Water Jet Cutting of Sedimentary Rock

Abstract

Depth and specific energy of breakage values are used to determine the relative efficiencies of a continuous water jet cutting sandstone and limestone. Results of using jet action alone compared with results obtained when mechanical breakage is also used to remove rock indicate that the latter method is the more effective. Introduction In the past few years there bas been a rapidly growing interest in adapting new and unusual techniques to meet the problems of rock excavation, particularly in drilling and tunneling. In his particularly in drilling and tunneling. In his initial analysis of methods that had potential for solving drilling problems, Maurer listed 30 such techniques that might be used. On the basis of Maurer's work and of more recent analysis and experimentation, water jet erosion of rock has been found to hold promise as a means of rock removal in hard- and soft-rock tunneling, in coat mining, and in drilling. To date, investigation of this technique has been generally confined to determining the factors that control the cutting rate of the jet through laboratory experiments on prepared samples of rock. Such testing has been related only indirectly to the practical problem of rock excavation inasmuch as the practical problem of rock excavation inasmuch as the rock likely to be removed in situ will be under ground stress and will be unlike the quasi-homogeneous, isotropic, nonfractured sample used in the laboratory. Nevertheless, the results of such experimentation indicate the potential water jet pressures that will be required in the field system and the level of power consumption. An advantage of water jets in such a system is that in some circumstances the water jet acts as fluid wedge so that where fractured rock or rocks with weaknesses and joints are attacked the performance figures will be higher than those attained performance figures will be higher than those attained in the laboratory. Two separate concepts may be envisaged in designing a tool for water jet drilling. In the first, an arrangement of water jet nozzles may be rotated so that the resulting jets remove all the rock at the face of the cut by first cutting slots in the rock and then removing the intervening ribs by water jet action alone. In the second concept the water jet may be used to cut slots, leaving ribs of rock that are then removed by mechanical means - for example by roller cutters rotating either within the slot to wedge out the ribs, or along the center of the intervening rib. To determine the relative efficiency of each of these techniques, calculations were made of the specific energies of cutting, relating the energy level required to remove a given volume of rock under various cutting conditions. Experiments were carried out on samples of rock, using a water jet delivered from a high-pressure pump through a nozzle 0.023 in. in diameter. Rock Cutting by Water let To determine the distance between adjacent cuts at which the water jet would not only cut a slot for itself as it traversed, but also remove the intervening rock rib between slots. samples of rock were placed on the horizontal carriage of a lathe and linearly traversed under the water jet nozzle to cut a straight slot. Two types of rock were used in this series of tests, Berea sandstone and Indiana limestone. JPT P. 797