# Investigating an Enhanced Contour Blasting Technique Considering Rock Mass Structural Properties
## 2 Materials and Methods  
At present, when compiling drilling and blasting design parameters, it is a common practice to calculate the required explosive charge to blast a given volume of rock mass based on the effective energy of the explosive; most of the time, the peculiarities of the rock mass properties are not taken into account. To account for these, the implementation of numerical modeling is usually recommended. For example, [PERSON], [PERSON] [24] investigated the damage caused by the seismic load of explosions on underground structures and rock masses using a numerical modeling approach. Hence, numerical modeling was also used in the current study. In this research, we carried out a series of experimental blasting in an excavation in the Akbakai mine, an underground mine operation located in the southern part of Kazakhstan, which served as a case study. The Akbakai gold deposit is located in the Moynykum District of the Zhambyl Region, 450 km northwest of the city of Almaty. A sublevel open stope mining system was implemented to exploit the ore vein, steeply dipping with a dip angle of 55-85\({}^{\circ}\); the deposit thickness ranged from 0.5 m to 3.0 m. The deposit was divided into three geotechnical domains primarily defined based on structural and strength properties along with the intensity of fracturing, alteration, and degree of weathering. Geological mapping, determined directly on the contour of the workings, revealed that three joint systems were clearly observed: dip direction/dip angle 345\({}^{\circ}\)/40\({}^{\circ}\), 159\({}^{\circ}\)/65\({}^{\circ}\), 256\({}^{\circ}\)/57\({}^{\circ}\), characterized by layering, longitudinal, and transversal directions in reference to the excavation axis, respectively. The \(RQD\) varied 40-80%; the UCS of the representative rock was 100 MPa. These data were used to estimate the geological strength index \(GSI\) using the equation as follows [25]:  
\[GSI=\frac{52J_{r}/J_{a}}{1+J_{r}/J_{a}}+\frac{RQD}{2} \tag{1}\]  
where \(J_{r}/J_{a}\) defines the inter-block shear strength or joint friction, \(J_{r}\), \(J_{a}\) are the joint roughness number and the joint alteration number, respectively, according to the Q-rating system [26]. For the segment of the excavation investigated in the Akbakai mine, the most representative values of the joint properties were \(J_{r}\) = 1.5; \(J_{a}\) = 2. The \(GSI\) was found to be 68 for the most representative rock domain according to Equation (1). The properties of the jointed rock mass were determined by the Hoek-Brown criterion [27; 28] using the geologic strength index \(GSI\). For the numerical modeling, RS2 application (version 11.005) of Roccience software package ([[https://www.rocscience.com/](https://www.rocscience.com/)]([https://www.rocscience.com/](https://www.rocscience.com/))) was used to simulate the strain stress states of the rock mass surrounding the excavations. It is a very popular tool for the two-dimensional analysis of rock mass. The simulation results can be used to determine unloading zones and stress concentrations, the magnitude of the principal stresses acting in the rock mass, zones of inelastic deformation, and the value of the rock strength factor. They were obtained according to the Hoek-Brown and Mohr-Coulomb criteria in the RocLab program, which considers the quality of the explosion impact on the contouring massif, i.e., the disturbance factor (D-factor). This factor is also employed in the RS2 program in the Generalized Hoek-Brown criterion. The D-factor range varies from 0 to 1.0. That is, if the D-factor = 0, then the influence of the explosion force on the excavation is insignificant or non-existent, and if the D-factor = 1, the perimeter is severely destroyed by the explosive impact. Using a trial-and-error approach, the explosive load that leads to a D-factor close to zero can be identified.