Stability of swelling clay embankments

1979 ◽  
Vol 16 (1) ◽  
pp. 140-151 ◽  
Author(s):  
R. A. Widger ◽  
D. G. Fredlund
Keyword(s):  
Shear Strength ◽  
Pore Water ◽  
Back Analysis ◽  
Triaxial Tests ◽  
Shear Strength Parameters ◽  
Strength Parameters ◽  
Total Strength ◽  
Swelling Soils ◽  
Pore Water Pressures ◽  
Matrix Suction

A common occurrence in cuts or fills of swelling soils is their reduction in strength with time. At the time of compaction, the clay generally has a high matrix suction. Correspondingly, it has a high strength and will stand at relatively steep side slopes. With time, the soil generally tends towards saturation and the matrix suction reduces towards zero. There is a reduction in total strength and if the gravitational forces are too large, the slope fails.During the past several years, numerous cut and fill slopes have been observed in the Regina area of Saskatchewan. Many of these slopes have remained stable for 4–6 years and then failed. There has been a 20 year history of observations on the Belle Plaine overpass west of Regina. Field and laboratory investigations have been conducted.With a knowledge of the geometry of the slope and failure plane, the simplified Bishop method of stability analysis was used to perform a 'back-analysis' to assess the shear strength parameters. The shear strength parameters from the laboratory program are compared with those calculated from the stability analyses. The analyses indicate that the peak shear strength parameters from triaxial tests on the softened Regina clay (i.e., c' = 5 kPa and [Formula: see text]), with the appropriate pore water pressures, give a factor of safety of 1 for the failed surface. The effect of spring thawing appears to be to produce the condition of most serious pore water pressures.

Shear strength parameters from back-analysis of single slips

Géotechnique ◽  
2001 ◽  
Vol 51 (4) ◽  
pp. 373-374 ◽  
Author(s):  
L. D. Wesley ◽  
V. Leelaratnam
Keyword(s):  
Shear Strength ◽  
Back Analysis ◽  
Shear Strength Parameters ◽  
Strength Parameters

A landslide in till near Warman, Saskatchewan, Canada

1985 ◽  
Vol 22 (2) ◽  
pp. 195-204 ◽  
Author(s):  
E. Karl Sauer ◽  
E. A. Christiansen
Keyword(s):  
Shear Strength ◽  
Water Table ◽  
Back Analysis ◽  
Clay Content ◽  
Aerial Photographs ◽  
Adjacent Area ◽  
Shear Strength Parameters ◽  
Strength Parameters ◽  
Residual Shear Strength ◽  
Insight Into

Little information is available about typical shear strength parameters of tills in southern Saskatchewan even though till is the most common earth material used for construction in this region. The Warman landslide in the South Saskatchewan River Valley provides some insight into the shear strength characteristics of a till, and the results are compared with laboratory tests. The till is from the Upper till of the Sutherland Group, which has a high clay content relative to the underlying and overlying tills. A back analysis of the landslide produced [Formula: see text]′ = 27° assuming c′ = 0. Comparison with laboratory test data and results from a similar landslide near Lebret, Saskatchewan, suggests that [Formula: see text]′ = 22.5° with c′ = 7 kPa may be appropriate "residual" shear strength parameters. A rising water table appears to have been the main contributing factor to instability between 1969 and 1984. There is a possibility, however, that at the 1:50 return interval for flood levels on the river, erosion at the toe of the landslide debris may be a significant factor. Numerous slump scars in the form of small amphitheatres, presently inactive, can be observed in the aerial photographs of the adjacent area. These failures likely occurred intermittently, depending on fluctuating water table and river flood levels. Key words: landslide, till, correlation, stratigraphy, back analysis, shear strength, residual, aerial photographs.

scholarly journals UNDRAINED SHEAR STRENGTH PARAMETERS OF SAPROCK FROM A WEATHERING PROFILE OVER PORPHYRITIC BIOTITE GRANITE AT KM 31 OF THE KUALA LUMPUR - KARAK HIGHWAY, PENINSULAR MALAYSIA

2021 ◽  
Vol 33 (2) ◽  
Author(s):  
John Kuna Raj
Keyword(s):  
Shear Strength ◽  
Friction Angle ◽  
Undrained Shear Strength ◽  
Triaxial Tests ◽  
Regression Analyses ◽  
Shear Strength Parameters ◽  
Weathering Profile ◽  
Strength Parameters ◽  
Zone Ii ◽  
Undrained Shear

