ANALYSIS OF GEOMECHANICAL PROCESSES IN THE DEVELOPMENT OF COMPLEX-STRUCTURED ORE DEPOSITS

ABSTRACT

The article examines geomechanical processes and their impact on mining operations in the complex-structured ore deposits of Muruntau, Yuzhny and Nikolaevsky, and considers methods for maintaining the stability of mining operations in connection with the increasing depth of development of complex-structured deposits.

АННОТАЦИЯ

В статье рассматриваются геомеханические процессы и их влияние на ведение горных работ на сложноструктурных рудных месторождениях Мурунтау, Южный и Николаевское, а также рассматриваются методы поддержания стабильности ведения горных работ в связи с увеличением глубины разработки сложноструктурных месторождений.

Keywords: mining, deposits, shaft, underground, blasting, geomechanical processes, horizons

Ключевые слова: добыча полезных ископаемых, месторождения, шахта, подземные работы, взрывные работы, геомеханические процессы, горизонты

Introduction

Due to the increase in the depth of mining operations, there are currently a number of difficulties associated with justifying the mine without emergency operation, since the development conditions are changing significantly. The calculation of stability at great depths consists in assessing the stress-strain state of the massif and the support of workings in a low-strength fragmented massif, taking into account the influence of constantly acting gravitational and tectonic stresses exceeding the tensile strength [1].

Complex–structured ore deposits are deposits characterized by different genesis of geological formations, complexity of petrographic composition (chemical, structural and mineralogical features of rocks), mineralization with different content and distribution of rocks, structural heterogeneity (contact layers, faults, fracturing, cleavage, contacts of individual mineral grains and geological disturbances) that arose during geological processes in the depths of the Earth's crust.

From a mining and technological point of view, complex-structured ore deposits are the spatial arrangement of ore bodies and host rocks, the morphology of ore bodies, their internal structure and relationship with host rocks, which is the result of complex interactions of rock and ore formation processes, as well as manifestations of tectonic movements [2,3].

The signs of complex-structured ore deposits are the sizes and shapes of ore bodies, conditions and angles of occurrence, physical and mechanical properties of rocks and the nature of mineralization.

According to these signs, complex-structured deposits are divided into natural and man-made ones.

Natural deposits are classified into nest, stockwork, vein and lens-shaped mineralization with variable capacity, the presence of substandard and oreless layers and combined - a combination of two or more previous types of deposits.

Research methods

Technogenic deposits are structurally altered or newly formed as a result of the application of various mining and processing technologies to mineral raw materials from natural deposits. Technogenic deposits are classified into on-board and quarry reserves (remaining in the subsoil during open-pit mining), underground reserves (remaining as a result of advanced mining of rich ores and during the mining of balance ores under simple (favorable) mining conditions), and off-balance reserves of ores from underground and open-pit mining, stored in dumps on the surface or in mined-out spaces of the mine [4].

Mining enterprises periodically need to restore mined-out areas that were previously in operation and ceased operations due to emergencies such as the presence of a large volume of methane, fire consequences, or rock burst. Typically, these are inaccessible and dangerous underground workings for humans. Therefore, unmanned aerial vehicles (UAVs) of various modifications, as well as ground vehicles moving along the ground of mine workings (autoscans), can be used for diagnosing the degree of disruption of rocks and structural elements of support of mine workings [5].

Geomechanical processes are processes of deformation, stress redistribution, and rock mass failure. The geomechanical processes themselves are usually hidden from the observer. The subject of observation is the manifestations of geomechanical processes or manifestations of rock pressure, as well as the geomechanical condition of the rock mass.

Geomechanical processes in rock masses of mineral deposits and underground construction occur in a variety of ways. In our country and abroad, studies of geomechanical processes have been conducted for quite some time, resulting in a large amount of normative database documents developed for regulating the state of the rock mass during open-pit and underground development of deposits.

