tunnel recovery by cement grouting
By PW MME 0 Comments

Tunnel Recovery Grouting Operations

Case description

A tunnelling contractor contacted Peter White for technical support and grouting expertise to assist with a tunnel recovery operation to control unexpected water inflows and difficult ground conditions.

The contractor had successfully excavated approximately 1.5 km of a planned 4 km watermain tunnel with a TBM. Unexpected high volumes of water began to enter at the tunnel face as the TBM passed through a shear plane and ground conditions rapidly deteriorated, so tunnel construction was stopped until remedial measures could be implemented.

Solution

Peter White designed the grouting plan and worked with the tunnelling crew to seal the source of the water infiltration and secure the tunnel face. A series of holes was drilled near the tunnel face for injection of cement and chemical grout.

The grout formulations consisted of both cement and chemical grouts to achieve water control and ground improvement in the vicinity of the TBM.

A cement grout curtain wall was also constructed ahead of the tunnel face to secure the surrounding area prior to future tunnel advancement.

Upon completion of all grouting work, the TBM resumed advance and completed the tunnel without encountering further water inflows.

Photo Gallery

Grouting application in tunnel lining
By PW MME 0 Comments

Tunnel Lining Reinforcement

Case description

The intake water supply tunnel for a hydroelectric station was constructed with shotcrete ground support and a spray-on lining to minimize water loss from a high-pressure section of the tunnel constructed through weak ground conditions.

Routine inspection of the tunnel revealed that the spray-on lining had failed at certain locations, allowing water seepage to escape from the tunnel during power plant operation.

The project owner retained Peter White to develop an appropriate repair methodology and to supervise grouting work by a local contractor.

Solution

Following a site visit, Peter provided a suitable drilling pattern to accommodate specific deficiencies observed in the spray-on tunnel lining.

Initial test work was undertaken with candidate injection materials and a two-component urethane elastomer was selected that provided performance characteristics that best suited the site conditions.

Peter worked closely with the contractor’s injection crew to undertake the required chemical grouting work, monitoring injection volumes, grouting pressures and connections with adjacent drill holes and defects in the spray-on lining.

Photo Gallery

Tunnel Water Inflow Recovery
By PW MME 0 Comments

Water Inflow Recovery in a Tunnel Construction Project

Case description

An unexpected water inflow of 1500 USGPM interrupted underwater tunnel construction for a hydroelectric expansion project when an open fracture was encountered that flooded the face of the tunnel and suspended further work until this high-volume inflow could be stopped.

The general contractor requested that Peter White come to the project site and provide hands-on direction of tunnel recovery activities.

Solution

Site inspection revealed that the 1500 USGPM water inflow was associated with a single open rock fracture that was connected to an unlimited water supply from an adjacent lake.

The first stage of recovery was to install several grouting pipes into the flowing aperture, following which a site-fabricated, steel water control gate was installed to cover the aperture location. A temporary wooden sluice was installed through the gate structure to divert as much water as possible through the open gate while subsequent preparations were made.

The perimeter of the steel gate structure was then sealed back to the adjacent rock surface using quick-setting hydraulic cement and water-activated chemical grout that enclosed additional large diameter drainage pipes. After the perimeter seal was in place, formwork was constructed and the steel gate structure was enclosed in concrete.

Prior to the start of cement grouting operations, valves attached to the large diameter drainage pipes were closed, the temporary wooden sluice was removed from the gate and the steel gate was closed and secured. After closing the gate, all of the water flow was stopped, so the only remaining requirement was to fill the water-filled fracture behind the gate.

A high density cement grout was prepared using conventional grouting equipment, with 2% calcium chloride accelerator, and pumped through the available grouting pipes. After placing several cubic meters of high density cement grout behind the steel gate, grouting operations were suspended and the cement grout was allowed to cure.

The following day, probe holes were drilled and confirmed that all open fractures had been sealed by the cement grouting operation.

Photo Gallery

Publication Article

“Tunnel Water Inflow Recovery” – by Peter White, P.Eng.

diamond drill hole
By PW MME 0 Comments

Water Cutoff in an Open Diamond Drill Hole

Case description

A mining contractor was developing an underground ramp through otherwise competent rock conditions when blasting exposed an ungrouted diamond drill hole from the surface that flooded the heading a substantial distance from the face.

The mining company engaged Peter White to travel to the site and supervise grouting operations to seal the flowing drill hole so that ramp development work could resume.

