| With the explosive growth of urban construction,high-speed railway,expressway and cross-sea bridges in our country,more and more pile foundations become passive pile subjected to various passive loadings.Generally,the loads acting on passive pile contain not only passive loading induced from soil movement,but also axial force on pile head and negative friction arising from surcharging pressure.However,there are few literatures available on the research on bearing mechanics of passive pile under combined loads,and few design guides and codes for reference,which makes it become difficult problem to calculate and design the bearing capacity of passive pile under combined loads.Thus,it is particularly important to systematically peroform the research on bearing mechanics of passive pile under combined loads.This topic comes from National Key Technology R&D program(No.2011BAG07B00)",the National Basic Research Program of China(No.2013CB036304),Chinese National Natural Science Foundation(No.51478109),Major science and technology projects of transportation during Twelfth Five-year Plan Period(No.2011318494160)and Research Project of Taizhou Bridge Construction in Zhejiang Province "The Mechanism of Bridge Pile by Imbanlance Surcharge Load of New Reclamation Area".Based on the theoretical derivations and on the supplementary verification composed of in-situ pile test,model tests in laboratory and available literatures,the main research works and conclusions are as follows:(1)On the basis of the available linear,nonlinear,linear elastic-plastic and nonlinear elastoplastic pile-soil interaction models,this paper proposed a kind of p-y curve with uniform linear elastic-plastic form.According to the one dimensional linear feature of transfer matrix method,the soil resistance factors,passive loads along pile shaft and displacement distribution of lateral soil movement,distribution model of axial force along pile shaft with consideration of the influence of negative side firction or not were all homogenized and changed into constants.Bases on which,the paper solved the generalized solutions for passive pile in multilayered soil deposits subjected to lateral soil movement and axial force of pile shaft by combining Laplace forward and inverse transformation with transfer matrix method.At the same time,this paper also obtained the general solutions for active pile,which is the special case of passive pile.(2)By further studying foreign codes and research status,this paper had proved the rationality and validity of Boussinesq's improved solution.Meanwhile,ignoring the influence of layered properties of soil mass on additional lateral stress,this paper derived and obtained the analytical solutions of additional lateral stress induced for arbitrary location by rectangular and triangular surcharging load with finite boundary and infinite boundary,respectively.(3)Combined conventional local plastic deformation theory with actural additional horizontal stress,this paper proposed a new method to obtain the actual passive load actiong on pile shaft determined by the equilibrium position of the inner force arsing from contrary and forward derivation.Moreover,the original theory and calculation method of determining passive load acting on pile shaft,excess lateral force and addition stress considering the short term and long term effects of surcharging load established in this paper and verified by in-situ pile test and model pile tests.Furthermore,the analysis of influence of axial force of pile shaft indicate that vertical load actted on pile head has an effect on pile response and this influence will become outstanding as the applied vertical load increasing,whether considering short term effect or long term effect of surcharging load.Particularlly,as the vertical load reaching to the vertical allowable level,the maximum deflection of pile shaft will be increased by 10?15%,as well as the maximum by 16?20%.The same influence also can be observed when increasing the surcharging load.(4)The results of parametric analysis of passive loads acting on pile shaft subjected to surcharging load illustrate that the passive loads acting on pile shaft incease as increasing the surcharging load,cohesion,friction angle and gravity of soil mass and as decreasing ratio of D1/d until the passive loads reach to the ultimate values.The excess lateral force and addition stress of passive pile also incease as increasing the surcharging load,but decrease with increasing the cohesion,friction angle,gravity of soil mass and decreasing ratio of D1/d.During the analysis,it could be found that the influence of chaning friction angle is more sensitive.(5)In multilayered soil deposits,the ultimate passive loading of pile shaft in softer layer is samller,and this ultimate value will decrease as increasing the depth of soft layer.The resonable pile spacing ratio(D1/d)crit should between the critical pile spacing ratio(D1/d)low under short term effect of surcharging load and the critical pile spacing ratio(D1/d)upper under long term effect of surcharging load.(6)Based on the doule soil-arching theory,firstly,this paper established the range of soil arching of soil mass which performe lateral force acting on passive pile shaft by Mohr Circle Pole method.Secondly,the analytical expressions of lateral stress acting on passive pile were obtained by principle stress rotation method and Coulomb method,respectively.Finally,combined with the improved solution of local plastical deformation theory,the analytical expressions of passive load acting on passive pile subjected to unstable sandy slope were obtained.The results of parametric analysis of passive loads acting on pile shaft subjected to unstable sandy slope indicate that the passive load and corresponding resultant force increase as the inclined angle ?,friction angle ? increasing,and pile spacing ratio D1/d decreasing.Meanwhile,vertical load applied at pile head has remarkable influence on response of anti-slide pile as increasing the applied vertical load.Furthermore,response of passive pile under combined loads will remarkably decrease as increasing the embedded depth.(7)Considering the long term effect of surcharging load,the increase of shear strength for soft soil as the incease of degree of consolidation should be taken into account.Moreover,it is necessary to evaluate the influence of negative friction of pile shaft when consider the long term effect of surcharging load.If the neutral point of negative friction of pile shaft is in the range of maximum pile deflection,the influence of negative friction of pile shaft should be taken into account because of the impact ranges around 5.5%.While,if the neutral point of negative friction of pile shaft is far from the range of maximum pile deflection,the influence of negative friction on axial force of pile shaft and on bearing capacity of passive pile under combined loads can be ignored.(8)During the calculation and design of passive pile subjected to surcharging load,the passive loads acting on pile shaft of first pile row should be determined by considering long term effect of surcharging load.However,for other pile rows except the first pile row,the passive loads acting on pile shaft of other pile rows should be evaluated by the excess additional lateral stress of first pile row on the basis of considering short term effect of surcharging load. |
PDF Full Text Request