Model Test And Numerical Simulation Of Vertical Bearing Characteristics Of Nodular Pile Group

Concrete nodular pile is a new type of variable section pile.Different from the traditional constant cross-section pile,bamboo knots are set at intervals on the pile body,which increases the contact area between pile and soil to improve the bearing capacity of the pile.Compared with the traditional constant section pile,it has better mechanical properties and economic benefits.At present,nodular pile has been used in some projects.However,due to its complex bearing mechanism,the compressive bearing characteristics of nodular pile still have research value.Predecessors have done some research on the bearing characteristics of single pile,but there is little research on the bearing characteristics of bamboo pile group.In engineering application,due to the influence of pile group effect,the bearing characteristics of single pile and pile group under pressure are quite different.Compared with single pile,the stress system composed of pile group and soil is more complex.Therefore,this paper uses indoor model test and numerical simulation software to study the bearing performance and bearing mechanism of nodular pile group in sand.The main research contents and conclusions are as follows:（1）The indoor model test device is studied and designed,and the comparative test of constant section pile and bamboo joint pile under pressure is designed.The test results show that the ultimate bearing capacity of nodular pile with equal diameter of 25mm is 1.25 times that of equal section pile.The ultimate bearing capacity of 35mm slub pile is 1.125 times that of 25mm slub pile.Different from the constant section pile,the axial force of nodular pile decreases nonlinearly along the pile body.When the load is large,the pile side friction of nodular pile will increase for the second time at the lower part of the pile body.The soil pressure at the bottom of nodular pile is obviously less than that of equal section pile.（2）The above three single piles are extended to the indoor model test of pile group.The experimental research shows that the pile group effect coefficient of nodular pile and constant section pile increases first and then decreases with the increase of pile spacing,and gradually approaches 1.The difference is that the ultimate bearing capacity of nodular pile group is the largest when the pile spacing is 3.5 times the pile diameter,and the ultimate bearing capacity of constant section pile is the largest when the pile spacing is 4 times the pile diameter.（3）The finite element simulation software is used to simulate the indoor model test.The simulation results show that the errors between the numerical simulation results of pile settlement and ultimate bearing capacity and the indoor model test results are controlled within 20%,and the numerical simulation results are consistent with the variation law of pile group effect coefficient of indoot model test.The settlement displacement nephogram shows that when the distance between pile centers is 6 times the pile diameter,the influence range of the overall settlement displacement of pile groups is closest to that of single pile.（4）The finite element model is used to study the influence of the length and spacing of bamboo joint piles on the bearing capacity of bamboo joint pile groups.The results show that under the condition of meeting the requirements of bearing capacity,it is the most suitable when the bamboo pitch is 7.5cm,and the ratio of bamboo pitch to pile diameter is 3.The ultimate bearing capacity of pile group approximately increases linearly with the pile length.The ultimate bearing capacity of pile group can be improved by increasing the length of pile body.