Numerical Simulation of Tieback Excavations with Soldier Piles Using a New Unified Soil Model Considering at Rest Condition

Abstract

The present research aims to understand the behavior of tieback retaining walls during the excavation. Employing the finite difference method (FDM), a 3D model was developed in this study to obtain the earth pressure diagram and horizontal movement of tieback walls during and after construction. A rigorous non-linear analysis of tieback retaining walls requires an efficient solving algorithm of the governing equations as well as a nonlinear soil constitutive law that could capture different stress paths including at rest condition during the sequences of construction. A newly proposed unified two-surface elasto–plastic model based on the critical-state soil mechanics is employed to simulate different stress paths of the matrix soil during the excavation. The model describes strain-softening and stress-dilatancy using non-associated flow rule and implements dilatancy parameter. This model is capable of adopting the proper function for the yield surface, simulating drained and undrained responses of soil under triaxial conditions as well as soil response under drained laterally confined (K0) conditions. Using the presented unified soil constitutive model, the effect of soil plasticity was incorporated into the finite difference method. In the numerical model of the tie-back retaining walls, cable structural elements are used to simulate the tendon anchors, while the shotcrete facing and soldier piles are modeled using shell and beam structural elements, respectively. Effects of different crucial factors were monitored during a comprehensive parametric study. The results gave information on the influence of the following factors on tieback walls behavior: the magnitude of anchors pre-tensioning load, the length of anchors bonded zone, the vertical position of the first anchor, and the stiffness of the soldier piles.