Research On Internal Force And Deformation Of Retaining Structure With Treble-Row Piles In Deep Foundation Pit

In order to adapt a variety of complex situations,row pile retaining structure developed from single row pile to Double-row piles.While along with the deepening of the foundation pit depth,more complex site conditions,Double-row piles has been unable to meet the demand at part of engineering.It need to use the combination of inner support and anchor stock.Thus,it lost some of advantages such as no internal support and convenient construction.Aiming at the problem of Double-row piles,a new type of foundation pit supporting structure appeared in foundation pit engineering——Treble-row piles retaining structure,this structure can provide greater lateral bending stiffness and better limit on the deformation of retaining structures and better performance resistance to overturning.Beside,it has strong practicability and good prospect in foundation pit engineering.However,Treble-row piles retaining structure is a new type of foundation pit support,it lacks of in-depth theoretical and practical research,the structure's calculation method and distribution of internal force and deformation law are in the blank stage.Therefore,this article revolved Treble-row pile retaining structure to conduct the thorough research: the calculation method of Treble-row pile was explored and verified;Some new Treble-row piles which can improve overturning resistance performance and the ability to control the deformation were put forward several kinds and applied for a national patent,it also has been carrying on numerical analysis;took a foundation pit engineering in WuChuang district as an example,the anti-overturning stability calculation method of Treble-row piles and the influence of each key factor were researched;A geotechnical finite element software Midas GTS was used to numerical simulated Treble-row pile,the internal force distribution and deformation of the structure and the influence of sensitive parameters on structure were analyzed.It makes up for the blank of the theoretical research on Treble-row piles retaining structure.The innovation and main research results of article lies in:(1)The combination of Treble-row piles and soil nailing wall as a new supporting structure has been authorized national patent.it include: In all or part of the back row pile set up vertical anchor or little i-beam is called Vertical Anchoring Treble-rows piles;The front row pile is set to an inclined pile is called Inclined treble-rows pile;enlarged the bottom of the pile is called Expanded treble-rows pile.Beside,It proposed a measure to improve the anti-overturning performance and reduce deformation of Treble-row pile such as reasonable interval of top bracing.(2)The calculation methods of internal force and deformation of Treble-row pile was proposed,such as based on the principle of equivalent stiffness and based on elastic resistance method of the standard of foundation pit and based on finite element analysis method.Although the calculation methods of Treble-row pile base on equivalent stiffness can get relatively accurate deformation law,the distribution of internal force is different.(3)Using limit equilibrium principle,the anti-overturning stability calculation model of Treble-row piles and the formula of safety factor was presented.Utilizing this calculation method analyzed a Treble-row pile foundation pit project in Wuchang,Obtained vertical anchor can play a resistive overturning effect.The reasonable interval of top bracing should be controlled in the range of 40m~60m.Through comparative analyzed of the influence of various key factors to anti-overturning,The optimal design method of anti-overturning ability was proposed,also get its influence size sort: pile length>overload>pile spacing>pile interval>pile diameter>vertical anchor force?interval of top bracing.(4)Through the finite element numerical analysis,the calculated results are consistent with the engineering monitoring data,The internal force and deformation of Treble-row pile decreased gradually from the front row piles to the back piles,when the row spacing between middle row pile with front and rear piles is difference,the influence of the internal force and deformation of the supporting structure is very small,so it can be flexibly arranged row piles,effectively avoid underground obstacles.The sensitivity of each parameter to influence comparative analysis of the internal force and deformation of the supporting structure: pile diameter> pile interval> pile row distance> pile length.The parameter setting of front pile to internal force and deformation characteristics of structures plays a key role.Inclined treble-rows pile and Expanded treble-rows pile can reduce the horizontal deformation of the retaining structure to a certain extent.