Presentation on theme: "Presentation by Bert J Huls Prepared by Les MacPhie August 13, 2005"— Presentation transcript:
1Presentation by Bert J Huls Prepared by Les MacPhie August 13, 2005 Design Concept for a Deep Excavation at the Oak Island Money Pit using the Ground Freezing ApproachPresentation byBert J HulsPrepared by Les MacPhieAugust 13, 2005Good afternoon ladies and gentlemen.I would like to first start off with a confession, which is that I do not profess to be a mining engineer with deep knowledge abour mining technologies, let alone the freeze ring concept.I am, however, associated with the mining industry for over 28 years, but as a metallurgical engineer. For the last 12 years I have been enployed by the biggest mining company inthe world, BHPBilliton, but certainly I am not here in an official capacity for this company. Any questions that you may have after this presentation can probably be answered by Les MacPhie.This presentation is being delivered to help a friend in need, and also, because i have become interested in the Oak Island quest, having read the material of previous excavation attempts and the treasure to be discovered.Hosted by
2Purpose of Presentation A 70 ft diameter shaft was selected as the most likely option to investigate the bottom of the Money PitSeveral 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 caissonThis presentation may attest that a viable option to carry forward to detailed design is ground freezingIn his presentation, Les MacPhie offered one concept for further exploration, which is sinking a shaft to sufficient depth that allows exploration of the cavities at the bottom of the Money Pit. The shaft dimension would be 70 feet in diamter and 200 feet deep, down to bedrock.
3Outline of Presentation Concept of the ground freezing (freeze ring) approach to shaft excavationCase History 1 – Mill Creek Cleveland, OhioCase History 2 – Aquarius Open Pit Timmins, OntarioFreeze ring concept for Oak Island shaftConclusionsSo, how am I going to introduce you to a proper ground preparation methodology for shaft sinking, and why would we contemplate such a thing?As noted by earlier explorers, sinking a shaft in this terrain posed its problems , primarily through water rushing into any excavation. Graham Harris and Les MacPhie in their book indicated that continuing on this premise is hazardous, if not impossible.In northern Ontario and Quebec, and around the Great Lakes in Wisconsin, mining boys have demonstrated that a freezing ring could be employed around a proposed shaft area. As a matter of fact, when I was in the Rouyn area last week, I was told that a 100 m diameter freezing ring was employed around the Casa Berardi shaft. In fact, easily reference can be found to at least 15 examples of freeze ring installations, up to a diameter of about 1 km! And up to 125 m (nearly 400 ft) deep. Typically, this is being done to avoid continual pumping of mine water from the botom of the shaft, or to avoid environmental contamination outwards.A freeze ring is exactly what is proposed for Oak Island. At Oak island we would like to arrest the incoming water flow, so that at ease the explorers can investigate in the cavities at the bottom of the Money Pit. In this presentation, I would like to show you how this can be done, while showing some pictures on the way may allow you to visualize the concept.
4Concept of Freeze Ring for Shaft Excavation Excavation inside continuous frozen wallCylinders of frozen soil form continuous wallForming cylinders of frozen soilFreeze Pipe (Typ.)Freeze Pipe (Typ.)Freeze Pipe (Typ.)The concept is easy to understand: Drill a number of holes into the ground at a distance of say 1 m, make the holes become very cold to allow freezing of the ground around the holes to set in. Like a deep winter, it establishes a permafrost in the ground at depth.Around each pipe we will get a ring of frozen ground, that will grow with continued freezing. Eventually the rings around each hole will connect. We will allow this connection to become very thick, and voilá we will establish a ring of frozen ground around an unforzen core. After we are satisfied that the freeze ring has attained the specified thickeness, a shaft can be sunk in its center.
5Typical Freeze Pipe Arrangement Brine supplyBrine ReturnGround SurfaceFrozenGroundThis slide shows a typical freeze arrangment. Freezing works like a heat exchanger. Brine of –35 C is injected and will create a temperature sphere of –30C at the bottom of the injection pipe, then returns to the chiller at the surface. Depending on various factors, it may take months to freeze the surrounding soil.John Wannacott made a cost estimation of about $ 15M to effect a freeze ring.
6Monitoring of Freeze Wall TemperatureMeasuring BoreholeThermocoupleProbe (Typ)FreezePipeShaftExcavationFrozen SoilsAt a certain distance from the injection hole (set by the desired thickness of the freeze wall, pilot holes will be drilled containing stagnant brine. Thermocouples placed in those holes will measure the temperature in the pilot hole, thus confirming the thickness of the freeze wall from the injection hole. Typically, pilot holes will be placed at six locations around the shaft, thus 12 holes in total.
