Experimental Research On Bearing Capacity Of Single Pile Of Cement-soil Mixed Pile Composite Foundation

Cement-soil mixing piles have been widely used in various industrial and civilian constructions in my country because of their advantages of short construction period,low cost,and wide application of soil types.The bearing capacity of composite foundations is one of the most important indicators for evaluating their reinforcement performance.In view of the changes in the load applied to the superstructure and the complex and diverse geological conditions in the area during the construction process,the design parameters of the cement-soil mixing pile are often changed to improve the bearing performance of the composite foundation and maximize its bearing capacity.This paper combined with a project in Zhengzhou,the indoor mix ratio test and the field static load test are carried out to study the determination of the bearing capacity of the composite foundation and the bearing properties of the pile body.At the same time,finite element software was used to establish a numerical model with the same size and applied load level as the field test,and the numerical calculation results were compared with the test results to verify the accuracy of the numerical simulation results.And by changing the model structure,the influence of the length of the pile body and the diameter of the pile body on the bearing properties of the cement-soil mixing pile composite foundation was explored.Through the research,the following main conclusions are drawn:(1)Under the same curing age,the unconfined compressive strength of cementsoil whose soil sample is silty clay increases with the increase of cement mixing ratio.And through fitting,it is found that when the cement mixing ratio is in the range of 14%to 16%,the unconfined compressive strength growth rate of cement-soil is the largest,that is,there is an optimal cement mixing ratio.(2)The P-s curves and s-lgt curves of the three test piles were obtained through the field static load test,the test results showed that the P-s curves of the test piles were "slowly variable".Through the calculation of the data,it is concluded that the characteristic value of the bearing capacity of the composite foundation of the cementsoil mixing pile is 184 k Pa,which is close to the characteristic value of the bearing capacity of the composite foundation calculated by the theoretical formula of193.82 k Pa,with an error of about 5.07%,which is relatively small and also verifies that the characteristic value obtained from the test is reasonable.(3)A pile-soil model of the same size was established by using finite element software combined with the field static load test results,and the P-s curves obtained by the two were compared to verify the reliability of the model;The degree of exertion and changing law of the axial force of the pile body and the resistance of the pile side during the loading process are analyzed.The results show that the curve of the axial force of the pile body varies nonlinearly with the different positions of the pile body,and the axial force of the upper part is larger than that of the lower part.At the initial stage of loading,the axial force curve is relatively steep,and the pile side resistance begins to play a role.As the pile top load becomes larger and larger,the axial stress on the pile becomes larger and larger,and the pile side resistance in the middle and lower part of the pile body gradually exerts its effect.(4)Through numerical simulation,the influence of the length of the pile and the diameter of the pile on the bearing shape of the cement-soil mixing pile is studied.The results show that the longer the pile length,the greater the bearing capacity and the settlement tends to decrease with increasing pile length.The larger the pile diameter,the flatter the P-s curve of the pile and the greater the pile top load corresponding to the same pile top settlement,which means the greater the single pile load capacity.Therefore,within the allowable range of settlement,choosing the appropriate pile length and diameter can not only save the engineering cost,but also give full play to the bearing capacity of the pile body and the soil surrounding the pile in the composite foundation,so as to achieve the goal of optimal design of foundation treatment.