Dynamic axial response of drilled piers in stiff sandy clays

摘要

A prototype pier load test program was performed to study the load-deformation and energy dissipation characteristics of the response of drilled piers under static and dynamic axial loads. The field tests consisted of six fully instrumented drilled concrete piers 61-76 cm in diameter and 5.8-9.1 m in length. The piers were constructed on a stiff sandy clay site adjacent to the UC Berkeley campus. Dynamic Fundex Pile Load Test (PLT) was performed on each pier, followed by static compression or tension test and a second PLT. The field tests revealed that the stiffness and capacity of a soil-pier system depend significantly on the loading rate. For the type of piers and soil considered in the field test, the increase in dynamic stiffness versus static stiffness is about 20-40% at almost all displacement levels. The ultimate dynamic capacity increases about 30% compared with the static case. The multiple PLTs conducted on the same drilled pier also indicated that a pier may experience up to 50% stiffness and strength degradation when subjected to full load reversal. The test program showed that the PLT test is a fast, innovative method to get useful site-specific information for seismic design of the pier foundation.