Deformation Control Of Suspension Side Piles And Support Optimization In Metro Tunnel Constructed Of PBA Method Upper Existing Metro Shield Tunnel

With the rapid development of urban economy and the expansion of urban scale,the pressure of urban traffic is increasing,which has greatly promoted the construction and development of urban underground rail transit.In the construction of urban rail transit,the PBA method has been widely used.Based on the subway project in Beijing,this paper establishes the calculation model of the suspended side pile in the PBA method.Furthermore,the theoretical analysis method,numerical simulation method and the method of monitoring steel shaft force are used to study the laws of internal force and deformation of the suspension pile in detail.Meanwhile,the original steel support was optimized for anchor pile supporting structure.Through calculation and analysis,the paper has made the following main conclusions:1.After the completion of the construction,the horizontal displacement value of the suspended side pile increases when the pile depth increases.The horizontal displacement value of the pile bottom is the largest that is about 5.1mm.The horizontal displacement law has shown that the horizontal displacement of the suspended side piles is large due to the insufficient depth of the suspended side piles,but still meets the design requirements.2.By comparing and analyzing the displacement and internal force of the suspended side pile and the adjacent long pile,it has found that the horizontal displacement value of the suspended side pile is greater than that of the long pile at the same depth while the internal force value of the suspended side pile is smaller than that of the long pile.The deformation of the short pile can be restrained by the long pile,therefore,the lateral restraint connection of the long pile and the short pile can be increased in the construction.3.The load carried by the suspended side pile mainly includes the axial force and bending moment applied by the upper soil and structure to the top of the pile and the horizontal lateral pressure generated by the lateral soil.Through theoretical analysis and calculation,it has found that the bending moment value of the side pile in the horizontal pressure of the lateral soil is the largest.Meanwhile,the horizontal displacement of the side pile is mainly generated by the horizontal pressure of the lateral soil.Therefore,it is necessary to focus on the lateral horizontal displacement of the soil and take reinforcement measures during construction if necessary.4.The support method was optimized.The horizontal displacement values of the suspended side piles were compared under the three conditions of unsupported,steel support and anchor cable support.Through calculation and analysis,the suspension side piles converge is 14.4mm under unsupported conditions,which is less than the control value of 20mm,and it can meet the requirements of deformation control.Therefore,the construction should be carried out without support considering other construction factors.