According to the interaction of three shallow tunnels with large section, the analytical solution to rock pressure has been derived and discussed. The load model is given when the bilateral tunnels are excavated. Acco...According to the interaction of three shallow tunnels with large section, the analytical solution to rock pressure has been derived and discussed. The load model is given when the bilateral tunnels are excavated. According to the model, the stresses of three tunnels and single tunnel are calculated and compared to analyze the distribution characteristics, where the stresses are influenced by controlling factors of clear distance, covering depth and inclination angle of ground surface. The results show that, in general, the bias distribution is more serious. Therefore, it is significant to settle down the load model of three shallow tunnels so as to determine the measure of reinforcement and design the structure of support. The model and results can be used as a theoretical basis in designation and further research of the three shallow tunnels.展开更多
Numerical simulation using finite differential code was conducted for the single line railway and four-lane road shallow tunnels subjected to unsymmetrical pressure. The mechanical behavior of weak rock mass was studi...Numerical simulation using finite differential code was conducted for the single line railway and four-lane road shallow tunnels subjected to unsymmetrical pressure. The mechanical behavior of weak rock mass was studied considering the influences of stress dilatancy on the failure mechanisms, and the results of numerical simulation were compared with the analytical solutions in specifications. The results show that the dilatancy angle has great influences on the surrounding rock displacement and the shape of failure face for the shallow tunnels. When the dilatancy angle equals zero, the failure face of the surrounding rock forms and extends to the ground surface. With the dilatancy angle increasing, the loose region decreases gradually, and failure surface discontinues. When the dilatancy angle equals the friction angle, the loose region is only distributed in a small range around the crown and sidewalls. On the side of smaller buried depth, the difference of break angle between numerical simulation and the code is less than 10% for single line railway tunnels with the dilatancy angle of zero. However, for the four-lane road tunnels, the difference reaches 20.8%. On the side of larger buried depth, the break angles are smaller than those by the code, the difference reaches 16.8% for single line railway tunnels, and 13.8% for four-lane road tunnels. With the dilatancy angle increasing, especially the dilatancy angle approximating to internal friction angle, it is on safe side to calculate the break angle using the analytical solution method of specifications. Therefore, the influence of stress dilatancy should be considered while determining the failure mechanisms of shallow tunnels subjected to unsymmetrical pressure in weak rocks.展开更多
In order to study the unsymmetrical load effect in geological bedding strata for the Muzhailing tunnel on the Lanzhou-Chongqing passenger dedicated line in China, we investigated the deformation, mechanical response a...In order to study the unsymmetrical load effect in geological bedding strata for the Muzhailing tunnel on the Lanzhou-Chongqing passenger dedicated line in China, we investigated the deformation, mechanical response and pressure of the surrounding rock and the mechanical characteristics of bolts of the tunnel. The results suggest that open zones appear at arch and invert where joints open up, when layered stratum is horizontal, or when the dip angle of in- clined bedding is small. Open zones occur perpendicular to a joint. The failure mode is bending disjunction at the arch tain shear displacement, and lead to obvious geological bedding unsymmetrical load. The failure mode is shear damage. For the joint dip angle in the range of 75-90°, the failure mode is flexural crushing at the wall and vertical shear rup- ture above the arch. The restraining effect of two sides weakens for vertical dip. On the whole, shear failure instabilitytrend would occur and the tunnel collapses evenly. When the angle between the bolt and structure plane is greater than 23°, bolts can enhance the shearing stiffness of joint plane. Unfortunately, in the general purpose graph of tunnel for 250 km/h of passenger dedicated lines, the bolts have equal length and spacing. The rationale behind this is worthy offurther study. For inclined bedding, the surrounding rock pressure at the left wall is more than that at the right wall. In addition, lining is likely to be damaged at left shoulder and side wall. With the dip angle increasing, the unsymmetrical load gradually achieves symmetry. Asymmetry design for support is recommended to reduce the unsymmetrical load on lining disturbed by excavation.展开更多
基金Projects(2013CB036004, 2011CB013800) supported by the National Basic Research Program of ChinaProject(51178468, 50908234) supported by the National Natural Science Foundation of ChinaProject(2011G103-B) supported by the Science and Technology Development of Railway in China
文摘According to the interaction of three shallow tunnels with large section, the analytical solution to rock pressure has been derived and discussed. The load model is given when the bilateral tunnels are excavated. According to the model, the stresses of three tunnels and single tunnel are calculated and compared to analyze the distribution characteristics, where the stresses are influenced by controlling factors of clear distance, covering depth and inclination angle of ground surface. The results show that, in general, the bias distribution is more serious. Therefore, it is significant to settle down the load model of three shallow tunnels so as to determine the measure of reinforcement and design the structure of support. The model and results can be used as a theoretical basis in designation and further research of the three shallow tunnels.
