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Case description

The sinking of a new shaft at an established gold mine was interrupted due to flooding by a blow-out at the shaft bottom while in the process of installing a grout curtain. Initial attempts at shaft recovery were unsuccessful and further shaft sinking was abandoned for several years.

After a subsequent change in company management, Peter White was invited to assess the site conditions and determine if the water inflow could be stopped to enable shaft sinking operations to resume.

Solution

Peter determined that the shaft could be salvaged by accessing the original blow-out location at shaft bottom and preparing the site for water cut-off grouting operations.

Shaft crews worked in water inflow conditions of 800 USGPM to recover the shaft bottom, remove debris and fractured rock, install drainage pipes and pour new concrete at the shaft bottom. Upon completion of this preparatory work, the original shaft bottom inflow had been reduced to 30 USGPM.

Cement grouting equipment was installed at the shaft collar and long grout delivery pipes were attached to the shaft lining. Sodium silicate grouting equipment was installed at a shaft station approximately 30 m above the shaft bottom.

Shaft bottom grouting work consisted of simultaneous injection of cement grout and sodium silicate to produce a fast curing grout mixture. After many months of preparation work, shaft bottom grouting work required several hours to successfully seal the primary water flow channels and permanently reduce the water inflow rate.

Subsequent drilling and cement grouting operations were undertaken to seal the fractured rock strata surrounding the shaft bottom, as well as below the floor of the shaft prior to resuming shaft sinking.

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