The Time-space Evolution Mechanism Of Stratum Deformation And Control Measures During Subway Station Construction By PBA

The idea of the PBA of the subway station is to reduce the excavation section of the large-span station and complete the structural construction with a small environmental disturbance.Although the PBA has been widely used in engineering,there are still many ambiguities about the design and construction of the PBA method.First of all,there are many process changes in the construction process of the construction method,there is no strict standard in the construction sequence,the timing relationship is not clear,and there are many vague places in the design details.Therefore,in the actual construction,a slight change in the construction sequence will have a greater impact on the formation deformation.Secondly,it is not particularly clear about the relationship between structural deformation,formation deformation and surface settlement during construction,the theoretical prediction model does not reflect the construction stress process,and there are many uncertainties in the actual monitoring work.These factors have greatly affected the accuracy of the early warning forecast.In many cases,the monitored data.has not yet reached the alarm condition,but an accident has occurred.In this paper,the actual project of some stations in Beijing Metro is taken as the research object,and the station with large surrounding environment risk is taken as the research object.The temporal and spatial variation of surface subsidence caused by shallow buried excavating method is studied.Through theoretical analysis,numerical simulation of excavation process,model test and a large number of measured data,the spatial variation settlement law is obtained,the settlement prediction empirical formula is improved,and reasonable settlement deformation control measures are proposed.(1)Aiming at the uneven deformation of the stratum caused by the asymmetric excavation of the PBA method of the subway station,the deviation of the arching and arching of the station beam-column structure is caused.Based on the stochastic medium theory,the space-time evolution model of group hole excavation is esTablelished.The operation sequence of PBA spatial block and the uneven deformation law caused by the space-time evolution of process transformation are studied.The deformation law of formation space caused by construction is obtained.The uneven deformation of the stratum caused by the block construction is the main cause of the misalignment of the arch,and the structural constraint concept of the cross-span arch of the side hole is proposed.(2)Combined with numerical simulation and similar model tests,the correlation analysis of monitoring data inside and outside the tunnel is carried out.The calculation results show that the final surface settlement caused by PBA construction is on the side of the construction tunnel,and the maximum convergence of the structure in the tunnel is on the side of the construction tunnel.The maximum convergence displacement is on the outer wall of the tunnel.It is clear that the side hole is divided into the cross arch and the middle arch is finally buckled,which makes it easier to control the surrounding risk sources,such as Irregular deformation and uneven settlement of bridges,pipelines or buildings,and more conducive to controlling the risk of deformation of the formation space.(3)In view of the particularity of sand pebble formation in Beijing,the traditional Peck empirical formula is corrected by introducing the section correction coefficient.The revised Peck settlement prediction is more in line with the trend of change in actual monitoring results.Provide reference values for this geological condition,provide theoretical and data support for settlement prediction of sand and gravel stratum.(4)In order to solve the phenomenon of beam-column offset error and crack of arch-beam structure caused by the misalignment of the arching during the construction of the construction method,the engineering countermeasures for the construction of the side-span spanning arching arch are proposed.The synchronous symmetry ideal model and the temporal and spatial evolution process of the stratum generated by the actual construction process are calculated respectively.The difference between the synchronous symmetry ideal model and the actual construction process on the spatial deformation of the stratum is compared.The design refinement proposal and construction optimization plan of the construction method were obtained,and the engineering countermeasures for the side hole sub-butting arch were put forward.The method was finally verified in the construction of Beijing West Railway and Heping West Bridge subway station.