Deep underground projects(e.g., coal mines), are often faced with complex conditions such as high stress and extremely soft rock. The strength and rigidity of the traditional support system are often insufficient,whic...Deep underground projects(e.g., coal mines), are often faced with complex conditions such as high stress and extremely soft rock. The strength and rigidity of the traditional support system are often insufficient,which makes it difficult to meet the requirements of ground control under complex conditions. As a new support form with high strength and rigidity, the confined concrete arch plays an important role in controlling the rock deformation under complex conditions. The section shape of the tunnel has an important impact on the mechanical properties and design of the support system. However, studies on the mechanical properties and influence mechanism of the new confined concrete arch are rarely reported. To this end, the mechanical properties of traditional U-shaped steel and new confined concrete arches are compared and comparative tests on arches of circular and straight-leg semicircular shapes in deep tunnels are conducted. A large mechanical testing system for underground engineering support structure is developed. The mechanical properties and influence mechanism of confined concrete arches with different section shapes under different loading modes and cross-section parameters are systematically studied. Test results show that the bearing capacity of the confined concrete arch is 2.10 times that of the U-shaped steel arch, and the bearing capacity of the circular confined concrete arch is 2.27 times that of the straight-leg semicircular arch. Among the various influencing factors and their engineering parameters,the lateral stress coefficient has the greatest impact on the bearing capacity of the confined concrete arch,followed by the steel pipe wall thickness, steel strength, and core concrete strength. Subsequently, the economic index of bearing capacity and cost is established, and the optimization design method for the confined concrete arch is proposed. Finally, this design method is applied to a high-stress tunnel under complex conditions, and the deformation of the surrounding rock is effectivel展开更多
In the Xiaowan arch dam there are massive temperature cracks nearly parallel to the dam axis. Obviously, whether the cracks may spread or not during the water storage process is one of the crucial factors for the safe...In the Xiaowan arch dam there are massive temperature cracks nearly parallel to the dam axis. Obviously, whether the cracks may spread or not during the water storage process is one of the crucial factors for the safety of a dam. In this paper, a new type of crack element, in which the contact component is implicitly included into the concrete component, is proposed to simulate the effects of the existing cracks. The crack element is proved by numerical example to share the merits of both conventional contact elements and joint elements. With a finite element model of the cracked arch dam together with its rock foundation established, the transient displacement and stress fields of the dam are obtained. The complicated rock foundation, the construction process of the arch dam, the massive cracks, the transient temperature field, as well as the water storage process have been taken into consideration in the simulation. In addition to the global model, several sub-models for typical crack tips are also generated with finer elements placed around the tips. Thus, more accurate displacement and stress distribution are obtained by simultaneous sub-model simulation. Based on the calculation of stress intensity factor for crack tips by extension method, the temperature cracks in the Xiaowan arch dam are finally proved to be stable.展开更多
基金supported by the National Natural Science Foundation of China (Nos. 42277174, 42077267, and 52074164)the Natural Science Foundation of Shandong Province, China (No. ZR2020JQ23)+2 种基金Major Scientific and Technological Innovation Project of Shandong Province, China (No. 2019SDZY04)the Project of Shandong Province Higher Educational Youth Innovation Science and Technology Program, China (No. 2019KJG013)the opening project of State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology (No. KFJJ21-02Z)。
文摘Deep underground projects(e.g., coal mines), are often faced with complex conditions such as high stress and extremely soft rock. The strength and rigidity of the traditional support system are often insufficient,which makes it difficult to meet the requirements of ground control under complex conditions. As a new support form with high strength and rigidity, the confined concrete arch plays an important role in controlling the rock deformation under complex conditions. The section shape of the tunnel has an important impact on the mechanical properties and design of the support system. However, studies on the mechanical properties and influence mechanism of the new confined concrete arch are rarely reported. To this end, the mechanical properties of traditional U-shaped steel and new confined concrete arches are compared and comparative tests on arches of circular and straight-leg semicircular shapes in deep tunnels are conducted. A large mechanical testing system for underground engineering support structure is developed. The mechanical properties and influence mechanism of confined concrete arches with different section shapes under different loading modes and cross-section parameters are systematically studied. Test results show that the bearing capacity of the confined concrete arch is 2.10 times that of the U-shaped steel arch, and the bearing capacity of the circular confined concrete arch is 2.27 times that of the straight-leg semicircular arch. Among the various influencing factors and their engineering parameters,the lateral stress coefficient has the greatest impact on the bearing capacity of the confined concrete arch,followed by the steel pipe wall thickness, steel strength, and core concrete strength. Subsequently, the economic index of bearing capacity and cost is established, and the optimization design method for the confined concrete arch is proposed. Finally, this design method is applied to a high-stress tunnel under complex conditions, and the deformation of the surrounding rock is effectivel
基金supported by the National Natural Science Foundation of China (Grant No. 51079109)
文摘In the Xiaowan arch dam there are massive temperature cracks nearly parallel to the dam axis. Obviously, whether the cracks may spread or not during the water storage process is one of the crucial factors for the safety of a dam. In this paper, a new type of crack element, in which the contact component is implicitly included into the concrete component, is proposed to simulate the effects of the existing cracks. The crack element is proved by numerical example to share the merits of both conventional contact elements and joint elements. With a finite element model of the cracked arch dam together with its rock foundation established, the transient displacement and stress fields of the dam are obtained. The complicated rock foundation, the construction process of the arch dam, the massive cracks, the transient temperature field, as well as the water storage process have been taken into consideration in the simulation. In addition to the global model, several sub-models for typical crack tips are also generated with finer elements placed around the tips. Thus, more accurate displacement and stress distribution are obtained by simultaneous sub-model simulation. Based on the calculation of stress intensity factor for crack tips by extension method, the temperature cracks in the Xiaowan arch dam are finally proved to be stable.