Analysis of accumulated examples and databases contributes to the formation of promising directions for regulating the state of rock masses and mining-technical processes. All deposits in Uzbekistan developed by underground methods, despite the differences in geological conditions, length, and cross-section, mainly use the same type of support. This results in significant costs for equipment repair and reinforcement of mine workings. In the CIS countries, the annual volume of reinforcement of main and preparatory workings reaches up to 25% of the total length of mine workings, and considering repairs and man-hours, this indicator reaches up to 35%.

In practice, due to the lack of precise information about the properties of the surrounding rock mass and the nature of geodynamic processes, the selection of optimal support parameters is difficult. When using multiple types of fastening materials, problems arise with transitioning from one type of support to another.

Therefore, prospective directions in solving the problem of managing the state of rock masses during mining operations include:

1. Improving methods of obtaining accurate and complete information about the state of surrounding rock masses;
2. Development of types and designs of supports that can flexibly adapt to changing conditions [6].

One of the key directions for improving the technology of developing complex-structured deposits is conducting field research on the stress-strain state of both natural and technogenically altered rock masses. Based on these studies, the design parameters of mining systems and methods of controlling rock pressure are justified, taking into account the morphology of ore deposits.

In the Far Eastern region, there is a need to transfer a significant portion of gold deposits from open-pit to underground mining. A characteristic feature of the combined development method is the presence of quarry and underground clearing spaces located in close proximity to each other. Through practice and analysis of deposit development using this method, certain geomechanical problems in choosing technological schemes and development parameters become evident  [7].

"Nikolaevsky" deposit

In the lower horizons of the Nikolaevsky deposit at a depth of 600 meters (below the -220 horizons), high pressure is observed on the roof of mine workings. Therefore, a methodology and variant of tracing block horizontal preparatory workings at an angle of 45° to the direction of maximum compressive stresses were developed; this solution ensures a reduction in the maximum stress level in the roof of workings by 12–14% (see Fig. 1).

Figure 1. Distribution of horizontal stresses σy in the roof of mine workings located at a mountain elevation of -323 meters, in the actual (a) and proposed (b) variants of the arrangement of drifts and crosscuts at an angle of 45° to the principal stresses [8].

For the safe development of the Nikolaevsky field, several methods have been developed for monitoring and controlling rock pressure in the lower horizons by changing the location of the sinking of drifts and orts at an angle of 45° to the main stress tensors, as well as ensuring safety is achieved through early drilling of vertical discharge wells in the roof of preparatory workings and directional control of the geomechanical process using the method of concussive blasting acceptable level of mining safety.

These solutions are very relevant for the development of other fields whose structures are close to the Nikolaevsky field. The distribution of horizontal stresses over the entire horizon of the mine field to ensure safety during rock excavation has many advantages, but the area of stressed zones increases several times. Following from these statements, it is possible to apply different types of fasteners depending on the stress indicators in certain sections of the mine workings. Which contributes to ensuring safety during cleaning operations at a horizon of -323 meters.

The world experience in the development of mineral deposits and the construction of underground mine workings shows that the factors determining the stability of the massif are the parameters of the structural disturbance of the mountain range, its strength and deformation properties and the parameters of the stress field acting in it. The relationships between the quantitative indicators of these factors determine the mechanism of deformation of the system of individual blocks and the nature of its loss of stability as a whole. The most widely used methods for predicting the stability of underground mining operations do not explicitly take these processes into account and therefore in some cases may turn out to be unreliable. [9].

The Yuzhny deposit.

In the lower part (below the horizon of 550 m) of the Southern deposit in the host rocks and sulfide ores, it is observed that the strength properties are characterized on average by values of 118 and 78.6 Mpa and a high modulus of elasticity up to 100 Gpa or more, as the mining deepens, these indicators only increase.

After working off 50% of the cleaning block (25 m) with a system of sub-storey drifts, it is necessary to take measures to reduce the impact hazard of the inter-chamber pillars of the two upper sub-floors by drilling loading wells in the roof and soil of the workings, perpendicular to the direction of action of maximum stresses (Fig. 2 a).

