water control underground karst limestone

Water Cutoff in Underground Karst Limestone

Case description

A high-grade underground silver mine was operating below the water table within a karst limestone formation that included numerous faults and other water-bearing structures.

Potential water inflows were controlled by drilling probe holes and injecting cement prior to advancing development and production headings.

While reaming a new ventilation raise, the reamer encountered an un-grouted fracture that resulted in a high volume water inflow of approximately 40,000 USGPM that rapidly flooded the mine workings.

Solution

The mining company contacted Peter White to direct mine recovery operations.

Surface exploration drill rigs were used to drill three holes that intersected locations near the water inflow.

Peter worked with a local ready-mix supplier to formulate a cohesive cement-sand grout mix to fill the mine openings beneath the water inflow location. A conventional concrete pump truck was used to deliver several ready-mix truckloads of cement-sand grout to fill the ventilation raise and associated access tunnel.

Surface holes were then re-drilled to verify site conditions and conventional cement grouting operations were undertaken to seal residual water-bearing fractures.

Within a few days after the mine flood event, crews were able to dewater the mine workings and resume mining operations. After additional probe drilling and grouting work near the inflow location, access to the ventilation raise was reopened and the ventilation raise was successfully constructed.

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workers at dam jobsite for consolidation grouting

Consolidation Grouting for Tailings Dam Construction

Case description

Upgrades to an existing tailings storage facility included construction of a water diversion channel and related berms to divert groundwater, as well as the construction of a new embankment dam downstream of the original tailings dam to satisfy current environmental standards.

The scope of work involved the construction of a bedrock foundation grout curtain over a length of 200 m and to a depth of 10 m into rock.

A major engineering challenge was to complete the grout curtain into bedrock beneath a deep rock trench that was filled with saturated soil that the general contractor was unable to excavate due to proximity to the original tailings dam.

Solution

The general contractor retained Peter White to provide grouting engineering services, cement grouting equipment and accessories, and to supervise and direct all aspects of grout curtain construction utilizing the contractor’s own personnel.

The contractor constructed a thick concrete pad within the deep rock trench.

Drill holes of 3-inch diameter were drilled through the concrete pad as required using a hydraulic top-hammer drilling rig.

Ready-mix high-density cement-slag grout mix was delivered by ready-mix trucks from a local batch plant and injected beneath the concrete pad to displace saturated soil situated between the concrete pad and underlying bedrock.

After a few days of injecting ready-mix cement-slag grout, the underlying zone between the concrete pad had been adequately consolidated that holes could be drilled down to bedrock and used for conventional cement grouting operations.

Within a few additional days of conventional cement grouting as directed by Peter, ground conditions had been improved sufficiently that drill holes could be advanced to bedrock to successfully complete final stages of grout curtain construction.

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