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Zhang Y.,CAS Wuhan Institute of Rock and Soil Mechanics | Zhang W.,China Railway Tunnel Survey and Design Institute Co.
Yanshilixue Yu Gongcheng Xuebao/Chinese Journal of Rock Mechanics and Engineering | Year: 2015

A method of determining the cohesion and internal friction angle of a dual-pore-fracture rock mass was improved by considering fracture connection ratio, and this method was introduced into the elasto-plastic thermo-hydro-mechanical(THM) coupling finite element method(FEM) code. Aiming at a model of hypothetical nuclear waste repository in a saturated dual-pore-fracture rock mass with a laboratory scale, the THM coupling FEM analyses were carried out for two assumed cases with orthogonal fracture sets and oblique-cross fracture sets, respectively. The results show that: compared with the axisymmetric distributions of various field quantities in the case with orthogonal fracture sets, the distributions of pore pressures and flow velocities of underground water are axisymmetric, but the distributions of stresses, fracture pressures and relative flow velocities, plastic zones in the rock mass are non-axisymmetric for the case with oblique-cross fracture sets. A large area of plastic zone occurs in the case with orthogonal fracture sets, but almost no plastic zone is produced in the case with oblique-cross fracture sets. The occurrence of fracture sets strongly influences the states of stress, plastic zone and fracture pressure in rock mass. ©, 2015, Academia Sinica. All right reserved. Source


Zhang Y.,CAS Wuhan Institute of Rock and Soil Mechanics | Zhang W.,China Railway Tunnel Survey and Design Institute Co.
Yanshilixue Yu Gongcheng Xuebao/Chinese Journal of Rock Mechanics and Engineering | Year: 2015

Considering the connectivity rate and spacing of fractures, volume fractions of pore matrix and fracture material in a representative element volume, a method of determining the cohesion cN and internal friction angle φN which vary with direction in a dual porosity medium was suggested, and the equations established for calculating the values of cN and φN were proved to be reasonable. Introducing the method solving cN and φN values into the elasto-plastic finite element method(FEM) code, the computations were carried out for a rectangular underground cave for two cases with different connectivity rates and spacing of fractures in a rock mass, and the stresses, displacements and plastic zones in the surrounding rock mass were analyzed and compared with each other. The results show: with the increase of fracture connectivity rate, the cohesion and internal friction angle of the rock mass decrease, the displacements in surrounding rock mass grow, the principal stress contours change obviously, the plastic zones accelerate development, and the distributions of displacements, stresses and plastic zones change from symmetric ones to asymmetric ones, as well as the anisotropy of surrounding rock mass displays more significantly; but with the increase of fracture spacing, the dynamic state of surrounding is just the reverse of what in the case of increasing fracture connectivity rate. ©, 2015, Academia Sinica. All right reserved. Source


Zhang X.-F.,China Railway Tunnel Survey and Design Institute Co.
Applied Mechanics and Materials | Year: 2014

By Changsha Xiangjiang River Camp Road tunnel geological conditions and the overall analysis, the paper proposed the overall and the inner contour design of the underwater tunnel interchange segment.Establishing calculation model of the north-south main line and C, D segments interchange ramp, and using ANSYS finite element software to calculate and determine the design parameters of the tunnel cross-section. For the upper and lower layers tunnel use excavation construction, and applying the Center-Cross-Diaphragm (CRD) method to tunneling. © (2014) Trans Tech Publications, Switzerland. Source


Fan G.,China Railway Tunnel Survey and Design Institute Co. | Fan G.,Enterprise Key Laboratory of Tunnel Design and Safety Assessment
Modern Tunnelling Technology | Year: 2015

Compared with the bottom-up method, which is widely used in the construction of shallow, medium and small foundation pits, the top-down method is more complex but has obvious advantages in controlling structural performance and deformation, which contribute to the safety of construction of deep and large foundation pits. Using the receiving shaft on the south line of the river-crossing large-diameter shield tunnel on Nanhu Road of Changsha City as an example, this paper compares and analyzes the forces applied on shafts constructed by the bottom-up and top-down methods, indicating that it's better to choose the top-down method for the working shaft construction of large-diameter shield tunnels. ©, 2015, Editorial Office of "Modern Tunnelling Technology". All right reserved. Source


Zhang X.,China Railway Tunnel Survey and Design Institute Co.
Modern Tunnelling Technology | Year: 2014

Compared with conventional tunnels, there are some varying features regarding the design of underwater tunnels, and the underwater tunnel can be constructed with different methods. The key points to consider in the design are demonstrated in terms of geological conditions, link conditions, environmental conditions and construction costs. As for the mined underwater tunnel, it is thought the depth of the rock cover, the type of waterproofing and drainage will directly affect tunnel safety and economy. Based on demonstration and analysis, the method and principles used to determine tunnel overburden, the type of water-proofing and drainage are presented. For the determination of water pressure, which has been a tough problem in tunnel design, corresponding calculations are given considering different methods of water-proofing and drainage. In addition, construction methods to ensure tunnel durability and safety are presented by using a specific tunnel as an example. Source

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