Refined numerical modeling of a laterally-loaded drilled shaft in an MSE wall
Due to space constraints, laterally-loaded drilled shafts have been increasingly constructed within the reinforced zones of MSE walls. Under such circumstances, the design of both MSE walls and drilled shafts differs significantly from the conditions under which the current design methodology is applicable. To develop a design method for such applications, an investigation of the interaction mechanisms between the drilled shafts and MSE walls is necessary. As a part of the investigation, a full-scale experimental study was conducted in 2007. Numerical models, calibrated by the experimental data, have been used to further investigate the mechanisms. This paper presents a numerical simulation of one of the test sections in the experimental study, which was refined from the previous numerical simulations completed before and immediately after the experimental study based on simplified numerical models. As compared with the simplified numerical models, this numerical simulation has been refined in four different ways: (1) the modulus of the backfill material was considered stress-dependent in a hyperbolic function of the confining stress; (2) the shear strain hardening/softening behavior of the backfill material was simulated by considering the mobilized friction angle (expressed as the percentage of the internal friction angle) as a function of the accumulative plastic shear strain; (3) the MSE wall facing blocks were considered discrete and their interactions were represented by vertical and horizontal interfaces of different properties; and (4) the construction compaction effort, though not considered as a dynamic force, was considered by modeling the permanent lateral earth pressure increase. The numerical results were compared with the data from the experimental study in terms of the load"“deflection curves of the drilled shaft, the deflection profiles of the MSE wall facing and the drilled shaft, the lateral earth pressure increase on the MSE wall, and the strain increase in geogrid reinforcement. Good agreement between the numerical simulation and the experimental study was found. In addition, the numerical simulation allowed a thorough examination of the lateral deflection of the MSE wall, the lateral earth pressure on the MSE wall, and the maximum geogrid tension. Based on the numerical results, the mechanisms have been discussed, such as the shape of the lateral earth pressure distribution due to the lateral load, the maximum tension in different layers of geogird. This numerical simulation not only provides a well calibrated numerical model for future study but also yields results which revealed a few important mechanisms for such application.