Burn Cut Research Articles

Investigation of Burn Cut Parameters and Model for One-Step Raise Excavation Based on Damage Evolution Mechanisms

One-step raise excavation with burn cut is a kind of technology which use the drilling and blasting method to excavate the raise quickly. Due to the limitation of the free surface in burn cut, determination of cut parameters such as the length of burden and diameters of empty hole and charge hole is important to achieve a good effect of cut blasting. Meanwhile, the choice of the cut model is also crucial to form a proper opening. In this study, a modified Holmquist-Johnson-Cook (HJC) model, in which the tension-compression damage model and tension-compression strain rate effect model are considered, is embedded in the LS-DYNA software to investigate the damage evolution of rock in cut blasting. A simplified numerical model of burn cut is built in the LS-DYNA. The numerical results indicate that there is a threshold value of the burden length to maximize the opening. The empty hole has the effect of transferring blasting energy, and the effect becomes more obvious with the increase of the hole size. Moreover, the linear charge density of the prime cut hole can affect the compression and tension damage. Further, the comparison among four typical burn cut models are conducted based on numerical results. It demonstrates that triangular prism cut and doliform cut, which have more empty holes arrangement surrounding the prime cut hole, are better than spiral cut and diamond cut that with less empty holes locating one side of the prime cut hole in terms of energy efficiency and damage zone control.

Measuring the Reduction of the Confinement along the Evolution of a Burn Cut

We provide an analysis of a tunnel opening cut in a tunnel face. In particular, we focus on the effect of a “burn cut,” which is a typical parallel hole cut. As the evolution of the opening consists of an increase in the volume of the cut prism and the consequent reduction of confinement of the holes along the initiation sequence, we analyze such an evolution using photographic documentation, as well as evaluating the reduction of confinement by measuring the energy transferred from the explosive charge to the rock mass. The energy was estimated by monitoring and analyzing the vibrations induced by the blasting at three different points. We adopted low-cost shock sensors for monitoring the effect of the detonation times at short distance from the blast (about 10 m). The results show an evident reduction of the shock transfer to the rock mass (i.e., a reduction of confinement) with the increase of the cavity opening. Nevertheless, when only the response of the piezometric sensors was considered, a disparity in behavior among the sensors was noted. On the other hand, when the sensor response was integrated over time, the behavior of all sensors normalized, showing the need to focus both on the oscillation and the duration to properly address the shock effect.

Controlled blasting in underground construction: A case study of a tunnel plug demolition in the Neelum Jhelum hydroelectric project

Blasting is a popular method of excavation in underground construction. Blast-induced vibrations, however, if not properly controlled, can negatively affect the rock mass surrounding the tunnel. During the drill-and-blast (D&B) excavation of twin headrace tunnels through a major fault zone below the Jhelum River, a 180-m3/h groundwater inflow occurred from the tunnel invert. A 610-m3 concrete plug and high-pressure grouting around the tunnel periphery were formed to stabilize the tunnel and control inflow. To complete the tunnel, the temporary tunnel plug was ultimately demolished using controlled blasting. Ground vibration monitoring data from the regular D&B operations were used to develop a site-specific vibration attenuation model. Using geotechnical data from the feasibility stage and tunnel mappings during construction, a critical particle velocity above which tensile cracking could be initiated was determined for the rock mass surrounding the plug. The critical particle velocity was incorporated into the vibration attenuation model to obtain permissible charge weights to limit blast damage to within a short distance from the charge. Using this approach, an innovative blasting pattern was adopted in which the tunnel plug was sequentially demolished by detonating a burn cut and separate contour blast rows. During blasting, rigorous supervision and data collection helped to record, evaluate, and when needed, adjust the blasting program. Overall, the tunnel plug demolition was completed in a safe and cost-effective manner.

Optimization for Blasting Scheme of Crown-Sill Pillar Based on CW-GT and GC-WTOPSIS

Blasting scheme for crown-sill pillar of a lead–zinc mine was optimized by a new combination optimization model on the basis of CW-GT and GC-WTOPSIS. Nine main evaluation indices influencing blasting were chosen from economy, technology and safety aspects to establish the synthetic evaluation index system of four blasting schemes. Then the synthetic superiority degrees of the four schemes were determined with the basic theory of CW-GT and GC-WTOPSIS. Scheme- III (burn cut, inclined hole and side collapse with an angle of 80°) had the highest superiority degree and hence was confirmed as the best. The result was consistent with AHP-TOPSIS, BP neural network and catastrophe progressing model. The practice showed that the selected blasting scheme achieved the desired blasting effect, and the new method was suitable for optimization of blasting scheme, which provided a new way for scientific and reliable optimization of similar programmes.

