Proposal And Mechanical Properties Analysis Of Compaction Pile With Expanders For Eliminating Negative Friction

As a new type of pile structure,the compaction pile with expanders is designed to solve the engineering problems of pile failure and uneven settlement of foundation caused by negative friction in poor soil areas like collapsible loess areas.In the new structure,the casing method and the squeezed branch technology are combined,in which the casing is used to reduce the negative friction while the expanders are used to form squeezed branches and bear force with surrounding soil together,so that the foundation engineering in poor soil areas like collapsible loess areas can be comprehensively treated.In the paper,the two methods of theoretical analysis and numerical simulation are combined together to analyze the compaction effect,bearing behavior and loading transfer behavior of the new pile.The specific contents and conclusions are as follows:(1)Through the detailed introductions of the structure composing,construction technology and structural characteristics of the compaction pile with expanders and the detailed analyses of its working mechanism and action effect,it can be known that the compaction effect that the expanders had on soil can be divided into plastic deformation zone and elastic deformation area according to the stress distribution of the soil around expanders.(2)According to the structural characteristics of the compaction pile with expanders,the reaming model of diamond hole of the expanders are established.The elastoplastic solution and the limit expansion angle of expanders during reaming are solved by the complex variable function method of elasticity;in the end,the computational formula of the ultimate bearing capacity of the new pile is obtained.(3)Combining with an example,the bearing capacity of the ordinary straight pile,the casing pile and the compaction pile with expanders with the same length and diameter under the same working condition are compared and verified.The results show that the negative friction resistance can be eliminated well and the bearing capacity can be increased remarkably by the new compaction pile with expanders.(4)Through the finite element software ADINA,the model of the compaction pile with expanders is established to analyze the compaction effect,bearing characteristics and load transfer behavior and to verify its elastic expansion solution.The results show that: the influence scope that the expanders had on the soil is about 2~3 times aslarge as the expansion width.Compared with the ordinary straight pile,the P-S curve of the compaction pile with expanders has no sudden increase of settlement,which proves the good load-bearing capacity.The force mechanism of the new pile is scientific and reasonable.The distributions of elastic expansion stress and displacement obtained by numerical simulation and theoretical calculation are basically consistent,which verifies the rationality of the proposed diamond hole reaming model and the analysis method for the squeezing effect of the expanders.(5)Through the finite element software ADINA,the ordinary straight pile contrast model is established in order to compare and verify the bearing characteristics of the compaction pile with expanders.The results show that: the ultimate bearing capacity by numerical simulation is basically consistent with that by theoretical calculation for the two types of pile with the same length and diameter and under the same working condition,which verifies the rationality of the computational formula on the bearing capacity of single pile.