Constitutive and multi-block modeling of landslides on saturated sands along slip surfaces

Abstract

The paper first proposes and validates a constitutive model simulating the change of resistance along slip surfaces in sands both for the undrained and drained cases, measured in ring shear tests. The proposed model is based on (a) the critical state theory and (b) the assumption that the critical state changes as a result of grain crushing, in terms of shear displacement. Model parameters depend only on sand type. Then, the developed constitutive model is implemented in the recently-proposed multi-block sliding system model for the prediction of the triggering and deformation of earthquake-induced landslides. The improved model is applied successfully at a simple slope and at the well-documented Nikawa slide triggered by the 1995 Hyogoken-nambu earthquake. Parametric analyses illustrated the ability of the improved model to simulate the effect of the applied motion, sand density, saturation conditions and geometric rearrangement on the seismic displacement of slopes.

Analytical solutions for the sliding displacement of model slopes simulating both the frictional and rotational effects under piecewise linear acceleration pulses

“…Thus, excess pore pressures may accumulate and this pore pressure build-up is large for loose sands and soft clays and may increase even more as a result of grain crushing in sands and re-orientation of particles in clays. 39,40,42 Usually, this excess pore pressures accumulation mainly occurs in a few mm of shear displacement 8,37 and decreases the shear soil strength to its residual value. It is inferred that in the saturated case, the residual strength, and thus the equivalent total frictional resistance, which indirectly simulates pressure build-up, also, may be in some cases very small, much smaller than their peak strength.…”

“…Under saturated conditions, as shearing along the slip surface is typically fast, undrained conditions prevail for both sandy and clayey soils. Thus, excess pore pressures may accumulate and this pore pressure build‐up is large for loose sands and soft clays and may increase even more as a result of grain crushing in sands and re‐orientation of particles in clays 39,40,42 . Usually, this excess pore pressures accumulation mainly occurs in a few mm of shear displacement 8,37 and decreases the shear soil strength to its residual value.…”

“…In fact, it may take a value less than the average inclination of the slope. In this case, static instability occurs and the critical acceleration value a c is less than zero, or negative 2,39 . A field example of a slope where such an earthquake‐induced static instability occurred is the Nikawa landslide triggered by 16/1/95 Kobe, Japan earthquake, where post‐failure analysis and laboratory testing illustrated the residual frictional angle along the slip surface was reduced to 8.5 o with a corresponding a c value of −0.10 g 39,40 …”

Non-Linear Dynamic Seismic Sliding Movement of Dry Slopes

“…The "conventional" sliding-block model simulates the basic mechanism of the generation of seismic displacement along slip surfaces. However, it is not accurate in some cases, primarily because of (a) the dynamic response of the sliding mass and the soil profile below the sliding mass [4][5][6][7], (b) the degradation of the shear modulus along the soil profile with shear strain [6], (c) changes of the geometry of the sliding mass towards a gentler inclination [8][9][10][11][12][13][14][15], and (d) the loss of strength in the slip surface with permanent shear displacement [16,17].…”

Simplified Multi-Block Constitutive Model Predicting the Seismic Displacement of Saturated Sands along Slip Surfaces with Strain Softening

“…In addition, Stamatopoulos and Korai [17] proposed and validated with a number of ring shear tests a constitutive model in terms of effective stresses simulating the change of resistance along slip surfaces with shear displacement for sands either under undrained or drained conditions. The model requires 12 model parameters evaluation, which require the availability or performance of ring shear tests at different densities and drainage conditions.…”