Comparison of Some Blast Vibration Predictors for Blasting in Underground Drifts and Some Observations

Drilling and blasting are the most economical excavation techniques in underground drifts driven through hard rock formation. Burn cut is the most popular drill pattern, used in this case, to achieve longer advance per blast round. The ground vibration generated due to the propagation of blast waves on the detonation of explosive during blasting is the principal cause for structural and rock damage. Thus, ground vibration is a point of concern for the blasting engineers. The ground vibration from a blast is measured using a seismograph placed at the blast monitoring station. The measured vibrations, in terms of peak particle velocity, are related to the maximum charge detonated at one instant and the distance of seismograph from the blast point. The ground vibrations from a number of blast rounds of varying charge/delay and distances are monitored. A number of scaling factors of these dependencies (viz. Distance and maximum charge/delay) have been proposed by different researchers, namely, square root, cube root, CMRI, Langefors and Kihlstrom, Ghosh–Daemon, Indian standard etc. Scaling factors of desired type are computed for all the measured blast rounds. Regression analysis is carried out between the scaling factors and peak particle velocities to establish the coefficients of the vibration predictor equation. Then, the developed predictor equation is used for designing the blast henceforth. Director General of Mine Safety, India, specified that ground vibrations from eight to ten blast rounds of varying charge/delay and distances should be monitored to develop a predictor equation; however, there is no guideline about the type of scaling factor to be used. Further to this, from the statistical point of view, a regression analysis on a small sample population cannot be accepted without the testing of hypothesis. To show the importance of the above, in this paper, seven scaling factors are considered for blast data set of a hard-rock underground drift using burn-cut blast design. The possible step by step approach to establish a vibration predictor equation is also proposed.

Investigations on Impact of Blasting in Tunnels

Blasting with longer advance per round leaves an impact both visible (in the form of overbreak) and invisible (cracks) in the surrounding rockmass, however, a number of controlled-blasting techniques, that is line drilling, pre-splitting, and smooth blasting, have been developed to minimise this problem. These techniques require additional drilling, controlled charging, and detonation, and thus, are not preferred in regular development activities. Investigations have been carried out in five different horizontal development drivages of metal mines to assess the blasting impact using burn cut and arrive at the blast-induced rock damage (BIRD) model. Vibration monitoring close to the blast was carried out using accelerometers for the first time in India to develop vibration predictors and overbreak threshold levels for individual sites. This paper reports the development of the overbreak predictive model (BIRD) for burn cut blasting in hard rock drivages by combining the relevant rock, blast design, and explosive parameters. A multivariate statistical model has been developed and validated and the same can find ready application in tunnels and mines for exercising suitable engineering controls both in blast design and explosive selection for reduced basting impacts.

Recent advances in burn cut technology : P. Haydon, Tunnels & Tunnelling, 27(6), 1995, pp 42–43

This article reports recent advances in burn cut technology, a modern explosive technique used in tunnelling. Changes in current thinking behind burnt cut design have come in response to changes in the accuracy of drills, and the increasing range of explosives available to tunnelling engineers. The article discusses various changes in explosives use and drilling technology that forced a redesign of the burn cut. Traditionally, the shot holes in the cut would be about 150mm from the void hole centre and 240mm from the next hole, but they failed to offer protection to each shot hole from its previous hole. Explosives manufacturer Exchem has designed a new arrangement of holes, which ensures that each charged hole is protected from its neighbour by a void hole. This increases the probabilities of a successful shot and the safe achievement of a longer pull. However, the new design is not superior under all conditions. As mining and tunnelling technologies progress, the burn cut becomes an ever more crucial restraint and consideration in the blasting process. Its technology has had to become more sophisticated and flexible, even though it has had no really revolutionary developments.

Greater safety and efficiency in tunnel blasting operations : Hagan, T N Paper to 3rd Australian Tunnelling Conference, Sydney, 12–15 Sept 1978, 6P

This paper is a positive contribution to the safe and cost-effective blasting of tunnels. It emphasizes the high dependence of blasting results on drilling accuracy. Attention is paid to the efficient, hazard-free drilling and blasting of burn cuts; failure in the burn cut is usually synonymous with a frozen round. Some advantages and limitations of water gel explosives (cf. Gelignites) are presented as are the relative merits of paper and plastic as cartridging materials. Inadequate mixing of anfo causes reductions in both the safety and efficiency of blasting. Overbreak resulting from perimeter blastholes containing anfo can be reduced significantly by continuously side initiating the charge; greater decreases in overbreak are achieved by using anfo/polystyrene mixtures. The phenomena and effects of sympathetic detonation and dynamic pressure desenitisation of explosives (especially in burn cuts) are described. Aspects of post blast fumes which are associated with the introduction of recently-developed explosives are briefly mentioned. /TRRL/