United States Department of Transportation
i
New Excavation Technologies for Underground Construction: Linear Cutting Machine Tests on Microwave-Irradiated Granodiorite
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2018-03-24
[PDF-10.39 MB]
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Edition:Final Project Report
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Abstract:Recent breakthroughs in thermally induced rock fragmentation research indicate the feasibility of utilization of microwaves during rock excavation and tunneling. Unfortunately, few studies have been conducted to systematically assess energy requirements if these emerging technologies were implemented. Additional potential payoffs from the development of such excavation technologies include minimal disturbance to neighboring infrastructure during excavation. The main challenge with current excavation techniques is that it is extremely expensive to break up and move large volumes of rock during blasting, drilling or mechanical excavation in difficult rock. The objective of this project is to measure the specific energy requirements for representative hard rock which has been weakened by microwave irradiation. Granodiorite rock blocks were collected from Boulder, Colorado and prepared at a local quarry. Three of the rock blocks were placed inside a commercial microwave and heated for 30 seconds, 100 seconds and 200 seconds. The four blocks were cast in concrete inside a fabricated metallic box and allowed to cure at the Earth Mechanics Institute (EMI) at Colorado School of Mines. Large scale linear cutting tests were conducted on the four blocks using a single disc cutter. During each linear cutting pass, displacements, horizontal and vertical cutting forces were measured by a computer monitoring system connected to the large scale linear cutting machine. The specific energies required during each cut were then calculated, compiled and analyzed. Further cutting tests are recommended to improve the statistical significance of the findings and to quantify the actual specific energy reductions after microwave preconditioning.
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