Distribution of the Subgrade Reaction Modulus for Anchor Piles With Various Inclination Angles

Abstract

In a seismic design of a pile foundation, a subgrade reaction generated with a displacement of piles when the seismic load is applied must be appropriately evaluated. The ratio of the subgrade reaction to the amount of displacement of a pile is defined as the subgrade reaction modulus (SRM). There are two ideas about the SRM's depth distribution: one assumes a constant depth distribution, while another assumes a monotonously increasing depth distribution. There are various types of pile foundations based on different inclination angles of a pile. In design practice, SRM is not seen as being dependent on the pile type. In this study, we targeted anchor piles with the main goal of bearing a horizontal load and conducted a horizontal loading experiment. We prepared a model considering that anchor piles are usually not embedded into the bedrock and evaluated the depth distribution of SRM by changing the inclination angle of the pile from 0 to 30° with 10° intervals. The experimental result showed that though SRM increases monotonously in the depth direction, the distribution was different from what was assumed in design practice, where a local maximum was present at a specific depth in the ground, and the value decreased below that depth. We then proposed equations to calculate the degree of change in SRM corresponding to the inclination angle of a pile. Furthermore, it was shown that the position of a local maximum for SRM depends on the location of the rotational center for the pile.