Remediation of a Sinkhole Induced by Quarrying
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On the morning of April 28, 1997, a sinkhole developed beneath a Burlington Northern Santa Fe Railway track. The sinkhole caused the derailment of 22 railroad cars, spilling diesel fuel from the engines that ignited, resulting in a fire and injuries to railroad personnel. Railroad personnel filled the sinkhole with about 500 cubic yards of rock fill, and traffic resumed while a subsurface study was carried out. The study resulted in a grouting program where 40 to 50 cubic yards of grout were injected into the subsurface. In August of 1999, the track subsided again. A second investigation conducted in October 1999, involved a tomographic imaging survey to define weaker zones beneath the track that may have contributed to the August ground movement. A much more extensive grouting program followed this study in April 2000. A total of 2746 cubic feet of neat cement/fly ash grout and 162 cubic feet of sand-cement/fly ash grout were injected into the underlying bedrock. In July of 2000 another and larger subsidence occurred, and a second tomographic imaging survey was conducted. In April of 2002, the sinkhole reactivated and continuing movement occurred over a period of weeks. About this time, a large volume of sand-laden water was reported entering the adjacent quarry. A third grouting program was conducted and involved injection of cement, chemical, and hot asphalt grouts. The grouting appears to have arrested both the subsidence as well as the inflow of water into the quarry.