Predictive model of explosive detonation parameters from an equation of state based on detonation velocity

This article describes a predictive model of explosive detonation velocity and pressure based on first-order approximation of the detonation velocity equation. Detonation pressure was calculated from equations derived from the ideal detonation theory since that pressure is functionally related to detonation velocity. In the model calibration process, several product formation hierarchies were explored, with the best results yielded by the Kamlet and Jacobs (KJ) hierarchy. The predictive capacity of our model (labelled DEoS) was tested using different experimental databases, and was compared with predictions by thermochemical models (BKW-RR, JCZ3-J and JCZS) and by the empirical KJ method. The prediction values obtained using an experimental database of 238 explosive substances (75 singles and 163 composites), for a range of densities (1 g cc −1 to 2 g cc −1 ), were excellent in terms of both velocity and pressure, with root mean square error values of 1.7% (519 data items) and 6.0% (263 data items), respectively. We analysed results, broken down by explosive type, in detail, finding that the model residuals did not correlate with the predictor variables and also that the model predicts reasonable values for other parameters in the detonation state, such as density, the Jones parameter, and the Grüneisen parameter.Xunta de Galicia | Ref. ED431C 2018/4

Influence of microroughness on the frictional behavior and wear response of planar saw-cut rock surfaces

Saw-cut rock surfaces, classically utilized to estimate basic friction angle of discontinuities by means of tilt test and other procedures, may seem planar to the naked eye. Nevertheless, they actually present roughness at a micrometric scale. Aiming at characterizing some of these saw-cut rock surfaces and assessing the possible implications between their microscale topography and the resulting tribological behavior, the authors of this study resorted to the 3D focus-variation technique to analyze different surface-texture parameters. Tilt tests were carried out on specimens cut on three rock types, and the involved sliding surfaces were evaluated at a microscale for different testing stages (prior to any test and after two series of repeated tests). An apparently logical inverse correlation between repeated testing and friction angle has been observed, more marked for the smoother surfaces. Higher roughness at the scale of the analysis tends to produce lower friction-angle values, as otherwise observed for mismatched natural rock surfaces. In addition, saw-cut rock surfaces present systematically negative skewness and high values of kurtosis for their height distributions, indicating the occurrence of narrow and deep pits or valleys. Directional hybrid parameters and, in particular, the root mean square (RMS) of the gradient of the surface in the direction of sliding correlates rather well with the measured sliding angle. The authors concluded that the 3D focus-variation technique represents a powerful tool to assess surface-texture parameters of saw-cut rock surfaces, in addition to being useful for understanding some features of the tribological, or wear and frictional, behavior of these type of surfaces.Agencia Estatal de Investigación | Ref. RTI2018-093563-B-I0

Analysis of the goodness of empirical approaches in predicting explosive detonation parameters

Goodness of empirical models for predicting explosive detonation velocity and pressure was analysed using 3 databases consisting of experimental velocity and pressure measurements for different explosives. The first database was used to estimate experimental errors for detonation velocity and pressure measurements. The second database was used to compare residuals obtained by the experimental models and by various thermochemical codes. Finally, the third database, consisting of some 600 data on 130 explosive substances, was used to estimate residual bias and dispersion resulting from the application of the experimental models. Also analysed was model coherence with the ideal detonation theory. Our main conclusion is that all the models introduce bias in their predictions depending on the density and oxygen balance values of the explosive. Of those analysed, the Xiong model was notable for its good results, with residual dispersion comparable to that obtained from application of the best thermochemical codes. Our results would indicate that the Xiong model is the only model that may be compatible with the ideal detonation theory. The pressure equation derived from the ideal detonation theory and calibrated with experimental data had excellent predictive capacity.Xunta de Galici

Differentiating between fatal and non-fatal mining accidents using artificial intelligence techniques

Using statistical methods for categorical data analysis, namely multiple correspondence analysis and Artificial Intelligence through Bayesian networks, we analysed a database of occupational mining accidents for Spain for the period 2004–2017 to identify the factors most associated with the occurrence of fatal and non-fatal accidents. The results obtained allow to shed light on the hidden patterns present in different work situations where accidents can have fatal consequences. In addition, this study exemplifies the application of statistical techniques suitable for Big Data and data-driven decision making in the mining sector.Xunta de Galicia | Ref. ED431C 2018/4

Convergence-confinement curve analysis of excavation stress and strain resulting from blast-induced damage

Using the convergence-confinement curves methodology, we analysed excavation behaviour for a range of rock masses of different geotechnical qualities, taking into account blast-induced damage. The novelty of the research is (i) we include blast-induced damage to the rock mass in ground reaction curve construction, and (ii) we analyse results for 54 rock mass and rock geotechnical quality scenarios. The research, an application of a previously developed methodology (González-Cao et al., 2013), provides practical guidelines for the preliminary design phase for an excavation resulting from blasting. Our main conclusions are (i) that rock mass quality has a greater bearing on the plastic radius and excavation maximum displacement than blast-induced damage, and (ii) that the plastic radius and maximum displacement around an excavation increase with the level of blast-induced damage, most especially for poor quality rock masses. This would justify the need to limit blast-induced damage in poor quality rock masses.Ministerio de Economía y Competitividad | Ref. BIA2014-53368

Study of size effects on the peak and residual strength of intact and artificially fissured granite samples

There are not many studies on jointed rock specimens, which can be considered small scale rock mass analogs. On the other hand, the scale effects in the mechanical properties of such samples have seldom been studied. With the aim of continuing previous research on intact granite rocks, the authors have carried out sets of 25 stress-strain triaxial compressive tests on 1 sub-vertical and 2 sub-horizontal 38 mm, 54 mm and 84 mm diameter jointed granite specimens at various confinements. Peak and residual strength values were obtained and compared to those recovered form intact rock samples. Results suggest that peak strength follows similar trends with scale to those observed on intact rock, even if lower strength values are logically recorded. Regarding residual strength, the obtained results are in line with those observed trends for standard size samples, showing a similar trend for all cases independently of scale, even if we observe larger variability for jointed samples. The authors have also compared the values fitting the generalized Hoek-Brown criterion for rock masses to better understand the behavior in relation to sample size. So scale effects clearly appear on jointed rock peak strength of jointed sample; even if residual strength seems hardly affected by scale.Agencia Estatal de Investigación | Ref. RTI2018-093563-B-I0

Scale effects on triaxial peak and residual strength of granite and preliminary PFC3D models

Research studies on the scale effect on triaxial strength of intact rocks are scarce, being more common those in uniaxial strength. In this paper, the authors present and briefly interpret the peak and residual strength trends on a series of triaxial tests on different size specimens (30 mm to 84 mm diameter) of an intact granitic rock at confinements ranging from 0 to 15 MPa. Peak strength tends to grow from smaller to standard-size samples (54 mm) and then diminishes for larger values at low confinement. However, a slight change in strength is observed at higher confinements. Residual strength is observed to be much less size-dependent. Additionally, this study introduces preliminary modelling approaches of these laboratory observations with the help of three-dimensional particle flow code (PFC3D) simulations based on bonded particle models (BPM). Based on previous studies, two modelling approaches have been followed. In the first one, the maximum and minimum particle diameter (Dmax and Dmin) are kept constant irrespective of the sample size, whereas in the second one, the resolution (number of particles within the sample or ϕv) was kept constant. Neither of these approaches properly represent the observations in actual laboratory tests, even if both of them show some interesting capabilities reported in this document. Eventually, some suggestions are provided to proceed towards improving modelling approaches to represent observed scale effects.Agencia Estatal de Investigación | Ref. RTI2018093563-B-I0