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In water-rich karst area, the lining structure of diversion tunnels is prone to cracking and gushing water problems under high water pressure, so water drainage design is often adopted for these diversion tunnels, that is, to drill holes on the lining structure and install drainage equipment to lower the external water pressure of the lining, therefore, accurately calculating the external water pressure of the lining is a very important work for the safety of the lining structure of tunnels. Based on the method of equivalent permeability coefficient, this paper regarded the drainage capacity of drainage equipment installed on the lining and the permeability of lining itself as a whole, and used the virtual equivalent permeability coefficient of the lining to describe it; then, this paper proposed a method for determining the equivalent permeability coefficient of lining and used it to analyze the drainage effect. Main conclusions of this paper are: 1) By designing tests for the drainage model of the tunnel drainage equipment and theoretically analyzing the seepage field of hydraulic tunnel, the equivalent permeability coefficient of the lining was determined and its accuracy was verified via numerical calculation; 2) Analytical calculation results and numerical simulation results of the tunnel were analyzed, and their conclusions about the effect of drainage capacity on the external water pressure of the lining were consistent; 3) The tunnel drainage design is an effective measure to reduce the external water pressure of the lining, the pressure reduction effect is obvious when k<1×10-6, and the groundwater level around the tunnel could be reduced at the same time. This paper provides a useful evidence for the design of high-pressure water diversion tunnels. [ABSTRACT FROM AUTHOR]

• Combined with field test and numerical simulation, the rock damage characteristics around peripheral hole are fully analyzed. • The influence of explosive spacing, blasthole spacing and smooth blasting layer thickness on different damage indexes of rock mass is analyzed, and the influence of boundary conditions is discussed. • Considering the influence of explosive spacing and blasthole spacing, a mathematical model is established firstly to predict the rock damage range and applied to engineering practice. • The research method in this paper provides a solution to similar engineering problems. The control of overbreak in blasting excavation is a significant technical challenge and a subject of extensive research in the field of engineering. This study examines the damage characteristics of the surrounding rock in a tunnel section through blasting test and numerical simulation conducted as part of the San Gavan diversion tunnel project in Peru. The orthogonal test of peripheral holes under the influence of explosive spacing, blasthole spacing and smooth blasting layer thickness was designed to analyze the characteristics of rock damage under different parameter combinations and the influence of various factors on rock damage. Based on the USBM formula, this paper deduces a mathematical model considering blasthole spacing and explosive spacing to predict the rock damage range. The main conclusions are as follows: on the tunnel section, the average damage range of vault and arch springer is slightly larger than that of spandrel and haunch. For a single blasthole, the rock damage range in different sections is: explosive > air > stem, and the degree of rock damage at the bottom of blasthole is the highest. Smooth blasting layer thickness has a significant effect on rock damage rate on the side of non-reflect boundary. When smooth blasting layer thickness is 45 cm and 55 cm, the boundary conditions of numerical model have a significant effect on the rock damage. The reflection of blasting stress wave on the free surface leads to the further increase of rock damage range. The blasthole spacing and explosive spacing have a significant effect on rock damage range on the side of non-reflect boundary, and both show a negative correlation. Based on the prediction model of rock damage, the combination of peripheral hole parameters satisfying the standard is obtained, which provides guidance for blasting design. [ABSTRACT FROM AUTHOR]

The cofferdam is a temporary water retaining structure built to protect the foundation pit in the construction of hydraulic engineering. Its layout has great influence to the flood safety, project progress and cost. Relying on the diversion tunnel project of a hydropower station, this paper firstly optimized the design of the cofferdam type at the outlet of the diversion tunnel, and then compares various construction schemes such as earth rock cofferdams, concrete cofferdams, stoplogs gate, and concrete cutoff walls. The cofferdam scheme was designed, and the construction technology and construction scheme of the cofferdam were systematically expounded. The analysis results show that the cofferdam at the exit of the diversion tunnel uses the stoplogs gate type to control the flood season, which meets the requirements of the project safety flood control, significantly reduces the amount of cofferdam engineering and the project cost, and has strong technical feasibility. [ABSTRACT FROM AUTHOR]

The corrosive water environment has a decisive influence on the durability of a diversion tunnel lining. In this paper, the effects of carbonation on cement-based materials in water-immersion and saturated-humidity environments were studied by increasing the CO2 concentration. The results show that under conditions of water-immersion and saturated humidity, the color of the non-carbonation region is dark, while the carbonation region is gray, and the color boundary is obvious. However, in an atmospheric environment, there is no zone with a dark color and the color boundary is not obvious. In a saturated-humidity environment, the carbonation depth increases over time and changes greatly, and its value is about 16.71 mm at 200 days. While in a water-immersion environment, the carbonation depth varies little with time and the value is only 2.31 mm. The carbonation depths of cement mortar samples in different environments generally follow a linear relationship with the square root of time. The carbonation coefficient in a saturated-humidity environment is more than nine times that in the water-immersion environment. In a water-immersion environment, the carbonation causes a large loss of calcium in cement-based materials, and their Ca/Si ratio obviously decreases. The calcium silicon ratio (Ca/Si) of cement-based materials in a water-immersion environment is 0.11, which is much less than 1.51 in a water-saturated environment and 1.49 in an atmospheric environment. In a saturated-humidity environment, the carbonation only reduces the pH of the pore solution in the carbonation region, and the structural stability of cement-based materials is not degraded. The number of pores of all radii after carbonation in a water-immersion environment exceeds that in a saturated-humidity environment, and the total pore volume and average pore radius in a water-immersion environment are also larger than in a saturated-humidity environment, so the water-immersion environment accelerates the development and expansion of pores. The research results can provide some theoretical and technical support for the design, construction, and safe operation of diversion tunnel linings. [ABSTRACT FROM AUTHOR]

