Laboratory Model Test Study on Bearing Characteristics of Super-Long and Large-Diameter Post-Grouting Piles in Clay Stratum

In this study, the impacts of various grouting methods and volumes on the vertical bearing characteristics of model piles in clay strata were investigated through indoor static load tests on one ungrouted model pile and two model piles with grouting at the pile tip, as well as two model piles with distributed grouting at the pile tip and along the pile side. These tests were performed in conjunction with data obtained from optical fiber sensors that monitored changes in the internal forces of the pile body. The results indicate that, compared to the ungrouted model pile Z1, the ultimate bearing capacities of the grouted model piles Z2 to Z5 were increased by 83.9%, 175.0%, 125.0%, and 253.6%, respectively. Additionally, the displacements at the pile tops after failure reached 57.6%, 62.3%, 69.5%, and 73.5% that of the ungrouted model pile Z1. These results demonstrate that post-grouting can significantly enhance the ultimate bearing capacity of model piles and reduce settlement at the pile top. Under various loads, the axial force of the pile body decreases gradually with the increasing depth of the pile foundation and increases with the increasing load at the pile top. The increase in the ultimate average side friction resistance and ultimate tip resistance of the grouted model piles (i.e., Z2 to Z5), in comparison to the ungrouted pile, was positively correlated with the grouting volume at the pile tip and along the pile side. All five model piles displayed the characteristics of friction piles.