Numerical Model with Finite Differences Approach for CRS Consolidation Test

Abderrahmane Henniche

doi:10.11648/j.es.20180303.11

Abstract

The Constant Rate of Strain (CRS) consolidation test is extensively used in last time to estimate the settlement of clayey soils in many geotechnical laboratories. Different theoretical solutions and numerical models have been developed to estimate consolidation parameters from CRS consolidation test data, and investigate the strain rate effect on the CRS consolidation results. In this study, a new numerical model is developed to simulate CRS consolidation test for small and large strain conditions and for both linear and nonlinear soils. This numerical model is based on the solution of Terzaghi’s classical consolidation equation by finite differences approach, with taking into account the variation of sample height with test time. Results of this numerical model indicate that applied vertical load at the top boundary of sample and excess pore pressure at its base are dependent on the applied strain rate. Evaluation of the consolidation parameters from numerical results of this model with small and large theoretical solutions shows excellent agreement between all methods in small strain level, and when large strain conditions are reached only use of large strain theories can produce good convergence with model results. However, when great strain rates (approximately β ≥ 0.1) are applied, a significant error can be observed in consolidation parameters calculation by using both small and large solutions. Finally, simulation of some experimental CRS tests reported in literature with this numerical model provides comparable consolidation parameters to those evaluated from the experimental CRS tests data.

Highlights

The Constant Rate of Strain consolidation test (CRS test) became in the last decades as an alternative procedure to the standard consolidation test (IL test) to evaluate the consolidation properties of clayey soils in many countries
Consolidation parameters obtained by CRS consolidation tests are dependent on the applied strain rates [2, 7, 11,12,13,14,15,16], and many criteria have been proposed by authors to select adequate strain rates for CRS tests [2, 3, 5, 17]
For RMMC, a good convergence is observed for the case of nonlinear soil between cv and kv variations obtained by this numerical model and experimental variations of cv and kv evaluated by large strain theories of CRS consolidation test, with a small deviation of cv variations at the start of steady state

Summary

Introduction

The Constant Rate of Strain consolidation test (CRS test) became in the last decades as an alternative procedure to the standard consolidation test (IL test) to evaluate the consolidation properties of clayey soils in many countries. The CRS consolidation test, comparatively to the standard consolidation test, can be completed in a reduced time (one to two days) for large range of soils, and produces continuous responses in particular the compressibility curve. Several studies based on large strain conditions, have been conducted [4,5,6] to take into account the continuous nature of CRS test with important total stain levels [7, 8]. Differences Approach for CRS Consolidation Test small time steps, the Terzaghi’s linear one-dimensional consolidation theory. The results of some experimental works are used to check the ability of this numerical model to produce consolidation parameters (cv and kv) comparable to those evaluated during experimental CRS tests

Model Structure

Model Results

Experimental Verification

Conclusions