Effect of Wall Stiffness on Excavation-Induced Horizontal Deformations in Stiff-Hard Clays

Abstract

Excavation-induced ground movements are affected by the stiffness of the support system as well as the soil properties. Displacement estimations of deep excavations are generally made using the finite element method (FEM). However, the accuracy and reliability of the results obtained from the finite element calculations will change significantly in proportion with the quality of the parameters employed in the program, thus, the use of probabilistic analysis that considers soil variability’s impact has become a popular approach in recent studies. Based on these considerations, this study aims to investigate the influence of wall bending stiffness on excavation-induced lateral displacements for deep excavations in stiff to hard clays, and provide a practical methodology to be used in preliminary design. For this purpose, finite element analyses were carried out using various practically achievable support system stiffness values and soil parameters. Considering the inherent variability of the soil, effective stress friction angle and effective cohesion of the soil were randomly generated by Monte Carlo simulations to be used in the finite element analyses. The performance of the analyses was evaluated using results from 22 case histories from deep excavations in stiff-hard clays. The results indicate that, lateral movement in excavations in stiff-hard clays is minimally affected by the stiffness of the wall. Soil variability was found to have a significant impact on the outcome of Monte Carlo simulations, resulting in a wide range of normalized maximum lateral deformations for a given wall stiffness. A new stiffness factor has been proposed that incorporates the horizontal spacing of the support elements, which is capable of covering a wider range of excavation support system types, thus enhancing the accuracy of the analyses.