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Design Concept for a Deep Excavation at the Oak Island Money

Pit using the Ground Freezing Approach

Presentation byBert J Huls

Prepared by Les MacPhieAugust 13, 2005

Hosted by http://forum.oakislandtheories.com

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Purpose of Presentation

• A 70 ft diameter shaft was selected as the most likely option to investigate the bottom of the Money Pit

• Several options exist to sink such shaft. The decision of the best option has to be based on results from a prefeasibility engineering study. Options include ground freezing, grout injection, jet grouting, and dewatered caisson

• This presentation may attest that a viable option to carry forward to detailed design is ground freezing

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Outline of Presentation

1. Concept of the ground freezing (freeze ring) approach to shaft excavation

2. Case History 1 – Mill Creek Cleveland, Ohio3. Case History 2 – Aquarius Open Pit Timmins, Ontario4. Freeze ring concept for Oak Island shaft5. Conclusions

Shaft Forming cylinders

of frozen soil

Freeze Pipe (Typ.)

Shaft Shaft

Concept of Freeze Ring for Shaft Excavation

Freeze Pipe (Typ.)

Cylinders of frozen soil form

continuous wall

Excavation inside continuous frozen

wall

Freeze Pipe (Typ.)

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Typical Freeze Pipe Arrangement

Brine supply

Brine Return

Ground Surface

FrozenGround

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Monitoring of Freeze Wall

Frozen Soils

ShaftExcavation

TemperatureMeasuring Borehole

Thermocouple Probe (Typ)

FreezePipe

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Typical Freeze Wall Construction

Drilling

Tunnel thruFreeze Pipes

ConcreteLining

Excavation

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Typical Steps in Freeze Wall Design and Construction

1. Define subsurface conditions2. Design for freeze pipe length and spacing3. Installation of freeze pipes with measurement of lateral

drift4. Installation of extra freeze pipes to fill gaps5. Installation of temperature monitoring boreholes for

placement of thermocouples 6. Freezing of soil with circulation of chilled brine through

the freeze pipes7. When freezing complete, carry out pump test to check

that the freeze wall is continuous8. Have contingency measures available to supplement

ground freezing

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Outline of Presentation

1. Concept of the ground freezing (freeze ring) approach to shaft excavation

2. Case History 1 – Mill Creek Cleveland3. Case History 2 – Aquarius Open Pit Timmins4. Freeze ring concept for Oak Island shaft5. Conclusions

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Case History 1 Mill Creek ShaftCleveland Ohio (2001)

• Ground freezing selected over slurry wall, jet grouting and deep soil mixing

• Shaft 32 feet diameter and 215 feet deep, but freeze ring required only in soil and terminated at 140 feet, 10 feet into shale

• Freeze pipes at 4 foot spacing and set back 4.5 feet from shaft line

• Brine 1.27 SG, temperature in chillers as low as -36 deg C

• Ground frozen to about 8 feet thickness in 50 days, ground temperature –10 to –20 deg C

• Polyurethane insulation provided on wall of shaft excavation before placement of permanent concrete liner

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Mill Creek – Monitoring Arrangement

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Mill Creek Temperatu

reMonitoring

Data

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Mill Creek – Brine Pipe Details at Surface and Shaft Excavation

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Mill Creek – Trimming Frozen Soil

Cutter Head

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Outline of Presentation

1. Concept of the ground freezing (freeze ring) approach to shaft excavation

2. Case History 1 – Mill Creek Cleveland3. Case History 2 – Aquarius Open Pit Timmins4. Freeze ring concept for Oak Island shaft5. Conclusions

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Case History 2 Aquarius Gold Mine Project Timmins Ontario

• A freeze wall in the soil was selected to prevent drying up of local lakes and streams during pit dewatering

• World’s largest artificial freeze barrier, length 3.5 km (2 miles)

• Proposed open pit gold mine with 45 to 125 m (150 to 400 foot) pervious soil layer over ore body

• The freeze wall was designed to operate over the mine life of 8 years

• 1950 holes were drilled using 17 drill rigs

• After the ground was frozen the project was cancelled

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Outline of Presentation

1. Concept of the ground freezing (freeze ring) approach to shaft excavation

2. Case History 1 – Mill Creek Cleveland3. Case History 2 – Aquarius Open Pit Timmins4. Freeze ring concept for Oak Island shaft5. Conclusions

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Typical Engineering and Execution Stages for a Deep Excavation at Oak

Island1. Detailed site investigation2. Detailed design of works, develop specifications for

archaeological requirements and preparation of bid documents

3. Conceptual engineering on how to deal with the cavities towards the bottom of the pit, followed by detailed engineering of this aspect

