An analysis of tunnel face stability generally assumes a single homogeneous rock mass.However,most rock tunnel projects are excavated in stratified rock masses.This paper presents a two-dimensional(2D)analytical model...An analysis of tunnel face stability generally assumes a single homogeneous rock mass.However,most rock tunnel projects are excavated in stratified rock masses.This paper presents a two-dimensional(2D)analytical model for estimating the face stability of a rock tunnel in the presence of rock mass stratification.The model uses the kinematical limit analysis approach combined with the block calculation technique.A virtual support force is applied to the tunnel face,and then solved using an optimization method based on the upper limit theorem of limit analysis and the nonlinear Hoek-Brown yield criterion.Several design charts are provided to analyze the effects of rock layer thickness on tunnel face stability,tunnel diameter,the arrangement sequence of weak and strong rock layers,and the variation in rock layer parameters at different positions.The results indicate that the thickness of the rock layer,tunnel diameter,and arrangement sequence of weak and strong rock layers significantly affect the tunnel face stability.Variations in the parameters of the lower layer of the tunnel face have a greater effect on tunnel stability than those of the upper layer.展开更多
Based on the active failure mechanism generated by a spatial discretization technique, the stability of tunnel face was studied. With the help of the spatial discretization technique, not only the anisotropy and inhom...Based on the active failure mechanism generated by a spatial discretization technique, the stability of tunnel face was studied. With the help of the spatial discretization technique, not only the anisotropy and inhomogeneity of the cohesion but also the inhomogeneity of the internal friction angle was taken into account in the analysis of the supporting forces. From the perspective of upper bound theorem, the upper bound solutions of supporting pressure were derived. The influence of the anisotropy and heterogeneity on the supporting forces as well as the failure mechanisms was discussed. The results show that the spatial discretization characteristics of cohesion and internal frictional angle impose a significant effect on the supporting pressure, which indicates that above factors should be considered in the actual engineering.展开更多
Midface injuries are normally the result of high forces impacted on the face, that can bypass the power of the connection buttresses, which are thick and strong, base of skull is also a rigid and toughstructure which ...Midface injuries are normally the result of high forces impacted on the face, that can bypass the power of the connection buttresses, which are thick and strong, base of skull is also a rigid and toughstructure which requires significant forces to break. In our case, multiple midface and cranial base fractures are presented, which reflect injury caused by high forces and normally, these result in instability in the facial skeleton, or cause CSF rhinorrhea, or sharp spicules to endanger the orbit or the anterior cranial fossa, or the presence of any other indication of surgery. It is unusual to find such an extent of facial trauma and such a multiplication of fractures on the midface and cranial base levels, yet they were stable enough and without a real indication to require surgical interference.展开更多
Objective： To evaluate the orthopedic effects of a new method to treat skeletal crossbite in the early mixed dentition. Methods ：Twenty cases （5.8-7. 5 years old ） with skeletal crossbite were treated by bonding t...Objective： To evaluate the orthopedic effects of a new method to treat skeletal crossbite in the early mixed dentition. Methods ：Twenty cases （5.8-7. 5 years old ） with skeletal crossbite were treated by bonding the bite plate combined with the face mask protracting the upper jaw. Cephalometric radiographs were taken and analyzed before and after treatments. Results： On average, in all 20 cases the maxilla was moved by 2.06 mm forwards the mandible was turned 2.45° downward and backwards the skeletal crossbites were corrected and the facial profiles were improved satisfactorily. The period of treatment was conducted for 1.7 months on average. Conclusion： A good effect can be achieved by bonding bite plate combined with the face mask protracting the upper jaw to treat skeletal crossbite in the early mixed dentition, which will benefit the craniofacial growth and the development of young children.展开更多
