Study On Stability Of Metro Tunnels And Lining Optimization Of Qingdao Subway Line R3

Qingdao is an important central city,coastal resort city and international port city in China's coastal areas.With the rapid development of Qingdao City,there is a need to build a large number of urban subway to alleviate the increased pressure on traffic;Qingdao's strata of "upper soft and lower hard" has brought new challenges to the subway tunnels construction theory and technology;given the unique stratigraphy,the existing theory and other urban engineering experience couldn't provide effective advice on the construction of Qingdao subway,therefore,it is necessary to carry out special research on the stability and support design of Qingdao subway tunnels.Under the engineering background of R3 line in Qingdao,based on certain section of R3 line's geological condition and the existing tunnel structure,the strength reduction method was used to calculate the stability of the surrounding rock of the cavern with support and without support;the existing initial support form was optimized based on the safety factor;this paper mainly completed the following work:1.The M-C constitutive,D-P constitutive and MCC constitutive models commonly used in the numerical calculation of geotechnical engineering were briefly introduced.The basic principle of strength reduction,the criterion of instability and the definition of safety factor in underground engineering were introduced.2.The stability of the caverns under the depth of lm to 20m of ?-? level surrounding rock in certain section of Qingdao R3 line was calculated and analyzed by the strength reduction method with the application of built-in D-P constitutive model of finite element software ABAQUS,and the spatial distribution of the surrounding rock stability during the excavation of the shallow tunnel was obtained:with the increase in the thickness of overlying rock,the stability of the surrounding rock increased firstly and then decreased;The failure mode caused by instability of the surrounding rock in stratum of upper soft and lower hard and the distribution of the plastic zone were obtained.3.The strengthening effect of the existing initial support form on the stability of ?-?level surrounding rock was calculated by the strength reduction method with the application of built-in DP constitutive model of finite element software ABAQUS;the initial support form of certain existing subway tunnel section was evaluated based on the safety factor of surrounding rock,and it was believed that the initial support currently used is too strong and has the optimized space.The initial support form after optimization was proposed,and the safety factor of the surrounding rock was calculated to ensure the safety of the optimal design.Finally,on the basis of the stratigraphic-structure method,the safety factor of the secondary lining after the initial support optimization was calculated.The results showed that the optimal design not only can maintain the sufficient stability of surrounding rock,but also guarantee the safety margin of the tunnel support structure to ensure the normal use.