Analysis of Dynamic Deformation Response of Closely Spaced Square Footings on Geogrid-Reinforced Sand under Cyclic Loading

In order to obtain the optimal spacing of closely spaced footings under cyclic dynamic loading, dynamic model tests of closely spaced footings were carried out on unreinforced and reinforced sand foundations. The influence of the center point spacing (S) of closely spaced footings on the bearing capacity of the foundation under cyclic dynamic load is discussed. The test results show the following: (1) The dynamic load peak of the unreinforced and reinforced sand foundation is the largest when S/B = 2.0 (B is the width of footing), and the ultimate bearing capacity of the reinforced sand foundation is 20% higher than that of unreinforced sand foundation. (2) The vertical soil pressure at different positions of closely spaced footings with different spacing ratios (S/B) on the reinforced sand foundation is lower than that of unreinforced sand foundation, and the vertical soil pressure at different buried depths (‘1-3’, ‘2-3’, ‘3-3’ positions) at the center of closely spaced footings are smaller than that below the footings (‘1-2’, ‘2-2’, ‘3-2’ positions). (3) When S/B = 2.0, the strain of geogrid and the peak acceleration at the center of the closely spaced footings are the smallest, indicating that the sand foundation has little transient change under this spacing. From the aspects of ultimate bearing capacity design and engineering economic benefits, it is suggested that the spacing between closely spaced footings should be arranged according to two times the width of the footing (S/B = 2.0).