Numerical investigation of spatial aspects of soil structure interaction for secant pile wall circular shafts

Implementation of fast and cost-effective shoring systems has become very necessary to overcome the technical challenges such as variable soil and rock profiles, high groundwater tables and limitations imposed by the built environment. Secant pile wall shoring systems allow the construction of overlapped piles in almost all subsurface conditions. They are constructed in a circular plan layout to form a vertical shaft which provides unique advantages such as compression ring behavior. This paper presents a numerical study to investigate various aspects of the behavior of circular shafts constructed using secant pile walls. The studied aspects include the identification of earth pressure distributions exerted on circular shafts, the impact of excavation of single and multiple holes on the shaft stresses, and the stresses in the shaft in the case of sloping bedrock. A three-dimensional finite element model is developed to conduct the present analyses taking into consideration the actual behavior of soils surrounding the walls. The stress concentrations calculated for circular shafts were seen to vary from the results of the infinite plate with hole solution. The sloping bedrock was also seen to result in significant deviations from the compression ring behavior. A large increase in the maximum compressive stresses and emergence of some significant tensile stress zones were observed for bedrock inclinations larger than 20°. The results presented in this study address some practical design concerns and were considered to be of interest to those involved in design and construction of vertical shafts.