Performance of water-coupled charge blasting under different in-situ stresses

Water-coupled charge blasting is a promising technique to efficiently break rock masses.In this study,numerical models of double boreholes with water-coupled charge are established using LS-DYNA and are calibrated by the tests of rock masses subjected to explosion loads to examine its performance.The crack levels of rock mass induced by water-coupled charge blasting and air-coupled charge blasting are first compared.It is found that water-coupled charge blasting is more appropriate to fracture deep rock mass than air-coupled charge blasting.In addition,the effects of rock properties,water-coupled charge coefficients,and borehole connection angles on the performance of water-coupled charge blasting are investigated.The results show that rock properties and water-coupled charge coefficients can greatly influence the crack and fragmentation levels of rock mass induced by water-coupled charge blasting under uniform and non-uniform in-situ stresses.However,changing borehole-connection angles can only affect crack and fragmentation levels of rock mass under non-uniform in-situ stresses but barely affect those under uniform in-situ stresses.A formula is finally proposed by considering the above-mentioned factors to provide the design suggestion of water-coupled charge blasting to fracture rock mass with different in-situ stresses.

Simulation of the relationship between roadway dynamic destruction and hypocenter parameters

Many factors can induce rock burst. Shock energy and shock distance are two key factors affecting rock burst. The 32101 roadway of the Xingcun coal mine, which has a tendency for rock burst, was used as an example. The dynamic module of Itasca’s FLAC (Fast Lagrangian Analysis of Continua) 2D explicit finite-difference software was used to simulate the roadway’s destruction. The vibration velocity and displacements of the rock surrounding the roadway were modeled for different shock energies and hypocenter distances. The simulation results indicate that the vibration velocity and displacement of rock surrounding the roadway have a quadratic relationship to the shock energy and a power law relationship to the distance of the hypocenter from the roadway. A dynamic view of the process was obtained from a series of "snap-shots" collected at 100 different time steps. This shows an isolating "river" is first formed at the hypocenter. The region above the "river" is a low stress zone while below the "river" a high stress zone exists. This high stress zone surrounds the ribs of the roadway in a "double ear" pattern. Continuous and repeated action of the high stress in the "double ear" shaped zone destroys the roadway.

Formation mechanism of rockburst in deep tunnel adjacent to faults:Implication from numerical simulation and microseismic monitoring

Rockbursts were frequently encountered in the construction of deeply buried tunnels at the Jinping-II hydropower station, Southwest China. In those cases, the existence of large structural planes, such as faults, was usually observed near the excavation boundaries. The formation mechanism of the “11·28” rockburst, which was a typical rockburst and occurred in a drainage tunnel under a deep burial depth, high in-situ stress state and complex geological conditions, has been difficult to explain. Realistic failure process analysis(RFPA3D) software was adopted to numerically simulate the whole failure process of the surrounding rock mass around the tunnel subjected to excavation. The spatial distribution of acoustic emission derived from numerical simulation contributed to explaining the mechanical responses of the process. Analyses of the stress, safety reserve coefficient and damage degree were performed to reveal the effect of faults on the formation of rockbursts in the deep tunnel. The existence of faults results in the formation of stress anomaly areas between the tunnel and the fault. The surrounding rock mass failure propagates toward the fault from the initial failure, to different degrees. The relative positions and angles of faults play significant roles in the extent and development of surrounding rock mass failure, respectively. The increase in the lateral stress coefficient leads to the aggravation of the surrounding rock mass damage, especially in the roof and floor of the tunnel. Moreover, as the rock strength-stress ratio increases, the failure mode of the near-fault tunnel gradually changes from the stress-controlled type to the compound-controlled type. These findings were consistent with the microseismic monitoring results and field observations, which was helpful to understand the mechanical behavior of tunnel excavation affected by faults. The achievements of this study can provide some references for analysis of the failure mechanisms of similar deep tunnels.