It is recommended to unload the superstructure and substructure targets formed during the development of the deposit by a system with ore storage at a height of 25 m of the mined ore by camouflage blasting of borehole charges into unloading wells with drilling wells in the direction of maximum stresses for the entire length of the treatment unit (Fig. 2 b)

Figure 2. Distribution of σavg in the rock mass after drilling boreholes in hazardous areas; a) inter-chamber protective pillars; b) inter-level pillars (cross-section through the ore body extension) [10]

Safety of underground facilities during construction and operation depends on assessing the risk of potential emergency situations [11-13], as well as the ability to prevent the causes of their occurrence [14]. Emergency situations are caused by specific engineering-geological, hydrogeological, and urban planning conditions of underground facility placement: the presence of thick layers of technogenic and karstified soils; dense urban development and confined conditions; high groundwater activity; suffusion manifestations; anthropogenic impacts on the geological component of the city, complicating the conditions for construction and operation of underground structures; involvement of a large number of non-specialized specialists and organizations in the construction process. These risk factors necessitate their identification and consideration throughout the entire lifecycle of the underground facility, which aims to optimize the selection of the site for the facility and corresponding protective measures [15].

Muruntau Deposit:

One of the main influencing factors on the stability of field preparatory workings is the increased stress-strain state of the rock mass, occurring in the zone of support pressure from clearing works. Capital workings (e.g., transport tunnels) may also fall into the hazardous zone during their operation, in the process of mining operations. Therefore, it is necessary to know the main patterns of distribution of technogenic stresses in the peripheral array of field workings located near the clearing space in order to timely forecast their stability and assess the terms of reliable operation. These tasks have been repeatedly posed by mining enterprises operating gold-bearing steep-dipping veins of small and medium thicknesses underground, where field preparation is widespread, especially at great depths, where it becomes dangerous to apply ore preparation [16-17].

The Muruntau mine is one of the largest gold deposits in Uzbekistan located in the southern wing of the Tashkazgan anticline. Muruntau has a stockwork origin of the main veins, the length of which varies from 250 to 400 meters, and the average thickness of quartz veins is 5-15 cm. The Muruntau deposit is developed by an open-pit method with the presence of Shaft "M," which is intended for geological exploration and drainage of underground groundwater.

During the period from 2018 to 2020, Shaft "M" was operated for the purpose of mineral development, lying in the peripheral zone of the quarry wall and considered as unbalanced reserves in the Muruntau quarry.

The development in the deposit was carried out by the sub-level chamber system with subsequent filling. The filling material used was a concrete mixture and waste rocks from the Muruntau quarry. The filling of the void space was intended to ensure the stability of the non-working quarry wall.

Support of capital workings in Shaft "M" is carried out using SVP-17, with a distance of 1 meter between them. In the presence of various-strength interlayers and cracks, the distance between links is reduced to 0.5 meters. When changing the cross-section of mine workings, the number of SVP links changes, and concrete rings are installed between them

Figure 3. A method for maintaining mine workings using SVP-17 in Mine “M” Muruntau

The transition to greater depths in the development of underground space and the conduct of mining operations in complex mining and geological conditions (MGC) has exposed the inadequacy of existing approaches and highlighted the need for their fundamental change. Previously, efforts were made to predict individual static parameters of the mining and geological environment (expected displacement of roof or floor rocks, load on the support, weight of the collapse, etc.). Now, it is particularly important to establish the main patterns governing the processes of rock deformation and destruction around the excavation. Therefore, it is currently necessary to move from a static view of rock equilibrium above the excavation to the study of the development of mining pressure over time, i.e., the study of the processes of rock destruction and deformation around the underground structure. [18].

Results and Conclusions

With the increasing depth of mining operations, to improve the technology for developing complex-structured ore deposits, it is necessary to conduct laboratory and field studies of the stress-strain state of the rock mass and assess the geomechanical processes affecting the stability of mine workings. To address these issues, methods for assessing the anisotropy of the rock mass are used, as well as structural weaknesses in the rocks related to their structural-textural heterogeneity and the impact of these weaknesses on the technology of mining operations. Ensuring the safety of mining operations is achieved by reducing the stress state of the rock mass through the application of development technologies that are reasonably aimed at mitigating the harmful effects of geomechanical processes.

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