compaction grouting in underground mine
By PW MME 0 Comments

Compaction grouting of underground sinkholes

Case description

A large underground gold mine encountered unstable ground conditions at the surface due to groundwater migration that resulted in the erosion of ground fault structures, widespread surface settlement and occurrence of sinkholes aligned with anomalous sub-surface soil/rock geometry.

Prior to engaging Peter White’s grouting engineering services, the mining company was relying upon a local contractor to mix and pump a high W:C ratio cement grout using bagged cement materials. This approach to cement grouting involved low productivity and low rates of cement placement.

Solution

The mining company immediately implemented the recommendations of Peter White and changed over to using low W:C ratio cement grout delivered from local batch plants using ready-mix trucks. This change resulted in an immediate and substantial increase in grouting productivity while reducing overall manpower requirement.

Additional grouting performance improvements were implemented through utilization of thixotropic admixtures to increase the cohesion of bulk cement grout mixtures as delivered from the batch plants.

Peter White subsequently provided suitable mix designs and trained local crews to undertake compaction grouting for critical areas of the site where surface settlement problems were evident.

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deep shaft construction
By PW MME 0 Comments

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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Publication Article

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

deep excavation for soil stabilization
By PW MME 0 Comments

Soil Stabilization for Deep Excavation

Case description

Defective sheet pile walls for a deep excavation project located on the shoreline of Burrard Inlet encountered frequent inrushes of water-bearing soils with development of adjacent sink holes that halted construction of a deep conveyor tunnel. Subsurface site conditions consisted of old dredging spoils from construction of the adjacent Lions Gate Bridge. After site work came to a standstill, our grouting engineer was called to the site to implement grouting operations that would enable site work to resume, as well to provide ongoing engineering support for completion of the remaining excavation work.

Solution

Peter White designed and supervised a $1 million sleeve pipe cement grouting operation to stabilize granular soil conditions beneath and adjacent to the planned deep excavation that enabled excavation work to resume “in the dry”. Supplementary grouting operations were undertaken using water-activated polyurethane resin and various cement grouting additives to tackle occasional inflows that occurred as excavation work proceeded.

Deep portions of the excavation exposed openings in the sheet pile wall, where adjacent sheet piles had split and at some locations where the excavation extended below the bottom of the sheet piles. In these circumstances, the pre-grouted ground conditions were self-supporting and impermeable.

With hands-on engineering support for grouting operations and deployment of various performance-enhancing grouting materials as required, the general contractor was able to complete deep excavation and conveyor tunnel construction as planned.

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test cell
By PW MME 0 Comments

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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