Research On Mechanicsl Performance And Experiment About Pile-Soil Interaction Of Prestressed Concrete Pipe Pile With Side Embedded Precast Short Limb

With continuous progress of modern science and technology,andimprovement requirements of structure foundation, it is promoted to be widelyused of prestressed concrete pipe pile. But in order to meeting the requirementsof higher bearing capacity and less deformation of the single pipe pile inengineering practice, usually the pile body is longer and its diameter is larger, sothe dosage of concrete is increased, the construction efficiency is lower andeconomic cost is higher. Existing researches have shown that the single pileultimate bearing capacity can’t be effectively improved after the pile length andpile diameter is increased to a certain extent. So it becomes the inevitable trendof development of prestressed pipe pile that it will be improved properties of pipepile-soil working together and the bearing capacity of single pile by improvingthe pile type and construction technology.Combining the "11th Five-year Plan" research project of Jilin provinceeducation department—"Research on Mechanical Performance and Pile-SoilInteraction of Prestressed Concrete Pipe Pile with Side Embedded Precast ShortLimb "(2009No.416), it is adopted specific construction technology to embeddedsome precast short limb in side of the traditional closed pipe pile, that is formed special pile type, that is prestressed concrete pipe pile with sideembedded precast short limb（CQPHC）.The aim is to improve bearing capacityof single pile by the secondary end-bearing capacity from short limb andincreasing the capacity of side friction, and can reduce the comprehensive cost.It has been carried out indoor model test research on the bearing capacityand deformation performance of CQPHC, and been respectively carried on thenumerical analysis on the bearing capacity and settlement deformation of singlepile, and the pile-soil interaction under the vertical and horizontal loads with theANSYS software according to the related parameters of physical properties of thepile and soil. And it is simulated and analyzed systematically on the influence ofdifferent parameters of the pile and soil on the bearing properties of CQPHC.Then, it is confirmed that reasonable distance, position and number of short limbin the different soil conditions, and considered comprehensive economy, theconstruction feasibility of new pile type and the design of the push-extendequipment. It is provided the certain reference value and theoretical basis for theactual engineering. The following research are mainly completed：1.The vertical bearing capacity of CQPHC is significantly increased thanordinary pipe pile, due to the secondary end bearing effect of lateral limbs in theprocess of the vertical load. The settlement of pile top is decreased with themoving down of the location, the increasing of numbers and the decreasingdistance of lateral limbs, that is, it is more beneficial to the improvement of thevertical bearing of CQPHC and decreases of settlement of pile top that it is setclosely short limbs on the lower part of pile body. But, the too small distance canmake disturbance enlarged to the soil between the short limbs, so it is difficultthat the secondary end bearing effect of the short limb is given full play. Analysisresults have shown that, when the distance is1000mm, it is most favorable to improve the vertical bearing capacity of single pile;2.The parameters of soil around the pile have obvious influences on thebearing and deformation performance of CQPHC. The settlement of pile top isdecreased with the increase of cohesion and angle of internal friction and frictioncoefficient and modulus of elasticity of soil. Particularly, the vertical ultimatebearing capacity of CQPHC is not always increase infinite with the increase offriction coefficient. When the pile-soil friction coefficient is greater than0.4, it isno longer obvious to improve the effect of single pile vertical ultimate bearingcapacity by increasing the friction coefficient;3.In terms of horizontal load-bearing properties, under the various loads, thehorizontal displacement of pile top under the loaded position decreases graduallywith the increasing of depth. When the loads continue to increase, the plasticdeformation of soil gradually produces, the growth rate of the horizontaldisplacement speeds up. In the case of good soil conditions and spacing to beallowed, if short limbs are more close to the upper part of the body, their quantityare more and their distance are smaller, that the effects of improvement of thehorizontal bearing capacity and reducing the maximum bending moment aremore obvious. But their effects are not obvious on the horizontal displacement ofpile top and body while the number of short limbs are too many. So it isbeneficial to the improvement of the level ultimate bearing capacity that it is setclosely3to5layer short limbs on the upper department of pile body, and it has agood economy;4.The parameters of soil around the pile have obvious effect on thehorizontal displacement of pile of CQPHC top, too. With the increase of cohesion,angle of internal friction and modulus of elasticity of soil, The horizontaldisplacement of pile top is decreased gradually and the magnificence of changes also reduce gradually. Because of the change of the internal friction angle of soil,the maximum bending moment of the section of pile can effectively be changed,while the elastic modulus has the most significant effect to the levelsdisplacement of CQPHC;5.According to the similarity theory, the contrast analysis is to be carried outabout indoor model test between ordinary pipe pile and CQPHC. It is simulatedto the mechanism of pile-soil interaction, and carried out the qualitative researchpile on the bearing and deformation performance. The indoor model test iscarried on to the vertical bearing properties research by the model piles withdifferent spacing and number of short limbs, and its result is almost the samewith the changing trends of the finite element analysis. But there exist certaindifferences between experiment and theoretical analysis results because of thelimitation of simulation conditions, including the differences of properties ofcontact interface, model parameters of pile body and the physical propertiesparameters of soil.CQPHC is a new kind of prestressed pipe pile, they are realized that theinnovation of pile type, load-bearing mechanism and pile driving technology. Itis systematically studied the main influence factors on bearing characters ofCQPHC, which lay the theoretical foundation for the further study on CQPHCand provide a certain reference value for technology and economy. If it can beput into the practical engineering, the good technology and economic benefit willbe achieved.