Method of driving a mine working in massif subject to tectonic stresses

Abstract

FIELD: underground mining in rocks.SUBSTANCE: method of mining a working in a rock mass exposed to tectonic stresses includes making a straight cut with the formation of a cutting cavity in the centre of the mine working, determining the direction of the greatest compressive stress in the massif and forming the mine working. If the greatest compressive stress is found in the horizontal transverse direction to the contour of the working, the cutting cavity is expanded by exploding pre-contour and contour blasthole charges in the horizontal transverse direction to the contour of the mine working, whereas as a result of the explosion, a dome-shaped part of the cavity of the mine working is formed due to the natural destruction of the rock.EFFECT: increase in the stability of the workings' boundary rocks.1 cl, 3 dwg

Description

[0001] The invention relates to the field of underground mining of minerals, to the excavation of workings for various purposes in rocks.

[0002] The depletion of mineral reserves located near the surface observed worldwide inevitably leads to an expansion of their underground extraction.

[0003] Underground mining has its own specific features, which are determined not only by the cramped conditions of work and the need for forced ventilation, but also by the influence of the stress state of rocks on the stability of workings and elements of mining systems for the extraction of minerals (Dinnik A.N. "On the pressure of rocks and the calculation of the support of a round mine" "Engineering Worker". 1925. No. 7, pp. 1-12).

[0004] In Russia, a significant portion of minerals are mined in massifs subject to tectonic forces (Gzovsky M.V. "Tectonic stress fields" Izvestiya AN SSSR. Geophysical Series, 1954, No. 5, pp. 390-410 and Stazhevsky S.B., Khan G.N. "On the relationship of increased tectonic stresses with endogenous ring structures" "Physical and Technical Problems of Mineral Development", 2017, No. 6, pp. 50-60). In these cases, the stress state of the massif is determined not only by the weight of the overlying rocks, but also by the influence of tectonic movements of individual blocks of the earth's crust. In these cases, the extraction of minerals can be carried out under conditions of significant horizontal stresses, often exceeding the weight pressure of the overlying rocks (Kvochin V.A., Lobanova T.V., Veselov A.I. et al. “Geodynamic processes in the area of ​​industrial facilities in the south of Western Siberia” “Geodynamics and stress state of the Earth’s interior” Novosibirsk, Publishing House of the Institute of Mining of the Siberian Branch of the Russian Academy of Sciences, 2006, pp. 110-119, Shrepp B.V., AMNokhrin "Assessment of the stress state of the rock massif of the Tashtagol deposit" "Experimental studies of the stress-strain state of the rock massif of mines and pits" Collection of scientific papers, Novosibirsk, Institute of Mining of the Siberian Branch of the USSR Academy of Sciences, 1990, pp. 138-142).

[0005] 1. An integral part of underground mining is the excavation of workings for various purposes in rock. Maintaining these workings in working order during their operation is an absolute requirement of both safety regulations and technological needs during mining. It is a priori clear that in the absence of damage to the rocks around a working, its stability will be maximal. However, when excavating using the drilling and blasting method, the blasts of blasthole charges, which destroy the rock within the working contour, also reduce the strength of the rocks in the boundary zone. To reduce this negative impact of blasting charges on rock strength, contour blasting is used (Baron, L.I. Contour Blasting in Excavation of Workings / L.I. Baron, A.V. Klyuchnikov. Leningrad: Nauka. 1967. 204 p.).In this case, to reduce the shaking effect on the contour mass, subsequent contouring is usually used, when explosive charges (HE) in boreholes (wells) located along the contour are detonated after the charges of the main set of boreholes have detonated.

[0006] A known method for combating rock bursts during mine development under conditions of high lateral tectonic compressive stresses is to prevent rock bursts from the roof. The purpose of the invention is to improve mining safety by taking into account the stress state of the rock mass and the location of the rock burst source. When driving a mine through a rock burst-prone area, the direction of the greatest compressive stresses is determined. The distance from the designed roof contour to the center of the potential rock burst source and the required depth of the wedge-shaped cavity are determined using electrical sounding of the rock mass. The distance between pilot boreholes (PB) and the minimum height from the roof of the PB are determined. After drilling the PB, explosive charges are placed in them in casings with directional slots. Simultaneous detonation of the explosive charges forms a wedge-shaped cavity in the PB. Then, blasthole excavation is performed.The angle at the apex of the wedge-shaped cavity is calculated using the derived relationship. The gap in the shell is positioned at an angle to the vertical axis of the borehole equal to half the angle at the apex of the wedge-shaped cavity and perpendicular to the direction of the greatest compressive stress (SU 1546665, 28.02.1998, E21F 5 / 00).

[0007] This decision is taken as a prototype.

