Shot Hole Drill
As part of the International Polar Year, Penn State University researchers in conjunction with the Center for the Remote Sensing of Ice Sheets (CReSIS) conducted a study of the Thwaites Glacier in West Antarctica. Using geophysical methods, the researchers are studying the vulnerability of this little studied region of the West Antarctic ice sheet to sea level rise and a warming climate. The researchers call on active source seismology, using acoustic waves that travel down through ice and reflect back from the internal layers and the ice-rock interface. The success of the project is determined by the performance to the equipment in the harsh polar environment. PSL, in collaboration with the UW Space Science and Engineering Center, constructed a reliable and transportable hot water drill. Related to this work, PSL also built a drill that works by cutting the ice, instead of melting it. Called the Shot Hole Drill, this drill works faster than previous options and is used for drilling more holes to shallower depths. These and other similar drills give researchers many tools for placement of equipment as dictated by conditions and by the goals of the study.
PSL has designed and manufactured the shot hole drill for the UW-Madison Ice Coring and Drilling Services (ICDS). ICDS provides ice coring and drilling services to NSF-sponsored researchers of polar regions and high altitude sites.
ICDS principal investigator Charles Bentley outlined the scope of the research and provided the specifications for a new drilling device. There are glacial ice flows that move faster than others. This experiment will examine if it is the type of geological mass underneath an ice flow that causes or contributes to its faster movement. Small explosive charges will be dropped into a set pattern of holes in the ice. Researchers will study the reflections recorded by seismic sensors during each explosion. Because of limited good drilling weather in the Antarctic, the several hundred holes required need to be done quickly, perhaps drilling up to 20 holes a day. The depth of each hole (75 m) requires a drilling rate in ice at a rate of 2 meters per minute.
PSL engineer Bill Mason took up the challenge of designing a drill that was fast, easily moved from one site to the next, and could withstand constant use over a very short period of time. The drill bit was also an engineering challenge. It had to be very reliable, not getting jammed up with ice chips. Three types of drill heads have been designed and prototypes built. This drilling system is the first of its kind. The drill body is 10 cm in diameter and 150 cm in length and is made from steel with tungsten for added weight. The high-speed drill is driven by air-powered turbines. An air hose suspends the drill over the ice and provides air at high pressure. The ice chips are blown out of the hole by the high flow rate of air. During development PSL engineer Lee Greenler did airflow and pressure analyses to determine how much air and pressure would give the needed speed. Two large air compressors outfitted on skis for mobility generate the needed pressurized airflow. A big hose reel winch was also designed to hold the 100 meters of hose. PSL engineer Jim Hoffman designed the control system for the winch.
The shot hole drill was built and assembled by PSL instrument makers. Bill Mason wanted to test this one of a kind drilling system. PSL purchasing staff tracked down a supply of ice, the largest size available being a block weighing 300 pounds (136kg). Six blocks were delivered one sunny day in early September 2001. The shot hole drill system was moved out into the back lot of PSL for several test runs. Representatives of ICDS along with PSL staff onlookers were there to witness the tests. It was a spectacular sight. The drill ran without problems. Ice chips were flying. The only disappointing moment was when the ice block cracked before the drill got deep enough to test the built in stabilizer control system. The ice block was too small and it had gotten warm sitting out in the sunshine. Here is an image of the drill under test on a block of ice near PSL, and a close up of the ice block.
The shot hole drill was disassembled, packed and shipped from PSL in a spool section and compressor and frame sections to McMurdo Station in Antarctica where it arrived in late October 2001. In mid-November, Bill Mason went to McMurdo to reassemble the drill system and to make sure it was operational. The past Antarctic summer (winter in the northern hemisphere) was a test season for the shot hole drill system. ICDS drillers tested the drill and different drill bits in ice near McMurdo. Here it is being transported from one location to another. The following year it will be moved to the actual research site near the South Pole.
The shot-hole drill was developed to allow geophysicists to obtain data relating to the dynamics of ice flows in West Antarctica. The scientists will do this by placing explosive charges in the holes drilled with the shot-hole drill and measuring the behavior of the seismic waves generated in the ice by the explosions. The holes were scheduled to be drilled during the months of December and January of 2002-2003 on icestream “D” and again during the months of December and January of 2003-2004 on icestream “C”. During each of the drilling seasons the drill will be used to drill between 600 and 650 holes about 200 meters apart. The holes will be 75 to 100 meters deep.
The drill was designed and built under a contract between the University of Wisconsin’s Ice Coring and Drilling Services (ICDS) and the National Science Foundation (NSF). ICDS has the responsibility to maintain the drill and to provide drilling personnel for its use.