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Chen B.,CAS Wuhan Institute of Rock and Soil Mechanics | Feng X.,CAS Wuhan Institute of Rock and Soil Mechanics | Zeng X.,Ertan Hydropower Development Co. | Xiao Y.,CAS Wuhan Institute of Rock and Soil Mechanics | And 3 more authors.
Yanshilixue Yu Gongcheng Xuebao/Chinese Journal of Rock Mechanics and Engineering | Year: 2011

According to the difficulties and shortcomings of real-time microseismic monitoring during tunnel boring machine(TBM) tunneling with overburden of over 2 000 m-thick hard and brittle rock mass, the traditional microseismic monitoring technology, used in the mines, is optimized and improved; and the new microseismic monitoring technology is utilized during the TBM tunneling in the diversion tunnel #3 of Jinping II hydropower station. The monitoring results show as follows: (1) The ambient noise is much and complex, but the main characteristic is clear during TBM tunneling; and it can be filtered through the proposed filtering method effectively. (2) There is an obvious relationship that microseismic activity increases with the increase in TBM tunneling rate between microseismic activity of surrounding rock mass and the TBM tunneling rate, vice versa. Microseismic activity is very weak during the period of TBM maintenance, but it becomes most active when TBM working lasts for 4-6 hours after TBM maintenance. (3) Before some rockburst occurred, distribution of microseismic events and energy release gradually convert from discrete to relatively concentrative in spatial domain, the number of microseismic events and the radiated energy increase rapidly in temporal domain; and apparent volume of surrounding rock mass has a sudden increasing trend; energy index has a sudden drop trend in the same time. (4) When microseismic monitoring is carried out during TBM tunneling covered with thickly hard and brittle rock mass, effective microseismic information can be acquired; the evolution characteristic and law of microseismic activity can be found and known; and more accurate early-warning information of rockburst can be provided. Therefore, it is possible and feasible to forecast the occurrence of rockburst by microseismic monitoring. Source


Huang R.,Chengdu University of Technology | Huang D.,Chengdu University of Technology | Huang D.,Chongqing University | Duan S.,Ertan Hydropower Development Co. | And 2 more authors.
Yanshilixue Yu Gongcheng Xuebao/Chinese Journal of Rock Mechanics and Engineering | Year: 2011

Jinping I Hydropower Station located in the Southwest China is a key cascade and control underground hydropower project at the Yalong River. The project is very huge and the underground powerhouse system is very complicated, as well as the complex geological conditions, lower strength for rock relative to very high geostress especially. The challenge which no found in historical projects is presented by two dominate aspects in the construction. The two ones are stability and reinforce of surrounding rock. The characteristics of deformation split of surrounding rock and failure of supporting structure is described based on the geological conditions, monitor and geophysical prospecting, investigations in-situ and tests data. The correlations are discussed which deformation failure of surrounding rock and supporting structure with geostress, rock mass structure and mechanical property of rock under loading and unloading. The geomechanics mechanism of deformation failure of the surrounding rock and supporting structure is explained. The tangential loading stress is rather large and inclined to split pressed at downstream side(especially hance) of main powerhouse and main transformer house, but the normal unloading stress is rather larger and inclined to tension and relaxation unloaded because of the high geostress and its direction. The rheological behaviour of the fracture surrounding rock is presented, and is gradually charactered from surface to deep, the time-dependent deformation of fracture rock mass with surrounding rock relaxation is showed. The surrounding rock at downstream side is easy to bend and break-off and low susceptibility to shear and slide of main powerhouse and main transformer house under secondary stress field, because that the upstream side is bedding but the downstream inverse slope with low dip angles. The powerhouse marble is presented that relative lower strength, heavy brittle and lower strain strength, are easy to tension pressed under unloading. Source


Feng X.,CAS Wuhan Institute of Rock and Soil Mechanics | Chen B.,CAS Wuhan Institute of Rock and Soil Mechanics | Ming H.,CAS Wuhan Institute of Rock and Soil Mechanics | Wu S.,Ertan Hydropower Development Co. | And 4 more authors.
Yanshilixue Yu Gongcheng Xuebao/Chinese Journal of Rock Mechanics and Engineering | Year: 2012

