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Please click on the image below to view a testimonial from The De Beers Mining Company.
During the excavation of a ramp an 80m section was exposed which intersects groundwater flow. The area was expected to dry out when development had passed through and moved away from the area. Water seeped and flowed from the hanging and much of the sidewalls. This also created safety problems with regard to wet and slippery footwall conditions
A year later the ground water flow was still strong at 7500 - 11000 l/h depending on the rainy season. It was clear that the water would not subside on its own. Much investigation showed that the water was structural and lithologically driven. The area intersected two faults, dolomite and a 15m thick carbonaceous dolomite and shale horizon. This lithological unit is weak and needed extra support. The length of time the area had been exposed to the water flow had further weakened the strata
The continuous water flow not only created a problem for the extra support to be installed but also for it to maintain its condition long term. Widespread water leaks would deteriorate the concrete fill and corrode the steel sets quickly. The water could not be left in free flow behind the set; it had to be diverted away from contact with the set and needed proper management. It was decided that the only option was to use chemical water sealing to dry out the area and then control the water flow through a number of drainage holes.
The sealing work was done by Liquid Waterproofing. A number of holes were drilled and pumping in the sealing agent sealed off the area. The sealing work was initially directed around the faults by intersecting them at an angle. This worked well and gave large sealing coverage areas. As these main water flows were now cut off, the water was directed to seepage areas. The main seepage zones could be identified and were targeted next. The now increased water flow in these areas created good flow to carry sealant some distance into rock. The sealing created a closed barrier, against the water, around the excavation walls but did not remove the water from the area. The water was now allowed back into the excavation through the drainage holes drilled some distance through the sealed area and into the water filled rockmass behind. The number of drainage holes was important as not to have water pressure build up behind the sealed area.
The area was very successfully sealed and dried out on the surface. The groundwater flow area was now controlled through the drainage holes, which made water management simple and safe by having a piping system from all drainage holes to a common gutter. The installation of the set was now possible and completed without incident. The area is in good condition; it will continue to be monitored and is expected to maintain long term integrity.
Interestingly enough during this sealing exercise another area that had been water stricken some 110m above had also dried up and is no longer a problem. This was found to be related to the same fault structure that intersects the ramp.