Solution

After assessing site conditions, Peter worked with contractor personnel to rig a rock bolt jumbo to mechanically install an inflatable borehole packer within the flowing diamond drill hole. This packer installation procedure was successfully accomplished using the drill jumbo without exposing any personnel to hazards associated with working directly beneath a high volume, cold water inflow.

After the packer was installed, a heavy cement grout was mixed on site using 2% calcium chloride as an accelerator. The required grout volume was calculated based upon the drill hole diameter and length.

After the required grout volume had been pumped into the drill hole, a final batch of cement grout was prepared by eliminating calcium chloride and substituting sugar as a retarder to prevent the cement grout from curing within the inflatable packer at the bottom of the borehole.

By observing samples of grout that were collected as the grouting work was underway, Peter was able to determine when the accelerated grout mixture had cured adequately so that mining crews could recover and clean the inflatable packer for subsequent use.

Mining crews were then able to resume regular development activities within the ramp.

Photo Gallery

Grouting at raise bore pilot hole
By PW MME 0 Comments

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.

Photo Gallery

Publication Article

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

Grouting and shaft sinking in Longos mine - Philippines
By PW MME 0 Comments

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.

Photo Gallery

Download Publication

water control in shaft construction
By PW MME 0 Comments

Water Control for Shaft Construction

Case description

Shaft construction associated with a mine expansion project was stopped when 1,200 GPM of water inflows were encountered within an aquifer zone at a depth of 43 meters below the 250 meter level at underground silver mine.

The mining company contacted Peter White to provide engineering direction to overcome the water inflow, supply specialized grouting equipment and accessories, as well as to provide on-site training for company crews to undertake the required drilling and grouting work.

Solution

To overcome the water inflow situation, Peter designed a systematic drilling and cement grouting program using long diamond drill holes collared from the underground 250 level that extended to the planned bottom of the mine shaft for a cement grouting operation to minimize water inflows for future shaft sinking, associated level development and loading pocket construction.

The grouting program involved cement grouting to reduce high volume water inflows through fractured rock and water-bearing ground conditions. Regular Portland cement was mixed at a W:C ratio of 2 by weight of cement, as thicker grout mixtures would not penetrate the water-bearing aquifer formation.

Cement grouting equipment supplied by Peter included a double-drum grout mixer and high-pressure plunger pump rated for the volumes and pressures required to undertake the project, as well as an electromagnetic grouting flowmeter, in-line diaphragm pressure sensors and liquid-filled pressure gauges.

Initial reductions in water inflow rates were observed after completing primary hole drilling and grouting operations. Subsequent secondary and tertiary holes were drilled and grouted to close in the spacing between adjacent drill holes, resulting in the successful overall reduction of water inflows that enabled resumption of shaft sinking activities.

Photo Gallery

water control underground karst limestone
By PW MME 0 Comments

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.

Photo Gallery

 

Bitumen/cement based injection to stop water inflows in a drainage tunnel below an open pit
By PW MME 0 Comments

Water Cutoff Grouting for Deep Drainage Tunnel

Case description

A major tailings inflow in an underground drainage tunnel, which peaked at approximately 7,000 l/sec needed to be sealed.

Solution

Provided technical grouting expertise during plugging of drainage tunnel located 500 feet below abandoned open pit filled with tailings using cement grout, polyurethane and hot bitumen grouting materials.

Photo Gallery

concrete repairs at hydro facility
By PW MME 0 Comments

Underwater Concrete Repairs at Pumped Storage Plant

Case description

A large pumped-storage hydroelectric power plant required underwater placement of rapid-curing, high-strength concrete to repair the intake structure apron situated at the bottom of the reservoir using barge-mounted concrete mixing and pumping equipment.

Solution

Based upon concrete performance specifications provided by the client’s engineering consultant, various materials and performance-enhancing admixtures were selected working in conjunction with local construction material suppliers.

The contractor assembled the project team and performed trial underwater concrete placement operations to test various concrete mix designs and optimize equipment operations.

Preparation of high-strength concrete was undertaken by a two-stage process of first preparing suitable cement grout mixtures (including all admixtures) using dedicated mixing equipment, followed by transfer of the prepared cement grout to secondary mixers for blending of aggregate materials prior to pumping.

Mixing and pumping equipment with appropriate capacity was selected by our grouting engineer to enable the required underwater scope of work to be undertaken by divers within a time frame of several hours while achieving the required concrete performance for rapid-curing and high-strength.

Photo Gallery