High volume-high value usage of flue gas desulfurization (FGD) by-products in underground mines: Phase 2, Field investigations. Quarterly report, October 1--December 31, 1996

In this quarter, activity focused on the placement of Flue Gas Desulfurization (FGD) grout into auger holes at the Sunny Ridge Mining Co. site. As discussed in previous reports, the grout was prepared using fluidized bed combustion (FBC) by-product obtained from the Costain Coal Company. The grout was thoroughly mixed with water and transferred to a concrete pumping truck. The nozzle on the pumper truck was attached to PVC pipe through which the grout was pumped into the auger holes. The first field test involved the placement of a very high slump, flowable grout into auger holes sing a simple, earthern bulkhead. These tests were conducted to explore the flowability of the grout. The second series of test was conducted with a lower-slump, higher-viscosity material pumped at high pressure and using sandbags as a bulkhead. The goal of these tests was to examine the feasibility of pressure grouting to completely fill auger holes with a material that will exhibit high long-term strength because of this low initial water content. Although there were many problems encountered during the field demonstration, these initial tests were, overall, successful. It was shown that a high-slump grout can be pumped the length of the auger holes, and can be successfully placed in holes containing standing water. Furthermore, this can be accomplished using available concrete emplacement equipment. In contrast, the pressure grouting proved more challenging than emplacement of the flowable grout mainly because of pipe-joint failures and difficulties in working the stiff, high-viscosity grout; the amount of water added to the mix is critical when placing this type of material. Cylinders of grout for compressive strength testing were prepared during field demonstration, and cores of the in situ hardened grout will be recovered after a minimum of 30 days. Additional field demonstration will focus on improving the procedure for placement of the flowable grout