Stress relaxation coefficient and formulation for soft soils

Abstract

Current studies rarely investigate the stress relaxation behaviour of soft soils. This paper proposes a practically useful coefficient with a formulation based on the behaviour of stress relaxation under onedimensional conditions. Firstly, the stress relaxation coefficient is proposed after summarising stress relaxation test results according to the linear relationship between the vertical stress and time in a double logarithmic plot. Secondly, from the newly developed rate-dependency based elastoviscoplastic formulations, an analytical solution for stress relaxation is derived. A unique relationship connecting the stress relaxation coefficient, the secondary compression coefficient and the ratedependency coefficient is then obtained. The applicability of the stress relaxation formulation with its key coefficient to determine time-dependent parameters is finally validated with published experimental results on reconstituted illite and Berthierville clay. Graham, 1989;Kutter & Sathialingam, 1992;Sheahan, 1995;Vermeer & Neher, 1999;Yin et al., 2010a;Wang & Yin, 2013 are conducted to evaluate the timedependent properties of soils. A few stress relaxation tests (e.g. Lacerda & Houston, 1973;Yin & Graham, 1989;Sheahan et al., 1994;Fodil et al., 1997;Kim & Leroueil, 2001;Yin & Hicher, 2008) have also been carried out and used to investigate the stress relaxation behaviour under different conditions. However, due to a lack of studies concerning the relationship between the key parameters of stress relaxation and strain-rate-dependency or creep parameters, the stress relaxation test is still not widely used to determine the timedependency related parameters of soft soils. This paper attempts to propose a stress relaxation coefficient with a formulation describing stress relaxation versus time, and investigates its relevance with the strainrate-dependency parameter and the secondary compression coefficient. First, studies on stress relaxation are briefly summarised and discussed. A new stress relaxation coefficient based on the stress relaxation oedometer test -one of the simplest tests for soils -is then proposed. By deriving a newly developed rate-dependency based formulation, a stress relaxation formulation is proposed and relationships connecting the stress relaxation coefficient, the secondary compression coefficient and the rate-dependency coefficient are obtained. Published experimental results on reconstituted illite and Berthierville clay are used to validate the proposed formulation and coefficient, and the relationships between different time-dependency parameters.

Numerical Modeling of Thermal‐Dependent Creep Behavior of Soft Clays under One‐Dimensional Condition

“…Actually, the intrinsic stress σ vi ′ in Equation (12) can be regarded as the reference stress as indicated in Equation (8), and the bonding ratio can be regarded as the scaling parameter. us, the present model is then composed of Equations (8), (9), and (12). Combining with the elastic strain rate in Equation (5), the stress-strain curve for a given temperature can be obtained.…”

“…e creep behavior of the soft clay has been investigated experimentally in [1][2][3][4][5]. Based on that, some practical models have been developed [6][7][8][9].…”

Effect of loading duration on uncertainty in creep analysis of clay

“…Buisman was probably the first to model the effect of time on the compression of clay by introducing the term secondary compression. Thereafter, researchers conducted a significant number of studies on one‐dimensional secondary compression . In general, a complex model with more parameters can better capture the creep deformation of soft soil.…”

Modelling the time‐dependent behaviour of granular material with hypoplasticity

“…For granular soil, however, the study on the time‐dependent behaviour has started only recently. Clayey soil, usually referred to as isotach material, follows a classical deformation pattern with time . Granular soil, however, does not follow this classical pattern and is referred to as non‐isotach material .…”

“…Clayey soil, usually referred to as isotach material, follows a classical deformation pattern with time. [11][12][13][14][15] Granular soil, however, does not follow this classical pattern and is referred to as non-isotach material. [16][17][18][19] Numerous triaxial tests with constant strain rates show that the effect of strain rate on the stress-strain relationships of sand is insignificant, 4,[20][21][22] which means that the stress-strain relationship is independent of the strain rate.…”