Numerical Analysis of Long Term Settlement of Piles Subjected to Combined Vertical and Lateral Loads

Abstract

Nowadays, many structures are built on soft soils that are very compressible in nature, making construction on these types of soil incredibly challenging. Soft soil generally results in a significant creep deformation. This leads to structural failure if settlement is very large or differential settlement at which the structure is on the verge of failure. There is still a lot of research being done in this area so that we can accurately predict the behaviour of soft soil. When the design loads are large and shallow foundations are insufficient to support the loads, we must go for deep foundations. Deep foundations can be used when there is a limited amount of space for a foundation and the design load is larger, or when the soil is weak beneath the foundation. In this study, the numerical analysis of time dependent behaviour of piles has been carried out. The time dependent settlement, i.e. consolidation and creep behaviour of soil would be estimated. In this thesis, the consolidation settlement and pore pressure dissipation of the soil strata under consideration have been numerically modelled using the Soft Soil Creep Model and data from the Lilla Mellösa site near Stockholm, Sweden have been used. The time-dependent settlement and the dissipation of excess pore water pressure for layered soil deposit has been studied for various time intervals and under single and double drainage conditions. The long-term settlement behavior and mobilized skin friction in single piles subjected to compressive loads and combined loads (compressive and lateral loads) embedded in layered soft soils have been investigated using PLAXIS 2D. Further, the creep deformation and mobilized skin friction for a 4×4 pile group has also been analyzed. The single pile and pile group's bending moment and shear force have been analyzed. The model has been validated with the reported literature and the error is within 0.15% for total settlement and the results for excess pore water pressure have been found to be nearly equal. The excess pore water pressure dissipation has been studied only for the clay layer, and after 57 years it has been found that one-way drainage showed settlement of 0.296m and when soil strata is allowed for two-way drainage, 0.4035m settlement is observed. After 100 years, the maximum settlement of the pile group is 0.425m. Also, for a single pile under combined loading, the maximum negative skin friction is determined as 69.12kN/m/m. The excess pore water pressure, bending moment, and shear force for a single pile with combined loading and a pile group with compressive loading have been analyzed.