Weakened section detailing for scoured/elevated pile groups in sands toward post-earthquake resilient behavior: Quasi-static tests

Abstract

Scoured or elevated pile-group foundations in coastal regions may experience noticeable residual deformation after strong earthquakes, leading to the loss of functionality and even collapse of the supported structures. To address this problem, a weakened section detailing, which is characterized by a large cover-thickness across a pile-length beneath the cap, is proposed to release constraints on the pile/pile-cap interface, and thereby reduce the residual deformation and meanwhile mitigate underground pile damage. To demonstrate the effectiveness of this section detailing, a pair of quasi-static tests were designed and conducted on two scaled specimens representing scoured pile-group foundations, one with the weakened section detailing and the other with the conventional one, under laterally cyclic loads that mimic horizontal earthquake loading. Test results are interpreted in terms of (1) structural failure mechanisms including damage modes and ductility capacity, and (2) post-earthquake resilient behavior reflected by residual deformation. Compared with the conventional one, the results well demonstrate the feasibility of the weakened section in reducing residual cap deformation (by as large as 34% and 80% for the translational and rotational deformation, respectively, at the ultimate state), mitigating underground damage, and improving ductility capacity under earthquake conditions, while almost maintaining the compression, shear and bending capacities under normal operational conditions. The test results also indicate a need to enhance the seismic shear capacity of the weakened section.