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1 Design Concept for a Deep Excavation at the Oak Island Money Pit using the Ground Freezing Approach Presentation by Bert J Huls Prepared by Les MacPhie.

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Presentation on theme: "1 Design Concept for a Deep Excavation at the Oak Island Money Pit using the Ground Freezing Approach Presentation by Bert J Huls Prepared by Les MacPhie."— Presentation transcript:

1 1 Design Concept for a Deep Excavation at the Oak Island Money Pit using the Ground Freezing Approach Presentation by Bert J Huls Prepared by Les MacPhie August 13, 2005 Hosted by

2 2 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

3 3 Outline of Presentation 1.Concept of the ground freezing (freeze ring) approach to shaft excavation 2.Case History 1 – Mill Creek Cleveland, Ohio 3.Case History 2 – Aquarius Open Pit Timmins, Ontario 4.Freeze ring concept for Oak Island shaft 5.Conclusions

4 Shaft Forming cylinders of frozen soil Freeze Pipe (Typ.) 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.)

5 5 Typical Freeze Pipe Arrangement Brine supply Brine Return Ground Surface Frozen Ground

6 6 Monitoring of Freeze Wall Frozen Soils Shaft Excavation Temperature Measuring Borehole Thermocouple Probe (Typ) Freeze Pipe

7 7 Typical Freeze Wall Construction Drilling Tunnel thru Freeze Pipes Concrete Lining Excavation

8 8 Typical Steps in Freeze Wall Design and Construction 1.Define subsurface conditions 2.Design for freeze pipe length and spacing 3.Installation of freeze pipes with measurement of lateral drift 4.Installation of extra freeze pipes to fill gaps 5.Installation of temperature monitoring boreholes for placement of thermocouples 6.Freezing of soil with circulation of chilled brine through the freeze pipes 7.When freezing complete, carry out pump test to check that the freeze wall is continuous 8.Have contingency measures available to supplement ground freezing

9 9 Outline of Presentation 1.Concept of the ground freezing (freeze ring) approach to shaft excavation 2.Case History 1 – Mill Creek Cleveland 3.Case History 2 – Aquarius Open Pit Timmins 4.Freeze ring concept for Oak Island shaft 5.Conclusions

10 10 Case History 1 Mill Creek Shaft Cleveland 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

11 11 Mill Creek – Monitoring Arrangement

12 12 Mill Creek Temperature Monitoring Data

13 13 Mill Creek – Brine Pipe Details at Surface and Shaft Excavation

14 14 Mill Creek – Trimming Frozen Soil Cutter Head

15 15 Outline of Presentation 1.Concept of the ground freezing (freeze ring) approach to shaft excavation 2.Case History 1 – Mill Creek Cleveland 3.Case History 2 – Aquarius Open Pit Timmins 4.Freeze ring concept for Oak Island shaft 5.Conclusions

16 16 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 Worlds 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

17 17 Outline of Presentation 1.Concept of the ground freezing (freeze ring) approach to shaft excavation 2.Case History 1 – Mill Creek Cleveland 3.Case History 2 – Aquarius Open Pit Timmins 4.Freeze ring concept for Oak Island shaft 5.Conclusions

18 18 Typical Engineering and Execution Stages for a Deep Excavation at Oak Island 1.Detailed site investigation 2.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 award 5.Shaft construction and archaeological investigation 6.Time for project completion about 2 years

19 19 Criteria for Freeze Ring and Shaft 1.Provide lateral support and prevent water inflow 2.Allow archaeological investigation as the shaft excavation proceeds 3.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

20 20 Location and Diameter of Shaft – Option 1 Shaft Diameter 70 feet X

21 21 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

22 22 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.

23 23 Plan of Proposed Freeze Ring and Shaft at Money Pit X Freeze Ring Diameter 70 feet inside 86 feet outside Outside Diameter of Shaft 70 feet X

24 24 Overview Section of Freeze Ring Freeze Ring

25 25 Freeze Ring Section Freeze Ring Speculated Excavation Limits in Rock Steel Liner for Shaft Excavation Beyond Freeze Wall

26 26 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

27 27 Outline of Presentation 1.Concept of the ground freezing (freeze ring) approach to shaft excavation 2.Case History 1 – Mill Creek Cleveland 3.Case History 2 – Aquarius Open Pit Timmins 4.Freeze ring concept for Oak Island shaft 5.Conclusions

28 28 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


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