Explosive deformations

EXPLOSIVE DEFORMATIONS (EN: blast deformation; DE: deformierende Sprengauswirkung, Schießdeformationen; FR: deformations de tir; ES: deformaciones de explosion; RU: взрывные деформации) is the change of the relative positions of the particles of the various solid bodies, which is associated with the movement of these particles under the action of the explosion. They categorize as the simplest types of the deformation the stretching, compression, shear, torsion, and bending. In the real cases, there may be observed simultaneously several types of the deformation.

The explosive deformations of the majority of the rocks belong to the elastic type, which are disappearing after the termination of the action of the blast wave, or to the explosive deformation, which is accompanied by the emergence of the new surfaces of the separation (ruptured) within the medium. The plastic deformations (which are not disappearing after the removal of the load) of the rocks are non-significant, and they usually do not take into account these deformations during the calculation of the action of the explosion. The explosive deformations of the soils are plastic even in case of the small loads. The study of the physical nature of the emergence of the deformations belongs to the physics of the solid body. The elastic and plastic deformations are considered within the theory of the elasticity and plasticity. The theory of the dislocations is the most complete theory, which is explaining the mechanism of the plastic deformations.

The action of the explosion, which is causing the explosive deformations, is manifested in the form of the propagation of the waves of the stress, or in the form of the quasi-static impact of the gaseous products of the detonation. Within the zone, which is near to the charge of the explosive substance, the waves of the stress cause the deformations, which are accompanied by the crushing of the rock, while within the far zone, the waves of the stress are transformed into the seismic waves (longitudinal, transverse, and superficial), which are causing only the elastic displacements. These elastic displacements, however, can serve as the cause of the destruction of the underground mine workings, or of the engineering built structures on the surface of the massif. The explosive deformations are most dangerous, when the frequency of the seismic oscillations coincides with the natural frequency of the oscillations of the engineering built structure.

The explosive deformations of the rocks and soils are accompanied by the certain increase of the temperature, which is caused by the dissipative losses of the energy of the propagating waves. In the certain point of the massif, the explosive deformations increase with the increasing of the mass of the charge, which is exploded simultaneously, and decrease with the increasing of the distance from the charge. They determine the explosive deformations of the rocks or soils, while measuring the displacements of the elements of the massif, or the stresses, which are causing these deformations. They perform such measurements, for example, using the strain sensors (the electric resistance of the sensor changes depending on the magnitude of its deformation), using the piezoelectric sensors (under the impact of the stress, there is generated within the sensor the electric moving force), using the electromagnetic or seismic sensors (the electric coil, which is associated with the casing of the sensor, moves relatively to the magnet, which is suspended freely), using the capacitor sensors (the exposed surface of the massif, which is covered with the conductive layer, which is serving as one electrode of the capacitor, is displaced relatively to the second electrode, which is suspended freely), and so on. They position the sensors immediately within the massif (the strain sensors, and the electromagnetic sensors), on the surface of the massif (the seismic sensors, and the capacitor sensors), or within the medium with the known properties (for example, water), which is bordering the massif (the piezoelectric sensors).

For the prevention of the damage to the engineering built structures on the surface of the massif, and also to the underground mine workings, during the explosive deformation, they use most often the method of the screening. The action of the screen is effective within the region, which is commensurate with the size of the screen. There serves as the screen, which prevents the transfer of the explosive deformation between the charge of the explosive substance and the protected built structure, the narrow aerial gap, which has been created on the path of the movement of the wave of the stress, using the mechanical method, or using the explosion of the row of the small vertical charges. There may also serve as the screen the rock at the boundary of the planned mine working, which has been crushed by the explosion of the contour charges. If they explode the charges of the explosive substance within the water, then they sometimes use as the screen the curtain of the bubbles of the air, which has been created on the path of the propagation of the shock wave. For the decreasing of the explosive deformation during the explosive breaking of the rocks, they use the short-delay blasting.