Drained Shear Strength Parameters for Analysis of Landslides

Abstract

This paper presents recommendations for selecting the type and magnitude of drained shear strength parameters for analysis of landslides. In particular, the importance, existence, and use of the cohesion shear strength parameter is reviewed. For slope stability analyses, it is recommended that the shear strength be modeled using a stress dependent failure envelope or a friction angle that corresponds to the average effective normal stress acting on the slip surface passing through that particular material instead of using a combination of cohesion and friction angle to represent soil shear strength. Other recommendations for stability analyses include using an effective stress cohesion of zero for residual and fully softened strength situations. To facilitate selection of shear strength parameters for landslide analyses, empirical relationships for the drained residual and fully softened strengths are updated from the previous empirical relationships presented by Stark and Eid. Finally, the paper presents torsional ring shear test results that indicate that pre-existing shear surfaces exhibit self-healing that results in increased shear resistance. The magnitude of healing appears to increase with increasing soil plasticity, and this increase could have implications for the size, timing, and cost of landslide remediation.

Case History of Landslide Movement during the Northridge Earthquake

“…Fig. 4͑a͒ also shows the estimated nonlinear strength envelope based on a correlation relationship between soil plasticity, overburden pressure, and residual friction angle by Stark et al ͑2005͒. A range of strengths from the correlation relationship is shown with shading because of the variable plasticity of the bedrock materials.…”

Reactivation mechanism of ancient giant landslides in the tectonically active zone: a case study in Southwest China

“…The consolidation undrained (CU) ring shear test was then conducted on each specimen under different normal stresses. An effective normal stresses of 100 kPa or less correspond to shallow landslides or shallow portions of a slip surface (\5 m) (Stark et al 2005). In this study, experiments were conducted under a normal stress of 100, 200, and 400 kPa, respectively, corresponding to the deepseated landslide situation.…”

“…A healing mechanism of the rupture surface may also help understand its high shear strength. Stark et al (2005) presented ring shear test results on two soil specimens with a period of 230 days and suggested that a failure surface which has achieved a drained residual strength condition may undergo ''healing'' and exhibit a higher strength than the earlier residual value. Carrubba and Del Fabbro (2008) also suggested that the strength along a pre-existing shear surface may increase with time if the sliding mass stops moving and remains stable.…”

An On-Situ Study of Stability Analysis on Slopes Using Undrained Shear Strength Parameters

“…Other recommendation for stability analysis includes using effective stress cohesion of zero for residual and fully softened strength situations. [8] Hsin-Fu et al, (2006) focused for calculating the safety factor for an unsaturated slope distress from rainfall infiltration. The relationship between effective degree of saturation and safety factor indicated linear decrease, and therefore the shear strength gets reduced caused due to water content increase.…”