Mechanism Of Interaction Between Layered Sand And A Laterally Loaded Pile Under Conditions Of Different Underground Water Levels

In recent years,the application demand of laterally loaded pile in engineering practice is increasing rapidly,because of the construction of offshore wind power,super-tall buildings and cross-sea Bridges is also on the increase.The design and construction of laterally loaded pile in various poor geological conditions has become an engineering roadblock.Based on a visual model test equipment,a model test of a laterally loaded pile under different groundwater depth conditions in the sand layer was carried out in this paper.The method of graded loading and cyclic loading were considered in the model test.In the model test,the influence of different groundwater depth conditions on the mechanism of pile-soil interaction was studied in two part of mechanical characteristics and displacement field.Based on Particle Image Velocimetry(PIV)technique,the macroscopic characteristics of soil particle movement around the pile affected by different groundwater depth conditions were studied.Finally,the results of model test were verified by finite element numerical simulation software.The results show that the stiffness of soil is from weak to strong,which is in the order of saturated sand,dry sand,groundwater depth 140 mm,90mm,40 mm sand.By the analysis of its main reason is that capillarity occurred in the soil when the groundwater is below the surface of the soil,which resulted in a pseudo-cohesive between soil particles in the capillary water zone.As the groundwater became shallower,the capillary water zone moved upward,the slope of the p-y curve of the upper soil layer increased significantly,thus the overall stiffness of the soil layer increased.From the analysis of the law of soil displacement field,it can be found that when the capillary water zone is located in the upper soil layer,the movement of the corresponding soil particles is obviously restricted by the pseudo-cohesion between the soil particles,while when it is located in the lower soil layer,it plays a role of cutting off the vertical movement path of soil particles.In addition,the capillary water zone not only brings mechanical properties enhancement effect to the soil particles around the pile,but also increases the risk of forming underground cavitation geological hazards.When the pile is subjected to lateral cyclic load,the variation of groundwater depth will affect the predictability of the pile's reciprocating motion at each step.The variation trend of laterally cyclic stiffness of pile is also related to groundwater depth and peak of cyclic loading.The potential risk of geological disaster is much higher when the pile is in reciprocating motion than when the pile is in one-way motion.