[0008] When driving a horizontal working with a cross-section of width b and height h along a rock burst hazardous section of the rock mass, the direction of the greatest compressive stresses δ is determined максThe distance and required depth of the wedge-shaped cavity (gap) to relieve the roof of the working being driven from these stresses are determined, for example, by electrical sounding, such as a four-electrode setup using the apparent resistivity method. Next, the minimum height of pilot holes from the roof of the working, their optimal diameter, and the explosive charge mass per running meter of the holes are determined, based on the rock strength and the distance between the hole and the intersection of the charge directions. The distance between the holes is determined based on the conditions of the drilling and blasting regulations. The pilot holes are drilled to a depth of three heading cycles. Then, blastholes are drilled to break the rock mass of the face to the depth of the cycle in the usual manner. The explosive charges in the holes are placed in casings with slots. Simultaneous blasting of the explosive charges in the pilot holes occurs, resulting in the formation of a wedge-shaped cavity.

[0009] In essence, the known solution is aimed at forming a stress concentrator in the upper zone of the workings, which is a corner crack, as regulated by the “Instructions for the safe conduct of mining operations at ore and non-metallic deposits, construction sites of underground structures prone to and dangerous for rock bursts” (approved by the Resolution of the State Mining Supervision Service of Russia dated 11 / 24 / 99 No. 86):

[0010] "Mine workings, chambers for various purposes, and rock mass sections classified as "Dangerous" are rendered rock-bump-safe by creating a protective zone using camouflage blasting, relief boreholes, relief cracks, cavities, and a combination of the above methods. "Dangerous" workings are rendered rock-bump-safe by creating a protective zone in the marginal portion of the rock mass. This zone is formed by creating a strip (layer) of broken rock or a continuous crack in the marginal (face-face) portions of the rock mass, provided that the plane of the broken rock (relief crack) is generally perpendicular to the direction of maximum stress in the rock mass…"

[0011] A rock burst is a brittle fracture of the extremely stressed portion of a rock (coal) seam adjacent to a mine working. The phenomenon occurs when the rate of change in the stress state in this portion exceeds the ultimate rate of stress relaxation due to plastic deformation. Although a rock burst occurs in the presence of tectonic stress in the rock mass, it is naturally a tectonic phenomenon. However, a rock burst involves the elastic energy of the seam at the impact site and the energy of the surrounding rock, meaning it directly depends on the properties of the rock itself.

[0012] Tectonic stresses in a rock mass are stresses caused by regional tectonic processes in the Earth's crust. They are superimposed on the gravitational field and cause deformations of large rock masses. Horizontal stresses are associated with the movements of tectonic plates in the Earth's crust.

[0013] Stresses can also arise due to bending forces during compression of folds in bedded rocks and the concentration of stresses in the vicinity of heterogeneities of various natures: ruptures, blocks, inclusions, folding nodes.

[0014] The magnitude of horizontal stresses depends on the shear resistance of the rocks between layers: weak rocks produce low stresses, while strong rocks produce horizontal stresses that exceed gravitational ones. In the near-surface portion of a geological section, the stress-strain state manifests itself as horizontal tectonic stresses that significantly exceed the vertical geostatic stresses due to the weight of the rocks.

[0015] 2. Experience with tunneling operations shows that, under significant horizontal stresses, even with contour blasting, significant rock contour failures occur. Analysis of drilling and blasting data sheets for tunneling operations shows that they are developed based on Section 156 of the Federal Industrial Safety Regulations "Safety Rules for the Production, Storage, and Use of Industrial Explosives" (Order of Rostekhnadzor No. 494 dated December 3, 2020), which does not specify the need to consider the stress state of the rock mass being tunneled. Meanwhile, the stress state of the rock mass significantly influences the nature of explosive destruction (Mashukov I.V. Development of methods for explosive crushing of unevenly stressed massifs during underground ore mining: Abstract of Cand. Sci. (Eng.) diss.: 05.15.11 / Mashukov Igor Vladimirovich. - M. - 1983. - 14 p., Hui C., Xianyang Q., Xiuzhi S.et al Experimental Study on Fracturing Characteristics of Double-Hole Blasting Under Static Stresses" Front. Earth Sci., 2022, V. 9, p. 1-11., Haoyu H., Daisuke F., Hong-yuan L. et al “Combined finite-discrete element modeling of rock fracture and fragmentation induced by contour blasting during tunneling with high horizontal in-situ stress” “International Journal of Rock Mechanics and Mining Sciences” 2020, V. 127, p. 322-345).

[0016] Thus, the solution to the issue of taking into account the stress state of rocks under conditions of significant horizontal stresses is important and relevant for the practice of mining operations.

[0017] The present invention is aimed at achieving a technical result consisting in increasing the stability of the boundary rocks of a working during drilling and blasting excavation based on the use of patterns of change in the stress state of the boundary massif during the formation of the working cross-section.

