## 1 Introduction  
Research conducted in the exploitation field Cukavec II (Figure 1) in the period from 2014 to 2016, proved the dependence of the amount of explosive charge and stem length on the formation of the volume of the spherical expansion, resulting from the detonation of the explosive charge in a borehole of 131 mm in diameter. The main goal was to expand the knowledge about the possibilities of using explosive charges in geotechnical practice. This especially refers to blasting in clay soil by which spheres or cavities of other shapes are formed at different depths below the soil surface by activating a certain type and mass of explosives [1, 2]. The structure of the deposit on the exploitation field Cukavec II is dominated by kaolinite, quartz, feldspar, and chlorite, and the granulometric composition shows that the mineral raw material contains about 75% of the clay component, while the rest is silt. Previous research was conducted with the goal of examining geotechnical properties of the clay soil, where cohesion \(c\), internal friction angle \(\varphi\) and volume weight \(\gamma\) were determined. Cohesion is \(c=23.4\) KN/m\({}^{2}\), internal friction angle \(\varphi=19.8^{\circ}\), and volume weight \(\gamma=18.7\) KN/m\({}^{3}\). Due to the characteristics of hydroalumosilicate clays, which means that it absorbs water and therefore becomes brittle, blasting is directly affected [2, 3]. Mass ranges of two different types of explosive charges (Permonex V19 and Pakaev) which achieve spherical expansions in clay soil were measured and determined. Experimental blasting was performed on a total of 48 boreholes, out of which 6 were test boreholes (Figure 2). The expansions created by the blasting in the boreholes were different in shape and size, but they were all basically in the shape of a sphere (Figure 3). Experimental blasting has determined the effective ranges of explosive charge masses of Permonex V19 and Pakaex which achieved spherical expansion in clay soil. It has been found that spherical expansion for a given borehole diameter of 131 mm and a borehole depth of 2.00-3.00 m can be achieved by explosive charge of Permonex V19 and Pakaex, ranging from 0.2 to 1.6 kg [2; 5]. Figure 1: Research was carried out on the exploitation field Cukavec II near the city of Varaždin [2; 4]. Figure 3: Formed spherical cavity expansion [2; 3; 5]. Figure 2: Training area on exploitation field Cukavec II [2]. The most significant result was certainly the determination of the volume of the resulting expansions in the clay soil during the blasting of a series of boreholes placed on a certain profile (Figure 2). To calculate the resulting expansion volume, the application \"Busotine\" was designed [2,5]. In addition to the application calculating the resulting expansion, it draws 2D and 3D models of it (Figure 3). Further, the compatibility of the application with other CAD tools greatly contributes to the verification and more detailed 3D model of the resulting expansion. Regarding the need to use the data processing method for the obtained data, Volume of the resulting cavity, \(\mathrm{V_{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{ \mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{ \mathrm{  }}}}}}}}}}}}}}\) [m], Resulting expansion of the borehole, \(\mathrm{L_{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{ \mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{ \mathrm{ }}}}}}}}}}}}}}}}\) [m], and Deepening of the resulting expansion, \(\mathrm{D_{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{ \mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{ \mathrm{\mathrm{\mathrm{ \mathrm{  }}}}}}}}}}}}}}}}}\) [m], during the preparation of the doctoral dissertation, [PERSON] 2018 [2] confirms and additionally proves this by introducing an additional supplemented model [2,6].