A laboratory investigation on an undisturbed silty sand from a slope prone to landsliding

A laboratory investigation is presented for undisturbed samples of a silty sand under saturated conditions. The soil was sampled from test pits south of Rüdlingen in North–East Switzerland, where a landslide triggering experiment was carried out on a steep forest slope. The aim of the work was to characterise the behaviour of the soil in triaxial tests, in the light of the possible failure mechanisms of the slope. Conventional drained and undrained triaxial tests were conducted to detect critical state conditions as well as peak shear strength as a function of confining pressure. Soil specimens were also exposed to stress paths simulating in situ water pressure increase to study the stress–strain response and to enhance the ability to predict failure conditions more accurately in the future. Possible unstable response along the stress paths analysed was investigated by means of second order work and strain acceleration. The results show that temporary unstable conditions may be encountered for this soil at stress ratios below ultimate failure and even below critical state line, depending on void ratio, drainage conditions and time dependent compressibility. A modified state parameter is explored as a potentially useful tool to discriminate conditions leading to eventual collapse.

[1]  C. Y. Cheuk,et al.  INFLUENCE OF STRESS RATIO AND STRESS PATH ON BEHAVIOR OF LOOSE DECOMPOSED GRANITE , 2004 .

[2]  J. P. Henry,et al.  ASSESSMENT OF SOME FAILURE CRITERIA FOR STRONGLY ANISOTROPIC GEOMATERIALS , 1998 .

[3]  G. Buscarnera,et al.  Modelling instabilities in triaxial testing on unsaturated soil specimens , 2011 .

[4]  S. Imposimato,et al.  Time dependent mechanical behaviour of loose sands , 1996 .

[5]  Cristina Jommi,et al.  An insight into the role of hydraulic history on the volume changes of anisotropic clayey soils , 2008 .

[6]  Jerry A. Yamamuro,et al.  STEADY-STATE CONCEPTS AND STATIC LIQUEFACTION OF SILTY SANDS , 1998 .

[7]  Jian Chu,et al.  Effect of fines on instability behaviour of loose sand , 2002 .

[8]  S. Imposimato,et al.  An investigation on the uniqueness of the incremental response of elastoplastic models for virgin sand , 1998 .

[9]  Félix Darve,et al.  Instabilities in granular materials and application to landslides , 2000 .

[10]  P. Vaughan,et al.  WEATHERING, STRUCTURE AND IN SITU STRESS IN RESIDUAL SOILS , 1984 .

[11]  S. Springman,et al.  Instabilities on moraine slopes induced by loss of suction: a case history , 2003 .

[12]  L. Olivares,et al.  Shallow flowslides triggered by intense rainfalls on natural slopes covered by loose unsaturated pyroclastic soils , 2003 .

[13]  Poul V. Lade,et al.  Instability and Plastic Flow of Soils. I: Experimental Observations , 1990 .

[14]  Jerry A. Yamamuro,et al.  Static liquefaction of very loose sands , 1997 .

[15]  R. Nova,et al.  CONTROLLABILITY OF THE INCREMENTAL RESPONSE OF SOIL SPECIMENS SUBJECTED TO ARBITRARY LOADING PROGRAMMES , 1994 .

[16]  C. Prisco,et al.  Mechanical modelling of drained creep triaxial tests on loose sand , 2000 .

[17]  Ken Been,et al.  A STATE PARAMETER FOR SANDS , 1985 .

[18]  Richard B. Nelson,et al.  Nonassociated Flow and Stability of Granular Materials , 1987 .

[19]  S. Imposimato,et al.  Experimental analysis and theoretical interpretation of triaxial load controlled loose sand specimen collapses , 1997 .

[20]  Malcolm D. Bolton,et al.  Evaluation of landslide triggering mechanisms in model fill slopes , 2004 .

[21]  Richard B. Nelson,et al.  INSTABILITY OF GRANULAR MATERIALS WITH NONASSOCIATED FLOW , 1988 .

[22]  Yoginder P. Vaid,et al.  Cyclic and monotonic undrained response of saturated sands , 1985 .

[23]  Eduardo Alonso,et al.  Secondary compression of clays as a local dehydration process , 2001 .

[24]  Cristina Jommi,et al.  Large shear box for analysing strength mobilisation in unsaturated conditions , 2009 .

[25]  Jian Chu,et al.  Unstable behaviour of sand and its implication for slope instability , 2003 .

[26]  R Nova.  The failure concept in soil mechanics revisited , 2002 .

[27]  Isam Shahrour,et al.  INSTABILITY AND STATIC LIQUEFACTION ON PROPORTIONAL STRAIN PATHS FOR SAND AT LOW STRESSES , 2004 .

[28]  Jerry A. Yamamuro,et al.  Effect of depositional method on the undrained response of silty sand , 2008 .

[29]  Kyoji Sassa,et al.  Factors affecting rainfall-induced flowslides in laboratory flume tests , 2001 .

[30]  A. Liapounoff,et al.  Problème général de la stabilité du mouvement , 1907 .

[31]  Amin Askarinejad,et al.  Landslide triggering experiment in a steep forested slope in Switzerland. , 2009 .

[32]  M. Coop,et al.  The mechanics of an Italian silt: an example of ‘transitional’ behaviour , 2006 .

[33]  Yoginder P. Vaid,et al.  Instability and liquefaction of granular soils under undrained and partially drained states , 1998 .

[34]  Instability of dilating sand , 1993 .

[35]  Kenji Ishihara,et al.  Normalized behavior of very loose non-plastic soils: Effects of fabric , 1997 .

[36]  Gonzalo Castro,et al.  Factors Affecting Liquefaction and Cyclic Mobility , 1977 .

[37]  Experimental observations of stability, instability, and shear planes in granular materials , 1989 .

[38]  C. Ng,et al.  Monitoring the Performance of Unsaturated Soil Slopes , 2008 .

[39]  Félix Darve,et al.  Diffuse failure in geomaterials: Experiments and modelling , 2006 .

[40]  R. Hill.  A general theory of uniqueness and stability in elastic-plastic solids , 1958 .

[41]  Félix Darve,et al.  Hydro-mechanical modelling of landslides with a material instability criterion , 2009 .

[42]  Félix Darve,et al.  Modelling of slope failure by a material instability mechanism , 2002 .

[43]  Nicholas Sitar,et al.  Analysis of Rainfall-Induced Debris Flows , 1995 .

[44]  S. Anderson,et al.  COLLAPSE OF SATURATED SOIL DUE TO REDUCTION IN CONFINEMENT. TECHNICAL NOTE , 1995 .

[45]  I. G. Vardoulakis,et al.  Plane-strain compression experiments on water-saturated fine-grained sand , 1991 .