ABSTRACT
IIT Research Institute has investigated the potential of high pressure water jets for rapid rock excavation. During this study, an attempt was made to correlate the extent of breakage effected to the mechanical properties of rocks. Six rock types were used in these experiments and nine properties were determined for each rock variety. A regression equation using the two most significant rock properties and one jet parameter (pressure) was established. Although tests were conducted to specific pressures of 35, no minimum in the specific energy consumption was noted.
INTRODUCTION
The past few years have seen a great deal of activity in the development of high energy rock destruction techniques. These techniques represent a radical departure from traditional mechanical techniques and appear to contain great potential. The term "high energy device" may be considered to include any device capable of concentrating dense energy fluxes on a portion of the rock face. This energy may be radiative, thermal, kinetic, or combinations of these. Examples of these cases would be microwave fracturing, flame or plasma jets, hypervelocity projectiles, or liquid jets. All have been used for rock destruction, some for many years. Flame jets are currently in commercial use in rock and concrete destruction, while water jets operating at modest pressures have a long history of operation in soft rocks and soil. This paper is concerned with the operation of high pressure water jets in a wide range of rocks, including rocks that normally would require drill and blast excavation. IIT Research Institute has recently investigated the influence of rock properties on the efficiency of water jet excavation in order to define the limits within which this tool may be used.
EXPERIMENTAL DESIGN
This research was directed toward a number of points, including the applicability of water jetting to various rock types. This phase consisted of water jet tests on six rock types: Massilion sandstone, Indiana limestone, Minnesota dolomite, Connecticut brownstone, Milford Pink granite, and French Creek gabbro. The results of these shots were correlated with various rock property data to determine the most significant standard test in terms of excavating efficiency.
Rock Properties
The rock types chosen for this project were found to have the properties listed in Table I. The specimens were in the form of cubes with a minimum dimension of one foot. Ten cube, of each rock type were purchased, one each of which was cored for test cylinders to measure compressive strength, tensile strength, density, sonic velocities and petrographic analysis. The remaining cubes were tested for Schmidt hammer and Shore scleroscope readings. The non-destructive tests were used to check for variations in properties parallel and perpendicular to the bedding planes. As a result of this analysis, the Massilion sandstone, Indiana limestone, and Connecticut brownstone were scheduled for water jet tests in both directions.
Water Jet Device
The water jet was produced by a single stage intensifier shown in Fig. 1. This unit has an intensification ratio of 28:1, a maximumpressure of 1. 4 x 109 N/m2 (206 ksi) and a working volume of 3300 cm3 (200 in.3 ).2