7Typical Freeze Wall Construction DrillingExcavationIn the top left picture we see how holes are being drilled from a drill truck, and how the freeze pipes are being installed. You will understand that these pipes require a safe connection so that there is no leakage at the joints. Typically, this connection is established trhough welding the pipes together, rather than flanging.The picture on the top right shows the excavation of the shaft after the freeze ring has been established. As indicated on the previous slides, proper monitoring has established the thickeness of the freeze wall, as well as its continuity. On that, later some further explanation. In this picture you see work men shaving the wall to roundness. The white spots on the wall indicate frozen soil.In some applications, the shaft, once sunk, is fitted with a concrete liner that will keep out the water, as shown in the bottom left picture. In such occasions, the concrete will then further hold out the water, and the freeze ring could be shut down. I think the concept for Oak island would be to place a permanent steel liner.The picture on the bottom right shows how a tunnel is being driven through the freeze wall. This is an application that we would also consider at Oak Island to explore the spaces at the bottom of the Money Pit, as we will see later. For the Oak island case, we would likely want to establish a horizontal freeze wall around the tunnel, which can be established by drilling horizontal holes from the bottom of the shaft, and installaing freeze pipes horizontally.Tunnel thruFreeze PipesConcreteLining
8Typical Steps in Freeze Wall Design and Construction Define subsurface conditionsDesign for freeze pipe length and spacingInstallation of freeze pipes with measurement of lateral driftInstallation of extra freeze pipes to fill gapsInstallation of temperature monitoring boreholes for placement of thermocouplesFreezing of soil with circulation of chilled brine through the freeze pipesWhen freezing complete, carry out pump test to check that the freeze wall is continuousHave contingency measures available to supplement ground freezingItem 7: Measuring the continuity of the freeze wall is accomplished by placing 3 piezometers at 120 degrees around the outside of the freeze wall, and on water well in the middle of the location where the shaft will be sunk. Water may rise inside the water well. Proof of continuity is delivered if the water level in the three piezometers does not drop or drops little when pumping water from the center water well. A separate slide may be made to show this (Les).Item 8: Contingency measures may be (1) time (allowing the formation of a thicker wall) or (2) the insertion of more freeze pipes to widen the area of influence from brine cooling
9Outline of Presentation Concept of the ground freezing (freeze ring) approach to shaft excavationCase History 1 – Mill Creek ClevelandCase History 2 – Aquarius Open Pit TimminsFreeze ring concept for Oak Island shaftConclusionsSo, let’s talk about a few actual case histories.
10Case History 1 Mill Creek Shaft Cleveland Ohio (2001) Ground freezing selected over slurry wall, jet grouting and deep soil mixingShaft 32 feet diameter and 215 feet deep, but freeze ring required only in soil and terminated at 140 feet, 10 feet into shaleFreeze pipes at 4 foot spacing and set back 4.5 feet from shaft lineBrine 1.27 SG, temperature in chillers as low as -36 deg CGround frozen to about 8 feet thickness in 50 days, ground temperature –10 to –20 deg CPolyurethane insulation provided on wall of shaft excavation before placement of permanent concrete linerIn the greater Cleveland area there was need for underground storm and sewer system. The shafts were built for the purpose of diverting water flow to the tunnel system. The reason why a freeze wall methodology was selected for Mill Creek was to provide a strong shaft support structure to resist soil and groundwater pressures. The shafts were to be located in a buried ancient glacial valley, meaning loose soil structure and boulders (130 feet of glacial sand with boulders then shale bedrock, water level at 7 feet depth). Concern was vertical alignment due to boulder obstructions and concern for maintaining vertical alignment.The top picture shows the top of the freezing pipes, which are spaced at 4 feet, and at a diameter of 41 feet. The 4.5 ft from the shaft line will allow a freeze ring thickness of 8 feet. Further can be seen two manifold pipes for the brine movement in and out the holes. Two temperature monitoring stations are visible, and we wil talk about that in the next slide.The botom picture shows the top of the shaft.
