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City Of Dearborn Tackles Complicated Grout ‘Curtain’ Project
Drilling was performed through the bottom of the OCSP to a depth of approximately 200 feet into bedrock, about 50-feet below the bottom of the future shaft. Rock drilling was done with down-hole water hammers which lessened the amount of hydrogen sulfide released into the atmosphere, increased production and provided cleaner holes for grouting.
After performing an acid stimulation program, each hole was injected in one stage and received only one grouting pass. Holes were tremie grouted before inflating the packer at the top of the bedrock to prevent the formation of chimneys. Grout holes that encountered initial permeability greater than 0.3 Lugeon typically were grouted with cement-based grout because the larger features were amenable to this type of grout.
The outside row of primary holes were drilled and grouted first, followed by secondary holes on the outside row, followed by drilling and grouting of all holes on the inside row. Typically four to seven holes were grouted at a time during bedrock grouting.
Grouting operations were monitored, evaluated and recorded by a real-time grout monitoring system. Two monitoring stations were located adjacent to the grouting footprint in a temperature-controlled trailer. Each was capable of monitoring as many as four separate grouting operations simultaneously. To maximize the performance and efficiency of the grouting program, two design team engineers constantly monitored and evaluated the grouting data and field operations.
Monitoring software evaluated the apparent permeability values in real time. Following each injection pass, the residual permeability values of the formation were evaluated.
Safety training for project personnel was also provided by the acrylamide grout supplier. Environmental concerns were addressed by a combination of double containment tanks, self-erecting portable containments and closed system designs. The central header container was designed to mix and control flow and pressure to eight separate enclosed and temperature-maintained grout carts, each containing powered grout reels to lower inflatable packer assemblies to depths of 230 feet.