Experimental Study On Stress And Deformation Characteristics Of Long-Short Pile Composite Foundation In Yuzhong Loess In Lanzhou

Long and short pile composite foundations are widely used in the foundation treatment of construction projects in China,and they are also used in the foundation treatment of coastal highways in soft soil areas.They perform well in economic and social benefits.For long and short pile composite foundations,many countries Scholars have conducted some relevant research.In northwest China's loess region,the study of the stress and deformation of long and short pile composite foundations is temporarily unable to meet the increasing engineering demand.Therefore,based on the project of the middle part of Yuzhong in the northern circle of Lanzhou,this paper studies and discusses the stress and deformation characteristics of long and short pile composite foundations in the loess area.Through an independently manufacture test device,the overall test steps are optimized and a relatively complete set Test model system of long and short pile composite foundation.Starting from the pile length ratio of long and short pile composite foundations,five kinds of test models of different pile length ratios were established,and the original foundation was designed to compare.Variations of the axial force of the pile body,the frictional force on the side of the pile,the stress ratio between the pile and the soil,and the overall settlement of the composite foundation for under vertical load conditions are studied.At the same time,in order to compare the accuracy of the model test,a 3D numerical simulation model was created with midas/GTS software and the numerical simulation was performed under the condition that the various conditions of the indoor model test were not changed.The main research contents include the following:(1)Systematic summary describes the action mechanism of long and short pile composite foundation,the calculation theory of bearing capacity of the foundation,the settlement calculation theory,the theory of pile-soil stress ratio,etc.and design indoor model tests;(2)Combined with relevant theories and specifications,design and make the required indoor test model,analyze the stress and deformation characteristics of the long and short pile composite foundation under different pile length ratios,and perform different pile length ratios according to the designed test stress and deformation test of long and short pile composite foundation;(3)Obtain test data by changing the length of the short pile.And under this condition,the change of the axial force of the pile body,the change of the frictional force on the side of the pile,the change law of the pile-soil stress ratio,and the overall settlement of the composite foundation are analyzed and analyzed,deformation of the long and short pile composite foundation model under the condition that only the pile length ratio n is changed is obtained regular pattern;(4)Using midas/GTS software,only considering the change of the pile length ration,establish an effective model according to the data obtained from the test and perform numerical simulation calculations,obtain the model calculation cloud diagram for each type of pile length ratio and perform effective analysis;(5)Arrange the finite element analysis data and cloud map,analyze and compare the obtained data with the measured data of model tests,summarize and draw the final rule.