11Mill Creek – Monitoring Arrangement It is evident that the temperature must be monitered to measure the rate of growth of the freeze ring wall, and the temperature of the frozen soil. Around the shaft, six full depth temperature monitors were installed, each consisting of six individual thermocouples. Note that the location of the thermometers is not at equidiametrical distance form the center of the ring.The next slide show the temperature drop of the soil measured by thermocouple 25A, which is outside the freeze ring
12Mill Creek Temperature Monitoring Data Plots show temperature drop per day over a 24-day period. The point at which the measurements were made is outside the freeze ring. After 24 days the temperature at the top is still above 0, indicating that the freeze wall is not yet quite set.Most importantly is to note that freezing starts at the bottom. For the Money Pit this will be of relevance as further excavations will be made at the bottom, where we would like to see the thickest walls. In addition, from the bottom of the sunken shaft the plan is to drill horizontal tunnels if required, after creating a horizontal freeze wall. This is done by injection of brine into the horizontal injection holes at the bottom, a similar process as for preparing the soil for sinking the shaft.
13Mill Creek – Brine Pipe Details at Surface and Shaft Excavation Again, here are a few more pictures of the Mill Creel installation. The top left picture shows the two manifolds for the brine flows.The soft core was excavated with a backhoe equipped with a 2-yard bucket, as shown on the top right silde. Ice crystals in the wall from the exposed freeze ring are clearly visible in this picture.Mucking was completed utilizing a crane to hoist a skip box, as shown on the bottom right picture.After trimming was complete, which was first done with a small road header, the workmen constanlty applied a layer of polyurethane insulation on the wall as can be seen in the bottom left picture.
14Mill Creek – Trimming Frozen Soil Cutter HeadThe cutter head of the roadheader consists of two moving bits that trim the inside of the frozen ring by chipping off ice crystals. The diagram on the left makes it clear why trimming is necessary.
15Outline of Presentation Concept of the ground freezing (freeze ring) approach to shaft excavationCase History 1 – Mill Creek ClevelandCase History 2 – Aquarius Open Pit TimminsFreeze ring concept for Oak Island shaftConclusions
16Case 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 dewateringWorld’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 bodyThe freeze wall was designed to operate over the mine life of 8 years1950 holes were drilled using 17 drill rigsAfter the ground was frozen the project was cancelledAt the proposed Echo Bay mine site, the water table was high. The primary objective of the freeze ring was to prevent a massive inflow of ground water. Again for this project a CaCl2 brine (5000 tons) was to be used to refrigerate the soil to –20C. Cooling was achieved by hp compressors (Poetsch process) (9 MW), which is similar as for making hockey rinks. It took about 20 weeks to freeze the soil. In this case, the system was planned to be operational for 8 years.
17Outline of Presentation Concept of the ground freezing (freeze ring) approach to shaft excavationCase History 1 – Mill Creek ClevelandCase History 2 – Aquarius Open Pit TimminsFreeze ring concept for Oak Island shaftConclusions
18Typical Engineering and Execution Stages for a Deep Excavation at Oak Island Detailed site investigationDetailed design of works, develop specifications for archaeological requirements and preparation of bid documentsConceptual engineering on how to deal with the cavities towards the bottom of the pit, followed by detailed engineering of this aspectContract evaluation and awardShaft construction and archaeological investigationTime for project completion about 2 yearsThis slide describes typical engineering stages for a deep shaft and the sequence of the process.As a note, the preferred route may well be grouting the walls and cavities from top to bottom. Also, the freeze ring may not be required for the top end of the shaft as this ground is very competent.
19Criteria for Freeze Ring and Shaft Provide lateral support and prevent water inflowAllow archaeological investigation as the shaft excavation proceedsFreeze 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 bedrockAllowance to be made for lateral excavation beyond the limits of the freeze wall to follow man-made tunnels or chambers in bedrockShaft diameter at bedrock surface to be of sufficient diameter (70 feet) to include the location where the original Money Pit excavation extended below bedrock surfaceDiameter of freeze ring at 200 feet depth to be of sufficient size to include most of the man-made chambers in bedrock
20Location and Diameter of Shaft – Option 1 XShaftDiameter70 feetNote that the proposed shaft encloses the main workings near the Money Pit: The Money Pit itself, and the Chappell and Hedden shafts. So it should be wide enough to circumference the slightly unsure location of the Money Pit and anything of interest in its immediate surrounding. Obviously, the freeze ring is offset to this shaft ring by at least 4 to 5 feet to allow fro freeze ring wall thickness.
