Calculation of active earth pressure on retaining walls with line surcharge effect and presentation of design diagrams in cohesive – frictional soils

Mohammad Karim Faghirizadeh,Mojtaba Ahmadabadi

doi:10.5377/nexo.v34i01.11303

Abstract

In this study, a formulation and models have been proposed to calculate the active earth pressure on the wall and to determine the angle of failure wedge with line surcharge effect and taking into account the soil cohesion. The proposed method has the advantage of taking into account soil parameters such as cohesion, the angle of friction between the soil and the wall, the surcharge effect in the elasto-plastic environment, and the range that determines the critical surcharge. This paper presents dimensionless diagrams for different soil specifications and surcharges. According to these diagrams, it is easy to determine the distribution of excess pressure caused by surcharge, the distribution of the total active earth pressure on the wall, the angle of the failure wedge as well as the minimum and maximum active coefficient of the pressure with respect to surcharge distance. Furthermore, all soil parameters, surcharge and the results have been addressed. In general, the results indicated that increasing the angle of internal friction of the soil and cohesion would result to a nonlinear reduction in the active earth pressure coefficient, contrary to the line surcharge, which increases the active earth pressure of the soil and ultimately increases the active earth pressure coefficient. In this research, a diagram has been presented that expresses the surface that the active earth pressure coefficient changes with respect to the surcharge distance. The lower limit of each graph expresses the minimum active earth pressure coefficient (kas (min)) at the minimum surcharge distance, whereas the upper limit indicates the maximum active earth pressure coefficient (kas (max)) at the maximum surcharge distance from the wall. Comparison of the results of the proposed method with previous methods, codes and numerical software shows that in general, the proposed method is able to simplify the analysis of walls with surcharge effect in cohesive-frictional soils. In addition to the formulation and diagrams, a computer program in MATLAB software has been written. Using the results of these codes, the pressure on the wall with the linear surcharge effect, angle of failure wedge and pressure distribution on the wall in the cohesive-frictional soils can be calculated for all scenarios.

Highlights

Important factors influence the active earth pressure on the wall
X H Mode 3: If the linear surcharge distance from the wall is greater than tan 1, it states that the existence of a linear surcharge on the wall is ineffective, and in order to calculate the pressure on the wall, one can consider the amount of surcharge equal to zero in equations 1 to 4, and equation 9 is presented
The results indicate that the increase of the angle of internal friction of the soil and cohesion will reduce the active pressure coefficient in a nonlinear way unlike a linear surcharge, which increases the active pressure of the soil and increases the Kas coefficient

Summary

INTRODUCTION

Important factors influence the active earth pressure on the wall. Various researchers have so far investigated such parameters. (Pain, Choudhury, & Bhattacharyya, 2017) investigated the stability of the retaining wall with a log-spiral failure wedge and in the reinforced soil The limitation of this method is to ignore soil cohesion and the angle of friction between the soil and the wall and the effect of surcharge. In (Mojtaba Ahmadabadi & Faghirizadeh, 2017) method, formulation was presented for retaining wall with linear surcharge and non-cohesive soils, which includes 3n equations and 3n unknowns Using such formulation, the active pressure coefficient, the angle of the failure wedge and the location of the resultant force at the level of failure with the effect of a linear surcharge is obtained. Kas Q Pa Paq Pas=Pasurcharge Pi Ni Si Wi coefficient of active pressure from the surcharge (dimensionless) Active earth pressure coefficient with the effect of surcharge (dimensionless) linear surcharge (kN/m) Active earth pressure without surcharge(kN/m) resultant lateral earth pressure from the surcharge (kN/m) Active earth pressure with the effect of surcharge (kN/m) Active pressure on wall in the ith wedge Normal force on failure surface for ith wedge (kN) shear force on failure surface for ith wedge (kN)

MATERIALS AND METHODS

Functional diagrams

CONCLUSIONS