Study on Distribution Characteristics of Damage Range along Smooth Blasting Hole Based on PPV

The damage range of surrounding rock has an important influence on optimization of blasting parameters. This study, based on the vibration attenuation law near the blasting source and the characteristics of the load acting on the wall of the smooth blasting hole, derives the distribution formulas of the damage range along the borehole during the expansion and quasistatic processes of detonation gas, respectively. More importantly, the quantitative relationship between the damage range and the charge weight of the single borehole is established. The experimental data are used to verify the correctness of the theoretical formulas. The results show that the damage range during the expansion process of detonation gas presents a continuous saddle-shaped distribution along the borehole and the maximum damage range is near the charge segment. The damage range during the quasistatic process of detonation gas is uniformly distributed along the borehole and can be more conservatively used to the practical prediction after corrected. The theoretical formulas are applicable to the perimeter hole with the radial and axial decoupled charge structure, which can provide a theoretical support for controlling the damage range of surrounding rock according to the charge weight.

Study on Catastrophe Instability of Support System in Gypsum Goaf Based on Energy Dissipation Theory

The stability of the goaf support system is the key to safe production in gypsum mines. Therefore, this study constructed a pillar-beam support system which contained pillar plastic zones. In this support system, the beam and pillar were taken as energy releaser and energy dissipater, respectively. Through establishing a cusp catastrophe model based on energy theory, the new criterion for instability was obtained which is related with geometric stiffness and system energy dissipation. The results indicate the instability of the support system is caused by the incompatibility of energy release, dissipation, and geometric deformation. When K > 1, the energy released by the support system is compatible with geometric deformation. The support system experiences a quasistatic process from the static state in bottom page to the static state in top page along Path I. When K < 1, the energy released by the support system cannot be in tune with geometric deformation. The support system experiences a catastrophe process along Path II. The evolution from the static state in bottom page to the static state in top page is not progressive, but catastrophic. The redundant energy released in this process leads to mechanical instability of the support system. This study provided theoretical foundation for the mining and treatment of mines. Based on actual engineering examples, the sensitivity of the geometric parameters of the support system was analyzed as well. These parameters are ranked by their sensitivity from high to low, as is shown below: beam thickness, plastic zone width, room span, pillar width, and pillar height. Then, the goaf was classified according to the geometric parameters. Energy catastrophe theory was applied to analyze the stability of the support system in different classes of goaf. The analysis results showed that Class D goaf should be labeled as the unstable zone, which was consistent with the result of field research. To conclude, energy catastrophe theory can be used to demonstrate the nonlinear mechanical mechanism of support system instability in room-pillar mining goaf.

Quasistatic Elastic Contact with Adhesion

The aim of this paper is the variational study of the contact with adhesion between an elastic material and a rigid foundation in the quasistatic process where the deformations are supposed to be small. The behavior of this material is modelled by a nonlinear elastic law and the contact is modelled with Signorini's conditions and adhesion. The evolution of bonding field is described by a nonlinear differential equation. We derive a variational formulation of the mechanical problem, and we prove the existence and uniqueness of the weak solution using a theorem on variational inequalities, the theorem of Cauchy-Lipschitz, a lemma of Gronwall, as well as the fixed point of Banach.

GEODYNAMICS

We investigate a role of the contact friction in thrusting within the framework of the critical taper theory and according to geological settings for orogenic belts including the Ukrainian Carpathians (in Early Cretaceous time). Finite element models are used to simulate tectonic compression of sedimentary rocks by submerged stage and take into account frictional slipping on the detachment horizon. We assume a simple wedge geometry (rectangular layer 60 km long, 1.5 km thick and 2.5 km deep), plane strain state, quasistatic process and use elastic constitutive relation. Mechanical loads include gravity, water pressure on top and lateral displacement (up to 0.5 km) from the left, whereas the right side is fixed. Numerical results show specific features of the inhomogeneous stress fields for small (0.01-0.5), middle (0.5-0.64), large (0.64—0.8) and overlarge (0.8-1.15) friction coefficients. The magnitude of the tangential contact stress controls the front between sliding and sticking zones. Stress trajectories enable to predict thrust structures using Mohr-Coulomb failure criterion.