Effect of prior small to moderate seismic events on monotonic undrained shear strength of sand

Ting-Wei Wu,Yusuke Suzuki,Brian Carlton,Carl Harbitz,Achim Kopf

doi:10.1016/j.soildyn.2020.106465

Abstract

In this study we investigate the effect of prior seismic shaking on the monotonic shear strength of saturated Ottawa Sand 20/30. We perform a series of stress-controlled undrained cyclic triaxial tests with different seismic intensities intentionally without causing failure, followed by drainage of the excess pore pressure and an undrained monotonic loading test to determine the undrained shear strength. The experimental data show that small to moderate seismic events that do not fail the specimen can significantly increase undrained shear strength without much change in relative density. One prior seismic event with peak ground acceleration ~ 1.3 m/s2 may increase the undrained shear strength of a specimen at ~ 10 m depth by around 30%. The results also show that as the intensity of the shaking increases, the increase in the monotonic shear strength increases. However, the strengthening effect does not increase with the number of seismic events although a small degree of global densification in the sample is observed. The results of this paper will help assess the change in static slope stability after a single or multiple small to moderate events occurred without causing initial instability.

Highlights

Submarine landslides are a major threat to offshore infrastructure and coastal communities because of their large displacements and po tential to trigger tsunamis
Sawyer and DeVore [3] showed from worldwide vane-shear data tested on previ ously unfailed sediments that active margin sites have consistently higher shear strengths than passive margins by a factor of approximately 2–3, at least until 10 m below the seafloor
The specimens were first subjected to undrained cyclic loading followed by reconsolidation allowing drainage

Summary

Introduction

Submarine landslides are a major threat to offshore infrastructure and coastal communities because of their large displacements and po tential to trigger tsunamis. On active continental margins there are surprisingly fewer observed landslides than passive margins, despite the increase in earthquake activity (e.g. Shanmugan [1]). Nelson et al [2] found shorter run-out distances of mass transport de posits on active margins compared with passive margins. Sawyer and DeVore [3] showed from worldwide vane-shear data tested on previ ously unfailed sediments that active margin sites have consistently higher shear strengths than passive margins by a factor of approximately 2–3, at least until 10 m below the seafloor.

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Conclusion