Clay-Based Grouting Into the EDZ for the Vault Sealing
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Figure-2 Schematic view of the room 425 of the TSX
Figure- I Layout of the experimental room of the TSX at the URL 331
Mat. Res. Soc. Symp. Proc. Vol. 608 © 2000 Materials Research Society
grouting effectiveness for the EDZ around the clay-block bulkhead. These tests were carried out at Room 419 (395m below the ground surface) and Room 425 (420m below the ground surface) as a part of the TSX. TRIAL BENTONITE GROUTING TEST IN ROOM 419 With regard to the effectiveness of the grouting, it is difficult to evaluate only bentonite grouting in the TSX since the EDZ is interrupted by the combination of the key, the bulkhead and the grouting (see Figure-2). In those terms, the trial bentonite grouting test was conducted in Room 419 to estimate the sealing effectiveness of only the bentonite grouting into the EDZ. In Room 419, a trial key, Im deep by 2m wide, was excavated for the examination of the feasibility of construction of a square-shaped key in the TSX (Figure-3). The EDZ is induced both by the blasting during the excavation and by the stress redistribution around the tunnel [3]. Room 419 has the same orientation and geometry as Room 425. Therefore, it was expected that the EDZ developing around the trial key had characteristics similar to the EDZ around the clay bulkhead in the TSX tunnel (Room 425). The procedure for the trial bentonite grouting test included drilling boreholes, grout injection and borehole filling. A seepage test was conducted to estimate the effectiveness of grouting by comparing the seepage before and after grouting. Figure-3 shows the layout of the boreholes for this test. The boreholes were 76mm-diameter with shallow inclinations. Boreholes Gtl, Gt2, Gt3 were inclined at 200 with a nominal length of 1.0 m and boreholes Gt4, Gt5 were inclined at 10' with a nominal length of 0.7 m. The appropriate shallow drilling angle allowed the borehole to intersect the EDZ for a longer distance. The collar of borehole Gt2 was situated at the direction of the minimum principal stress in the key surface. The other boreholes were drilled around this borehole, collared on the vertical face of the key. The concrete dam was constructed for the seepage collection for the connected hydraulic conductivity test. To prevent direct seepage through the concrete-rock interface, two lines of bentonite strips were placed across the floor under the dam. An overflow pipe was put at a height of 1.Om on the dam to keep a constant water level in the reservoir. To collect and monitor the water seepage and outflow of the grout slurry, V-shaped trays were inserted into saw cuts on the - 325* EDZ . 145*.. Table-I Results of hydraulic test . ... ."_.. - ._..- ..... of the trial test
2m
1Gt2,Gt3 ____ 7,,'-,Gt "' IGt4,Gt5 -10" -20" t"lastic tub
Hydraulic Borehole Test interval conductivity [m] [m/s] Gtl 0.85 6.63E-13 Gt2 0.64 2.06E-12 Gt3 0.78 2.40E- I1 0.69 1.95E-12 Gt4 0.50 4.56E-14 3.86E-14 0.57 Gt5 Borehole Gt3
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Figure-3 La
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