LAUSR

Cushion is a layer of granular materials between the raft and the ground. The shear behavior of the interface between the cushion and the raft may influence the seismic performance of the superstructure. In order to quantify such influences, horizontal shear tests on the interfaces between different cushion materials and concrete raft under monotonic and cyclic loading were carried out. The vertical pressure Pv, material type and cushion thickness hc were taken as variables. Conclusions include: 1) under monotonic loading, Pv is the most significant factor; the shear resistance Phmax increases as Pv increases, but the normalized factor of resistance μn has an opposite tendency; 2) for the materials used in this study, μn varies from 0.40 to 0.70, the interface friction angle δs varies from 20° to 35°, while umax varies from 3 mm to 15 mm; 3) under cyclic loading, the interface behavior can be abstracted as a “three-segment” back-bone curve, the main parameters include μn, the displacement u1 and stiffness K1 of the elastic stage, the displacement u2 and stiffness K2 of the plastic stage; 4) by observation and statistical analysis, the significance of different factors, together with values of K1, K2 and μn have been obtained.