tunnel recovery by cement grouting
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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.

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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.

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Publication Article

“Tunnel Water Inflow Recovery” – 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.

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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.

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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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Publication Article

“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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Publication Article

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

water cutoff in kasrt limes power station niagara
By PW MME 0 Comments

Water Cutoff in Karst Limestone

Case description

An elevator shaft accessing Sir Adam Beck I powerhouse was excavated through karst limestone and shale in the early 1900’s; shaft dimensions are approximately 5 m x 5 m x 60 m deep. Water from the power house forebay intake canal was infiltrating through karst limestone rock formation and entering the brick-lined elevator shaft, creating maintenance problems for elevator equipment and corroding installed structural and electrical components within the shaft.

Solution

A series of large diameter holes were cored through the brick lining to expose the rock walls of the shaft for inspection purposes. It was observed in many locations that loose rock debris had fallen from weak zones and accumulated behind the brick lining.

After reviewing information from adjacent vertical core holes, it was determined that the majority of water infiltration was associated with limestone formations situated near the top of the elevator shaft.

These water-bearing rock formations were isolated from dry rock formations by strategic injection of water-activated polyurethane resin between the brick lining and the shaft rock excavation. Staged drilling and systematic injection of holes at progressively longer lengths displaced infiltrating water away from the shaft wall and gradually reduced active water inflow rates.

Deeper core drilling in conjunction with cement grouting was subsequently used to systematically fill open water flow channels and prevent water from migrating fromthe forebay intake canal towards the elevator shaft.

Water inflow rates as measured at the bottom of the elevator shaft throughout the project were systematically reduced as work was underway and were eventually eliminated. The original water-bearing channels did not propagate or cause water to migrate elsewhere within the elevator shaft.

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Featured Article

“Overcoming Water Inflow Issues at Sir Adam Beck 1 Generating Station” – by Peter White, P.Eng., Canadian Tunnelling Magazine

test cell
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Soil Stabilization for Test Cell Excavation

Case description

A multinational equipment manufacturing company required a deep foundation to be excavated through granular soils with a high water table for installation of a new test cell within an existing plant facility, without disrupting adjacent equipment operations or causing settlement of building structures. Due to space constraints and ongoing equipment operations, conventional deep foundation shoring systems could not be utilized within the existing manufacturing plant.

Solution

A sleeve pipe grouting plan was designed and implemented by our grouting engineers to consolidate perimeter walls around the proposed deep excavation using water-activated polyurethane resin.

Where possible, sleeve pipes were installed at a spacing of 18 inches apart to a depth of 10 feet around the perimeter of the proposed excavation. At locations where various obstructions precluded sleeve pipe installation, conventional open drill holes were systematically drilled and injected using down stage techniques to complete soil stabilization around the perimeter of the excavation.

Water-activated, low-viscosity polyurethane resin with low accelerator dosage was systematically injected by our grouting specialists at a flow rate of 1/2 gallon per minute through each sleeve pipe port and drill hole to effectively permeate and stabilize the surrounding soil.

Upon completion of soil stabilization grouting work, the general contractor was able to proceed with test cell excavation and foundation construction as planned without encountering any delays or problems.

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deep shaft construction jobsite toronto
By PW MME 0 Comments

Deep Shaft Construction through Quicksand Soil Conditions

Case description

Construction of a deep shaft for repair of the Coxwell Trunk Sewer encountered ultra-fine quicksand soil conditions at the interface between the original tunnel lining and shaft excavation that could not be dewatered using conventional well points.

Shaft wall construction consisted of secant piles down to the top of existing sewer tunnel, with subsequent jet grouting to close residual areas surrounding and beneath the existing sewer tunnel. Due to complex geometry at the shaft lining to tunnel lining interface, residual layers of ultra-fine soils remained under high hydrostatic water pressure that flowed into the shaft excavation and delayed construction work.

Solution

Based upon past experience with other similar projects, Peter White developed a drilling and grouting plan involving sodium silicate injection, in conjunction with the use of water-activated polyurethane resin, to systematically consolidate and stabilize water-bearing, ultra-fine soils so that shaft excavation could proceed in a safe and controlled manner.

Shaft excavation crews, with assistance from Peter White’s technical personnel, were able to successfully stabilize quicksand conditions and proceed with the remaining excavation work required to complete construction of the Coxwell Trunk Sewer Bypass.

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