Abstract
A pile foundation is one of the most popular forms of deep foundations. They are routinely employed to transfer axial structure loads through the soft soil to stronger bearing strata. Piles generally used to increase the load carrying capacity of the foundation and reduce the settlement of the foundation. On the other hand, many cases in practice where piles pass through different layers of soil that contain weak layers located at different depths and extension, also some time cavities with a different shape, size, and depth are found. In this study, a total of 96 cases is considered and simulated in PLAXIS 2D program aiming to understand the influence of weak soil on the ultimate pile capacity. The piles embedded in the dense sand with a layer of weak soil at different extension and location. The cross section of the geometry used in this study was designed as an axisymmetric model with the 15-node element; the boundary condition recommended at least 5D in the horizontal direction, and (L+5D) in the vertical direction where D and L are the diameter and length of pile, respectively. The soil is modeled as Mohr-Coulomb, with five input parameters and the behavior of pile material represented by the linear elastic model. The results of the above cases are compared with the results found in a pile embedded in dense soil without weak layers or cavities. The results indicated that the existence of weak soil layer within the surrounding soil around the pile decreases the ultimate capacity. Furthermore, it has been found that increase in the weak soil width (extension) leads to reduction in the ultimate capacity of the pile. This phenomenon is applicable to all depth of weak soil. The influence of weak layer extension on the ultimate capacity is less when it is presentin the upper soil layers.
Highlights
Pile foundation is one of the most popular forms of deep foundations
The results show that the variation between the ultimate capacity ratios with weak soil layer thickness seems to be linear for all cases for weak soil layer properties
The research focused on presenting a numerical model using (PLAXIS 2D) as a finite element method to simulate and analyzed the behavior of the pile under axial loads and to find the ultimate pile capacity regards to presence of weak soil layer and cavity at different locations and different extension
Summary
Pile foundation is one of the most popular forms of deep foundations They are routinely employed to transfer axial structure loads through the soft soil to stronger bearing strata. Piles generally used to increase the load carrying capacity of the foundation and reduce the settlement of the foundation. [7], performed a numerical study using (Plaxis 2D) to analyze the performance of the piles subjected to axial loads and to find the effect of existing weak soils and cavities on ultimate pile capacity with different locations, thickness, and soil properties. The research focused on presenting a numerical model using (PLAXIS 2D) as a finite element method to simulate and analyzed the behavior of the pile under axial loads and to find the ultimate pile capacity regards to presence of weak soil layer and cavity at different locations and different extension. This means that the end bearing capacity is less dependent on the changes in drilled shaft diameter provided the associated tip displacement be equal to 5% pile diameter
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