Projects

Case description

A new mine shaft was being constructed through deep overburden consisting of heavy clay layers on top of fractured bedrock.

The general contractor had driven sheet piles into bedrock and was in the process of excavating the shaft collar when soil migration was observed at the interface between sheet pile perimeter wall and underlying rock strata, resulting in a delay in construction.

The contractor was able to excavate within the shaft collar on day shift but overnight and on weekends, the surrounding clays would gradually seep through openings beneath the sheet piles and partially refill the shaft collar.

Solution

Vertical steel pipes were driven with the pile driver down to the bedrock interface around the outside of the sheet pile perimeter and a thick cement grout was injected to compact disturbed soil conditions and create stable lenses of cement grout at the overburden/rock interface. As compaction grouting progressed and increased grouting pressures were achieved, the vertical grout pipes were systematically raised to create columns of stable material within a few meters above the bedrock interface.

Following compaction grouting operations around the perimeter of the shaft collar, the general contractor was able to complete shaft collar excavation to bedrock interface without further creep of surrounding clay materials and to proceed with shaft collar construction.

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Case description

A property developer acquired two adjacent buildings in the SoHo area of New York and was in the process of constructing new roof-top penthouse and adjacent structures.

To support the additional structural building loads, building design engineers required that soil conditions beneath the existing 90-year-old building foundations be improved by soil grouting operations.

The geotechnical contractor engaged by the property developer retained Peter White to design the cement grouting operation, provide rental cement grouting equipment and accessories and to supervise the startup of grouting operations by the contractor’s personnel.

Solution

As anticipated, drilling quickly revealed that foundation conditions were not as shown on the original construction drawings, so the contractor’s drilling and grouting methodology was quickly adapted by Peter according to the existing site conditions.

Cement grouting was successfully undertaken using microfine cement to achieve satisfactory penetration and consolidation of the existing foundation soils without causing uplift or damage to the existing building structures.

The cement grouting equipment selected for this project was small and portable for moving through various sub-basement rooms where grouting operations were undertaken but with appropriate discharge volume and pressure for the encountered site conditions.

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Case description

Building the Antamina mine in Peru required the construction of a 1,000 m long x 130 m high concrete-face, rock-fill tailings starter dam to impound water for start-up of milling operations and for subsequent retention of tailings.

The sedimentary bedrock geology consisted of siltstones and mudstones with interbedded limestone layers, including various discontinuities such as faults and open joints.

The grout curtain for the tailings starter dam required 40,000 m of drilling and injection of 2,800 tonnes of cement.

It was critical that the grout curtain be completed to the required performance standards prior to the winter rainy season to impound sufficient water for startup of the mill.

The project engineers were concerned that the dam contractor did not have sufficient expertise and resources to accomplish the required scope of grouting work on schedule and retained Peter White to provide ongoing technical support for the contractor’s grouting operations.

Solution

Working with the owner’s engineering team and the contractor’s construction crews, Peter White was involved in all aspects of the tailings starter dam grout curtain, providing hands-on direction of grouting operations being undertaken by various specialty subcontractors.

In addition, Peter quickly designed and site-fabricated real-time grout monitoring equipment with computer-based data collection to provide relevant grouting and water testing information for review and analysis by the project engineering team.

After months of around-the-clock drilling and grouting work, the tailings starter dam grout curtain was successfully completed on schedule in advance of the winter rainy season. The Antamina mill was commissioned on schedule the following year.

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Case description

As part of the remediation of the Sydney Tarponds and Coke Ovens site, two large-diameter concrete drainage pipes were to be decommissioned by filling with low-strength cement grout.

Solution

A general contractor contacted Peter White for engineering assistance to develop a grouting plan and to prepare a list of required equipment and bill of materials for decommissioning of two drainage pipes.

Peter recommended a low-strength cement-bentonite grout mixture for this application to complement existing grouting equipment owned by the contractor.

Bentonite slurry was prepared in advance and hydrated overnight using a series of portable plastic tote tanks.  Decommissioning operations were accomplished under Peter’s supervision using diaphragm pumps to transfer bentonite slurry to the grouting plant where dry cement was mixed and the resulting cement-bentonite mixture pumped to fill the respective concrete drainage pipes.

The general contractor’s crews successfully completed cement-bentonite work within each pipe at a high rate of production, completely filling each pipe within a few hours.  The cement-bentonite grout produced a stable, thixotropic and cohesive mixture.

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