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Stabilisation of rock slopes
Published in Duncan C. Wyllie, Rock Slope Engineering, 2017
Since the purpose of a drainage tunnel is to lower the overlying water table, and the water pressure in the slope, it is necessary that the volume of the water that is removed by the drainage system is greater than the surface infiltration rate plus the water that is removed from storage within the rock mass. That is, for rock formations with low porosity and low-specific storage, it is likely that transient conditions will develop where the head diminishes with time as the slope drains. The layout of the tunnels, and drain holes drilled from the tunnel, can be optimised using the 3D numerical modelling of the ground water flow. Because the flow within the rock mass will usually be strongly influenced by the geological structure, the tunnel and drain holes should be oriented to intersect the set(s) of discontinuities in which most of the water is expected to flow, such as persistent bedding planes rather than less persistent joints. In practice, it is often found that most of the flow occurs in a few discontinuities, with flow in some areas, while other areas may be entirely dry. In all cases, the calculated flow and drawdown values will be estimates because of the complex and uncertain relationship between ground water flow and structural geology, and the difficulty of obtaining representative conductivity values.
Open pit slope design
Published in Xia-Ting Feng, Rock Mechanics and Engineering, 2017
Drainage tunnels installed behind the pit slope or underneath the pit are being increasingly considered by some of the larger open pit mining operators for dewatering. A significant operational advantage of a drainage tunnel is that once the portal is established the drains can be installed and operated from within the tunnel itself, without interfering with mining operations. An obvious potential downside of a tunnel is the up-front cost and time required for planning although, for larger pits, the cost of a tunnel is often comparable with the overall cost of drilling a large number of drains from within the pit for a number of sequential pushbacks. As for all of the drainage and/or depressurisation options, the overall cost must be viewed in terms of the potential benefit of achieving steeper slope angles.
Microseismic monitoring, analysis and early warning of rockburst
Published in Geomatics, Natural Hazards and Risk, 2021
Tian-hui Ma, Chun-an Tang, Fei Liu, Shi-chao Zhang, Zhi-qiang Feng
The Jinping II Hydropower Station locates on the Jinping Bend of Yalong River at the border of Liangshan Yi Autonomous Region, Sichuan, Southwest China. The Jinping II Hydropower Station, with the total installed capacity of 480 MW, generates power using the natural water head drop of about 310 m within 150 km on the lower reach of Yalong River. The water diversion system consists of 4 headrace tunnel, 2 auxiliary tunnel and a drainage tunnel (highlighted by red line), as shown in Figure 8. The drainage tunnel is excavated by the TBM with a circular cross-section, and it is 7 m in diameter and 16.73 km in length. The auxiliary tunnels have an average length of 17.5 km with a cross-sectional dimension of 5.5 m × 5.7 m (width × height) and 6 m × 6.25 m, respectively. The headrace tunnels 2# and 4# were excavated by the drill and blast method, with the diameter of 13 m and 11.8 m after lining. While, the east sections of headrace tunnels 1# and 3# were excavated by TBM with the diameter of 11.2 m after lining. The headrace tunnels pass through the main peak of Jinping mountains with the burial depth of 1500-2525 m, and surrounding rocks of the headrace tunnels are mainly marble, limestone, crystalline, limestone and sandstone. Rock masses are hard, intact and compacted, with the saturated uniaxial compressive strength and elastic modulus of 30-114 MPa and 25-40 GPa, respectively. The measured maximum principal stress of the Jinping II Hydropower Station is 46 MPa, and the maximum principal stress by regression analysis is 70 MPa (Li et al. 2012).
An elastoplastic coupling mechanical model for hard and brittle marble with consideration of the first stress invariant effect
Published in European Journal of Environmental and Civil Engineering, 2018
Fanjie Yang, Hui Zhou, Chuanqing Zhang, Dawei Hu, Jingjing Lu, Fanzhen Meng
The geological survey indicated that the surrounding rockmass is fresh marble, noted as T2b. The rockmass is intact, and no major fault was found. In order to know the in situ stress distribution in surrounding rockmass, a three-dimensional mathematical model is developed. Figure 18 shows the size of the model. Both the width and height of the model are 300 m, and the length is 600 m. The numerical model contained 450,484 units and 76,808 nodes. Figure 19 shows the size and spatial location of the tunnels. The cross section of Headrace tunnel #3 and drainage tunnel are in the circular form, and their diameters are 12.4 and 7.2 m, respectively. The two-bench excavation method was used in headrace tunnel #4. The rockburst occurred during the excavation of the upper bench. The excavation height of the upper bench is 8.5 m. The horizontal distance between the headrace tunnel #4 and drainage tunnel is 45 m. The horizontal distance between the headrace tunnel #4 and the headrace tunnel #3 is 60 m. And the vertical distance between the headrace tunnel #3 and drainage tunnel is 6 m.
Peridynamic investigation on crack propagation mechanism of rock mass during excavation of tunnel group in cold regions
Published in Mechanics of Advanced Materials and Structures, 2023
The Dangjinshan Tunnel, with a total length of 20.1 km, is currently the longest single-track tunnel in China. The average altitude of the tunnel is 3 km, and the maximum buried depth is 764 m. The average and the lowest temperatures of the coldest month are −13.1 °C and −34.3 °C, respectively. It is composed of the main tunnel, drainage tunnel and parallel pilot. The 12.5 km long parallel pilot is located on the left side of the main tunnel. The drainage tunnel with a length of 835 m is situated below the main tunnel and parallel pilot, as shown in Figure 8.