Evaluating the Effect of Selecting Constitutive Models on Prediction of the Ground Movement Adjacent to Deep Excavations

Limiting displacement of soil around excavation area in highly populated urban regions in order to avoid damages to building and abutting roadway is one of the most important challenges in excavation problems. Selecting an appropriate and economically justifiable retaining system with the ability to reduce the vertical deformation of the soil adjacent to the excavation area (and subsequently abutting structures) to an allowable value and make a stable retaining system is based on the displacement values of retaining structure and the adjoining soil, analysis of excavation stability and stress analysis of retaining structure elements (including retaining wall and anchor). Stability analysis can be performed using conventional limit equilibrium equations, while displacement evaluation of retaining structure as well as inside and outside soil can be conducted taking advantage of numerical methods such as Finite Element Method (FEM). One of the most important parameters affecting the displacement prediction of soil adjacent to excavation site is the selection of proper soil constitutive model in numerical modeling. In this study, effect of selecting hardening soil, Mohr-Coulomb, and soft soil model on displacement assessment of the ground adjacent to tranches is evaluated using nonlinear finite element analysis with PLAXIS 8.2. The results demonstrate that hardening soil model is more consistent with empirical results and therefore application of this model in excavation problems leads more accurate results. On the other hand, Mohr-Coulomb elastic-perfect plastic model overestimates amount of basal heave in deep excavation. This model also predicts soil displacement behind the wall as heave that contradicts results obtained from previous experimental studies. Furthermore, soft soil model although offers a more accurate pattern of displacement of the soil adjacent to excavation site, due to a wide range of elastic strains in this model, displacements are estimated less than actual values.