the residual friction
angle was verified in the present research only for P2-S2 soil
(Table 5), probably because the variation of moisture content
used, ranges from 14% to 21% and is low, compared to the
variation of 35% used by Xeidakis (1993).
The results of residual shear strength tests are often
presented by plotting the values of residual friction coefficient,
τ
r
/σ’
n
, against the corresponding values of effective normal
stress, σ’
n
, (Lupini et al. 1981, Hawkins and Privett 1985).
Thus, the “complete residual failure envelopes” (Hawkins and
Privett 1985) can be obtained and the effect of effective normal
stress on residual shear strength can be evaluated. The residual
friction angle can be expressed as (Hawkins and Privett 1985):
n
r
R
1
tan
(1)
The results of ring shear tests conducted on specimens with
optimum water contents were analyzed using Equation 1 and
the resultant values of residual friction angle are presented in
Figure 3. It is observed that the residual friction angle decreases
with increasing effective normal stress and that P2-S2 soil
presents the most pronounced curvature of failure envelope and,
as a result, the maximum variation of residual friction angle.
Finally, it appears that the “lowest constant residual strength”
(Hawkins and Privett 1985) was not reached by the tested soils
for the range of effective normal stresses used in this study.
Optimum water
contents
6
8
10
12
14
0
200
400
600
800
Effective normal stress, σ'
n
(kPa)
Residual friction angle, φ'
R
(
o
)
P1-S2
P2-S1
P2-S2
Figure 3. Complete residual failure envelopes of swelling soils tested
with optimum water contents.
5 CONCLUSIONS
Based on the results of this investigation and within the
limitations posed by the soils used and the number of tests
conducted, the following conclusions may be advanced:
The behavior of swelling soils in the consolidation stage of
ring shear tests depends on the specimen moisture content
and the effective normal stress used.
The residual failure envelopes obtained for swelling soils,
tested with the optimum moisture contents resulted from the
Standard compaction test, are curved. Consequently, the
residual friction angle decreases with increasing effective
normal stress and does not attain a minimum constant value
for the range of effective normal stresses used in this study.
All residual failure envelopes obtained in this investigation
can be considered as linear for effective normal stresses up
to 250 kPa, regardless of the moisture content of soils.
The residual friction angle does not always decrease as the
moisture content of soil increases.
6 ACKNOWLEDGEMENTS
The ring shear tests described in this paper were conducted at
the Soil Mechanics & Foundation Engineering Laboratory of
Democritus University of Thrace by the students M. Georgi-
adou and Ch. Trigousi, whose careful work is acknowledged.
7 REFERENCES
ASTM D698 1998. Standard test method for laboratory compaction
characteristics of soil using Standard effort (12,400 ft-lbf/ft
3
(600
kN-m/m
3
)).
Annual Book of ASTM Standards
04.08 (I), 77-84.
ASTM D4546 1998. Standard test methods for one-dimensional swell
or settlement potential of cohesive soils.
Annual Book of ASTM
Standards
04.08 (I), 663-669.
BS 1377 1990.
Soils for Civil Engineering Purposes – Part 7: Shear
Strength Tests (Total Stress)
. British Standards Institution, London.
Bishop A.W., Green G.E., Garga V.K., Andresen A. and Brown J.D.
1971. A new ring shear apparatus and its application to the
measurement of residual strength.
Géotechnique
21 (4), 273-328.
Bromhead E.N. 1979. A simple ring shear apparatus.
Ground
Engineering
12 (5), 40-44.
Chandler R.J. 1966. The measurement of residual strength in triaxial
compression.
Géotechnique
16 (3), 181-186.
Christodoulias J. and Gasios E. 1987. Investigation on the motorway
damage due to expansive soil in Greece.
Proc. 6th Int. Conf. on
Expansive Soils
, New Delhi, 241-245.
Gibbs H.J., Hilf J.W., Holtz W.G. and Walker F.C. 1960. Shear strength
of cohesive soils.
Proc. Research Conf. on Shear Strength of
Cohesive Soils
, Boulder, 33-162.
Hawkins A.B. and Privett K.D. 1985. Measurement and use of residual
shear strength of cohesive soils.
Ground Engineering
18 (8), 22-29.
Kalteziotis N. 1993. The residual shear strength of some Hellenic clayey
soils.
Geotechnical and Geological Engineering
11, 125-145.
Kollaros G. and Athanasopoulou A. 1997. The character and
identification of swelling soils in road construction projects.
Proc.
Engineering Geology and the Environment
, Marinos et al. (eds.),
Balkema, 187-192.
Koudoumakis P. 2000.
Personal communication
. Democritus
University of Thrace, Xanthi, Greece.
Lupini J.F., Skinner A.E. and Vaughan P.R. 1981. The drained residual
strength of cohesive soils.
Géotechnique
31 (2), 181-213.
Mesri G. and Cepeda – Diaz A.F. 1986. Residual shear strength of clays
and shales.
Géotechnique
36 (2), 269-274.
Papakyriakopoulos P. and Koudoumakis P. 2001. Swelling soils in the
area of Thrace.
Proc. 4th Hellenic Conf. on Geotechnical and
Geoenvironmental Engineering
1, Athens, 163-170. (in Greek)
Skempton A.W. 1964. Long-term stability of clay slopes.
Géotechnique
14 (2), 75-101.
Skempton A.W. 1985. Residual strength of clays in landslides, folded
strata and the laboratory.
Géotechnique
35 (1), 3-18.
Stamatopoulos A., Gassios E., Christodoulias J. and Giannaros H. 1989.
Recent experiences with swelling soils.
Proc. 12th Int. Conf. on
Soil Mechanics and Foundation Engineering
2, Rio de Janeiro,
655-658.
Stamatopoulos A., Christodoulias J. and Giannaros H. 1992. Treatment
of expansive soils for reducing swell potential and increasing
strength.
Quarterly Journal of Engineering Geology
25, 301-312.
Stark T.D. and Eid H.T. 1994. Drained residual strength of cohesive
soils.
Journal of Geotechnical Engineering
120 (5), 856-871.
Tsiambaos G. and Tsaligopoulos Ch. 1995. A proposed method of
estimating the swelling characteristics of soils: some examples from
Greece.
Bulletin of the International Association of Engineering
Geology
52, 109-115.
Xeidakis G. 1993. Swelling soils in Thrace, Northern Greece: origins
and properties.
Proc. Geotechnical Engineering of Hard Soils –
Soft Rocks
1, Anagnostopoulos et al. (eds.), Balkema, 863-870.