Three broad zones can be differentiated at the weathering profile; an upper, 9.4 m thick, pedological soil (zone I), an intermediate, 31.7 m thick, saprock (zone II) and the bottom bedrock (zone III). The saprock (zone II) comprises gravelly silty sands that distinctly preserve the minerals, textures and structures of the original granite and can be separated into sub-zones II A, II B, II C, and II D, based on differences in preservation of relict structures and content of litho-relicts (core-boulders). To characterize the undrained strength of saprock, samples were collected from sub-zones II A, II B, II C and II D and their physical and soil index properties determined before unconsolidated undrained triaxial tests were carried out on remolded samples. Three to four individual samples from each sub-zone were compressed under confining pressures of 138 kPa, 207 kPa, 276 kPa and/or 345 kPa. Plots of pf = [(σ1 + σ3)/2] versus qf = [(σ1 - σ3)/2] were then used to calculate apparent cohesions of 41.9 kPa, 100.3 kPa, 76.1 kPa and 73.9 kPa, and friction angles of 32.2o, 28.1o, 26.6o and 27.8o, for the samples from sub-zones II A, II B, II C, and II D, respectively. Regression analyses show apparent cohesions to decrease with increasing clay contents, and degrees of saturation; features indicating the influence of negative pore water (or suction) pressures. Regression analyses also show apparent friction angle to increase with increasing sand contents; a feature attributed to greater inter-locking and resistance to displacement of these particles. It is concluded that the undrained shear strength parameters of saprock are characterized by an average apparent cohesion of 54.6 kPa, and friction angle of 30.5o; the parameters influenced by the degree of saturation as well as clay and sand contents.

Shear strength of the weathered Champlain clay measured in a large diameter triaxial test

1982 ◽  
Vol 19 (4) ◽  
pp. 413-420
Author(s):  
J. Lafleur ◽  
G. Lefebvre ◽  
M. Marcotte ◽  
V. Silvestri
Keyword(s):  
Shear Strength ◽  
Triaxial Test ◽  
Large Diameter ◽  
Back Analysis ◽  
Sampling Procedure ◽  
Triaxial Tests ◽  
Large Sample Size ◽  
Compression Tests ◽  
Strength Parameters ◽  
Triaxial Cell

This paper describes the sampling procedure and the results of large diameter (150 mm) CID triaxial tests made on samples recovered from the weathered clay crust of the Champlain sea deposits.A visual inspection of the fissures at the depth of sampling (3 m) revealed two types of discontinuities: (a) sub-vertical joints containing black organic matter, spaced approximately every 10 cm, and (b) closed microfissures, randomly distributed in spacing and direction. In order to recover unremoulded samples of this material and avoid a difficult retrimming in the laboratory, a double core barrel 150 mm in diameter (the same as that of the triaxial cell base) was used. Eight compression tests under low confining stresses were made; they showed that the post-peak strength parameters were substantially higher than those back-calculated from a landslide involving the same weathered crust. Examination of the shape of the failure planes and of the stress–strain curves led to the conclusion that, in spite of the large sample size, the propagation of the fractures was controlled by the intact clay matrix rather than by the fissures. Since this was not believed to reproduce the actual field behaviour, a complementary test programme was undertaken, which indicated that the strength parameters were better evaluated from CID tests performed in the normally consolidated range. Keywords: fissured clays, weathering, landslides, triaxial test, shear strength parameters, sampling, back-analysis.

Behaviour of the stiff and sensitive Saint-Jean-Vianney clay in intact, destructured, and remoulded conditions

2002 ◽  
Vol 39 (5) ◽  
pp. 1075-1087 ◽  
Author(s):  
Faten Saihi ◽  
Serge Leroueil ◽  
Pierre La Rochelle ◽  
Ivan French
Keyword(s):  
Shear Strength ◽  
Large Deformation ◽  
Limit State ◽  
Triaxial Tests ◽  
Compression Tests ◽  
Shear Strength Parameters ◽  
Strength Parameters ◽  
Soft Clays ◽  
The Difference ◽  
State Curve

The role of the degree of microstructure on the behaviour of clayey soils has been the focus of many studies. However, none so far have quantified the evolution of the shear strength parameters for a given soil for degrees of microstructure going from an intact condition to complete remoulding. In the present study, a series of compression triaxial tests have been performed on specimens of the naturally highly structured Saint-Jean-Vianney clay under the following conditions: intact, destructured by straining outside the limit state curve, and reconstituted and reconsolidated after complete remoulding. The results show that the limit state curve is influenced by the level of destructuration reached before testing, and moreover, that the shear strength parameters at large deformation are influenced by the level of destructuration at the beginning of the test. The compression tests infer that the soil seems to retain the memory of its initial microstructure, at least for consolidation volumetric strains up to 14%. The observed behaviour has implications for the understanding and modelling of natural clays; it also explains to some extent the difference in strength parameters used in stability analyses of embankments on soft clays and natural slopes in clay.Key words: clay, microstructure, destructuration, shear strength, large deformation shear strength, triaxial test.

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