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2015WinterShotcreteEMag

As crews advanced into the tunnel, shotcrete was used to establish the initial structural support and safely assess the condition of the tunnel interior (refer to Fig. 2). LRL advanced through the tunnel in about 30 ft (9 m) long reaches. This was done by pulling invert muck back toward the open portal with a trackhoe and removing it with a front loader (refer to Fig. 3). Crews then moved for- ward safely scaling the roof and sidewalls. When ground temperatures and air quality conditions allowed, ACI Certified Nozzlemen placed shot- crete on the ceiling/walls with hand nozzles and a robot to establish initial support. When applied to the coal seams, the shotcrete effectively halted degassing and extinguished visible flare-ups. The high temperatures and CO levels within the tunnel diminished as the shotcrete was applied. As workers cooled down the muck pile and Fig. 2: Initial shotcrete roof support hydroscaled the ceiling and walls, the ground kept “popping” due to rapid cooling. The shot- crete significantly slowed down the cooling process of the rock, and enabled workers to safely press on. LRL workers used an offtrack rubber tire shotcrete operation for the explora- tion phase because the rail inside the tunnel was deformed. Equipment included a robot tractor mounted arm manufactured by Shotcrete Tech- nologies, a batch plant, and a concrete pump. LRL and the balance of the project team worked 24 hours a day for 24 days to complete this exploration. In this time, LRL installed three- hundred thirty-two 8 ft (2.4 m) long CT-bolts supplied by DSI Underground and placed 100 yd3 (76 m3) of shotcrete. Based on the findings from the exploration, the tunnel engineering design team developed a final liner solution that involved additional rock bolts and shotcrete. Once initial roof support was Fig. 3: Muck removal with loader installed, CSXT crews replaced the track through the tunnel and resumed revenue rail service to the mines on June 10, 2014. Then LRL worked around rail traffic using its rail-mounted shotcrete operation for final liner construction. LRL was able to place 100 yd3 (76 m3) of shotcrete per 12-hour shift. LRL loaded 50 yd3 (38 m3) of shotcrete onto their shotcrete train, mobilized 1/4 mile (1/2 km) to the tunnel, placed 50 yd3 (38 m3) of shotcrete, flushed hoses, cleaned out the pump, and then cleared the track for a coal train to pass. This process was repeated two times per shift. Final liner construction took approxi- mately 2 weeks. A total of one-hundred seventy- five 13 ft (4 m) and three-hundred seventeen 8 ft (2.4 m) long CT-bolts and 1270 yd3 (970 m3) of shotcrete were installed in the tunnel. The shot- crete included 80 lb/yd3 (47 kg/m3) of steel fiber reinforcement and yielded a 28-day unconfined compressive strength of 6000 psi (41 MPa). Fig. 4: ACI Certified Nozzleman applying shotcrete to east portal Shotcrete • Winter 2015 21


2015WinterShotcreteEMag
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