Study of hydroerosion process parameters of zeolite-smectite tuffs and underlying rock

The paper considers the expediency of complex processing of zeolite-smectite tuffs using the method of borehole hydro-mining. The basic information about deposits of zeolite-smectite tuffs in the Rivne-Volyn region of Ukraine and the main areas of their application in industry are presented. Also, the method of calculating the parameters of the process of hydraulic erosion of tuffs and underlying rocks by the method of borehole hydro-mining is given, and the dependence of the specific consumption of the working agent during erosion of tuffs and underlying rocks on the diameter of the nozzle at variable pressure is presented. The dependences for determining the rational forms of recess chambers with the specified erosion radius are given.


Features of occurrence of zeolite-smectite tuffs in the Rivne-Volyn region
At the current stage of development of mining science, intensive research and industrial development of Ukraine's raw resources are being carried out [1][2][3][4][5].The Rivne-Volyn region of Ukraine is rich in deposits of zeolite-smectite tuffs, which are of great interest to the industry of Ukraine.Currently, their industrial extraction is not carried out, however, in the development of basalt deposits, in particular (Berestovetske deposit, Ivano-Dolynsk basalt deposit (Rivnen district), Rafaliv basalt deposit (Varas district)), tuffs are the host rock, and, as a rule, when loading the blasted basalt mass for processing tuffs are sent to the dump [6][7][8][9].
Those tuffs that have low sound and thermal conductivity are loose and porous.Calcareous tuffs are used as building materials, floor and facing tiles are made from travertine.Calcareous tuff is used for the construction of buildings as a light building stone, thermal insulation material, for the production of lime.
At the same time, the zeolite-smect tuffs of these deposits deserve special attention and study.Their use in the national economy is already widely known as a feed supplement for animals and poultry, to increase soil fertility and their deactivation in radioactively contaminated soils, and wastewater treatment.In construction, tuffs are used to make bricks, roof tiles, ceramic tiles, and as a pigment for paints.Zeolites have valuable physical and mechanical properties, in particular, resistance to aggressive environments and ionizing radiation, reversible low-temperature dehydration, high mechanical strength, absence of toxic compounds and contamination by microorganisms, the ability to readsorb water, gaseous tuffs are prone to easy ion exchange of cations at normal temperature and pressure [10,11].
According to the forecasts of geologists of the Rivne expedition, the tuff resources of the Rivne region amount to hundreds millions of tons and lie along the western flank of the Poliska saddle and the western slope of the Ukrainian crystalline shield in the form of a strip 1...10 km wide at depths 5...200 m.On the territory of the Rivne region, in particular, the Rafaliv basalt deposit (figure 1), tuffs lie at a depth 4...60 m and are stretched in the form of a strip from north to south.The mineralogical and petrographic characteristics of these tuffs, their mineral composition (table 1), structural features have been studied in sufficient detail [12][13][14], which allows them to be used purposefully and effectively.
Complex processing of zeolite-smectite tuffs should be carried out in two ways: well hydraulic production and quarrying.The mine method is not considered due to the high cost of works, difficult mining and geological conditions, high level of groundwater [15,16].

