Abstract:
Deep excavations have been used globally for underground construction, but they inevitably alter the ground conditions and induced ground deformation which may cause damage to adjacent building structures and utilities. Previously, conventional soil mechanics and empirical data were used by geotechnical engineers to predict the performance of shallow excavations, but those methods were not suitable for deep excavations. However, the advanced numerical method is proved to be capable of simulating the excavation process, investigating the mechanism of soil-structure interaction, estimating ground and retention system movements nowadays. This study aims to conduct numerical analysis in order to compare in between the sheet pile wall and contiguous pile wall-the two retaining systems available in Bangladesh. The feasibility of both the retaining system has been checked based on the comparison. This thesis uses advanced numerical analysis by employing a finite element code PLAXIS 3D to simulate the construction sequences of deep excavation, using a range of foreseeable soil parameters to carry out predictions of sheet pile wall and contiguous pile wall deflections. Also, the numerical model is validated by two case studies, and a parametric study of the model is also been carried out. In general, the results indicate that contiguous pile wall exhibits a better performance in resisting wall movement with or without the presence of nearby structures, reducing internal forces and bracing components and also offers economic benefits through reducing cost.
On average, Contiguous pile wall offers 19% and 43% more resistance to wall movements than the sheet pile wall in the Dhaka site and Chittagong site respectively in case of single basement system by incorporating Mohr-Columb as a soil model. Moreover, the resistance of contiguous pile wall to wall movements in Dhaka site is almost 42.5% and 21% higher than the sheet pile wall in case of double and triple basement systems respectively and the resistance is also higher in the Chittagong site. However, it is observed from the results that HS model predicts lower than the MC model due to the incorporation of three different stiffnesses (tri axial loading secant stiffness, tri axial unloading/reloading stiffness and oedometer loading tangent stiffness).
Contiguous pile wall also shows better performance than sheet pile wall in the comparison of study results with the available literatures. The effectiveness of countering wall displacements in case of contiguous pile wall is also higher than the sheet pile wall in the presence of adjacent structures. Besides, the effect of reducing the number of bracing components is also negligible in case of contiguous pile wall which helps to reduce cost associated with deep excavation.
