Settlemen Calulation Analysis And Model Test Study Of The Super-long Piles Groups

With the rapid development of the economic and the dramatic ascension of thecomprehensive national strength, large bridges and high building construction aredeveloping rapidly. To make the bearing capacity and deformation of the pile meet therequirement of design,Super-long pile groups foundation are mostly used. comparedwith common pile groups, the influence factors of deformation character of theSuper-long piles groups is more complex, although scholars both at home and abroadhave carried on a lot of theoretical and experimental research on the pile groups andmade great theoretical and practical results, But the further system research of theload transfer mechanism and deformation characteristics are still lacked. Therefore,those problem are investigated and researched systematacially from theory and testfields in this dissertationt so so as to put forward a mixed calculation method of pilegroups settlement which can consider the complexity of the foundationcomprehensivly,and discuss the load transfer characteristics and influence factors ofdeformation character of the pile groups, combined with one of the key project“Theresearch of design and construction technology of Super-long pile groups in the deepsoft soil area(No.CXKJSF0108-2)” of the demonstration project of the Ministry ofTransort.Firstly, the present study situation both at home and abroad about the setlementof pile groups and Super-long pile groups foundation under vertical load arediscussed,and the main calculation method of the pile groups settlement. On this basis,the shear displacement method is used to consider the lateral stress transfer of soilaround piles, and the load transfer method is adopted to analysis the vertical loadtransfer of pile in pile groups.Meanwhile,the blind-effect between piles isconsidered,and then put interact factors of pile to pile in pile groups into the basicdifferential equation of vertical load transfer. Therefor, a mixed computation modelwhich can reflect homogeneity and heterogeneity of soil and interaciton between pilesare established on the account of solving respectively in homogeneity andheterogeneity soil.The indoor model load-bearing test of the super-long pile, super-long pile with acap and super-long pile groups are the designed and completed. The the load transfermechanism and settlement characteristics of the super-long pile, super-long pile with a cap and super-long pile groups are discussed through the measurement body axialforce，the counter force of soil underneath cap and settlement of pile top.The resultsshow that the Q-S curve of single pile belongs to the type of steep dipping, and theQ-S curve of pile with a cap and super-long pile groups belong to the type of gradualdescend; The change rule along the depth of axial force and fricton force of single pliehavs obvious difference with pile with a cap and super-long pile groups; the soilunderneath cap of single pile is damaged before plate the soil on the edge of cap andin the cente of cap.The rule of deformation damage of soils underneath the cap of thepile groups is similar to single pile with cap. In addition, the accuracy of thecalculation method in this thesis is proved based on the measured results. Finally, thefinite element analysis software ADINA is applied to establish three dimensionalcalculation model of the pile groups in homogeneous foundation,and discussed thethe influence of the ratio of length and diameter, space of pile and modulus of soil onthe settlement of pile groups.The results show the settlement of pile groups decreasegradually with the increasing of the ratio of length and diameter, space of pile andmodulus of soil,but the settlement change trend of pile groups is not completely samebetween different factors. These conclusions can provide certain theoretical referencefor the actual project.