Residual Shear Strength Measured by Laboratory Tests and Mobilized in Landslides

Abstract

Drained residual shear strength measured by multiple reversal direct shear or ring shear tests has been successfully used for over four decades for stability analyses of reactivated landslides in stiff clays and clay shales; A body of literature has accumulated in recent decades, claiming that "healing" or "strength regain" is realized in time on preexisting slip surfaces already at residual condition. In other words, the shear stress required to reactivate a landslide is claimed to be larger than the drained residual shear strength determined using laboratory tests. This article presents (1) a comparison of secant residual friction angle determined from laboratory tests and secant mobilized friction angle back-calculated for reactivated landslides; (2) explanations that field evidence used to claim "healing" can be attributed to alternative factors, and the laboratory evidence on "strength regain" upon reshearing is the result of either the testing apparatus or testing procedure, or is inapplicable to stiff clays and shales; and (3) laboratory aging test results, which show no "strength regain" on preexisting shear surfaces at residual condition.

Determination of Residual Shear Strength from Reversal Direct Shear test: Analysis and Recommendation

“…In this manner, peak shear strength of soil sample can be obtained and failure plane for pre-cutting can also be exactly determined. Precutting specimen was observed to have had a slight advantage due to the proper alignment of particles on both side of shear plane and generation of horizontal and planar shear surface [7,8]. The cut portion of soil sample should be exactly in between the shear box else the failure plane will vary and the results can't be relied upon.…”

“…Likewise, the vertical displacement is observed due to loss of soil in the center gap in the shear box [7]. Hence, precutting specimen has a slight advantage due to the proper alignment of particles on both side of shear plane and generation of horizontal and planar shear surface [7,8]. Fast shearing followed by slow shearing gives a steady shearing strength and lowest value of residual strength.…”

Numerical Analysis of Slope Stability by Strength Reduction in Finite Elements Using ANSYS a Case Study of Qinglong-Xingyi Expressway Contract Section T1(K11+790~K11+875)

“…Besides the numerous numerical studies, numerous investigations have also been carried out on the residual strength of different types of slip zone soils by researchers like Skempton [26] and Chen and Liu [27]. Mesri and Nejan's [28] work in comparing residual strengths obtained in laboratory tests and those measured in the field has greatly improved the understanding of the mechanism of reactivation of ancient landslides.…”

Slope stability in slightly fissured claystones and marls

“…However, there is evidence showing that chemical processes lead to a modification of the laboratory measured residual strength. Any process leading to a change of the clay content and clay mineralogy in the sliding surface will lead to a modification of shear strength (Mesri and Huvaj-Sarihan, 2012). Some of these features will be described in the paper and discussed further in connection with some slope stability case histories.…”

“…Alonso (2012) provides a recent account of some experimental data on strength recovery in terms of "resting" time. Mesri and Huvaj-Sarihan (2012) question the gain in residual strength in resting periods. They believe that the gain observed in drained reversal shear box tests as well as in torsional shear tests is a consequence of spurious experimental results.…”