21Preliminary Design Concept for Freeze Ring and Shaft Special procedures to be implemented where open (water filled) cavities are encountered since such zones cannot be successfully frozenDuring 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 freezingAfter setting the grout/foam section to be redrilled for installation of freeze pipesTemperature monitoring during ground freezing and pump test to identify when freeze wall is completeInstall 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 completedProvide permanent access for public viewing of in-situ or restored workingsThe important aspect of these criteria is the planned lateral excavation. This will become clearer when we look at some cross sections of the area to be excavated in the following slides. It refers to the horizontal tunneling through the freeze wall, although horizontal freeze walls may have to be established to support tunnel excavation.An important aspect that must be noted that the freeze ring concept has only been proven for soils that have adequate saturation for ground freezing. Usually, soils below the groundwater table have a degree of saturation of greater than 90 percent that is required for ground freezing to work. For example, at Mill Creek workmen first tried to freeze soil above the groundwater table that contained only 7 % moisture content, and they failed. A plate/rb installation was required to stabilize the soil for any shaft sinking. The minimum mositure content is 10 percent (equivalent to about 70 % degree of saturation).On the reverse side, at Oak Island we have to contend with “open” waterflows, which in addition, are tidal. These can not be frozen, therefore an alternative method must be developed. Success was reported on grouting open cavities, while we could also think of injecting polyurethane foam to temporarily block the cavity and support the closure of the gap by fast-setting grout.In an earlier slide I already discussed how the completeness of the freeze wall is to be monitored.A permanent access for public viewing is a neat concept. It could become part of an all-rounded museum for the site as a tourist attraction.
22Design Concept for Grouting Open Cavities in Till or Broken Anhydrite 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.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.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.There are numerous successful precedents for this procedure in grouting of voids at potash mines, coal mines and karstic limestone.After the grout sets (4 to 7 days) the holes would be redrilled and the freeze pipes would be installed.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.Based on industry experience, a special grout mix is required to prevent bleeding (decomposition) of the grout in the saline groundwater and to minimize the extent of grout migration in the cavity. The special grout mix includes cement, fly ash, salt saturated water and a biopolymer
23Plan of Proposed Freeze Ring and Shaft at Money Pit Diameter70 feet inside86 feet outsideOutsideDiameterof Shaft70 feetXXAn important note to take away of this pictorial is that the freeze ring will enclose the manmade chambers in the rock at the bottom of the shaft. This can be seen on the next slide.
24Overview Section of Freeze Ring The freeze ring will extend to below the bedrock to ensure that there is a seal for the ground water. The essence of this slide is that the freeze ring will enclose the man made cavities in the rock. It will cut off water inflow from the flood tunnel and underground connection to shaft 10X and Mahone Bay. Herein lies the tricky part of this design, Typically, the freeze ring will not freeze free water, especially not if connected to tidal motions. Conceptual engineering, followed by trials are required to determine the most pratcial and economic method of sealing those cavities.Note that depth of competent bedrock is at 210 ft, compared to 200 ft on the following slide, which is related to the new datum ground surface established in 1965.
25Freeze Ring Section Freeze Ring Steel Liner for Shaft Speculated ExcavationLimits inRockThe essence of this slide is that the shaft will be sunk to the depth of the speculated excavation limits in the rock. At that point further digging will take place to remove sticks and puddled clay down to the horizontal level from where we expect to dig horizontal tunnels. First these will expand in different directions, as we expect will be indicated by the expected presence of the chambers. Then these tunnels may be extended through the freeze ring, but only after creating a horizontal freeze ring, which is to be deployed in similar manner as done to sink the shaft.This slide also better shows the open cavities or very loose soil through which water flows.ExcavationBeyondFreeze Wall
26Lateral Excavation Beyond Freeze Wall Identify area of interest by nature of findings inside freeze ringExtend freeze pipes laterally through the freeze ring to a configuration surrounding the area of interestCreate a frozen shell around the top, bottom, sides and end of the zone of interestVerify complete freezing of the shell by relieving water pressure in the isolated zone and measuring responseProceed with lateral excavation after successful test of water tightnessThis slide summarizes the sequential steps for boring horizontal tunnels within a horizontal freeze ring.
27Outline of Presentation Concept of the ground freezing (freeze ring) approach to shaft excavationCase History 1 – Mill Creek ClevelandCase History 2 – Aquarius Open Pit TimminsFreeze ring concept for Oak Island shaftConclusions
28ConclusionsGenerating a Freeze Rings is an established technology. Various successful examples can be quoted.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.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 inflowThe 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 ringThe 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 sectorsThe approach to excavation of a deep shaft can be developed to allow archaeological investigation thus maintaining the historical and archaeological integrity of Oak IslandThe shaft excavation can be designed for conversion to a permanent public attraction with access to the bottom by elevator