Research On The Impact Of Subway Construction On The Adjacent Ancient Pagoda And Disaster Control In Loess Stratum

Based on the open projec"Study on the influence of subway construction on adjacent ancient pagodas and disaster control in undercompacted saturated loess strata"of Shaanxi Urban Geology and Underground Space Engineering Technology Research Center,this study studies several typical ancient pagodas in Shaanxi,and investigates and analyzes the surrounding engineering environment,hydrogeological conditions,disease status and causes.Furthermore,the physical and mechanical properties of the masonry pagoda building foundation and the constitutive parameters of typical loess strata under the condition of adjacent excavation are studied in depth.On this basis,the numerical analysis of the mechanical response of the tunnel construction near the ancient pagoda is carried out.Finally,reasonable control measures are put forward for the construction of the subway tunnel near the ancient pagoda,and the stability evaluation and analysis platform of the ancient pagoda considering the construction conditions of the adjacent tunnel is compiled.The specific research results are as follows:（1）Through extensive research on the surrounding engineering environment,disease status,protection measures and stratigraphic conditions of masonry pagodas（Greater Wild Goose Pagoda,Small wild goose Pagoda,Wanshou Temple Pagoda,Elephant Temple Pagoda,Jingguang Temple Pagoda）with a high span ratio of 1.5～7.6,it is found that most of the ancient pagodas have water seepage,efflorescence,inclination and other diseases.The bearing characteristics of typical loess foundation in which the masonry pagoda foundation is located are greatly affected by the fluctuation of groundwater level and the construction of adjacent underground space.（2）The typical loess strata in which the foundation of the ancient masonry pagoda is located are mainly new loess,ancient soil,old loess,silty clay,etc.Through the numerical inversion analysis of the measured data of a foundation pit project in Xi’an,it is shown that the MMC model is more suitable for the ground movement caused by underground excavation than the MC model,and when theE₅₀^ref=1.1Es of the loess stratum is close to the actual situation.（3）The mechanical response of tunnel excavation at different spatial locations to adjacent ancient pagodas（overall inclination,local inclination,tensile stress state）is studied by numerical analysis method.The results show that the critical control distance of adjacent tunnel construction for masonry pagodas with different heights is:the buried depth should not be less than 15 m,and the horizontal distance should not be less than 4D（underground cavern diameter）.（4）Taking the Greater Wild Goose Pagoda as an example,the influence of overall and local groundwater level fluctuations on the deformation of the ancient pagoda was studied.The results showed that under the condition of water level rise,the problem of rectifying the deviation of the ancient pagoda is more favorable.However,under the condition of overall water level drop,it is recommended that the spatial distance between the adjacent tunnel and the Dayan Pagoda be:the burial depth is greater than 15m,and the horizontal distance should not be less than 4.4D;Under the condition of local decrease in water level,it is recommended that the buried depth of the tunnel be greater than 15m,and the horizontal distance should not be less than 4.6D.（5）Using the analytic hierarchy process and fuzzy mathematics theory,nine risk factors affecting the stability of masonry pagodas were determined,and the risk level standards were divided.The pagoda stability evaluation system was constructed and applied in engineering.