Numerical modeling of a deep excavation and comparison with monitoring data

Abstract

With urbanization, space available for construction is limited and available space has to be used very effectively. As a result, people tend to use underground spaces for parking and other service requirements. Accordingly, deep excavations with several levels of basements have become a standard practice in the construction of high rise buildings in urban areas. Any excavation which extends beyond the ground water level is required to be supported by an appropriate earth retaining system to retain the soil and ensure the water tightness of the retaining system while proceeding with the excavation. The main purpose of the retaining systems is to maintain both horizontal and vertical ground movements within allowable limits to avoid any damage to the adjacent built environment and the excavation itself. To achieve the main purpose of retaining walls for deep excavations, the estimation of lateral deformation is required to be done very precisely during the design stage. Further, the estimated deformations are required to be compared with the actual monitoring data during the execution stage. In this research, monitoring data of an excavation supported by a diaphragm wall laterally supported at several levels were compared with the results of the numerical simulation obtained by the finite element method, and for the first analysis Mohr-Coulomb model was used as a constitute model. Then the finite element modelling method was streamlined to obtain more accurate results. Two modifications were adopted for the basic model to improve the performance. First, the elastic modulus of soil was increased considering the unloading effect of soil and next the small strain theory was used. The results of the analysis showed that the model with the combination of both modifications provides more sensible results. There were some anomalies in the actual monitoring data.