Experimental Study on Effect of Pile-raft Connection Type on Seismic Response of Piles Improved with Cement-treated Soil

To reveal the effect of pile-raft connection types on the seismic response of piles that are improved with cement-treated soil in liquefiable soils, 1g shaking table tests of connected and disconnected piled raft foundations were performed. In the two scenarios, the natural frequency and damping ratio of the model system, the macro-phenomenon of the tests, the excess pore pressure and acceleration response of the soils, the acceleration and displacement response of the superstructure, and the moment response of the piles were evaluated and compared. Both models were subjected to the El Centro earthquake wave with different peak accelerations. Results show that the natural frequency of the model system in the disconnected piled raft (DPR) case is lower than that in the connected piled raft (CPR) case, whereas the damping ratio is larger in the DPR case. The use of the DPR foundation can mitigate the degree of soil liquefaction, and the maximum reduction in the excess pore pressure ratio can reach 19.3% compared to the CPR case. Due to the seismic-isolation effect of the cushion, the acceleration responses of the soils and superstructure in the DPR case are clearly lower than in the CPR case. Under the 0.4g El Centro wave conditions, the acceleration amplification of the superstructure in the DPR case is 13.5% less than in the CPR case. The integrity and rigidity of the DPR foundation are relatively poor, which results in an increase of more than 50% in the lateral displacement of the superstructure and the settlement of raft compared with those of the CPR foundation. Soil liquefaction leads to a sharp increase in the bending moment of pile. In the CPR case, the peak bending moment generally occurs at the top of the pile improved with cement-treated soil. However, the peak is located near a depth of a 1/3 to a 1/2 pile length beneath the pile head in the DPR case. Moreover, the peak pile moment in the DPR case is approximately 50% lower than that in the CPR case. Therefore, the difference in the pile-raft connection type has a significant influence on the seismic response of piles improved with cement-treated soil. The results of the study may provide evidence for the seismic design and research of pile-raft foundations improved with cement-treated soil in liquefiable soil. © 2021, Editorial Department of China Journal of Highway and Transport. All right reserved.