Advanced Materials Research Vols. 446-449

Abstract: The cracks-tip field on collinear periodic cracks of infinite orthotropic fiber reinforcement composite plate subjected to anti-plane shear force is studied in this paper. With the introduction of the Westergaard stress function and application of complex function theory and undetermined coefficients method, mechanical problem is changed into partial differential boundary value problem. The undetermined coefficients and the stress function are obtained with the help of boundary conditions. Due to the distribution of periodic cracks, stress intensity factor depends on the shape factor. The results show that interaction happens between the collinear periodic cracks. When the ratio of crack length and crack spacing is less than 1/3, the interaction between the cracks is very small. When the ratio gradually increases to 1, strong interaction between the cracks will be found. Cracks-tip field has scale effect. When the ratio of crack length and the given reference crack length decreases, the displacement field is significantly smaller.

Abstract: This paper focuses on finding a more effective bolting design method. Stress and displacement of variable stiffness beam were calculated by using material mechanics, variable stiffness bolting designs was simulated using FLAC5.0 software. The calculation indicates that the maximum displacement of a variable stiffness beam is less than that in a constant stiffness beam, while same material quantity is used; and proper variable stiffness designs can improve the bolting effect while same total quantity of bolts is used according to the simulations.

Abstract: Recently, response problems of extant structures under dynamic loads have been hot spots with the increase of earthquake disasters. Dynamic response analyses of underground rock tunnel have been made using the dynamic mode of 3D finite difference software FLAC3D, considering the impacts of different lateral pressure coefficients on the rock tunnel under the same earthquake load. Some conclusions are drawn: the vertical displacement of the bottom of rock tunnel arch is the maximum under the same earthquake load; the maximum vertical displacement at the tunnel top decreases with the increase of lateral pressure coefficient; the maximum vertical velocity at the tunnel shoulder increases with the lateral pressure coefficient; the maximum vertical acceleration at the tunnel bottom first increases and then decreases with the lateral pressure coefficient.

Abstract: Taking the Hongqi west road station construction of Dalian metro line 2 as an example, the regularities of the temperature and the smoke concentration distribution are analyzed. Basing on FDS, the simulation model of the metro station fire is set up. Assume six fire points in the station to simulate the smoke diffusion velocity and the personnel evacuation time in fire. Results show that the chimney effect is obvious at the back of the station. The highest temperature of every export is 180°C and the lowest temperature is 40°C during the effective duration. The time duration can meet the needs of the personnel evacuation from the fire metro station. Basing on the analysis of variation of the smoke flows and the temperature, the metro station project is reasonable.

Abstract: The new type of segment lining for shield tunnel was developed, which is a kind of universal ring applied in metro tunnels. Based on Beam-spring Model, mechanical characters and controlling assembling modes of universal segment lining were obtained by simulating the possible assembling schemes.

Abstract: Measurement of the loose zone of tunnel surrounding rock is of great significance in the determination of its support measures and stability analysis. By identifying the loose zone, the effective measures can be adopted to ensure a safe tunnel construction. The ultrasonic test is conducted to the TBM construction of Zhongtianshan Tunnel to specify the disturbance range of the TBM construction on the surrounding rock and the anchoring lengths of bolts.

Abstract: The numerical simulation results of 12 typical fire scenarios prove that the boundary conditions of tunnel entrance exert a significant influence on the accuracy and reliability of the fire numerical simulation results in metro station. In the fire scenarios with four 400-metre-long tunnels at both ends of the platform, the fire numerical simulation result is the most accurate, but the total numerical calculation time is twice more than the other fire scenarios, due to the additional volume of the computational meshes of the 4 tunnels. In order to guarantee the accuracy and reliability of the fire numerical simulation results on the condition that the computational mesh volume and numerical calculation time have not to be increased, 18 new fire scenarios with the different width of the tunnel entrance have been designed to simulate fire smoke movement in metro station, and the results are inserted into Lagrange's Interpolation Equation, then the equivalent width coefficient ε of tunnel entrance is found to be in the range of 0.34～0.55. In consideration of the mesh cell size and evacuation safety, ε is suggested to be 0.375.

Abstract: Fault fracture zone is an important factor that leads to tunnel seismic damage. In order to research failure mechanism and anti-seismic measures of tunnels across large fault fracture zone, theoretical analysis and numerical simulation has been done to Jiaozhou Bay submarine tunnel in Qingdao. The research results indicate that: in fault fracture zones, surrounding rocks instability resulting from ground motion, the huge earthquake inertial force, and the deformation energy by bedrock surface wave with macro energy all can cause damage to tunnel lining, yet the latter is the primary reason; when the differences of mass density and stiffness between tunnel lining and wall rocks become big, ductile tunnels with light weight will aggravate damage to tunnels rather than improve their anti-seismic capability; keeping stability of surrounding rocks and guaranteeing mass density and stiffness of tunnel lining to be the same as or similar to that of surrounding rocks could prevent tunnel damages in fault fracture zone, yet the latter is the most effective way. This research achievement can set particular examples for research on seismic damage mechanism and for anti-seismic design of tunnel structure in highly seismic regions.

Abstract: According to the model tests of the broken rock behind the tunnel lining impacting on the structural safety, and numerical simulation studying the tunnel in 3 different stress fields while the broken rock locates 2 different positions, the article studies the safety of tunnel structure. The results showed that: in a uniform stress field, the lining played a maximum carrying capacity whenever the broken rock on the vault or behind the right side of the wall. In the horizontal pressure based stress field, when broken rock is on the vault, the grouting effect is most significant and the negative moment was controled by the rate of 75%. In the vertical pressure based stress field, when the broken rock is behind the right side wall, the disease spread sporadically throughout the arch after grouting.

Abstract: Abstract. Coal being one of the main energy resources in China. Coal industry plays an important role in the domestic economy. Roadway support is a key technology in coal mining, and the mechanical properties of surrounding rock directly affect the stability of roadways and their supporting structure. In order to solve the problem of gateway support for C8 coal seam, In terms of the rheological data got from the argillaceous siltstone samples and the influence that loading history has on rock deformation, it employs Burgers model to reflect the creep characteristics of rock. The analytical results demonstrate that the creep test curves of rock sample basically tallies with the theoretical curves and Burgers clearly describes the creep characteristics of rocks. The relationship between surrounding rock stress and surrounding rock deformation provides roadway support with reasonable evidence.