An experimental study of the effect of detonation of horizontal cylindric ejection charges in homogeneous and stratified rock

Abstract

Planning of blasts in stratified rocks, including explosions detonated to form ejection cavities, is hampered by the absence of reliable methods for predicting the results of an explosion, because of a tangle of interlinked processes in rock masses of a complex structure.Homogeneous rocks are exceptionally rare in mine blasting; most beds include alternating layers with distinctly different properties (density, humidity, strength, etc.) or are characterized by a gradual but considerable depth variation of physical and mechanical parameters.Previous theoretical and experimental studies of underground ejection explosions (includingblasts of horizontal cylindrical charges) in homogeneous rocks have yielded methods for calculating the parameters of blasting operations to produce cavities with characteristics that satisfy the practical needs.No such methods have been created for stratified rocks.The few studies [1][2][3][4][5] that have been done either were not systematic or applied to narrowly specified conditions and never produced general formulations for predicting the results of an explosion or calculating the parameters of blasting operations.The objective of this study was to determine, by means of modeling, the parameters of explosion funnels formed by underground blasts of horizontal cylindrical charges of a finite length in two-layer beds consisting of rocks of significantly different strength and with one kind of rock being loosely cemented. Experimental Conditions and Processin~ of DataExperiments on the effect of blasts in homogeneous rocks were conducted in mediumgrained quartz sand. The ground density was P0 = 1550-1670 kg/m a at humidity Wg = 2-5% and free porosity ~z = 32.0-39.6%.Cylindrical hexogen charges (specific energy c, = 5.36 MJ/ kg) and a plastic C-4 explosive (e, = 4.87 MJ/kg) were the explosion sources.In the first series of tests the charge length was s = 0.05-0.33 m at a diameter d = 0.0075-0.035 m and the loading density Pex = 1050-1500 kg/m 3. The placement depth of the charges was W = s In the second series of tests, s = 0.12-0.79 m with the placement depth W = 0.01-0.31 m. The charges were triggered by ~D-8~ detonators placed at the endface of the charge to cover two-thirds of the detonator length.The weight of detonator explosive was added to the charge weight.Crater parameters were measured; the data indicated no significant effect of the detonator on the symmetry of the ejection crater.The stratified model was formed as a ground bed of the layer half-space type.In one case the layer was represented by loose quartzose medium-grained sand in an air-dry state at P0 = 1467-1650 kg/m 3 and ~i = 41.24-45.85%.The half-space was sand-loam with an intact structure at Pl = 1862-2089 kg/m 3, Wg = 7.5-12.7%, =z' = 33.0-36.5%, and the ultimate shear strength 9 = 9.3-55.9 kN/m 2. The overburden thickness varied in the range of h = 0.03-0.2 m. In another case, the overburden was represented by rock with strength, namely dense clay of disrupted structure Pl = 2020-2140 kg/m3; Wg = 7.4-13.5%; el'...