Study On Pile-soil Interaction And Vertical Bearing Capacity Of Pile Groups In Sand

With the wide application of pile foundation,the problem of the ultimate bearing capacity of the pile calculation is becoming more and more prominent.And the accurate calculation of the ultimate bearing capacity of the pile is beneficial to improve the design of the pile foundation and the economic efficiency.Research shows that with the "group pile effects",there is a significant difference between the base loading-displacement characteristics of group pile and single pile.Meantime,the mechanism of pile-soil interaction in group pile foundation and the load-sharing ratio of different piles are the key to optimize the ultimate bearing capacity of the pile design.In this paper,a series of studies are carried out on the base pile-soil interaction and its vertical bearing capacity characteristics in sands by combining model test and numerical simulation.The details of the study are as follows:(1)The characteristics of sand shear strength and the calibration of earth pressure box.Using triaxial apparatus,three kinds of relative compaction and four kinds of confining pressure shearing test were carried out,which showed that the strength of sand shear resistance gradually increased with relative compaction and confining pressure.Meanwhile,it is provided soil parameters that in the process of the numerical simulation.Using a new multi-functional calibration tank developed independently,the loading-unloading calibration test of the earth pressure box under different confining pressure is carried out.It is verified that the earth pressure box has good response characteristics,and effectively reduces the lag of the earth pressure box in the process of unloading,and prepares for the measurement of the soil pressure surrounding of the pile in the model test.(2)The characteristics of the loading-displacement under vertical load.Using the numerical simulation,research on the strength of the soil shear and the pile length influence of ultimate bearing capacity of the pile.Proposed that the ratio of the load-sharing at the critical load,which the resistance of the pile end and the resistance of the pile side is changing.With the ratio of between pile length and pile diameter increased,the level of the load added to the process of the load-sharing.The soil elastic modulus and the strength of the soil shear increased to the vertical bearing capacity increasing.Meantime,the soil elastic modulus increased to the displacement of pile foundation decreased.The vertical bearing capacity increased with the friction angle of soil.Hence,at the actual project,it is beneficial to improve the vertical bearing capacity of pile foundation that with the soil elastic modulus and the soil friction angle increased.(3)The influence of the distance between piles on the carrying capacity of the group pile and the pile-soil interaction.Laboratory model test and numerical simulation show that during the dual pile vertical carrying force,the soil between piles has been relatively shifted,the additional stress in the horizontal direction of the pile end appears,and the reinforcing phenomenon of the side resistance of the pile end appears.When the pile spacing is 4D,this phenomenon is most obvious,which can exert greater carrying capacity under the smaller settlement.Therefore,it is recommended that the long diameter ratio of 30 high-stage double pile base pick pile spacing is 4D.(4)The load transfer characteristic of the group pile under the vertical load.The numerical simulation results show that the carrying capacity of each individual pile in the 3×3 group pile is not played synchronously.When the load is within 20% of the group pile limit carrying capacity,the angle pile load is 1.18 times the average vertical load of each individual pile and the center pile is 0.83 times.As the load increases from 30% to 50% and80%,shear stress gradually passes from the angle pile to the center pile.When the group pile base reaches the limit carrying capacity,the load of a single pile is basically the same.