The ideas and methodology for the in situ monitoring of rockburst preparation of deep tunnels was described firstly. The time and space evolution law of immediate rockburst observed, which occurred usually during or after excavation immediately and affected mainly by excavation unloading effectiveness, was analyzed. Based on a series of in situ monitoring of deep tunnels, process of crack initiation, propagation, opening and closing, evolution of wave velocity, deformation, acoustic emission and microseismicity were observed. Based on moment tensor analysis of the monitored microseismicity during the excavation of deep tunnels, the difference of mechanism of strain rockburst and strain-structure slip rockburst was found. The former was mainly from tensile cracking but the latter mainly from tensile cracking, shear cracking, and tensile-shear/compressive shear cracking which was from shearing of stiff structures and formed boundary of rockburst pit. The results are used as a guide of prediction of rockburst and its dynamic control based on evolution of the monitored microseismicity and other information. Source


Chen B.,CAS Wuhan Institute of Rock and Soil Mechanics | Feng X.,CAS Wuhan Institute of Rock and Soil Mechanics | Ming H.,CAS Wuhan Institute of Rock and Soil Mechanics | Zhou H.,CAS Wuhan Institute of Rock and Soil Mechanics | And 3 more authors.
Yanshilixue Yu Gongcheng Xuebao/Chinese Journal of Rock Mechanics and Engineering | Year: 2012

The time delayed rockburst(TDR) is named based on mechanism and characteristic of rockburst occurring in the diversion tunnels of Jinping II hydropower station; and then it is analyzed and investigated systematically in terms of microseismic and rockburst data in situ. The conclusions are acquired as following: (1) Stress adjusting after rockburst zone is excavated and disturbing outside of stress adjusting range of rockburst zone work together results in the TDR bursting out. 80% of TDR occur from 6 to 30 d after the rockburst zone is excavated and inside of 80 m ranges from tunnel face. (2) All kinds of structural planes, such as joint, fracture, weak intercalation and so on, are main characteristic of surrounding rockmass in rockburst zone, the strike of structure plane is parallel or has a small angle with the axial of the tunnel. (3) As the rockburst zone is excavated, the magnitude and rate of stress adjusting is very large; fracture frequency of surrounding rockmass is quite high; and the microseismic events are located at the same zone in three-dimension space and its number increases continuously with time. Apparent volume of surrounding rock mass has a sudden increasing trend. Energy index has a sudden drop trend in the same time. Before the TDR burst out, microseismic activity has an obviously "sleep" period and the changes of apparent volume and energy index of surrounding rock mass are not very obvious. (4) The tensile, shear and mixed fracture all live during process of rockburst zone excavated. Then the fracture along the structure plane is main trend and tensile fracture is main fracture form. At last, the shear failure is main as the rockburst occurring. A union prevention scheme that firstly the concrete layer with steel fibre is built in time; secondly, the rock bolts are constructed; thirdly, the steel mesh is connected to the surrounding rockmass; lastly, the concrete with steel fibre is built again, which is proposed for TDR, based on the evolution characteristic, law and mechanism of TDR. Source


Wang J.,Ertan Hydropower Development Co. | Duan S.,Ertan Hydropower Development Co. | Hu S.,Ertan Hydropower Development Co. | Hu S.,Yangtze River Scientific Research Institute
Yanshilixue Yu Gongcheng Xuebao/Chinese Journal of Rock Mechanics and Engineering | Year: 2012

To deal with the toppling deformation and fracture rock-mass problem at the embankment slope in Jinping hydropower station, the whole slope surface is reinforced by shotcrete support, rock bolting and frame pier with prestressed cable. The integral stability of left slope is controlled by the potential large sliding body which is composed by fault f 42-9, deep crack SL 44-1 and lamprophyre dike X. Some three-layer anti-shear tunnels on the sliding body are designed; and a lot of deep perstressed cables across the faults are placed at the slope surface to reinforce the sliding body. A management system, which follows the principle of dynamic design, scientific study tracking, safety monitoring and immediate reacting analysis, and dynamic management informationization, is established. According to the geological conditions and safety monitoring data during excavation, combining with construction situation, slope stability analysis and real-time safety monitoring could be conducted; in addition to the optimization of design and strict controlling of construction procedure, excavation work of the left embankment slope finally goes on smoothly. Source

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