[0018] The specified technical result is achieved in that the method for driving a mine working in a rock mass exposed to tectonic stresses consists of expanding the cutting cavity with pre-contour and contour blasthole charges in a horizontal transverse direction in relation to the cavity contour with the coincidence of the vector of the long side of the cavity cross-sections in the zones of the greatest compressive stresses in the rock in the side walls of the working cavity.

[0019] The specified features are essential and are interconnected to form a stable set of essential features sufficient to obtain the required technical result.

[0020] The present invention is explained by a specific example of implementation, which, however, is not the only possible one, but clearly demonstrates the possibility of achieving the required technical result.

[0021] Fig. 1 - a section of a horizontal working showing collapses from the roof;

[0022] Fig. 2 - schematically shows an intermediate section of the workings during vertical expansion of the cutting cavity;

[0023] Fig. 3 - cross-section of the working during driving (horizontal expansion of the cutting cavity.

[0024] The present invention considers a new method for excavating a mine working in a rock mass subject to tectonic stress. The determination of conditions for reducing the stress state of the rock mass during the formation of the working cross-section is based on studies based on the laws of stress field formation in an elastic medium around openings, as well as on a theoretical estimate of the relaxation time of the rock mass stresses during the expansion of the cutting cavity.

[0025] During the development of a 27-square-meter horizontal permanent mine working in rock with a hardness of f=12-14, constant rock failures (rock falls 1) were observed in the working roof, despite contour blasting (Fig. 1). These failures not only resulted in a significant deviation of the working cross-section from the design, but also significantly reduced the rate of development due to the lengthy process of exfoliation of the rock broken in the working roof.

[0026] The excavation was carried out using a straight cut. The design support was anchors. However, due to constant rock failure in the roof of the working, the workings required concrete lining.

[0027] In the rock mass in which the above mentioned working was carried out, horizontal stresses equal to σ act Г =35 MPa and vertical - σ В =15 MPa.

[0028] The magnitude of the contour stress at point A can be estimated based on the solution of the problem of stress distribution around an elliptical hole under the action of compressive stresses (Savin G.N. “Stress distribution around holes” Kyiv, “Naukova Dumka” 1968, Khan X. “Theory of elasticity. Fundamentals of linear theory and its application” M, “Mir” 1988):

[0029]

[0030] where:

[0031] B=5.0 m, H=5.9 m - width and height of the workings, respectively.

[0032] Based on (1) and data on the stress state of the medium, we determine (σ xx ) А ≈100 MPa.

[0033] The obtained value of compressive stress in point A is less than the compressive strength of the medium material, i.e. destruction of the working roof should not occur.

[0034] To explain the causes of roof destruction, it was suggested that the stressed state of the massif is reflected in the stresses arising in the environment during the formation of the cross-section of the working as it advances, which can lead to the formation of a destruction zone in the roof of the working, therefore, contour blasting occurs in a weakened massif and does not achieve its goal.

[0035] It should be noted that during the formation of the cross-section, the stresses in the environment have time to redistribute in accordance with the forming configuration of the intermediate cross-section after the explosion of each borehole.

[0036] Indeed, if the time interval between explosions of charges is τ>>T, where T is the period of natural radial oscillations of the intermediate section of the working, then the stresses in the environment have time to redistribute, and the explosion of each charge will occur in an array whose stress state corresponds to the static stresses for the corresponding configuration of the intermediate section.

[0037]

[0038] where d is the characteristic size (diameter) of the intermediate section of the working;

[0039] s s - the speed of transverse waves in the massif in which the working is located.

[0040] For the conditions under consideration: d=1.7-4.5 m; s s =2000-3000 m / s (M.M. Protodyakonov, R.I. Teder, E.I. Ilnitskaya et al. “Distribution and correlation of indicators of physical properties of rocks” Reference manual M, “Nedra” 1981), in accordance with (2), we have -T=1-3.5 ms.

[0041] The obtained values ​​of stress redistribution time are consistent with the data of the work (Mikhalyuk A.V., Zakharov V.V. "Relaxation effects in the dynamics of soils and rocks" "Journal of Applied Mechanics and Technical Physics" 2000, No. 3, pp. 202-212). In the work (Tyupin V.N., Ponomarenko K.B. "Determination of the stress state of the mining massif by the explosive and vibroacoustic method" "Mining Industry" 2024, No. 6, pp. 34-40) differences in the magnitude of stresses in the area of ​​cutting and auxiliary boreholes and in the area of ​​pre-contour and outlining boreholes are noted.

[0042] Typically, with short-delay blasting, the delay time τ between blasts of the pre-contour and auxiliary holes is 25-100 ms, and that of the pre-contour and contour holes is 100-250 ms. Therefore, the condition τ>>T is satisfied.

