Laboratory Test And Bearing Capacity Calculation Of Base-enlarged Tension Piles

In order to meet the requirements of bearing conditions and construction environment of building foundation in engineering,base-enlarged tension piles,as a kind of variable section pile,can improve ultimate bearing capacity greatly and have better bearing performance by increasing the structure size of the pile at the pile end.Therefore,it is great significance to study the bearing capacity and deformation of the uplift pile.Based on this,the following researches are carried out on the uplift characteristics of piles in sand:At first,this paper designed the pull-out test of loading device and testing scheme,two equal section test piles were tested in laboratory,test conditions and other variables are the same only pile diameter were different,determination the vertical displacement of pile head when pile body under pulling load on each level is stable,it is concluded that the larger the pile diameter,the greater the ultimate uplift capacity and the better bearing capacity.This paper introduces several commonly used theoretical calculation models of equal section tensile pile,and taking various test parameters to obtain the theoretical calculation results of ultimate bearing capacity of uplift pile,and makes a comparative analysis with the test results.In this paper,the indoor tensile tests of different types of base-enlarged tension piles were carried out,and the load-displacement(Q-S)curve of pile top,axial force distribution curve of pile body and average friction resistance distribution characteristics of pile side were studied and discussed under different conditions of pile diameter,development Angle of enlarged end and buried depth of test pile.The results show that the bearing capacity of the enlarged pile can be improved significantly by increasing the pile depth,the ultimate bearing capacity can be increased by 55.6%,and the bearing capacity of the belled pile can be increased by22.2% and 27.3% by increasing the pile diameter and the developing Angle at the top of the enlarged end.At the same time,the comparison shows that the bearing capacity of the belled pile is improved by 28.6%?75% compare with the equal cross section pile,and the bearing capacity increases with the improve of the pile diameter,the buried depth of the pile and the development Angle of the upper part of the expanded end.According to hypothesis when base-enlarged tension piles damaged,the failure surface shape and equation under the ultimate load,the expression of ultimate bearingcapacity of belled pile is derived,the theoretical prediction results compare with indoor pull-out test results of the above analysis.It is found that when the diameter of the expanded end is larger,the predicted results are more consistent with the experimental results.