基金Project(200631878557) supported by the West Traffic of Science and Technology of ChinaProject(200550) supported by the Foundation for the Author of National Excellent Doctoral Dissertation of ChinaProject(05-0686) supported by the Program for New Century Excellent Talents in University
文摘Numerical simulation using finite differential code was conducted for the single line railway and four-lane road shallow tunnels subjected to unsymmetrical pressure. The mechanical behavior of weak rock mass was studied considering the influences of stress dilatancy on the failure mechanisms, and the results of numerical simulation were compared with the analytical solutions in specifications. The results show that the dilatancy angle has great influences on the surrounding rock displacement and the shape of failure face for the shallow tunnels. When the dilatancy angle equals zero, the failure face of the surrounding rock forms and extends to the ground surface. With the dilatancy angle increasing, the loose region decreases gradually, and failure surface discontinues. When the dilatancy angle equals the friction angle, the loose region is only distributed in a small range around the crown and sidewalls. On the side of smaller buried depth, the difference of break angle between numerical simulation and the code is less than 10% for single line railway tunnels with the dilatancy angle of zero. However, for the four-lane road tunnels, the difference reaches 20.8%. On the side of larger buried depth, the break angles are smaller than those by the code, the difference reaches 16.8% for single line railway tunnels, and 13.8% for four-lane road tunnels. With the dilatancy angle increasing, especially the dilatancy angle approximating to internal friction angle, it is on safe side to calculate the break angle using the analytical solution method of specifications. Therefore, the influence of stress dilatancy should be considered while determining the failure mechanisms of shallow tunnels subjected to unsymmetrical pressure in weak rocks.
基金supported by the National Natural Science Foundation of China (No. 51078318)
文摘In order to study the unsymmetrical load effect in geological bedding strata for the Muzhailing tunnel on the Lanzhou-Chongqing passenger dedicated line in China, we investigated the deformation, mechanical response and pressure of the surrounding rock and the mechanical characteristics of bolts of the tunnel. The results suggest that open zones appear at arch and invert where joints open up, when layered stratum is horizontal, or when the dip angle of in- clined bedding is small. Open zones occur perpendicular to a joint. The failure mode is bending disjunction at the arch tain shear displacement, and lead to obvious geological bedding unsymmetrical load. The failure mode is shear damage. For the joint dip angle in the range of 75-90°, the failure mode is flexural crushing at the wall and vertical shear rup- ture above the arch. The restraining effect of two sides weakens for vertical dip. On the whole, shear failure instabilitytrend would occur and the tunnel collapses evenly. When the angle between the bolt and structure plane is greater than 23°, bolts can enhance the shearing stiffness of joint plane. Unfortunately, in the general purpose graph of tunnel for 250 km/h of passenger dedicated lines, the bolts have equal length and spacing. The rationale behind this is worthy offurther study. For inclined bedding, the surrounding rock pressure at the left wall is more than that at the right wall. In addition, lining is likely to be damaged at left shoulder and side wall. With the dip angle increasing, the unsymmetrical load gradually achieves symmetry. Asymmetry design for support is recommended to reduce the unsymmetrical load on lining disturbed by excavation.
