ANALYTICAL SOLUTION TO THE PROBLEM OF PASSIVE SHAFT RESISTANCE DUE TO LOWERING OF GROUNDWATER TABLE

Ala N. Aljorany

《Journal of GeoEngineering》 12卷3期 (2017/09) Pp. 119-127

https://doi.org/10.6310/jog.2017.12(3).3

摘要

Lowering of groundwater table (GWT) is ordinarily accompanied by soil compression. The increase in the effective overburden stress is the main reason behind this compression. The submerged unit weight of soil before the lowering of GWT changes to the total unit weight along the dewatered depth. Analysis of the passive shaft resistance (PSR) that is often induced along the shaft of an existing pile in such a consolidating soil is the main subject of this study. After imposing the calculated distribution of final soil compression along the pile length, the governing differential equation of the pile displacement problem is analytically solved. By means of the obtained solution, the pile displacement, axial load and the induced PSR are expressed as continuous functions along the pile length. The proposed solution is first applied to analyze a reported case in which field measurements of the soil settlement, the pile top displacement and the dissipation of excess pore water pressure were continuously monitored for a time period of 260 days after pile driving. The finite element method is utilized as well to solve the whole behavior of the pile-soil system. The obtained results agree well with the measured values of pile displacement and soil settlement and with those obtained by the finite element method. The present solution is then utilized to perform a parametric analysis to investigate the most important parameters that affect the induced PSR. It is found that the depth of dewatered zone has a significant effect on the magnitude of the induced PSR. It is realized also that the depth of the neutral plane, where both the pile and the surrounding soil are displaced equally, gets close to the pile tip as the stiffness of the bearing layer below the pile base becomes great.

關鍵字

Soil compression ； lowering of groundwater table ； pile ； passive shaft resistance ； analytical solution