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Dai F.,University of Sichuan | Li B.,University of Sichuan | Xu N.,University of Sichuan | Xu N.,Shandong University | And 4 more authors.
Yanshilixue Yu Gongcheng Xuebao/Chinese Journal of Rock Mechanics and Engineering | Year: 2015

The in-situ tests on the excavation damaged zone (EDZ) in the high sidewall rock mass of the underground powerhouse at Houziyan hydropower station were performed. Microseismic monitoring and conventional testing methods such as multiple position extensometers, acoustic wave test and borehole TV were used in these tests. Through analyzing the results from a series of conventional tests and microseismic monitoring, the deformation and failure characteristics of surrounding rock were revealed, and the development of fractures of surrounding rock such as the initiation, the coalescence and the extension during excavation processes of the underground powerhouse were obtained. The relationship among EDZ of surrounding rock mass, crack development and construction status were also analyzed so that the whole process of the formation, development, interaction and extension of cracks were obtained. The depth of EDZ was identified and the relationship between the development of fractures and the progress of construction was revealed. The mechanism of the formation and evolution of EDZ was discussed as well. ©, 2015, Academia Sinica. All right reserved.


Xu N.,Shandong University | Xu N.,University of Sichuan | Dai F.,University of Sichuan | Li B.,University of Sichuan | And 3 more authors.
Yanshilixue Yu Gongcheng Xuebao/Chinese Journal of Rock Mechanics and Engineering | Year: 2016

In order to real time monitor and evaluate the surrounding rock mass stability and identify the potential hazardous regions of the underground caverns at the Houziyan hydropower station subject to excavation, the comprehensive method incorporating numerical simulation, microseismic(MS) monitoring, traditional monitoring and field observation was adopted. Some results are obtained as follows: (1) MS monitoring can realize the real-time monitoring, analysis and evaluation of surrounding rock mass stability of the underground caverns due to excavation-induced unloading. (2) micro-fractures concentration areas of surrounding rock mass and potential hazardous regions in the underground caverns were delineated by the temo-spatial evolution of microseismicity. (3) the initiation, propagation and coalescence of micro-fractures due to excavation can be reflected by MS monitoring. With regard to the field construction and reinforcement of the underground caverns, the obvious and intense concentrations of MS events have already been regarded as the early warning of reducing the construction schedule. (4) the conventional monitoring methods such as multi-point extensometers, convergence gauges and anchor stress gauges, etc., were used to verify the truthfulness and effectiveness of the results of MS monitoring. The presented results demonstrate that the combination of MS monitoring, numerical modeling, traditional surveying and in situ observation approaches lead to a better understanding of excavation behavior of underground caverns and a more satisfactory control of the working in terms of safety in the complex geological and excavation-induced unloading conditions. Furthermore, the results can provide some guidelines for later excavations and supports of the underground powerhouse. © 2016, Science Press. All right reserved.


Xu N.W.,University of Sichuan | Dai F.,University of Sichuan | Li B.,University of Sichuan | Zhu Y.G.,China Guodian Dadu River Houziyan Hydropower Development Co. | And 2 more authors.
ISRM International Symposium - 8th Asian Rock Mechanics Symposium, ARMS 2014 | Year: 2014

The underground powerhouse of Houziyan hydropower station is a typical deep-buried powerhouse, with the depth of 280m 510m horizontally and 400 m 660m vertically. The ground stress is high and the geological conditions are very complicated. In order to monitor and analyze the surrounding rock mass stability during continuous excavation of the underground powerhouse and locate the potential instability failure areas, an ESG (Engineering Seismology Group) microseismic monitoring system manufactured in Canada was installed in April, 2013. The wave velocity range of the rock mass in the underground powerhouse was measured by the digital acoustic instrument. The overall equivalent wave velocity of the monitoring system was determined through the blasting tests. The seismic source location error was less than 10 m. The microseismic event waveforms were manually processed to acquire high position accuracy and the interference events were filter out. Combining the temo-spatial distribution regularity of the seismic events with field observation, micro-fracture clusters and potential instability failure areas of the underground powerhouse were identified and delineated. The results could provide references for later excavations and supports of the underground powerhouse. Furthermore, a new research idea is opened up for the stability analysis of the deep-buried underground powerhouse subjected with excavation-induced unloading. © 2014 by Japanese Committee for Rock Mechanics.


