Study Of Vertical Bearing Capacity And Settlement On Composite Pile Of Large Diameter PHC Pile And Jet-Mixing Cement

The composite pile is a kind of pile suitable for soft soil,which is made by inserting PHC pipe pile into the jet-mixing cement pile before the latter reaches certain strength.Now experience on the application of the composite pile with large diameter PHC pipe pile as inner core is not much,and the mechanism of the force under vertical load is still lacking.This paper studied the mechanical behavior of the composite pile with large diameter PHC pipe pile as inner core under the vertical load by both using test result obtained from the in-suit test by inserting three PHC pipe piles with the diameter of 800 into the cement soil and ABAQUS finite element variable parameter analysis.The main work and results of this paper are as follows:(1)This subject accurately measured the axial force of piles in different vertical positions,and deduced the distribution of side resistance of large-diameter pipe piles by adding the steel bar gauge on the steel pipe pile.It studied the ratio of cement soil pile material and mixing method under different soil conditions convenient for the sinking of large diameter pipe pile.It also verified the reliability of the large diameter PHC pipe pile connection by full scale test.(2)Three composite piles with large diameter PHC pipe pile under the vertical load were carried out by the anchor pile method,and the test results show that the Q~s curve of large diameter pile composite are changing slowly;Further analysis of test data shows that the actual bearing capacity of the bearing stratum at the pile end is higher than that which is provided by the geological survey reports and the soil plugging effect coefficient is 1;On the basis of these,the formula and parameters in the normal composite pile regulation are modified to obtain the formula for calculating the bearing capacity of large diameter composite piles.The settlement of large diameter composite pile was calculated by theoretical formula,and the reasons for the differences are compared with the measured results.(3)The finite element analysis software ABAQUS was used to simulate the test piles,and the reliability of the model was verified by comparing the analysis results with the experimental data.On the basis of these,the variable parameter analysis of composite pile was carried out.The results show that the settlement of the pile decreases with the increase of the pile diameter and the length of the pile,and the change of modulus of elasticity of cement soil has little influence on the settlement.When the coefficient of friction between pile and soil varies from 0.2 to 0.35,the settlement of composite pile changes greatly.When it varies from 0.35 to 0.45,the settlement of composite pile changes little.