[0043] Thus, the explosion of each charge (group of charges) will occur in an array whose stress state corresponds to the static stresses with the corresponding configuration of the intermediate section.

[0044] Fig. 2 schematically shows an intermediate section of the working with vertical expansion of the cutting cavity: the section of the working during driving (vertical expansion of the cutting cavity, where 2 is the cutting cavity, 3 is the expansion of the cutting cavity). The magnitude of the compressive stress at point A1 is equal to

[0045]

[0046] When h1≈2.4 m, b1≈5.5 m, the compressive stress at point A1 is equal to (σ xx ) А ≈180 MPa, which significantly exceeds the compressive strength limit of the medium material, i.e. at point A1 and its environs, destruction of the medium will occur under the action of compressive stresses.

[0047] Due to the significant speed of shear cracks (~10 2 -10 3m / s) (Cherepanov G.P. “Mechanics of brittle fracture” M, “Science”, 1974) the time between explosions of pre-contour and contour blasthole charges is sufficient for their growth to an extent determined by the acting stresses and strength properties of the medium.

[0048] Additional calculations showed that when the intermediate section shown in Fig. 2 is formed, the stresses in point A also exceed the compressive strength of the medium and are equal to (σ xx ) A ≈150 MPa.

[0049] The total depth of the rock mass damage caused by compressive stresses will be up to 0.3-0.4 m at the roof. The delaminations increase the height of the workings, creating a dome-shaped vault. Stress concentrations at the top of the vault increase, and the damage progresses. Falls 1 from the roof are observed, as shown in Fig. 1.

[0050] To eliminate the negative consequences caused by the manifestation of the stress state of the environment, it is proposed to carry out the expansion of the cutting cavity in such a way that the long side of their cross-sections is directed towards the greatest compressive stresses (horizontal expansion of the cutting cavity) (Fig. 3). Fig. 3 shows the cross-section of the working during excavation (horizontal expansion of the cutting cavity, where 4 is the cutting cavity, 5 is the expansion of the cutting cavity).

[0051] To achieve the desired result, you can change the order of blasting the blasthole charges.

[0052] In this case, the circumferential stresses at points B and C are equal to:

[0053]

[0054] Based on (3), (4), with b2≈4.2 m and h2≈2.2 m, we have (σ yy ) B ≈40 MPa and (σ xx ) С ≈60 MPa.

[0055] During horizontal expansion of the cutting cavity, the greatest compressive circumferential stress in the process of forming the workings arch is determined by equation (1) and is equal to (σ xx ) A ≈100 MPa. The circumferential stress on the contour of the wall of the formed working will be equal to

[0056]

[0057] Analysis of the obtained results shows that by changing the blasting sequence, it is possible to achieve the formation of intermediate cavities in such a way that the stresses on their contours will not reach critical (destructive) values.

[0058] To improve the quality of the formation of the working arch, it is advisable to use contour blasting.

[0059] Thus, a new method for excavating a mine working in a rock mass subject to tectonic stresses can be developed. This method involves widening the cutting cavity using pre-contour and contour blasthole charges in a horizontal transverse direction relative to the cavity contour. This aligns the long-side vector of the cavity cross-sections with the zones of greatest compressive stress in the rock within the cavity's sidewalls. Since the time it takes for stress redistribution in the rock and its transition to a static state after each blast is significantly shorter than the time between blasts during sequential blasting, horizontal blasting allows for widening the mine working contour to a specified size, while the dome-shaped portion of the cavity is formed through natural rock fracture due to vibrations induced by blasting processes.

[0060] The present invention is industrially applicable and demonstrates that when blasting auxiliary and pre-contour boreholes, it is necessary to shape the resulting cavity so that the long side of its cross-section is directed toward the direction of the greatest compressive stresses. To achieve a positive result, it is advisable to use an appropriate sequence of blasting the blasthole charges. These measures do not negate the advisability of using contour blasting.

[0061] This invention has not been experimentally tested, as the application of the new method requires initial legislative approval in existing regulatory documents. Therefore, the invention is based on extensive published material, recognized as official sources, from various studies of stresses in rock masses, and the calculated numerical data provided in these sources.

Claims

A method for driving a mine working in a rock mass exposed to tectonic stress, which includes making a straight cut with the formation of a cut cavity in the center of the mine working, determining the direction of the greatest compressive stress in the mass and forming the mine working, characterized in that in the event that the greatest compressive stress is found in the horizontal transverse direction to the contour of the working, the cut cavity is expanded by exploding pre-contour and contour blasthole charges in the horizontal transverse direction to the contour of the mine working, whereby as a result of the explosion a dome-shaped part of the cavity of the mine working is formed due to the natural destruction of the rock.

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