Slope Stability Analyses in Stiff Fissured Clays

Results of torsional ring shear, direct shear, and triaxial compression tests on cohesive soils reveal that the fully softened shear strength is stress-dependent and related to the type of clay mineral and quantity of clay-size particles. An empirical relationship for the fully softened friction angle is presented that is a function of liquid limit, clay-size fraction, and effective normal stress. Studies of first-time slides, i.e., slopes that have not undergone previous sliding, in stiff fissured clay with a liquid limit between 41 and 130% suggest that the mobilized shear strength along the failure surface can be lower than the fully softened shear strength. Recommendations are presented for estimating the mobilized shear strength in first-time slides based on soil plasticity. Soils with a liquid limit greater than 30% exhibit a large difference between the fully softened and residual friction angles. In these soils, the presence or absence of a pre-existing shear surface should be clarified.

[1]  R. Chandler.  Lias clay: the long-term stability of cutting slopes , 1974 .

[2]  Alec Westley Skempton,et al.  JOINTS AND FISSURES IN THE LONDON CLAY AT WRAYSBURY AND EDGWARE , 1969 .

[3]  P. J. Rivard,et al.  Shear strength of soft fissured clays , 1978 .

[4]  Hisham T. Eid.  Drained shear strength of stiff clays for slope stability analyses , 1996 .

[5]  A. Skempton.  Slope Stability of Cuttings in Brown London Clay , 1984 .

[6]  Mohsen M. Baligh,et al.  End Effects on Stability of Cohesive Slopes , 1975 .

[7]  A. Skempton,et al.  The design of permanent cutting slopes in stiff fissured clays , 1974 .

[8]  Alec Westley Skempton,et al.  Residual strength of clays in landslides, folded strata and the laboratory , 1985 .

[9]  E N Bromhead,et al.  A SIMPLE RING SHEAR APPARATUS , 1979 .

[10]  Gholamreza Mesri,et al.  Cohesion Intercept in Effective Stress‐Stability Analysis , 1993 .

[11]  Magdy Emadel-Din Mohamed Abdel-Ghaffar.  The meaning and practical significance of the cohesion intercept in soil mechanics , 1990 .

[12]  P. W. Rowe.  The Relationship Between the Shear Strength of Sands in Triaxial Compression, Plane Strain and Direct Shear , 1970 .

[13]  L. Bjerrum,et al.  Comparison of shear strength characteristics of normally consolidated clays , 1960 .

[14]  G. Mesri,et al.  Residual shear strength of clays and shales , 1986 .

[15]  A. Skempton,et al.  The failure of Carsington Dam , 1993 .

[16]  D. Potts,et al.  Finite element analysis of progressive failure of Carsington embankment , 1990 .

[17]  G. Mesri.  Engineering properties of montmorillonite. , 1969 .

[18]  Alec Westley Skempton,et al.  First-Time Slides in Over-Consolidated Clays , 1970 .

[19]  E. Spencer.  A Method of Analysis of the Stability of Embankments Assuming Parallel Inter-Slice Forces , 1967 .

[20]  R. J. Chandler.  Recent European experience of landslides in over-consolidated clays and soft rocks , 1984 .

[21]  L. Bjerrum.  PROGRESSIVE FAILURE IN SLOPES OF OVERCONSOLIDATED PLASTIC CLAY AND CLAY SHALES , 1967 .

[22]  R. Chandler,et al.  Lias clay: weathering processes and their effect on shear strength , 1972 .

[23]  Harry G. Poulos,et al.  Stress deformation and strength characteristics , 1977 .

[24]  T. Lambe,et al.  INSTABILITY OF AMUAY CLIFFSIDE , 1981 .

[25]  K. Terzaghi,et al.  Soil mechanics in engineering practice , 1948 .

[26]  A. Skempton,et al.  Discussion: The failure of Carsington Dam , 1995 .

[27]  R. E. Gibson,et al.  Influence of Duration of tests at Constant Rate of Strain on Measured “Drained” Strength , 1954 .

[28]  Hisham T. Eid,et al.  Drained residual strength of cohesive soils , 1994 .

[29]  H. Eid,et al.  Modified Bromhead Ring Shear Apparatus , 1993 .

[30]  A. Skempton.  Long-Term Stability of Clay Slopes , 1964 .