Numerical investigation of effect of eccentric decoupled charge structure on blasting-induced rock damage

Eccentric decoupling blasting is commonly used in underground excavation.Determination of perimeter hole parameters(such as the blasthole diameter,spacing,and burden)based on an eccentric charge structure is vital for achieving an excellent smooth blasting effect.In this paper,the Riedel-Hiermaier-Thoma(RHT)model was employed to study rock mass damage under smooth blasting.Firstly,the parameters of the RHT model were calibrated by using the existing SHPB experiment,which were then verified by the existing blasting experiment results.Secondly,the influence of different charge structures on the blasting effect was investigated using the RHT model.The simulation results indicated that eccentric charge blasting has an obvious pressure eccentricity effect.Finally,to improve the blasting effect,the smooth blasting parameters were optimized based on an eccentric charge structure.The overbreak and underbreak phenomena were effectively controlled,and a good blasting effect was achieved with the optimized blasting parameters.

Numerical simulation study on hard-thick roof inducing rock burst in coal mine

In order to reveal the dynamic process of hard-thick roof inducing rock burst, one of the most common and strongest dynamic disasters in coal mine, the numerical simulation is conducted to study the dynamic loading effect of roof vibration on roadway surrounding rocks as well as the impact on stability. The results show that, on one hand, hard-thick roof will result in high stress concentration on mining surrounding rocks; on the other hand, the breaking of hard-thick roof will lead to mining seismicity, causing dynamic loading effect on coal and rock mass. High stress concentration and dynamic loading combination reaches to the mechanical conditions for the occurrence of rock burst, which will induce rock burst. The mining induced seismic events occurring in the roof breaking act on the mining surrounding rocks in the form of stress wave. The stress wave then has a reflection on the free surface of roadway and the tensile stress will be generated around the free surface. Horizontal vibration of roadway surrounding particles will cause instant changes of horizontal stress of roadway surrounding rocks; the horizontal displacement is directly related to the horizontal stress but is not significantly correlated with the vertical stress; the increase of horizontal stress of roadway near surface surrounding rocks and the release of elastic deformation energy of deep surrounding coal and rock mass are immanent causes that lead to the impact instability of roadway surrounding rocks. The most significant measures for rock burst prevention are controlling of horizontal stress and vibration strength.Key words

Application of slotting-pipe shaped blasting for hard-rock rapid driving

The cumulative blasting using PVC slotting pipe was tested for rapid driving in hard-rock roadway construction. First, the outhors optimized blasting parameters on 2.2 m scheme, and did both-sides comparative experiment of the surrounding holes after the blasting success. The results show that the application of slotting tube obtains four more cut contours than the case without it. Finally we did full-section control and non-control blasting comparative experiment, the results show that the rates of half-hole marks and the non-smooth grades of the cut contours can reach 95%, hole spacing is expanded to larger than 550 mm, and 550 mm is the best under the K2 limestone conditions.

Numerical simulations on rock damage and fragmentation by blasting

a damage constitutive model comprising two dynamite sticks is established and handled with the transient dynamics finite element computer program PRONTO-3D to study rock damage and fragmentation during blasting. Simulation tests find that tensile stress by detonation gives rise to tensile bulk strain and consequently damage in the material. Maximum bulk strain is observed in simultaneous detonations of the two dynamite sticks. It is demonstrated that the proposed method is applicable to studying the process of rock damage by blasting as well as its affecting factors.

THE CALCULATION OF INITIAL SHOCK WAVE IN ROCK WITH UNCOUPLING CHARGE BLASTING

According to the structure of explosive charge in rock blasting, a physical model has been set up in this paper. Based on the model, a methodology for calculating initial shock wave of uncoupling charge has been given. The pressure p3 has been calculated when high explosives act on granite, limestone, marble and shaIe respectively. Some important conclusions are also gained by the analysis of results.

Sizing of rock fragmentation modeling due to bench blasting using adaptive neuro-fuzzy inference system and radial basis function

One of the most important characters of blasting, a basic step of surface mining, is rock fragmentation. It directly effects on the costs of drilling and economics of the subsequent operations of loading, hauling and crushing in mines. Adaptive neuro-fuzzy inference system （ANFIS） and radial basis function （RBF） show potentials for modeling the behavior of complex nonlinear processes such as those involved in frag- mentation due to blasting of rocks. In this paper we developed ANFIS and RBF methods for modeling of sizing of rock fragmentation due to bench blasting by estimation of 80% passing size （Kso） of Golgohar iron ore mine of Sirjan, lran. Comparing the results of ANFIS and RBF models shows that although the sta- tistical parameters RBF model is acceptable but the ANFIS proposed model is superior and also simpler because the ANFIS model is constructed using only two input parameters while seven input parameters used for construction of the RBF model.