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Geology Disaster
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Applications of Remote Sensing Techniques in the Prediction of water gushing in the Dayaoshan Tunnel
Verification of the prediction of water gushing in the construction of the tunnel
- Water-gushing in the Shaft
On April II, 1985, when the tunnel was driven from the shaft in the Bangu'ao trough towards Guangzhou to the mile post DK 1994 +213 , a water flow of 4175 t/d happened suddenly six drill holes in the face of a parallel pilot tunnel.
As the water contained 20% silts, pumps failed to drain the water containing voluminous silts; thus groundwater rose from the bottom of the shaft to the elevation of
405 m and inundated the shaft. This water-gushing spot was only 57m from the RF16 structural zone predicted by remote sensing and was also the first water-gushing spot predicted by remote sensing (Fig. 5)
- Ground Regimes
When the shaft was inundated, a series of ground collapses, drying up of springs, ground cracking and subsidence of building foundations happened with pumping of the water gushing. What are interesting are that these ground changes were mostly regularly distributed in RF15, RF16, RF17 and RF31 that were recognized by remote sensing and that ground collapses all appeared on the right side of the axial line of the tunnel (Fig. 6) . The above fully shows that the water -gushing of the tunnel was derived from the centre of the hudong syncline on the right side of the axial line of the tunnel and that groundwater's in these structural zones were connected. This fully verified what was predicted before.
- Verification of the Prediction of the water gushing in the construction of the tunnel
After water flowed into the shaft of the tunnel, a parallel pilot tunnel was driven from the entrance of the tunnel. With the progress of the construction of the tunnel, water gushing were also encountered in RF17 , RF18 and RF19. During the construction of the Dayaoshan Tunnel, there were six localities where substantial water gushing happened, of which four were situated within the limits of remote sensing prediction. This fully demonstrated that the interpretations of remote sensing images could furnish precise information of prediction (Table1)
Table 1 Verification of the Water-gushing Predicted by Remote Sensing in the Dayaoshan Tunnel.
Serial
No. |
Remote sensing prediction |
Verification by construction |
| Mileage |
Case |
Mileage |
case |
| 1 |
DK 1994+156 |
RF 16 structural zone |
DK 1994+213 |
Inflow 4175 t/d |
| 2 |
DK 1994+604 |
RF17structural zone |
DK 1994+591-638 |
Inflow 8200 t/d |
| 3 |
DK 1994+947 |
RF18 stuctural zones |
DK 1994+840 |
Inflow 17000 t/d |
| 4. |
DK 1995+056 |
RF19structural zone |
DK 1995+065 |
Inflow 10000 t/d |
| 5 |
|
|
DK 1995+271 |
Inflow 3000 t/d |
| 6 |
|
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DK 1995+713 |
Inflow 5000 t/d |
Features of water gushing in the dayaoshan tunnel
The Dayaoshan Tunnel is 14.295 km long, but the localities with substantial water gushing were mostly distributed within about 1 km of the hanging wall of the Jiufeng fracture. This is because the Jiufeng fracture (RF15) is a compressive fracture, which is well cemented and impermeable. All the ground springs that are located in the hanging wall of the fracture have dried up because of the water-gushing of the tunnel, while all the ground springs that are located in the footwall of the fracture have not (Fig.7); therefore the Jiufeng fracture (RF15) is conspicuous cut-off interface. The water-gushing of the tunnel concentrate in the hanging wall of the fracture, which is a typical water gushing feature encountered in the construction of long tunnels in China(Fig.8) as well as case to which special attention should be paid when a hanging wall water rich zone of the fracture is encountered in the future construction of long tunnels.
From above, it is concluded that a abundant information can be obtained by utilizing macroscopic features of remote sensing images. In particular, the full application of remote sensing techniques in areas with dense vegetations, thick over burdens and difficult conditions of engineering surveys is of major significance for the evaluation of the stability of engineering works.
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