Shaanxi Hanjiang River to Weihe River diversion tunnel water inrush problem is one of the key technical problems that restrict the smooth development of the project. In this paper, aiming at the problem of water inrush in the typical section of acrossing Jiaoxi River, the ADINA software was used to establish the hydrogeological conceptual model, and the variation law of the groundwater table, the velocity vector and the water inflow were calculated under different conditions. The results show that the fault location is greatly affected by the excavation disturbance, and there is concentrated leakage. Therefore, it is very easy to form the leakage channel and occur the water inrush in the fault location. [ABSTRACT FROM AUTHOR]

In high latitude region of western China, the environment is in harsh condition that it is cold and dry in winter and has long ice period, which causes many water resource problems. In order to relieve the serious water shortage condition in cold and dry region, a large number of long distance water diversion projects were established to improve the water resource condition, such as increasing farm irrigation, human and animal drinking. While the ice damage occurs frequently under severe ice conditions in cold and dry region, especially in ice period in winter and thawing period in spring, it is easy to form drift ice with different velocities, different plan sizes and different thicknesses, which produces different extrusion forces or impact forces to damage tunnel lining, causing project failure. The failure project could not realize the original planning and construction goal, giving rise to the water allocation pressure. The water allocation would cause water shortage which influences diversion irrigation and farming production in spring. Based on the intense researches on the collision simulation problem of the interaction between drift ice and diversion tunnel, this paper used the symmetric penalty function in the finite element contact-impact algorithm to conduct the theoretical study on collision simulation problem between drift ice and water diversion tunnel. ANSYS/LS-DYNA was adopted as the platform to establish tunnel model and drift ice model. LS-DYNA SOLVER was used as the solver to solve and analyze the damage degrees of drift ice on tunnel. The physical model tests were conducted to verify and reveal the impact damage mechanism of drift ice on diversion tunnel. The physical model was constructed by the geometric scale of 28, which is the ratio of the experiment facility to the prototype in the test. The results show that tunnel lining surface will form varying degrees of deformation and failure when the tunnel lining is impacted by the drift ice with different velocities, different plane sizes and different thicknesses. It is also discovered that the impact stress increases with the flow velocity and their relationship presents linear variation. The impact stress also increases with the drift ice’s plane size and their relationship presents nonlinear variation. The impact stress increases with the drift ice thickness when the drift ice thickness is less than 0.5 m. While the drift ice thickness is greater than 0.5 m, the maximum stress value shows little change. The relationship between drift ice’s plane size and maximum stress shows approximately linear variation. Meanwhile, the software simulation and test observation results are almost the same. The impact of drift ice on the tunnel lining would cause the deformation of lining, but the deformation has little influence on the tunnel stability. The drift ice’s long time erosion would cause the tunnel lining surface to fall off, and further break the strength and stability of the tunnel structures. The study supplies theoretical support and technical guarantee for water diversion project security in cold and dry region of western China. [ABSTRACT FROM AUTHOR]

To identify problematic geological structures which would be encountered when driving tunnels in the high mountainous area of South West China, a joint geophysical and engineering geological study was made. The tunnels will form part of a project to divert water from the Yangtze to the Yellow Rivers. A controlled source audio-frequency magnetotelluric method (CSAMT) was carried out in 2004 between the Ma-ke and Jia-qu rivers in high, steep terrain. The paper discusses the method of data collection, processing, and analysis for the West route. The faults/fractures identified will need to be taken into account in the design and construction of the tunnel. [ABSTRACT FROM AUTHOR]

Former studies, the methods for estimating the ventilation time are all empirical in construction schedule simulation. However, in many real cases of construction schedule, the many factors have impact on the ventilation time. Therefore, in this paper the 3D unsteady quasi-single phase models are proposed to optimize the ventilation time with different tunneling lengths. The effect of buoyancy is considered in the momentum equation of the CO transport model, while the effects of inter-phase drag, lift force, and virtual mass force are taken into account in the momentum source of the dust transport model. The prediction by the present model for airflow in a diversion tunnel is confirmed by the experimental values reported by Nakayama [Nakayama, In-situ measurement and simulation by CFD of methane gas distribution at a heading faces, Shigen-to-Sozai 114 (11) (1998) 769–775]. The construction ventilation of the diversion tunnel of XinTangfang power station in China is used as a case. The distributions of airflow, CO and dust in the diversion tunnel are analyzed. A theory method for GIS-based dynamic visual simulation for the construction processes of underground structure groups is presented that combines cyclic operation network simulation, system simulation, network plan optimization, and GIS-based construction processes’ 3D visualization. Based on the ventilation time the construction schedule of the diversion tunnel is simulated by the above theory method. [Copyright &y& Elsevier]

This paper presents the results of the support capacity estimation for the diversion tunnel of the Urus¸ dam site in highly weathered tuff and weak zone. Tunneling in weak rock requires some special considerations, since misjudgment in support design results in costly failures. There are several ways of estimating rock support pressure and selecting support. However, all systems suffer from their characteristic limitations in achieving objectives. Thus, it is more useful to use different methods for estimating support pressure and type of support. The support pressure pi was established by three different methods. These methods are the (1) empirical methods based on rock mass rating (RMR) and rock mass quality index (Q-classification systems), (2) ground support interaction analysis (GSIA) and (3) numerical methods, namely, Phase2 finite element (FEM) program. Rock masses were characterized in terms of RSR, RMR, Q-system and GSI. Drill-core samples were tested in the rock mechanics laboratory to determine physico-mechanical properties. Rock mass strength was estimated by empirical methods. Finally, the required support system is proposed and evaluated by different methods in the highly weathered tuff and weak zone of the diversion tunnel. [Copyright &y& Elsevier]