为有效降低综采工作面上隅角瓦斯积聚浓度,本文结合王家岭煤业18103工作面实际情况,提出了“以孔代巷”上隅角瓦斯治理技术,并设计了现场试验方案,通过分析不同钻孔布置参数的抽采效果,确定出钻孔孔径为127 mm,钻孔抽采负压30 k Pa左右...为有效降低综采工作面上隅角瓦斯积聚浓度,本文结合王家岭煤业18103工作面实际情况,提出了“以孔代巷”上隅角瓦斯治理技术,并设计了现场试验方案,通过分析不同钻孔布置参数的抽采效果,确定出钻孔孔径为127 mm,钻孔抽采负压30 k Pa左右,分支孔数量2个最佳。现场应用结果表明,18103工作面采用“以孔代巷”治理采空区瓦斯技术后,在瓦斯含量相对较高的区域,上隅角瓦斯浓度明显降低,能控制在0.6%以内,瓦斯含量相对较低的区域上隅角瓦斯浓度能控制在0.2%左右,治理效果明显。展开更多
基金supported by the Key Innovation Team Program of Innovation Talents Promotion Plan by MOST of China(Grant No.2016RA4059)the Science and Technology Project of Yunnan Provincial Transportation Department(No.25 of 2018)。
文摘An analysis of tunnel face stability generally assumes a single homogeneous rock mass.However,most rock tunnel projects are excavated in stratified rock masses.This paper presents a two-dimensional(2D)analytical model for estimating the face stability of a rock tunnel in the presence of rock mass stratification.The model uses the kinematical limit analysis approach combined with the block calculation technique.A virtual support force is applied to the tunnel face,and then solved using an optimization method based on the upper limit theorem of limit analysis and the nonlinear Hoek-Brown yield criterion.Several design charts are provided to analyze the effects of rock layer thickness on tunnel face stability,tunnel diameter,the arrangement sequence of weak and strong rock layers,and the variation in rock layer parameters at different positions.The results indicate that the thickness of the rock layer,tunnel diameter,and arrangement sequence of weak and strong rock layers significantly affect the tunnel face stability.Variations in the parameters of the lower layer of the tunnel face have a greater effect on tunnel stability than those of the upper layer.
基金Project(2013CB036004) supported by the National Basic Research Program of ChinaProjects(51178468,51378510) supported by the National Natural Science Foundation of China
文摘Based on the active failure mechanism generated by a spatial discretization technique, the stability of tunnel face was studied. With the help of the spatial discretization technique, not only the anisotropy and inhomogeneity of the cohesion but also the inhomogeneity of the internal friction angle was taken into account in the analysis of the supporting forces. From the perspective of upper bound theorem, the upper bound solutions of supporting pressure were derived. The influence of the anisotropy and heterogeneity on the supporting forces as well as the failure mechanisms was discussed. The results show that the spatial discretization characteristics of cohesion and internal frictional angle impose a significant effect on the supporting pressure, which indicates that above factors should be considered in the actual engineering.
文摘Midface injuries are normally the result of high forces impacted on the face, that can bypass the power of the connection buttresses, which are thick and strong, base of skull is also a rigid and toughstructure which requires significant forces to break. In our case, multiple midface and cranial base fractures are presented, which reflect injury caused by high forces and normally, these result in instability in the facial skeleton, or cause CSF rhinorrhea, or sharp spicules to endanger the orbit or the anterior cranial fossa, or the presence of any other indication of surgery. It is unusual to find such an extent of facial trauma and such a multiplication of fractures on the midface and cranial base levels, yet they were stable enough and without a real indication to require surgical interference.
文摘Objective： To evaluate the orthopedic effects of a new method to treat skeletal crossbite in the early mixed dentition. Methods ：Twenty cases （5.8-7. 5 years old ） with skeletal crossbite were treated by bonding the bite plate combined with the face mask protracting the upper jaw. Cephalometric radiographs were taken and analyzed before and after treatments. Results： On average, in all 20 cases the maxilla was moved by 2.06 mm forwards the mandible was turned 2.45° downward and backwards the skeletal crossbites were corrected and the facial profiles were improved satisfactorily. The period of treatment was conducted for 1.7 months on average. Conclusion： A good effect can be achieved by bonding bite plate combined with the face mask protracting the upper jaw to treat skeletal crossbite in the early mixed dentition, which will benefit the craniofacial growth and the development of young children.
文摘为有效降低综采工作面上隅角瓦斯积聚浓度,本文结合王家岭煤业18103工作面实际情况,提出了“以孔代巷”上隅角瓦斯治理技术,并设计了现场试验方案,通过分析不同钻孔布置参数的抽采效果,确定出钻孔孔径为127 mm,钻孔抽采负压30 k Pa左右,分支孔数量2个最佳。现场应用结果表明,18103工作面采用“以孔代巷”治理采空区瓦斯技术后,在瓦斯含量相对较高的区域,上隅角瓦斯浓度明显降低,能控制在0.6%以内,瓦斯含量相对较低的区域上隅角瓦斯浓度能控制在0.2%左右,治理效果明显。
