Experimental Testing and Numerical Modelling of Mechanical Behaviors of Silty Clay under Freezing-Thawing Cycles

Tianfei Hu,Hui Wu,Dawei Liu

doi:10.1155/2020/9693156

Abstract

Seasonal freezing-thawing cycle is one of the most common physical weathering processes in cold regions, which can significantly affect the mechanical behaviors of soil. In this paper, a series of freezing-thawing (F-T) cycle and consolidated drained triaxial tests have been carried out on silty clay samples collected from Tibetan Plateau. To do so, a modified numerical model was developed taking into F-T effect. Test results showed that the stress-strain curves of original soil specimens presented strain hardening characteristics, accompanied with shear shrinkage. In F-T experienced specimens, volumetric strain in triaxial loading stage was gradually increased, while failure strength was decreased. Elliptic and parabolic functions were selected in numerical modelling to describe volume and shear yield surfaces on ap-qplane, respectively. Moreover, a double-yield surface constitutive model was developed to describe relationships among deviatoric stress, axial strain, and volumetric strain. Furthermore, equations for model parameters with the number of F-T cycles as variable were derived based on the triaxial test results which were then substituted into the established model to take into account the effects of F-T cycles. Finally, numerical results were validated with experimental findings.

Highlights

In cold regions, ground bases, and soil foundations such as subgrades, generally suffer seasonal and diurnal freezingthawing (F-T) cycles due to atmospheric temperature changes
Numerical constitutive models can quantitatively predict the mechanical behaviors of soil [1]. erefore, numerical modelling of soil mechanical behaviors is one of the main geotechnical engineering research issues in cold regions
Elastoplastic models mainly refer to the Cam-clay model which was first proposed by Roscoe and Schofield [3] and a series of modified singleyield surface models developed on the basis of the original one

Summary

Introduction

Ground bases, and soil foundations such as subgrades, generally suffer seasonal and diurnal freezingthawing (F-T) cycles due to atmospheric temperature changes. Asaoka et al [4] established a modified model capable of reflecting historical stress path and soil structure characteristics, by embedding super-consolidation and structural parameters into the Cam-clay model yield function to form upper and lower loading yield surfaces in the p-q plain. Mathematical Problems in Engineering proposed UH models suitable for both super- and normal consolidated soils, based on the Cam-clay model and lower loading surface concept. Yin et al [13, 14] proposed yield and hardening functions relating to compress and shear loadings, respectively, and established another two-yield surface model using correlated flow law. Chang et al [22, 23] established a two-yield surface model considering F-T effect by fitting the equations of hardening function coefficients as a cubic polynomial with the number of F-T cycles. A modified model was proposed and validated to predict the deviatoric stress, axial strain, and volumetric strain of soil under F-T cycles

Soil Specimens and Test Scheme

Test Results and Analysis

Two-Yield Surface Constitutive Model

Functional Expressions for Model Parameters

Conclusions