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A method developed specifically to help designers forecast the performance of a hydro-mole tunneling machine where only limited laboratory data are available is discussed herein. Experimentally determined data were used to forecast the cutting rates for sandstone, limestone, and granite. Pressures ranging from 5000 to 20,000 psi were used in this study, and the flow rates considered at these pressures ranged from 60 to 240 gpm. The horsepower transmitted to the rock face, penetration of the jet into the rock, specific energy, nozzle thrust, and the tunnel cutting rates to be expected when rock of a given type is cut are presented.
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The rate of tunneling through rock has been improving during the last few years. Drilling and blasting techniques normally used in mining operations have been replaced by continuous tunneling machines, and the prospects for using a combination of methods to tunnel at higher velocities are good. Each rock-breaking technique has a potential contribution which must be considered during the design of specific tunneling projects. The cost per cubic foot for cutting holes or tunnels usually increases drastically if the height of the opening is less than 8 feet. In such cases, water jets may be suitable cutting tools.
The use of water jets for mining and tunneling has been investigated and adapted to mining of coal. However, the application of water jets to hard rock has been limited to laboratory tests. Water jets have tremendous kinetic energy, and their ability to erode sandstone, limestone, and granite has been demonstrated in laboratory tests.
For the study reported herein, an experimental hydraulic tunneling machine was designed to determine many of the performance parameters governing the advance rates for tunneling machines that use high-velocity water jets as the cutting tool. To obtain a better understanding of the relationships between these performance parameters, a computer program was written to serve as a model of the tunneling machine. Experimentally established data were used to select various combinations of parameters as input to the program, and the organized computer output permitted selection of the best combinations. The resulting data were used in the development of equations for determining the cutting rates and other performance parameters for the hydro-mole tunneling machine.
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Before proceeding with the discussion of this study, the following terms should be introduced and defined.
y (E): the energy required to remove a unit volume of rock from the sample being cut. The terminology of water jets suggests that the amount of energy applied to the rock equals the kinetic energy of the water as it leaves the nozzle.
r (do): the minimum diameter of the nozzle bore. The length of this bore is usually two to three times the diameter of the bore, and it is polished to improve the flow characteristics of the nozzle.
f (So): the distance from the end of the nozzle to the rock face of the tunnel.
y (Vt): the velocity at which the nozzle travels across the rock being cut.
