Analysis Of Influence Of Urban Shallow Tunnel Construction Dewatering On Surrounding Buildings

In the process of urban tunnel construction,it is inevitable that there will be crossing and adjacent to various existing structures,especially in the central area of the city through dense buildings on the ground,which causes many engineering and safety problems.Based on a highway tunnel passing through a building in Fuzhou,this paper studies the surface subsidence form,the stress and deformation characteristics of the building and the deformation law of the surrounding rock through a series of field tests and the numerical analysis and field construction validation of the optimized reinforcement scheme for dewatering in shallow tunnel construction in strongly weathered granite stratum are carried out.The deformation of surrounding buildings under different dewatering depths and the influence of tunnel construction dewatering on surrounding buildings under different spacing are studied.The minimum safe distance between buildings and tunnel boundary is summarized,which accumulates experience for the analogical design of shallow tunnel engineering in such geological cities in the future.(1)Through the analysis of monitoring data of surface settlement and building deformation in the early stage of precipitation,it is concluded that the maximum settlement is in the center of two pumping wells,and the farther away from the pumping wells,the smaller the settlement value is.The surface settlement caused by pumping of precipitation wells is basically funnel-shaped.When the precipitation depth of precipitation wells is 10 m,the maximum surface settlement is about 22 mm.In buildings,the maximum settlement is 12.5mm and the maximum inclination is H/238.(2)By comparing the numerical analysis with the field measured data at the dewatering depth of 10 meters,it is concluded that the settlement law of surface and building in the numerical model is similar to that of field monitoring.Therefore,the results of numerical analysis model are of reference value.Numerical analysis of the continuous precipitation shows that the maximum surface settlement is 34.7 mm,which will results the maximum settlement of house is 24.1 mm,and will increase the tilt of the house.On this basis,tunnel excavation will continue,and the settlement of the house will continue to increase,with the maximum inclination rate of the house reaching H/91.This inclination will exceed the stipulated value that the limit value of lateral displacement of multi-story reinforced concrete frame structure is H/200.in Table 7.3.10 which is from the Standard for Reliability Appraisal of Civil Buildings(GB50292-2015).The building will be in dangerous condition and at this stage,precipitation must be stopped and optimization measures must be taken.(3)A comprehensive optimum reinforcement scheme is proposed,which includes reinforcing the soil above the tunnel,constructing a row of water-stop curtains on both sides of the tunnel and reinforcing the side retaining wall of Tian shuiyuan District by using surface jet grouting piles.The numerical analysis of the optimized scheme shows that the average settlement of 1# and 2# buildings in Tianshuiyuan District increases by 1.6 mm,and that of foreign trade dormitories in the province increases by 1.7 mm which shows that the water-stop curtains can effectively control the settlement of the building during the process of the dewatering by using the dewatering well.During tunnel excavation,surface jet grouting pile strengthening soil and the water-stop curtain of surface jet grouting pile on both sides can reduce the impact of tunnel excavation on the surface.The field monitoring data analysis of the optimized scheme shows that the maximum settlement of the building caused by dewatering in the later stage of dewatering well and tunnel excavation is 2 mm and the maximum inclination rate is H/214 after the reinforcement of the optimized scheme.The comprehensive effect of three reinforcement schemes,that are water-stop curtain,soil reinforcement and retaining wall reinforcement by using surface jet grouting piles,can effectively reduce the influence of tunnel dewatering construction on surrounding buildings.(4)The results of numerical analysis show that under the condition of changing the precipitation depth of precipitation wells,the deeper the precipitation of precipitation wells,the larger the surface settlement will be,but with the increase of precipitation depth,the increment of surface settlement caused by precipitation becomes smaller and smaller.In the initial stage of precipitation,the increment of surface settlement changes dramatically,while the relative increment of surface settlement decreases with the increase of precipitation depth in the later stage.By changing the distance between buildings and tunnels,the numerical analysis results shows settlement control requirements can be guaranteed when the distance between building and tunnel boundary is more than 70 M and when the distance between the building and the tunnel boundary is more than 40 meters,the requirement of controlling the inclination of the building can be guaranteed.Therefore,the distance between the building and the tunnel boundary should be controlled at least 70 meters to ensure the safety of the building during the construction of tunnel dewatering.