Mechanical Ice Drilling Technology

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The annual layers within the ice are very flat, easy to interpret. Near bedrock, meters below the surface, the ice should easily be 40, years old.

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The West Antarctic Ice Sheet WAIS once extended over top of this site, but since the end of the last ice age has retreated to the southeast some kilometers 1. Conway et al. Ice streams around the Ross Sea. Note the slow-flowing ice on Roosevelt Island. The WAIS has been a major focal point for Antarctic research since international programs were initiated during the International Geophysical Year, with intensified interest since the s when it was hypothesized that the WAIS may be prone to collapse if support from its bounding ice shelves were removed 2.

Mercer, ; 3. Bindshadler, ; 4. Joughin and Alley, This core provides a record at unprecedented resolution spanning 68, years 5. WAIS Divide project members, Roosevelt Island is at the terminal end of the WAIS system, and an ice core from this site will provide new spatial information about climate in West Antarctica. Building this camp, selecting a drill site, and installing the drill has taken three years planning and equipment development spanned nearly a decade. The deep borehole was initiated during the austral summer, using a newly-built electromechanical ice coring drill manufactured in New Zealand.

Drilling an ice core is not unlike drilling a hole to install a doorknob, though there are a few complications after all, the door in this metaphor is hundreds to thousands of meters thick. Since we want to retrieve core samples and not just destructively bore our way through the ice sheet, our drill has to be hollow.

It turns out that, especially at a low-elevation site like Roosevelt Island, keeping the ice cores cold is a big challenge! Since this is one of the primary interests in ice cores—measuring ancient samples of atmospheric gases like carbon dioxide and methane—we have to store and ship the ice cores at low temperatures.

The solution to this problem is an ironic one—we bring a freezer with us to Antarctica! The ice cores are stored in a snow cave dug about meters below the surface, and ducts are plumbed into the cave to circulate air through the freezer unit. Loading boxes of ice into the airplane for their trip back to Scott Base. The next step in the process is to get an airplane to come out and pick up the ice cores! When the weather is cooperative enough for this to happen we once waited three weeks , the plane is loaded up and takes off with a heavy load of ice.

A few hours later, the ice cores are unloaded from the plane and put into a mobile freezer on a big sled, to be towed back to Scott Base where yet another freezer container sits. This is the final container that eventually will be shipped by oceangoing vessel back to New Zealand! In January, after nearly another month of cleanup, taking things apart, and packing equipment into boxes for shipment home or for storage over the winter, we hitch a ride off the island and follow our ice cores home to New Zealand.

To retrieve a core, an annulus of ice must be removed from around the cylindrical core. Once the core is removed, the core barrel is lowered to the bottom of the hole and reattached to the drill. Over a depth range known as the brittle ice zone, bubbles of air are trapped in the ice under great pressure. When a core is brought to the surface, the bubbles can exert a stress that exceeds the tensile strength of the ice, resulting in cracks and spall.

The bubbles disappear, and the ice becomes stable again.

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The brittle ice zone typically returns poorer quality samples than for the rest of the core. Some steps can be taken to alleviate the problem. Liners can be placed inside the drill barrel to enclose the core before it is brought to the surface, but this makes it difficult to clean off the drilling fluid. In mineral drilling, special machinery can bring core samples to the surface at bottom-hole pressure, but this is too expensive for the inaccessible locations of most drilling sites.

Keeping the processing facilities at very low temperatures limits thermal shocks. Extruding the core from the drill barrel into a net helps keep it together if it shatters. Brittle cores are also often allowed to rest in storage at the drill site for some time, up to a full year between drilling seasons, to let the ice gradually relax. A percussion drill penetrates ice by repeatedly striking it to fracture and fragment it.

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The cutting tool is mounted at the bottom of the drill string typically connected metal rods [note 1] , and some means of giving it kinetic energy must be provided. A tripod erected over the hole allows a pulley to be set up, and a cable can then be used to repeatedly raise and drop the tool. This method is known as cable tool drilling. A weight repeatedly dropped on to a rigid drill string can also be used to provide the necessary impetus. It can be collected with a tool capable of scooping it from the bottom of the hole, [23] or the hole can be kept full of water, so that the ice floats to the top of the hole, though this retards the momentum of the drill striking the ice, reducing its effectiveness.

