Grouting at raise bore pilot hole
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Water Cutoff in Raise Bore Pilot Hole

Case description

A gold mining company had pre-drilled a 380 mm diameter raise bore pilot hole from surface to a depth of 600 m when it was discovered that water-bearing rock fractures were allowing groundwater to enter the pilot hole at a depth of 122 m below surface.

Project engineers requested Peter White to devise a suitable grouting plan and supervise their contractor’s crews to eliminate the water inflow prior to reaming the ventilation raise to full diameter.

Solution

Peter designed a diamond drilling layout to intercept the water-bearing fractures from the surface. Completed drill holes were gyro-surveyed so that drill hole locations were established for planning subsequent drill holes.

A large diameter inflatable packer was suspended within the pilot hole below the water-bearing fractures and inflated to allow the pilot hole to fill with water and eliminate water flow down the pilot hole. Filling the pilot hole with water enabled cement grouting of the water-bearing fracture to be accomplished under no-flow conditions.

Water testing and evaluation of drill cores established that aperture size of the water-bearing fractures was relatively narrow, so Peter determined that microfine cement was the appropriate grouting material for this project.

After drilling and grouting of 12 holes surrounding the ultimate ventilation raise diameter, the inflatable packer was recovered from the pilot hole and it was shown that the residual water flow rate from the pilot hole was negligible, allowing reaming of the ventilation raise to proceed.

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“Water Cutoff in Raise Bore Pilot Hole” – by Peter White, P.Eng.

Grouting and shaft sinking in Longos mine - Philippines
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Shaft Sinking Through Water-bearing Ground

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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ground improvement Ventilation Raise Construction
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Ground Improvement for Ventilation Raise Construction

Case description

An underground gold mine was rapidly expanding and urgently required additional ventilation capacity to support the operation of its trackless equipment fleet. Ground conditions were exceptionally poor, with exploration drilling results indicating very low RQD values and many zones with no core recovery.

After geotechnical consultants advised that ventilation raises could not be constructed through such adverse ground conditions, the mining company contacted Peter White to ask if the ground improvement was feasible.

Solution

Based upon Peter’s experience working in similar ground conditions, the mining company decided to proceed with a cement grouting operation to improve ground conditions prior to raise boring the required ventilation raises.

Peter assembled a turn-key grouting plant, complete with ancillary equipment and accessories for undertaking the planned scope of work, and arranged shipment to the remote mine site in Indonesia.

Ground improvement work involved sequential diamond drilling of 8 holes around the perimeter of each ventilation raise using down-stage methodology. Drilling crews would advance each drill hole stage between 15 to 30 m depending upon ground conditions encountered.

Cement grouting was undertaken using microfine cement to thoroughly penetrate and consolidate fractured ground conditions prior to drilling of the next down stage in each drill hole. Detailed records were maintained of ground conditions encountered, as well as quantity of cement consumed and the applied grouting pressures.

After injecting approximately 40 tonnes of cement along the alignment of each ventilation raise, raise bore crews were able to successfully undertake pilot hole drilling and subsequent reaming to full diameter without difficulty. The excavated ventilation raises remained open without collapse or caving for several weeks until a shotcrete lining was applied.

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“Ground Improvement for Vent Raise” – by Peter White, P.Eng.

deep dive bypass grouting
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Deep Dive Shaft Grouting

Case description

A deep bronze bypass pipe positioned between two adjacent water supply shafts had a defective shut-off valve at a depth of 140 m below surface. The general contractor required the deep bypass pipe to be decommissioned by filling with cement grout that met NSF/ANSI Standard 61 for drinking water system components.

Since the water supply system could only be shut down for brief overnight periods when city water demand was low, diving activities were undertaken using two Atmospheric Diving Suits, with one “suit” working in each of the adjacent shafts in combination with remote submersibles (ROV) that provided lighting and underwater cameras to monitor work activities.

Solution

The first step in planning the deep dive grouting operation by our grouting engineer was to choose suitable grouting materials.  For this project, Type I/II Portland cement and ground granulated blast furnace slag (GGBFS) were selected, both of which conformed to NSF/ANSI Standard 61.  No other additives or admixtures were required for this grout mixture.

The second step was to configure appropriate cement grouting equipment to prepare a consistent high-quality grout mixture, provide for redundancy of critical equipment components and incorporate variable frequency drives to facilitate rapid and controlled adjustment of grout flow rates and grouting pressures.

The third step in planning the deep dive grouting operation was to select an appropriate grouting hose for transfer of mixed grout from the surface grouting plant to the point of injection at a depth of 140 m below surface.

After months of detailed preparations, hundreds of diving hours using the Atmospheric Diving Suits, and several days undertaking mockup trials, the grouting operation supervised by our grouting engineer was successfully completed in less than 3 hours from start to finish.  The day following the underwater grouting operation, diving crews recovered grouting manifolds from the shaft bottom that were plugged solid with cured cement grout – a positive indication of the state of the sealed bronze bypass pipe.

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“Deep Dive Shaft Grouting” – by Peter White, P.Eng.

cofferdam construction
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Cofferdam Construction in Faulted Ground Conditions

Case description

Construction of a run-of-river hydroelectric power plant required an extensive cofferdam to be built within a steep river valley aligned with a major regional fault structure. Cofferdam construction was at risk of being undermined through porous rock formations during the summer runoff season when high water levels flow through the river valley.

Solution

The contractor used overburden drilling equipment to install casing and systematically drill open holes using down stage drilling techniques as deep as 25 m below surface. Adjacent drill holes were sequentially positioned following primary, secondary and tertiary spacing.

High-density cement-flyash grout was delivered to site from a central batch plant using ready-mix trucks and pumped through drill casing using small concrete pumps to achieve high rates of grouting performance while monitoring grout delivery volumes and pressures.

Drilling and grouting operations proceeded on a split spacing pattern to consolidate faulted and porous ground conditions and to strengthen foundation conditions beneath the cofferdam.

Cofferdam remained intact during summer runoff and provided suitable working conditions for ongoing construction work within the cofferdam area.

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“Large Scale Cement Grouting for Forrest Kerr Cofferdam Construction” – by Peter White, P.Eng.

deep shaft construction
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Soil Stabilization for Deep Shaft Construction

Case description

A mining contractor was constructing a surface collar for a new ventilation shaft and encountered quicksand conditions at the interface between the sheet pile perimeter wall and underlying rock strata that delayed the deep shaft excavation. Rock strata were too hard for sheet pile tips to penetrate, resulting is openings beneath adjacent sheet piles. Excessive excavation had destabilized the surrounding soil mass and caused sinkholes to occur adjacent to the shaft collar.

Solution

Working from within the shaft, grouting engineer Peter White and his technical crew commenced chemical grouting operations at the highest point along the rock-sheet pile interface using water-activated polyurethane resin and systematically stabilized soil conditions around the perimeter of the shaft to prevent soil or water from infiltrating.

The shaft sinking contractor was then able to install steel plates to reinforce the grouted openings prior to continuing with the excavation work. The grouting crew continued working to systematically eliminate problems at lower elevations with quicksand inflows until the entire perimeter was sealed.

The final stage of grouting work was to stabilize a ring of soil outside the shaft at the soil-rock interface so that the shaft collar would withstand subsequent rock blasting within the shaft.

After 10 days of chemical grouting work that consumed over 1,500 kg of chemical grout, all the shaft bottom had been excavated down to solid rock with no further water infiltration.

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“Shaft Collar Construction Through Quicksand Ground Conditions” – by Peter White, P.Eng.