Research On Ultimale Bearing Capacity And Relationship Betweem Shear And Displacement Of Pile-Soil On Push-extend Multi-under-reamed Pile

Radial multi-bulbs push-extend multi-under-reamed pouring pile is a kind of variable cross-section pouring pile which push-extends and reams channels in radial direction.The push-extend multi-under-reamed pouring pile is called push-extend multi-under-reamed pile for short,which is a kind of radial multi-bulbs push-extend multi-under-reamed pouring pile (multi-under-reamed bored pouring pile).It is a kind of new type of variable cross-section pile and has been developing based on uniform section.The push-extend multi-under-reamed pile is between friction bearing pile and end bearing pile which contains the advantanges of both piles,adds its capability to plate resistance and side resistance,the reasonnable site of plate makes good result.The push-extend multi-under-reamed pile has many advantages,such as high bearing capacity,flexible design,high suitability,convenient operation,quality-controlled,low cost,wide application,shortened construction period and so on,so the research and application are increased gradually day by day.At the present time,the test and application of push-extend multi-under-reamed pile has gained some achievements,but its theory research is relative laggard in comparison of pile foundation technology.The research of ultimate bearing capacity of push-extend multi-under-reamed pile more limited study of the analysis of load transfer characteristics,the study of interacion of pile-soil and failure mechanism is seldom relatively.This article is funded by the National Natural Science Foundation of China(NO:50878096).In this paper it researches the relationship of shear and displacement of pile-soil , estabishes the rigid-plastic model , obtains the friction coefficient,anlayizes the effective factors of design and certains its ultimate bearing capacity and other relative problems, supplies reliable basis for theory and plays the advantages of push-extend multi-under-reamed pile absolutely, the research contributes to large-scale application of this technology, so creates much greater economic and social benefits.In this article,it anlyzes push-extend multi-under-reamed pile of different pile-soil boundaries in use of ANSYS by taking finite elment method,and tests on undisturbed soil of actual project site.The combination of theory research and test data make some related conclusions.The conclusions are as following:Firstly,it anlyzes the effecive factors of push-extend multi-under-reamed pile. The paper focuses from the plate's slope of angle,position and spacing of push-extend multi-under-reamed pile.Pile and soil's models are established separately,then all kinds of models in different situations are established and meshed with loading and solving and so on,anlyzes and summarizes the results of deformation figure,stress contour and strain contour.It analyzes the elastic-plastic status in use of usual slope angle of plate,the usual slope angle contains the degree of 30,45 and 60.The article researches the impact of slope on the push-extend multi-under-reamed pile on the some conditions,and finds that the greater slope angle is,the smaller function of plate's end resistance.So,the reasonal slope angle is 30 degree in the calculation of single pile ultimate bearing capacity. It analyzes the site of plate in use of single pile,established models of plate when it is upper,middle,lower and bottom,and gets some conclusions at last.The conclusion is that the closer the distance to the bottom of pile,the better the plate is.So, the reasonal site is lower site in the calculation of single pile ultimate bearing capacity,that is to say,when it is bottom to.The clear space was researched when it is one meter,one and a half meters,two meters and two and a half meters,the bearing capacity is increasing gradually with the clear space of plates.The conclusion is that the quantity of plates is up to two which best clear space is two meters in the range of nine meters length of pile.Secondly,the paper tested the undisturbed clay in actual project by use of electro-hydraulic servo testing machine control system,it could measure clearly descending pile-soil damage.Large amounts of data is collected through laboratory tests and the results is analyzed at the same time to find similar shape of curve.Take special points to solve assumption function and get the curve of load-settlement of pile-soil,the curve is also shear-displacement curve.This curve does not only represent this project's relationship of shear-displacement,but also reflects the nature of a class of soil.When indicators differ,the value of curve is different,but the shape of curve is the same.The real constant of spring element has been found to come ture the relationship of pile-soil,and makes computer can simulated finite elment model authenticly.Thirdly,the paper analyzes the ultimate bearing capacity of push-extend multi-under-reamed pile with finite elment method.The relationship of pile and soil has three conditons,which are no displacement of elment node,contact and spring.It used this three conditions to analyze the capability of push-extend multi-under-reamed pile and to find reasonal boundary to calculate ultimate bearing capacity. Analysis focuses on two fronts,the one is process of preprocessor,the other is how to anlyze the results of postprocessor. According to the results,it suggests that the best relationship of pile and soil is spring element which can use test data.The article could put the conclusion into practice to anlyze its ultimate bearing capacity,and put out several loading points to research the process that stress changes along with settlement. Pile should meet the requirements of capacity and deformation,specificati-ons limites its settlement to control capacity, How much is ultimate bearing capacity in design,it depends on the condition of soil and requirements of settlement. Fourthly,it researches the lateral friction ultimate bearing capacity of push-extend multi-under-reamed pile.The rigid-plastic model is estabished, the friction coefficient is obtained and the formula of ultimate bearing capacity of push-extend multi-under-reamed pile is derived.The research provides a reliable theoretical support to design pile foundation in this paper,makes the design of push-extend multi-under-reamed pile more meet practical engineering and play its advantages fully.It complements and improves the existing research results further to facilitate the promotion of the technology and application of large-scale, to lay a solid theoretical foundation to promote the wider use of the technology and to create greater economic and social benefits for push-extend multi-under-reamed pile to provide broader space.