Grouting Program to Stop Water Flow through Karstic Limestone: A Major Case History

摘要

A massive inflow of water developed within the limestone bedrock of a quarry for a cement producing facility in Cape Girardeau, Missouri. The water inflow increased rapidly with time from an initial flow of approximately 2,500 gpm to a maximum estimated flow of approximately 40,000 gpm. Karstic infill material was removed from the formation and carried with the water into the quarry creating sinkhole concerns and potential damage to structures. The loss of sediment needed to be stopped in order to reduce the potential for sinkhole development. Therefore, the water needed to be stopped. The use of a deep grout curtain was recommended to intercept the deep voids/fractures that were present and to reduce the water inflow to the quarry. The location of the curtain was ultimately based on the results of the anomalies identified by geophysical testing, and the location of existing sinkholes, quarry seepage, the projection of a fracture within the quarry and confirmation of karstic features during exploratory drilling. During drilling, two major void zones were discovered in the area where the grout curtain was ultimately constructed. These void zones generally extended from 230 to 275 feet below the surface and 300 to 325 feet below the surface. The majority of the void zones were grouted successfully with conventional cement based grouts. Both high mobility grouts (HMG) and low mobility grouts (LMG) were used. However, the water flow through one area located within an approximately 20 foot wide portion of the upper void zone of the grout curtain, referred to as the "hot zone" could not be stopped using conventional cement grouts. Dye traces conducted during the drilling and grouting confirmed the direct connection between the hot zone and the water outflow into the quarry. The use of specialized hot bitumen grouting in conjunction with HMG and LMG was performed to plug the hot zone. The grouting performed ultimately stopped the previously discussed flow of water and therefore the sediment being removed from the formation and deposited into the quarry. To date the grout curtain is performing well, and based on observations of the quarry and piezometers, no indications of a deterioration of the hydraulic effectiveness of the curtain since its implementation have been observed.