To do this efficiently with manual labour, it is usual to set up a tripod or other supporting scaffold, and a pulley to allow the drill string to be raised by a rope. This arrangement, known as a cable-tool rig, can also be used for mechanical drilling, with a motor raising the drill string and allowing it to fall. The earliest scientific ice drilling expedition used percussion drilling; Louis Agassiz used iron rods to drill holes in the Unteraargletscher , in the Alps , in the summer of Two other percussion methods have been tried.

Pneumatic drills have been used to drill shallow holes in ice in order to set blast charges, and rotary percussion drills, a type of drilling tool once in common use in the mining industry, have also been used for drilling blasting holes, but neither approach has been used for scientific investigations of ice. Percussion drilling is now rarely used for scientific ice drilling, having been overtaken by more effective techniques for both ice and mineral drilling.

A soil sampling auger contains a pair of blades at the bottom of an enclosed cylinder; it can be driven and rotated by hand to pick up soft soil. Figure 4 Ice auger with offset brace handle Andreaze, public domain. Augers have long been used for drilling through ice for ice fishing.

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Augers can be rotated by hand, using a mechanism such as a T handle or a brace bit, or by attaching them to powered hand drills. Augers have a helical screw blade around the main drilling axis; this blade, called the "flighting", carries the ice cuttings up from the bottom of the hole. With a platform such as a stepladder, a longer auger can be rotated from higher off the ground. Commercially available ice augers for winter fishing, powered by petrol, propane, or battery power, are available for hole diameters from 4.

For holes deeper than 2 m a tripod can be used to winch the auger from the hole. A folding brace handle with an offset design is common; this allows both hands to contribute to the torque.

Figure 5 Coring ice auger with no barrel. Designs like this proved difficult to make sufficiently rigid. Augers that are capable of retrieving ice cores are similar to noncoring augers, except that the flights are set around a hollow core barrel. Augers have been devised that consist of the helical cutting blades and a space for a core, without the central supporting cylinder, but they are difficult to make sufficiently rigid.

Coring augers were originally designed to be manually rotated, but over time they have been adapted for use with handheld drills or small engines. As with noncoring augers, extensions can be added to drill deeper.

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Drilling deeper than 6 m requires more than one person because of the weight of the drill string. A clamp placed at the surface is useful for supporting the string, and a tripod and block and tackle can also be used for support and to increase the weight of string that can be handled.

As the drill string gets longer, it takes more time to complete a trip to extract a core, since each extension rod must be separated from the drill string when tripping out, and re-attached when tripping in. Drilling with a tripod or other method of handling a long drill string considerably extends the depth limit for the use of a coring auger.

Usually a hole deeper than 30 m will be drilled with other methods, because of the weight of the drill string and the long trip time required. Modern coring augers have changed little in decades: an ice coring auger patented in the US in closely resembles coring augers in use eighty years later.

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The Prairie Dog auger, designed in , adds an outer barrel to the basic coring auger design. Cuttings are captured between the auger flights and the outer barrel, which has an anti-torque section to prevent it from rotating in the hole. IDDO also provides a lifting system for use with hand augers, known as the Sidewinder.

It is driven by an electric hand drill, which can be powered by a generator or by solar cells.

This extends the maximum practical depth for hand augering to about 40 m. Sidewinders have proved popular with researchers. A piston drill consists of a flat disc at the bottom of a long rod, with three or four radial slots in the disc, each of which has a cutting edge. The rod is rotated by hand, using a brace handle; the ice comes through the slots and piles up on top of the disc.

Pulling the drill out of the borehole brings the cuttings up on the disc. In the s some patents for piston drill designs were filed in Sweden and the U. They are less efficient than auger drills, since the drill must be periodically removed from the hole to get rid of the cuttings. Some hand drills have been designed to retrieve cores without using auger flights to transport the cuttings up the hole. These drills typically have a core barrel with teeth at the lower end, and are rotated by a brace or T-handle, or by a small engine.

The barrel itself can be omitted, so that the drill consists only of a ring with a cutting slot to cut the annulus around the core, and a vertical rod to attach the ring to the surface. A difficulty with all these designs is that as soon as cuttings are generated, if they are not removed they will interfere with the cutting action of the drill, making these tools slow and inefficient in use.

Rotary rigs used in mineral drilling use a string of drillpipe connected to a drillbit at the bottom of the hole, and to a rotary mechanism at the top of the hole, [87] such as a top drive [88] or rotary table and kelly. These projects have usually been undertaken with commercially available rotary rigs originally designed for mineral drilling, with adaptations to suit the special needs of ice drilling. When drilling in ice, the hole may be drilled dry, with no mechanism to dispose of the cuttings.