Study On The Influence Zone Dividing And Countermeasures Of Urban Tunneling Adjacent To Existing Tunnel

This thesis based on National Key research and Development Program of China,which estimates the effects and countermeasures of urban tunneling parallel to or crossing the existing tunnel.The influence zone of two parallel tunnels and orthogonal tunnels and the effects of construction are proposed in this paper.In according to distinct influence zones,this paper suggests effective countermeasures in order to ensure the safety of construction.Combining theoretical analysis,references research,and numerical simulation,the main conclusions are as follows:(1)Considering the real failure procedure of geomaterials and limit strain criterion,which was assumed losing bearing capacity when arriving ultimate strain.The failure of interlaid rock and soil are judging by whether plastic zones develop cross geomaterials,which was regarded as a criterion of strength reduction method and acquires safety factor through iteration.(2)Safety factor can be utilized to evaluate the effects of the adjacent construction,firstly,obtaining safety factor of different types of the individual tunnel by strength reduction method based on limit strain criterion.In addition,acquiring safety factor of adjacent construction by the same method under different conditions,then compares with the safety factor of a single tunnel.Moreover,dividing influence zones of tunneling adjacent to existing tunnel by combining superior and inferior limit of surrounding rock parameter,which was defined as the strong influence zone,the weak influence zone,and the non-influence zone.Lastly,the regulation of the distribution of influence zones was comprehensively analyzed in this paper based on mechanical behavior of tunnel.(3)Analyzing the regulation of influence zones induced by distinct factors such as the ratio of buried depth to existing tunnel diameter(H/D),the ratio of newly-built tunnel diameter to existing tunnel diameter that called relative scale(D/D?),and surrounding rock grade,the functional relationship between impact factors and the size of influence zone can be obtained.The predicted model of influence zones of tunneling adjacent to the existing tunnel was proposed in this paper based on BP neural network,which can be used to predict influence zones of adjacent construction under distinct conditions.(4)According to the influence zone division,there were three different objects in adjacent construction that include existing tunnel,newly-built tunnel,and interlaid rock and soil,respectively.Strengthen the bearing capacity of tunnel structure,reducing construction disturbance,and reducing surrounding rock displacement and stress are the main principle of countermeasures.This paper suggests adopting distinctive countermeasures for different objects in a certain project,which could ensure the safety of construction effectively.