ABSTRACT:

A simple criterion for creep induced failure is proposed for drained loading of over-consolidated clays. The criterion is proposed for the prediction of the long-term shear strength for assessment of stability of slopes and for the estimation of the time to the onset of failure (onset of tertiary creep) based on the accumulated strain. The criterion is based on the results of long-term, drained laboratory creep tests on overconsolidated and structured sensitive, strain weakening clays. A summary of the general characteristics of creep is presented followed by the proposed criterion and the results of published laboratory test data that support the criterion.

INTRODUCTION

Creep induced instability in clayey slopes often occurs at strengths less than the peak strength, with the time to failure ranging from days to tens of years. Several empirical models have been proposed for the prefailure deformation behaviour in such slopes, including the relationships for creep at decreasing and increasing strain rates with time (e.g. see Singh and Mitchell, 1968, and Saito and Uezawa, 1961). Presented in this paper is a strain criterion for the Òfirst timeÓ failure of slopes in over-consolidated clays due to creep under constant shear stress. The basis for the criterion is the process of the creep induced plastic deformations and strain weakening, leading to failure at stress levels below the peak strength. The main aspect of the criterion is that the level of total strain at which the onset of failure due to creep occurs is equivalent to the shear strain to the peak strength on the stress-strain relationship of the soil determined from conventional drained strength test. Hence, the strain (and time) to the onset of failure can be predicted based on the accumulated shear strain.

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