Constructing a metro station by enlarging shield tunnels combined with a mining/cut-and-cover method provides a new method to solve the contradictions of construction time limits of shield tunnels and stations. As a n...Constructing a metro station by enlarging shield tunnels combined with a mining/cut-and-cover method provides a new method to solve the contradictions of construction time limits of shield tunnels and stations. As a new-style construction method, there are several specific risks involved in the construction process. Based on the test section of Sanyuanqiao station on Beijing metro line 10, and combined with the existing methods of risk identification at present, including a review of world-wide operational experience of similar projects, the study of generic guidance on hazards associated with the type of work being undertaken, and discussions with qualified and experienced staff from the project team, etc., the specific risks during the construction process of the metro station constructed by enlarging shield tunnels combined with the cut-and-cover method are identified. The results show that the specific risks mainly come from three construction processes which include constructing upper enclosure structures, excavating the soil between shield tunnels and demolishing shield segments. Then relevant risk mitigation measures are put forward. The results can provide references for scheme improvement and a comprehensive risk assessment of the new-style construction method.展开更多
The section of shield tunnel of the Chengdu Metro line passes primarily through sandy cobble strata. There are many buildings with spread foundations along the lines. Shield tunnel construction will disturb the ground...The section of shield tunnel of the Chengdu Metro line passes primarily through sandy cobble strata. There are many buildings with spread foundations along the lines. Shield tunnel construction will disturb the ground, causing displacement or stress to adjacent spread foundations. Based on the similarity theory, a laboratory model test of shield tunnel driving was carried out to study the influence of shield tunnel excavation on the displace ment of adjacent spread foundation. The results show that foundation closer to the tunnel has greater displacement or settlement than that further away. The horizontal dis placement is small and is influenced greatly by the cutting face. The displacement along the machine driving direction is bigger and is significantly affected by the thrust force. Settlement occurs primarily when shield machine passes close to the foundation and is the greatest at that time. Uneven settlement at the bottom of the spread foundation reaches a maximum after the excavation ends. In a numerical simulation, a particle flow model was con structed to study the impact of shield tunnel excavation on the stresses in the ground. The model showed stress con centration at the bottom of the spread foundation. With the increasing ground loss ratio, a loose area appears in the tunnel dome where the contact force dropped. Above the loose area, the contact force increases, forming an arch shaped soil area which prevents the loose area from expanding to the ground surface. The excavation also changed the pressure distribution around spread foundation.展开更多
基金Beijing Science and Technology Planning Project(No.D0604003040921)
文摘Constructing a metro station by enlarging shield tunnels combined with a mining/cut-and-cover method provides a new method to solve the contradictions of construction time limits of shield tunnels and stations. As a new-style construction method, there are several specific risks involved in the construction process. Based on the test section of Sanyuanqiao station on Beijing metro line 10, and combined with the existing methods of risk identification at present, including a review of world-wide operational experience of similar projects, the study of generic guidance on hazards associated with the type of work being undertaken, and discussions with qualified and experienced staff from the project team, etc., the specific risks during the construction process of the metro station constructed by enlarging shield tunnels combined with the cut-and-cover method are identified. The results show that the specific risks mainly come from three construction processes which include constructing upper enclosure structures, excavating the soil between shield tunnels and demolishing shield segments. Then relevant risk mitigation measures are put forward. The results can provide references for scheme improvement and a comprehensive risk assessment of the new-style construction method.
基金funded by the National Natural Science Foundation of China (Nos. 51278422 and 50925830)the National 973 Plan Topics of China (No. 2010CB732105)+1 种基金the National Science and Technology Pillar Program of China (No. 2012BAG05B03)the Sichuan Youth Science and Technology Foundation, China (No. 2012JQ0021)
文摘The section of shield tunnel of the Chengdu Metro line passes primarily through sandy cobble strata. There are many buildings with spread foundations along the lines. Shield tunnel construction will disturb the ground, causing displacement or stress to adjacent spread foundations. Based on the similarity theory, a laboratory model test of shield tunnel driving was carried out to study the influence of shield tunnel excavation on the displace ment of adjacent spread foundation. The results show that foundation closer to the tunnel has greater displacement or settlement than that further away. The horizontal dis placement is small and is influenced greatly by the cutting face. The displacement along the machine driving direction is bigger and is significantly affected by the thrust force. Settlement occurs primarily when shield machine passes close to the foundation and is the greatest at that time. Uneven settlement at the bottom of the spread foundation reaches a maximum after the excavation ends. In a numerical simulation, a particle flow model was con structed to study the impact of shield tunnel excavation on the stresses in the ground. The model showed stress con centration at the bottom of the spread foundation. With the increasing ground loss ratio, a loose area appears in the tunnel dome where the contact force dropped. Above the loose area, the contact force increases, forming an arch shaped soil area which prevents the loose area from expanding to the ground surface. The excavation also changed the pressure distribution around spread foundation.