4. Contract evaluation and award5. Shaft construction and archaeological investigation6. Time for project completion about 2 years

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Criteria for Freeze Ring and Shaft

1. Provide lateral support and prevent water inflow2. Allow archaeological investigation as the shaft

excavation proceeds3. Freeze ring to extend to a depth of 240 feet below

existing ground surface to achieve penetration of about 20 to 30 feet into competent anhydrite bedrock

4. Allowance to be made for lateral excavation beyond the limits of the freeze wall to follow man-made tunnels or chambers in bedrock

5. Shaft diameter at bedrock surface to be of sufficient diameter (70 feet) to include the location where the original Money Pit excavation extended below bedrock surface

6. Diameter of freeze ring at 200 feet depth to be of sufficient size to include most of the man-made chambers in bedrock

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Location and Diameter of Shaft – Option 1

ShaftDiameter70 feet

X

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Preliminary Design Concept for Freeze Ring and Shaft

1. Special procedures to be implemented where open (water filled) cavities are encountered since such zones cannot be successfully frozen

2. During drilling for freeze pipes the open (water filled) cavities in the till and broken anhydrite to be identified and filled with special grout paste to facilitate ground freezing

3. After setting the grout/foam section to be redrilled for installation of freeze pipes

4. Temperature monitoring during ground freezing and pump test to identify when freeze wall is complete

5. Install a permanent steel liner to support all soil and water pressures so that the frozen ground can be allowed to thaw when shaft excavation is completed

6. Provide permanent access for public viewing of in-situ or restored workings

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Design Concept for Grouting Open Cavities in Till or Broken Anhydrite

1. When an open (water filled) cavity is encountered during rotary drilling for freeze pipes, installation of the pipes will be delayed until the cavity is defined by further drilling and then filled with grout.

2. A special grout mix (includes cement, fly ash, salt saturated water and a biopolymer) is required to prevent bleeding (decomposition) of the grout in the saline groundwater and to minimize the extent of grout migration in the cavity.

3. Grout decomposition is prevented by using the salt saturated water (SG of 1.2) for the grout mix. Grout migration is limited by adding the biopolymer to obtain a thixotropic (quick set) effect. In certain conditions migration can be limited by pumping the grout into expandable geotextile bags.

4. There are numerous successful precedents for this procedure in grouting of voids at potash mines, coal mines and karstic limestone.

5. After the grout sets (4 to 7 days) the holes would be redrilled and the freeze pipes would be installed.

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Plan of Proposed Freeze Ring and Shaft at Money Pit

X

Freeze RingDiameter

70 feet inside86 feet outsideOutside

Diameter

of Shaft70 feet X

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Overview Section of

Freeze Ring

FreezeRing

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Freeze Ring

SectionFreezeRing

SpeculatedExcavationLimits in

Rock

Steel Linerfor Shaft

ExcavationBeyond

Freeze Wall

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Lateral Excavation Beyond Freeze Wall

1. Identify area of interest by nature of findings inside freeze ring

2. Extend freeze pipes laterally through the freeze ring to a configuration surrounding the area of interest

3. Create a frozen shell around the top, bottom, sides and end of the zone of interest

4. Verify complete freezing of the shell by relieving water pressure in the isolated zone and measuring response

5. Proceed with lateral excavation after successful test of water tightness

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Outline of Presentation

1. Concept of the ground freezing (freeze ring) approach to shaft excavation

2. Case History 1 – Mill Creek Cleveland3. Case History 2 – Aquarius Open Pit Timmins4. Freeze ring concept for Oak Island shaft5. Conclusions

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Conclusions

1. Generating a Freeze Rings is an established technology. Various successful examples can be quoted.

2. Conceptually, a freeze ring could be employed at Oak Island, but requires adaptation of specific grouting technology to deal with cavities through which water rushes, and which is connected to tidal motions.

3. Once a freeze ring has been created, it is feasible to construct a shaft to a depth of 200 feet at the Money Pit with appropriate control of water inflow

4. The technique of a vertical freeze ring can be adapted to bore horizontal tunnels from the chambers at the bottom of the pit, which will protrude the vertical freeze ring

5. The size and complexity of the project is not exceptional compared to recent and current successful projects of a similar nature in the mining and industrial sectors

6. The approach to excavation of a deep shaft can be developed to allow archaeological investigation thus maintaining the historical and archaeological integrity of Oak Island

7. The shaft excavation can be designed for conversion to a permanent public attraction with access to the bottom by elevator