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Xiao Y.-X.,CAS Wuhan Institute of Rock and Soil Mechanics | Feng X.-T.,CAS Wuhan Institute of Rock and Soil Mechanics | Chen B.-R.,CAS Wuhan Institute of Rock and Soil Mechanics | Feng G.-L.,CAS Wuhan Institute of Rock and Soil Mechanics | And 2 more authors.
Yantu Lixue/Rock and Soil Mechanics | Year: 2011

Tunnel boring machine(TBM) should face the risk of very strong rockburst directly in intact and brittle rock mass section with ultrahigh stress concentration for full-face excavation in deep tunnel; then safety of equipment and personnel will be under great threat. The excavation test through "part-pilot heading + TBM" is carried out in the diversion tunnel #3 of the Jinping II hydropower station and the rockburst risk of TBM part-pilot excavation is researched via real-time microsesimic monitoring. The results show that: (1) The daily number of microseismic events, the daily accumulative radiated seismic energy, number of big events and frequency and strength of rockburst in the field during part-pilot excavation are far lower than in the period of full-face advance. (2) The time domain evolution of logarithm of energy index and accumulative apparent volume indicates that the risk of strong rockburst in part-pilot section is smaller; and the excavation in field also proved this. (3) In comparison to full-face advance, the degree of concentration, number, magnitude and radiated energy of microseismic events in space in section of part-pilot are far lower. Therefore, the rockburst risk of TBM for part-pilot driving is more less than for full-face advance. In very strong rockburst section, when construction condition is indispensable, the part-pilot can be excavated in advance and then TBM pass, the risk of rockburst can be controlled availably.

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.

Zhao Z.,Jilin University | Li L.,Jilin University | Huan X.,Beijing Vibroflotation Engineering Co. | Bo K.,Jilin University
Communications in Computer and Information Science | Year: 2014

In order to solve the problem that cuttings running out through the annular space between the drill pipe and borehole wall in Reverse Circulation drilling with Down-The-Hole (DTH) hammer, the ejector theory and orthogonal test design as well as Engineering Fluidic Dynamics (EFD) technology were utilized to optimize the structural parameters of the reverse circulation drill bit, including: the diffuser slot depth(H), the diffusion angle (β)of diffuser slot, the diameter of inner injection nozzle (d) ,inclination angle of inner injection nozzle (θ) and the number of suction nozzles (N) of the internal orifice. Research has shown that the H=20mm, β=10°, d=7mm, O{middle tilde}=25°, N=3 is the best configuration when air consumption is 12m3/min. © Springer-Verlag Berlin Heidelberg 2014.

Zhang Z.-T.,Beijing Vibroflotation Engineering Co. | Chen Z.,Beijing Vibroflotation Engineering Co. | Chen B.-R.,CAS Wuhan Institute of Rock and Soil Mechanics | Jiang H.-L.,Beijing China Coal Mine Engineering Co. | And 2 more authors.
Meitan Xuebao/Journal of the China Coal Society | Year: 2011

Considering the features of rock burst in the headrace tunnel and combining the site conditions, a series of new material and new construction methods were tested. In the intensive rock burst section, construction method like pilot tunnel pre-treated with drill & blast method and then excavated with TBM was also studied and tested. Based on the test results, some practical measures were concluded for dealing with the rock burst.

Liu L.-P.,China Institute of Water Resources and Hydropower Research | Liu L.-P.,Beijing University of Technology | Wang X.-G.,China Institute of Water Resources and Hydropower Research | Jia Z.-X.,China Institute of Water Resources and Hydropower Research | And 3 more authors.
Zhongnan Daxue Xuebao (Ziran Kexue Ban)/Journal of Central South University (Science and Technology) | Year: 2011

The stress distribution process in surrounding rock mass near excavation surface of typical cross-section in Jinping II hydropower station drainage-hole during excavation was simulated using the FLAC3D numerical software. The characteristics of stress alteration in different depths of the surrounding rock and the potential rock burst energy source were analyzed by the key point stresses monitoring. Based on the hypothesis of rock mass stress release rate around the wall, the delay characteristic of the rock burst was researched from the angle of rock mass stress release rate. The results show that the major and minor principal stresses of the shallow surrounding rock reduce during excavation, and the rock mass in this region yields in stress-reduce way which is not easy to accumulate elastic strain energy. Surrounding rock mass of a certain distance from the tunnel wall yields in plastic way and accumulates considerable elastic strain energy, which becomes the rock burst energy source, while the rock yields, the energy releases, which affects the stability of shallow stress-reduce yield rock mass and eventually leads to rock burst. The deep rock mass which is in elastic state also accumulates great stain energy, aggravates the degree of rock burst and damage. The rock burst will not occur when the stress release is low; as the stress release rate gradually increases, the distribution of the elastic strain energy and plastic strain energy change and the risk of rock burst obviously increases; rock burst happens when stress release rate reaches 70%-80%.

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