ASSESSMENT IMPACTION OF EXCAVATION SCHEMES ON ROCK MASS AROUND HUOI QUANG UNDERGROUND POWER CAVERN IN VIET NAM PhD.Candidate. Tran Tuan Minh1*, PhD.Candidate. Nguyen Duyen Phong1 1 Ha Noi university of mining and geology PhD. Candidate. Nguyen Viet Dinh2 2 Institute of mining science and technology
*Authors to correspondence should be addressed via email:
[email protected] Keywords: Stress/ deformation/ tunnels big - cross cut/ geomechanics/ rock engineering/Phase 2. Abstract: Power cavern is one of the most important parts in the underground hydroeletric power plant. Nowadays designers ussually use many other schemes for excavation this construction. There are many other schemes for building power cavern for example as following: pilot tunnels and bench or top advance and bench, pilot tunnel and expansion for two sides,...ect. This paper introduces assessment impact of scheme excavation on the stability of rock mass around power cavern in Huoi Quang hydroelectric power - Viet Nam and recommends appropriated supports when building this construction in Viet Nam.
Zone hydroelectr ic plant
1. INTRODUCTION Viet Nam is one of many countries in ASEAN located in the north of globe, which has S form with total areas much more 331.11k km2 and population approximately 90milions. The north of Viet Nam located near the China, Lao and the south near the Kampuchea and one other side is the eat sea. Viet Nam has many coals, golden, silver, antimony and other materials for industry and for exporting. Specially under the eat sea Viet Nam has many oils and gases. To develop industry in Viet Nam in the future we need building many hydroelectric power plants, thermal power plants, atom power plants and other energies to develop country. Huoi Quang hydroelectric power plant is located in Son La provinces, which has power 520MW and built on the Nam Mu rivers, which flows between Son La and Lai Chau. Hydroelectric power plant consists of three power caverns, two of them are the same as forms and dimensions. Tunnel systems in plant consist of technical tunnels, two shafts with diameter 20m. Hydroelectric plant location described as in figure 1. 2. GEOLOGY CONDITIONS, SCHEME POWER CAVERN AND SCHEME EXCAVATION.
Fig.1 Zone Huoi Quang hydroelectric plant Huoi Quang power cavern driven in quitter stiffness rock, coefficient stiffness f = 6 8. Model 3D and long section geology conditions for plant are
described as figure 2. Characters of geology conditions, where plant located following as in table 1.
Tab.1 Characters of rock mass for analysis Name parameters Symbol Unit Model material Model 3 Unit weight MN/m Module elastic E E MPa Coefficient Poisson Strength of tension MPa st Pressure cohesion c MPa Friction angle Degree Expansion angle Degree Residual friction angle Degree re Residual tensile strength
stre
MPa
Rock Mohr - Coulomb 0,026 4500 0,25 0 0.8 40 0 40 0.8
Fig.2 Long geology section in Huoi Quang hydroelectric power plant
Fig. 3 Model 3D hydroelectric power plant
Fig.4 Cross section power cavern with horizontal tunnel between two power caverns
Fig.5 Cross section power cavern no tunnel between two power caverns To design stability power cavern, in the first stage model predicts and selects bolt and shotcrete for we use excavation stages, after excavation we use bolt power cavern. In this case we use bolts from steel bar support and shotcrete for stability roof and side walls and cement bonding total bolts. Characters of bolts power cavern. Supports are selected for stability over and shotcrete liner are described in table 2 and 3. time while using power plant, using Tab.2 Characters of rock bolt Name parameters Symbol Number Units Type material behaviour elastic Diameter of steel d 32 mm Capacity of tensile Cn 0,6 MPa Capacity of residual tensile d 0,6 MPa Module elastic Et 200000 MPa Parameters Type material Thickness liner Module elastic Coefficient Poisson Compressive strength Strength of tensile
Tab.3 Parameters of shotcrete liner Symbol Number Behaviour elastic d 10 Ebt 35000 0,15 40 b 3 bk
Units cm MPa MPa MPa
3. NUMERICAL MODELING By using program Phase 2 we can be simulate
process excavations and supports power cavern as figure 6 and 7.
Fig.6 Model analysis two power caverns
Fig.7 Model analysis in сross-section with tunnel between two power caverns After running model analysis, we can be received distribution of vertical and horizontal stress and sum deformation, vector deformation with stages excavation around power cavern from figure 8 to 12.
a) stage 1
Effects of support and failure zone can be seen as in figure 11, seeing in figure 11 we can see that length of rock bolt and thickness shotcrete 10cm, power cavern will be stability.
b) stage 5 Fig.8 Distribution of vertical stress with excavation stages
c) stage 11
a) stage 1
b) stage 5 Fig.9 Distribution of horizontal stress with excavation stages
c) stage11
a) stage 1 b) stage 5 c) stage 11 Fig.10 Distribution of deformation around power cavern with excavation stages
a) stage 4
b) stage 8 Fig.11 Failure zone and effects of support after analysis
c) stage 11
a) stage 8 b) stage11 Fig.12 Vector sum deformation around power cavern at stage 8 and 11 Seeing in red zone we can be seen that, tunnel between two power cavern located in this zone is the optimal position. Phase 2
can analyses in cases power cavern and tunnels between them, results in this case can be seen in figure 13, 14 and 15.
a) stage 5 b) stage 11 Fig.13 Distribution of vertical stress at location with horizontal tunnel between two power caverns
a) stage 5 b) stage 11 Fig.14 Distribution of horizontal stress at location with horizontal tunnel between two power caverns
a) stage 5 b) stage 11 Fig.15 Results vector sum deformation with stages excavation at location with tunnel between two power caverns Seeing results in figures from 13 to15 we can seen that rock strength at position of tunnel between power caverns is be lower than other positions around power cavern. In this case we need support much more in this length for stability power cavern. 4. CONCLUSION AND DISCUSSION After above analysis we can see that, by using numerical software Phase 2 we can establish model faster and receive results good support. Base on seeing deformation, failure zone and working of support and massive rock we can control stability of support and design support parameters. We can control length of bolts, bolt characters and thickness of shotcrete and other factors. For higher effective design we can analysis again many times and with excavation stages after that we can see much more detail changing of inter pressure in support liner and effective support.
In Huoi Quang hydroelectric power plant should be used bolt from concrete and steel bar with length 10m, axa = 2x2m and shotcrete thickness 10cm for stability rock mass around power cavern. However, for using cavern in long time we should use permanent support by concrete liner with thickness 25cm or needing calculation parameters concrete liner for power cavern. Support received when increasing thickness concrete liner or changes other parameters of liner in case rock around power cavern doesn’t collapse, appropriated support. By numerical method and Phase 2 we can change this work very easy and simply. In fact we can use this method for analysis and calculate stability faster, one other hand we too need comparison with other numerical methods for example Plaxis, Flac, close solutions for higher effects.
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