Study of Foundation Behaviors Consisting of Single Piles Penetrating Bedrock in Taipei Basin

Abstract

For the stratum distribution around Taipei Basin, it is typical that the top part of stratum formation is covered in soft or very soft soil with uneven thickness and sits on bedrock with extremely high bearing capacity. For the tall building located at the basin rim, pile foundations are often required due to lack of bearing capacity, as these buildings are sitting on soft or extremely soft soil. When it comes to calculating the bearing or pulling capacity, there are two major ways of calculation, equation of static mechanics and estimation with “N” value from in-situ penetration tests, as specified in the current “Design Code for Building Foundations.” However, the methods mentioned above apply only to general soil, and there is no specific recommendation for the friction and pile tip resistance. Therefore, in foundation pile design, the calculation of friction and pile tip resistance on the part of piles in bedrock is always bothering engineers. Yet, the contribution from the part of piles in bedrock, in fact is significant. As a result, the characteristics of the part of piles in bedrock are a topic worth studying. In this study, pile loading tests at 7 locations at Nangang, Taipei City are taken as examples. Finite element method (FEM) is introduced for simulation of in-situ drilled foundation piles mentioned above that are commonly used. The result of simulation is compared with that of actual static pile loading tests, and it is found that there is consistency between the simulation result and that of loading tests when the bedrock penetration depth of foundation piles reaches 1.6~2.0 times of pile diameter, as FEM is introduced for the simulation of the relationship of axial loading of pile versus pile-head top settlement.