The propagation of shock waves in various media has been studied extensively, but the experimental data for certain media, such as rock, do not provide an exhaustive description of the process [1][2][3]. This is due to the difficulty of measuring a rapid passage of the high stresses caused by detonation of an explosive charge.In this study, we investigated the propagation patterns of plane shock waves by means of manganin sensors placed in the near zone of the blast.The results of the study pertain to the behavior of marble in the propagation zone of shock waves. METHODS AND RESULTSPlates 5, i0, 15, and 20 mm thick were cut from marble of density po = 2670 kg/m3 and polished.Manganin sensors were placed between the plates. The sensitive element size was 5 x 5 mm, with initial resistance Ro = 2.3 -2.6 ~. The model was built of plates and subjected to plane shock waves caused by the blasting of a commercially available explosvie (granulated TNT, a mix of AS + DT, grammonite 79/21, and GLT-20) and an emulsion of liquid fuel in a solution of saltpeter ammonia.The charge diameter was 60 mm, its height 100-181ram.The pressure was measured in each test at three or four points. One of the manganin sensors was placed at the charge--rock contact.Along with pressure measurements, the explosive detonation speed and the propagation velocity of the shock wave front in the rock were measured.The method of pressure measurement by manganin sensors has been described in [3,4]. When the pressure was measured at the charge-rock contact, the sensor was separated from the explosive by a teflon layer of 1-1.5 mm.Inside the marble specimen, the sensors were placed without insulation. Figure 1 shows the experimental curves P(T) obtainad at the fixed points of the marble block loaded by the charge of granulated TNT with a charge height of 181 mm.For distances of 0. i0 and 21 mm, curves 1-3 display the shape of a shock wave preceded by an elastic precursor.Curve i has a sagged peak portion of the front due to the effect of teflon insulation.At 31 nun (curve 4), only the elastic precursor and the beginning of the plastic flow are shown.Further recording of the sensor was distorted by the influence of the tensoeffect.
Investigation of compressional wave propagation in hard rocks is of interest in order to estimate the possibility of shock-wave formation since a number of researchers, H. Kuk [i, 2] say, consider industrial high explosives (HE) not to develop sufficient pressures needed for shock-wave origination.Investigations performed earlier [3, 4] clarified the characteristics of compressional wave propagation in rocks of low and medium hardness.It has been established that defornmtion is plastic in nature in weak rock (schist) in the near zone of an explosion and that the compressional wave velocity changes with distance from the charge.In medium-hardness rocks (marble, limestone) elastic-plastic deformation predominates, where the compression wave has a complex two-front structure for a practically constant velocity of the elastic forerunner.The purpose of the present paper is to investigate the behavior of hard rock masses subjected to dynamic loads. An investigation of the physical characteristics of hard rocks in the initial period of compression-wave propagation also permits estimation of the dynamic compressibility of the rock. The experimental method is described in [5]. The specimens are loaded by using granulotol charges (PHE " 0.97 g/cm 3) in which detonation was excited by a plane-wave explosion lens. Presented below are experimental data on compressional wave damping in diabase (P0 = 3.05 g/cm 3, C O = 6200 m/sac) and granite (P0 = 2.77 g/cm 3, Co = 440 m/sac) specimens.Records of the normal stress P(t) at 5.0, 11.25, 16.05, and 32.3 mm distances are presented in Fig. i. Analyzing the profiles obtained, we note that they have a number of characteristics: I) the growth phase duration equal to 1.3 • 0.i gsec is constant; and 2) linearity of the dependence of the maximum normal stress Pmax on the charge-sensor distance P~,,~--i8.2--0.29h GPa.(1)No specific compressional wave characteristics (forerunner, multifront wave structure, additional maximums, etc.) are noted in diabase. The drop on the P < 1 GPa section of the records could be explained by errors that occur during recording. The Lagrange analysis method, utilized extensively to solve such problems [5, 6], was used to process the records. Linearity of the dependence P(h), remainin 8 behind the wave peak, and the constant value of the compressional wave velocity N -6.2 • 0.05 km/sec were taken into account in the computations. Presented in Fig. 1 are computed dependences of the mass flow rate u and the specific volume v on the time for measured distances h. The mass flow rate profiles practically duplicate the pressure profiles over the whole section under investigation. Disagreement between the maximums P(t) and u(t) for the first sensor is characteristic, and indicates the influence
In recent years in the USSR there have been plans to extend the range for use of water-filled (slurry) explosives. From simple compositions containing an oxidant, water, and a sensitizer (akvatols, akvanits, ifzanites, and GLT compositions ), the explosives have been developed toward more efficient and energy-bearing types containing metal powders as combustible ballistic additives.It has been shown that replacement of part of the explosive sensitizer and oxidant in these compositions by high-energy metal combustibles is advantageous and economically justified. It increases the crushing action of water-filled explosives. The list of blasting materials released for continuous application in 1977 includes mechanically mixed hot cast water-filled explosives (WFE) --karbatol of grade GL-10V, including 15% of GOST [All-Union State Standard] ~058-73 aluminum powder. The presence of a thickening agent and a crosslinking agent in karbatol GL-10V enables us to charge blast holes containing static or slowly flowing water, but does not eliminate losses of ammonium nitrate (AN) from the charge while it remains in the water-laden hole. In waterlogged conditions, the process of charging boreholes with WFE based on a hot solution of oxidant by mechanized means can be effected as follows: a) charging from the blast-hole mouth; b) under a column of water; c) under a separating layer. Charging of WFE by the first method can be effected with a small amount of water (0.5-2.5 m) in the hole, part of which is trapped during charging and part displaced by the charge. In this case the AN losses from the charge are slight, and as a rule they do not affect the rock crushing quality. If the water column is higher, charging from the mouth leads to large AN losses from the charge (up to 95-100% ).If the WFE are injected under a column of water by the second method, the charge is compactly laid, displacing water as the borehole is filled. In this case, even if a thickening agent is used the AN loss from the charge is 10-15%; the height of the water column does not influence the AN losses, but does affect the injection pump power needed. To reduce the AN losses from the charge, as well as using thickeners and structureforming agents it is necessary to reduce the surface of contact between the charge and the water.Charging under a separating layer by the third method completely avoids contact between the WFE and the water and minimizes AN losses from the charge.At present the most widely used methods are charging from above (from the mouth) and under a water column; however, the second and third methods require powerful pumps to overcome the resistance of the water column. Practice has revealed that the pressure of the charge mixture at the end of the charging hose should be 2.5-3.0 atm. In this case there is no need for an attachment for withdrawing the charging hose.As well as reducing the AN losses from the charge during charging to a minimum, it is also necessary to keep the charge stable during the time up to the moment of explosion; this ...
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