Development of a methodology for calculating the parameters of the hydroerosion process of tuffs and underlying rocks by the method of borehole hydro-mining
The influence of well-known laws of mechanics is manifested in the conditions of borehole hydromining (BHM).They are expressed in the manifestation of the balance law of mining pressure work, the results of which, in the conditions of hydraulic mining, are proportional to the loss of minerals in the subsoil [17].Based on this, the main task of mountain pressure management is to maximize the share of work that goes to the safe deformation of the massif outside the excavation chambers, and to minimize it -to the deformation of the roof and protective units.The specifics of field testing and development by these methods is to conduct excavation chambers without fastening.Continuous extraction of chambers followed by collapse is rational [18,19].In the process of excavation, an unloading zone is formed in the roof of the chambers, which perceives only the mass of the roof directly, the pressure of which is mainly transmitted to adjacent massifs and collapsed rocks of the produced space [19][20][21].Using this solution, it is possible to reduce the pressure of the roof on the security cells by up to 10%.
For systems with different shapes of recess chambers, the limit erosion radius R is set as a function of the limit span of the roof: • for a rhomboid chamber • for a square camera where L -the ultimate length of the jet, m; α -the angle of inclination of the jet to the horizon, °.
The most rational parameters R = f (L) there are systems with round and square chambers in which R ≤ L. Magnification R > L (systems with rhomboid chambers) leads to a significant increase in the consumption of the useful component on the bottoms of the chambers: R = 3.9dH 0.526 8.02 + 4.34 where R -the radius of tuffs erosion in the chamber, m; d -nozzle diameter, m; H -the pressure of the working agent (WA) in the nozzle, P a.
Checking the axial dynamic pressure of the jet at the distance of the washout radius is carried out according to the equation: where P -axial dynamic jet pressure, P a; l -the length of the initial section of the jet, m; t -the indicator, which for a camera at a distance of 5. . .7 m, is recommended to be equal to 0.25 m.The productivity of erosion of tuffs P is determined from the equation: where K -the coefficient that takes into account the strength properties of rocks, K = 0.0356...0.042; e -the base of the natural logarithm.
The specific consumption of the working agent (WA) and the energy consumption during washing of tuffs: where a, b, c -constant approximations, the values of which are given in the table 2. In figure 2 the dependences of the specific consumption of the WA when washing tuffs on the diameter of the nozzle at variable pressure in the range of 1. . .2.2 MPa are presented.As a result, we can draw a conclusion about the linear dependence of these parameters.
The erosion radius of the underlying rocks R 1 is calculated according to empirical relationships: Erosion productivity of underlying rocks P 1 : where l 1 -the distance of the nozzle to the hole, m.
The specific consumption of the WA for erosion of the underlying rocks is equal to: where a, b, k, c -constant approximations, the values of which are presented in the table 3.
The specific energy capacity of erosion of the underlying rocks E is equal to:  According to the results of research in figure 3 the dependences of the specific consumption of WA during washing of the underlying rocks on the diameter of the nozzle at variable pressure in the range of 1. . .2.2 MPa are presented.
The amount of minerals loss on the surface of the underlying rocks is determined by dependence: where P 2 -the productivity of the hydraulic elevator, m 3 /t; m -a constant value characterizing the level of minimum consumption of minerals on the surface of the underlying rocks; for tuffs m = 10%.The results are presented in figure 4.
The working time of the excavation chamber is set as a fraction of the volume of the excavation chamber divided by the productivity of erosion of minerals (6) plus the volume of the underlying rocks that are being eroded by the depth of the timing of the useful component, divided by the productivity of erosion (10).
The working time of the excavation chamber is equal to the time of the roof collapse.If the working time of the camera exceeds the time of collapse, the correction of the camera span is made in the direction of its decrease, and the means of strengthening the security cells at depths  of 50 m are provided by dividing the size of the reservoir capacity by the number of layers with the subsequent paving of the produced space.
The proposed technology of hydroerosion of tuffs and underlying rocks by the method of borehole hydro-mining has been experimentally investigated within the Rafaliv basalt deposit and is at the stage of implementation at PrJSC "Rafaliv Quarry" (Ivanchi village, Varas district, Rivne region, Ukraine).

Conclusions
Zeolite-smectite tuffs are increasingly used in the national economy, and due to their trace element composition, they are valuable raw materials for industry.Significant man-made reserves of tuffs in basalt quarries can be selectively extracted due to their weakening with water and subsequent screening, and with the well method of mining, weakening allows to increase the productivity of the process.
Based on the calculation of the hydroerosion process parameters of tuffs and underlying rocks, the shape of excavation chambers with the specified radius of erosion is recommended.The most rational forms of cameras, formed taking into account the radius and length of the span, are round, star-shaped and square.
The dependence of the productivity of tuff erosion in the chamber is presented, taking into account the working time, rock strength properties, chamber geometry, water consumption by the hydromonitor and air lift, and the energy consumption of the process.At the same time, the working time of the excavation chamber is adjusted with the time of the roof collapse and the strengthening of the security cells.

Figure 1 .
Figure 1.The Rafaliv deposit near the villages of Polytsi and Ivancha, Rivne region (taken from open sources).

Figure 2 .
Figure 2. Dependencies of the specific consumption of the WA when washing tuff on the diameter of the nozzle at variable pressure.

Figure 3 .
Figure 3. Dependencies of the specific consumption of WA when washing the underlying rocks on the diameter of the nozzle at variable pressure.

Figure 4 .
Figure 4. Dependence of hydraulic washing productivity on nozzle diameter at variable pressure.

Table 1 .
Content of elements in tuff samples at different quarries, concentration, %.

Table 2 .
Value of constant approximations.

Table 3 .
Value of constant approximations.