Xu N.W.,University of Sichuan | Xu N.W.,Chengdu University of Technology | Li T.B.,Chengdu University of Technology | Dai F.,University of Sichuan | And 3 more authors.
Engineering Geology | Year: 2015

The stability of underground caverns and the excavatability of rock masses are important for geotechnical engineering practices during the design and construction stages. The risks associated with underground caverns at the Houziyan hydropower station in Southwest China are growing due to excavation-induced unloading. To assess the instability of underground caverns and resolve the complex subsurface conditions of the highly fractured rock mass, a high-resolution microseismic monitoring system was established in deep underground caverns. This system was used to determine the relationship between the measured microseismic activities and the excavation damage zones of the surrounding rock mass. The excavation damage zones and potential risk regions in the underground caverns were identified by analyzing the tempo-spatial distribution of microseismic activities. In addition, the correlation between microseismic activities and pre-existing geological structures was determined, and traditional monitoring results were analyzed. To validate the correlation between seismicity and the excavation damaged zones of the underground caverns, a numerical model was employed to further evaluate the deformation and stability of the surrounding rock mass. The monitoring results demonstrate that microseismic events mainly occurred in high-stress-concentration regions, corresponding with the results obtained from the numerical analysis. Therefore, this comprehensive method, which incorporates microseismic monitoring, numerical analysis, traditional monitoring and field observations, is promising for predicting the deformation and instability of surrounding rock masses in the underground caverns subjected to excavation. © 2015 Elsevier B.V.


Li B.,University of Sichuan | Dai F.,University of Sichuan | Xu N.,University of Sichuan | Zhu Y.,China Guodian Dadu River Houziyan Hydropower Development Co. | And 3 more authors.
Yanshilixue Yu Gongcheng Xuebao/Chinese Journal of Rock Mechanics and Engineering | Year: 2014

The underground powerhouse of Houziyan hydropower station is a typical deep-buried powerhouse with the depths of 280-510 m horizontally and 400-660 m vertically. The ground stress is high and the geological conditions are very complicated. In order to monitor and analyze the surrounding rock mass stability during continuous excavation of underground powerhouse and locate the potential instability failure areas, an ESG (engineering seismology group) microseismic monitoring system manufactured in Canada was installed in April, 2013. The wave velocity range of rock mass in underground powerhouse was measured by digital acoustic instrument. The overall equivalent wave velocity of P wave was 5 700 m/s in monitoring system which was determined through several blasting tests. The seismic source location error was less than 10 m. The microseismic event waveforms were manually processed to acquire high position accuracy and the interference events were filtered out. On the basis of geological conditions and field observation, micro-fracture clustering areas of surrounding rock mass and the potential instability risk areas in the underground powerhouse of Houziyan hydropower station were revealed and delineated by the tempo-spatial evolution laws of microseismicity. Results could provide some references for later excavations and supports in the underground powerhouse of Houziyan hydropower station. Furthermore, a new research idea is opened up for the stability analysis of deep-buried underground powerhouse subjected to excavation-induced unloading.


Xu N.,University of Sichuan | Li T.,University of Sichuan | Dai F.,University of Sichuan | Li B.,University of Sichuan | And 2 more authors.
Sichuan Daxue Xuebao (Gongcheng Kexue Ban)/Journal of Sichuan University (Engineering Science Edition) | Year: 2016

Aiming at the stability problems of the surrounding rock mass in the underground caverns at the Houziyan hydropower station subject to excation, based on the discrete element theory, the numerical simulation of excavation of the underground powerhouse caverns was performed using PFC2D software. The influences of the controlling structural planes on surrounding rock mass deformation and failure were simulated, and the damage evolution law was reproduced. Moreover, a high-resolution microseismic monitoring system was adopted to real-time monitor and analyze the microseismic activity in deep underground caverns. Then the results of numerical simulation were compared with microseismic monitoring. The results showed that excavation damage zone of surrounding rock mass was closely related to faults, and the surrounding rock mass damaged regions obtained from numerical simulation was in good agreement with those revealed by microseismic monitoring. Therefore the approach of combining numerical simulation and microseismic monitoring was proven to be very promising for evaluating the excavation damage zones and predicting the potential instability of surrounding rock mass in the underground caverns subjected to excavation. © 2016, Editorial Department of Journal of Sichuan University (Engineering Science Edition). All right reserved.


Dai F.,University of Sichuan | Li B.,University of Sichuan | Xu N.,University of Sichuan | Zhu Y.,China Guodian Dadu River Houziyan Hydropower Development Co. | Xiao P.,China Guodian Dadu River Houziyan Hydropower Development Co.
Shock and Vibration | Year: 2015

To study the stability of underground powerhouse at Houziyan hydropower station during excavation, a microseismic monitoring system is adopted. Based on the space-time distribution characteristics of microseismic events during excavation of the main powerhouse, the correlation between microseismic events and blasting construction is established; and the microseismic clustering areas of the underground powerhouse are identified and delineated. The FLAC3D code is used to simulate the deformation of main powerhouse. The simulated deformation characteristics are consistent with that recorded by microseismic monitoring. Finally, the correlation between the macroscopic deformation of surrounding rock mass and microseismic activities is also revealed. The results show that multiple faults between 1# and 3# bus tunnels are activated during excavation of floors V and VI of the main powerhouse. The comprehensive method combining microseismic monitoring with numerical simulation as well as routine monitoring can provide an effective way to evaluate the surrounding rock mass stability of underground caverns. © 2015 Feng Dai et al.

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