Calculation of Tangent Modulus of Soils under Different Stress Paths

Hua Huang,Min Huang,Jiangshu Ding

doi:10.1155/2018/1916761

Abstract

During excavation of foundation pit, soils of different sites may undergo different unloading paths. This study focuses on the tangent modulus of soil under different stress paths and provides theoretical basis for the deformation calculation of soil. In this paper, conventional triaxial compression test andK0consolidation unloading test were conducted with mucky soil and silty clay to obtain the deformation characteristics of soils under different stress paths. Experiment results show that the soil samples exhibit distinct stress-strain characteristics under different stress paths, but they all show nonlinearity. The initial tangent modulus increases as the consolidation confining pressure intensifies. Then, based on the test data, the power function relationship between initial tangent modulus and confining pressure under unloading was verified. Simultaneously, a hyperbola function to express stress-strain relation of soils under theK0consolidation unloading condition was proposed and proved. Finally, the formulas of the tangent modulus underK0consolidation unloading were established referring to the derivation of that in Duncan–Chang model. The theoretical calculation results agree well with the test results. It can expand the use of the Duncan–Chang model and improve its application to engineering practice.

Highlights

Excavations alter the initial stress states of soil around the foundation pit and unavoidably have varying degrees of impacts to surrounding existing structures
This study focuses on the tangent modulus of soil under different stress paths and provides theoretical basis for the deformation calculation of soil
Studying the mechanical characteristics of soils on different sites during deep excavation is greatly significant to its design and construction

Summary

Introduction

Excavations alter the initial stress states of soil around the foundation pit and unavoidably have varying degrees of impacts to surrounding existing structures. Chen et al [23], Li [24], and He et al [25] obtained the stress-strain relationship of soil under lateral unloading and derived the tangent modulus under lateral unloading stress path on the basis of the Duncan–Chang model. The scope of the aforementioned studies is narrow They focus mainly on the stress-strain relation and modulus formula under lateral unloading stress path. With the increasing number of foundation pits, obtaining the tangent modulus of soil under different stress paths is important to satisfactorily predict the deformation of soil during excavation. In order to derive the calculation formulas of tangent modulus under different stress paths, the conventional triaxial compression test and the K0 consolidation unloading test were conducted on the representative mucky soil and silty clay.

Mechanical Properties of Soil under Different Stress Paths

Non-unloading area

Initial Tangent Modulus of Soil under Unloading Condition

Calculation Formula of Tangent Modulus

Verification for the Tangent Modulus under Unloading

Conclusions