Study on Critical Hydraulic Gradient Theory of Flow Soil Failure in Cohesive Soil Foundation

Faning Dang,Chuangzhou Wu,Mei Zhou,Jun Gao,Jiulong Ding,Yutao Li

doi:10.1155/2021/5599977

Abstract

The current formula of critical hydraulic gradient is not adapted to solve critical hydraulic gradient of cohesive soil. Assume that the seepage failure mode of the cohesive soil foundation was cylindrical or inverted circular truncated cone, based on the calculation formula of the critical hydraulic gradient of Terzaghi, the analytical formula of the critical hydraulic gradient considering the influence of the shear strength of the soil was derived. Then, the seepage failure process of the clay layer was simulated numerically, and the effects of the clay layer thickness, failure radius, and shear strength indexes on the critical hydraulic slope were analyzed. The comparison results show that the numerical test results are in good agreement with the calculated results of the new formula. In addition, the critical hydraulic gradient of sandy loam and loess under different working conditions was studied severally by a self-made permeation failure instrument. The results show that the critical hydraulic gradient decreases with the increase of soil thickness and failure radius, and the maximum error between the test and the corresponding formula results is no more than 16%.

Highlights

Infiltration is one of the important factors of engineering accidents such as dams and foundation pits, which can drive people to deeply explore the characteristics of seepage failure for better prevention and control of the occurrence of engineering accidents [1, 2]
There are many theoretical formulas for the critical condition of seepage failure, there is no unified method so far to calculate the critical hydraulic gradient, when the flow soil failure phenomenon of the clay foundation occurs. In view of this situation, this paper considers the effect of clay shear strength; based on the existing theoretical results, the formula which can calculate the critical hydraulic gradient of cohesive soil foundation when the flow soil occurrence is derived, and its rationality is verified by a series of numerical experiments and laboratory tests
The results show that the critical hydraulic gradient of cohesive soil foundation decreases with the increase of failure radius

Summary

Introduction

Infiltration is one of the important factors of engineering accidents such as dams and foundation pits, which can drive people to deeply explore the characteristics of seepage failure for better prevention and control of the occurrence of engineering accidents [1, 2]. The crack direction of the soil during the infiltration process is an important factor affecting the seepage failure. A famous formula was proposed by Terzaghi for calculating the critical hydraulic gradient according to the balance principle of self-gravity, hydrostatic buoyancy, and seepage force of soil particles in water [13]. Changxi considered the influence of the shape resistance of soil particles [2] to the critical hydraulic gradient based on the former theory. Israr and Indraratna obtained a calculation method of hydraulic gradient considering the friction between particles in the soil by introducing a stress reduction coefficient [14, 15]. Wu and Gao established the calculation formula of critical hydraulic gradient in case where piping happened, based on the particle gradation curve and porosity of the soil [18]. The empirical formula of critical hydraulic gradient of piping, which was expressed via confining pressure [19, 20], was performed by Luo et al The whole

Results

Discussion

Conclusion