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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
Interpretation of Remote Sensing Images
Through an interpretation of multiple space and aerial remote sensing images coupled with an analysis of regional geological data, it was considered that the hydro geological conditions in the Bangu'ao trough in the central part of the tunnel were complex and that the trough was key sector of consubstantial water-gushing would be encountered in the sector. Here the grounds for predicting the water gushing are given as follows.
- Interpretation of Landsat Images
From an analysis of U.S. Landsat images, it was found that the Dayaos has Tunnel is located in the central part of the Dayaoshan block . The Dayaoshan-block is a raised rock body, bounded mostly by fractures with ductile space as the boundaries 9Fig.2 and 3). The Dayaoshan Tunnel penetrates the central part of the block and does not penerate the vunerable sector of the geological structure on the peripheries of the block, which is a complex sector of the geological structure and also a vunerable sector of engineering geology.
- Analysis of Regional Geological Structure
On the 1:200000-scale geological map (Fig.1) it is clear that the jiufeng fracture cuts through the centre of the Hydong sycline at a place 3.5 km from the axial line of the tunnel on the right after the fracture transverses the tunnel in the Bangu'ao trough. This place is an intermontane basin where surface water and subsurface water in its surroundings gather. As shown clearly by remote sensing images, in limestone strata in the centre of the syncline karts is well developed and there is a river on the surface, which fully demonstrates that this place is a syclinal structure with very plentiful groundwater. On the other hand, the ground elevation of this place is 190 m higher than the designed elevation of the tunnel, with a hydraulic gradient 0f 6%, and in addition
the place is connected with the tunnel by the jiufeng fracture, thus creating good conditions for the Water-gushing in the tunnel. Moreover, the Luopqunzhai sycline south of the hydong sycline is also cut by the jiufeng fracture; therefore groundwater in the Luoqunzhai sycline is likely to be connected with that in the Hudong sycline, thus bringing substantial water-gushing in the tunnel
- Interpreation of Aerial remote Sensing Images
From an analysis of aerial remote sensing images, there occur a series of lineamentzones parallel to the Bangu'ao trough in the central part of the tunnel, for example RF14, RF15,RF17,REF18 and RF19, but at a distance of 3 km on the left side of the axial line, all the above-mentioned lineament zones are cut off by an oblique structure (RF42) , except RF15 (Jijfeng fracture ) which passes the structure.
Therefore the Jiufeng fracture becomes a bundle of fractures in the tunnel area, of which RF15 is the major fracture of the Jiufeng fracture bundle (Fig.4) Apart from the above-mentioned fracture structures parallel to the Bangu'ao trough, there are also tranverse fratures, forming a criss-cross pattern of lineaments, thus providing favourable conditions for interconnection of groundwater between various structural zones. Therefore, it was predicted that water-gushing would occur at several
localities in the construction of the tunnel
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