Fly Ash Grouts for Subsidence Control

by John J. Bowders, Jr., West Virginia Univ, Morgantown, United States,
W. J. Head, West Virginia Univ, Morgantown, United States,
Chandra Sharma, West Virginia Univ, Morgantown, United States,
Mumtaz A. Usmen, West Virginia Univ, Morgantown, United States,

Document Type: Proceeding Paper

Part of: Energy in the 90's


A laboratory investigation was undertaken to examine procedures for evaluating candidate grouts and to develop quality grouts for use in abandoned mines. The objective of this grout application is to reduce surface subsidence due to caving mines. Grouts consisting of fly ash and admixtures of cement and silica fume were examined for strength, permeability and durability. Findings indicated that a minimum cement content of 4 percent (dry weight) was required for grouts to develop a 28-day compressive strength of 3500 kPa (500psi). In addition, a high range water reducer must be added to the 4 percent cement mixture to obtain these strengths. The addition of silica fume had no discernable effect on the grout strength permeability of the grouts ranged from 1.5 to 5.OE-6 cm/sec for three to four percent cement. At 8.5 percent cement, the permeabilities were reduced to 8.OE-7 cm/sec. The silica fume addition did not affect the permeabilities. Overall, cement contents reduced to half of the levels used previously provided adequate strength when appropriate admixtures were incorporated into the grout. Permeabilities of the grouts at these reduced cement contents were in the range of 1.OE-6 cm/sec.

Subject Headings: Cement | Strength of materials | Permeability (material) | Silica | Fly ash | Grouting | Land subsidence | Coal mining

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