Numerical Analysis For Technology Of Underpinning Structure Composed Of Piles And Beams

Foundation underpinning is the core technology in the existing building underground space development, it needs to truncate the pile foundation of the buildings during the construction of the subway, civil air defense and underground pipeline facilities at the bottom of the existing buildings, underpinning composed of beams and piles can translate the upper loads by underpinning pile along the subway on both sides. Underpinning composed of piles and beams has complex stress state, and the subsidence deformation is large, so it has great significance to study the underpinning load conversion and settlement deformation law.The origin of Foundation underpinning technique can be traced back to ancient times, its application range is wide, it can be used in reinforced and rectify, add layer, extend and shift, etc. to the buildings or structures, but the application in engineering of foundation underpinning composed of piles and beams is less, until the1930s it gets larger development when began of the construction of the subway. This article firstly reviewed the development process and the application present situation in project of underpinning technology composed of piles and beams. Then use the method of finite element analysis for typical underpinning structure to modeling and analysis, the stiffness matrix of typical underpinning structure composed of piles and beams is needed to be derived by applying the method of matrix displacement, laying theory basis of numerical analysis to underpinning technology composed of piles and beams.By numerical analysis to shenzhen subway underpinning engineering of phase one department square pile foundation as an example, we study the load-bearing characteristics of single span underpinning structure, and we compare the load transfer rule and rule of foundation settlement between the passive underpinning and the active underpinning, and by changing the design parameters to reduce the differential settlement and additional internal force of upper structure as the goal, to optimize the underpinning structure. We give some method to decrease the settlement and differential settlement under the underpinning place such as decrease the underpinning beam span, or increase the underpinning beam height.On the basis of the research in single span underpinning structure, we take Tianjin light railway bridge piers underpinning marina as example, do more research in load-bearing characteristics of the multi span underpinning structure composed of piles and beams. Compared with single span underpinning,it is difficult to determine the jacking displacement of the active underpinning, we can see from the data of this example, the displacement of pile top settlement in multiple span underpinning is mainly caused by underpinning beam deflection, and the beams of multi span underpinning structure deflect in vertical direction, the two direction deflection plus with each other, making the settlement of pile top displacement of multi span underpinning larger, so the jacking displacement of the multi span underpinning is more larger than single span underpinning.