Dynamic multi-point method for evaluating the pile compressive capacity

Abstract

The dynamic load test (DLT) is commonly applied for evaluating pile capacity due to its fast mobilization and cost savings compared to conventional static load test. This paper proposes a new DLT method, denoted multi-point method (MPM) to solve the empirical problems in existing dynamic methods. The proposed method involves measuring accelerations at multi points along the pile shaft, and assumes the soil resistance related to damping is zero at the zero-velocity moment of pile segment. Two-dimensional axisymmetric finite-element models (FEMs) were constructed to verify the method of calculating pile strain through acceleration measurements. A nonlinear discrete spring-dump numerical model was established to simulate the pile-soil system under static and dynamic condition, and subsequently to be used for validation of MPM and parameter analysis. The derived static curves by MPM, UPM, and modified UPM (M-UPM) were compared with theoretical static curves. Finally, laboratory model tests of DLT on pipe pile were conducted to verify the MPM. The results demonstrated the MPM is applicable for deriving the static curve of piles with various sizes. It also demonstrated the MPM is more accurate than other dynamic methods. As a direct method, MPM is more realistic as it eliminates the need to estimate a damping constant and it accounts for the pile elastic shortening.