Stabilization of Deep Roadways in Weak Rocks Using the System of Two-level Rock Bolts

Large rock mass deformation around deep roadways in the weak rocks was a significantproblem in mining activities in Vietnam and other countries. The excavation of roadways leads to highreleasing stress, which exceeds the peak strength of spalling surrounding rock and causes it to enter thepost-failure stage. Tensile failures then initiate and develop around the roadways, which causes thefragmentation, dilation, and separation of surrounding rock. The capacity of the primary support systemis low, which results in a severe contraction in the whole section of roadways, which requires findingsolutions to prevent the deformation of rock mass around roadways and technical solutions fromstabilizing for deep roadways. To stability analysis of roadways can be applied analytical, experimental,semi-experimental, and numerical methods. This paper introduces the prevention mechanism of largedeformation of rock mass around roadways using 2-level rock bolts. The research results show that usingthe system of two-level rock bolts can reduce the values of tensile stress on the boundary of roadwaysrange from 10 to 15% compared with only one. The importance of the total displacement of rock mass onthe boundary of roadways will be reduced from 3.47 to 13.85% using six long cable bolts.

Prospects for the development of underground ore mining geotechnologies at the Talnakh and Oktyabrskoye deep mines

Rich sulphide, cuprous and impregnated ores are currently mined in the underground mines of the Talnakh and Oktyabrskoye deposits at the depths from 250 to 1,700 m. The reserves of rich ores are depleted, and therefore the growth of cuprous and impregnated ores is gaining importance. Their share may reach 80% of the total production by 2030. A distinctive feature of such deposits is the occurrence of cuprous and impregnated ores above the rich sulphide ore, which reserves have been mined out using mining systems with curing backfill mixtures. In this context, mining of impregnated ores will be done in the undermined zones, which will lead to significant rock mass deformation, opening of existing natural and formation of new cracks, will affect the stability of mining structures and will require special measures to control rock pressure in the mines. The paper presents the results of assessing the stress-and-strain condition of the undermined mass of impregnated ores mined using the room-and-pillar cut-and-fill method at the depths of 500, 1000 and 2000 m. The assessment shows that no dangerous stress concentrations arise in the mining structures at great depths which creates preconditions for the safe development of such deposits. A significant increase in ore extraction will require upgrading of existing underground facilities. It is proposed to carry out pre-concentration of the mined ore in the underground conditions using modern crushing complexes, high-capacity mine separators to remove waste rock, which can subsequently be used as the backfill material. In this way, a closed-loop mining system is created that meets the efficiency requirements of mining production and integrated subsoil development.

Application of Hydraulic Backfill for Rockburst Prevention in the Mining Field with Remnant in the Polish Underground Copper Mines

In the polish underground copper mines owned by KGHM Polska Miedz S.A, various types of room and pillar mining systems are used, mainly with roof deflection, but also with dry and hydraulic backfill. One of the basic problems associated with the exploitation of copper deposits is rockburst hazard. Aa high level of rockburst hazard is caused by mining the ore at great depth in difficult geological and mining conditions, among others, in the vicinity of remnants. The main goal of this study is to investigate how hydraulic backfill improves the geomechanical situation in the mining filed and reduce rockburst risk in the vicinity of remnants. Numerical modeling was conducted for the case study of a mining field where undisturbed ore remnant, 40 m in width, was left behind. To compare the results, simulations were performed for a room and pillar mining system with roof deflection and for a room and pillar mining system with hydraulic backfill. Results of numerical analysis demonstrate that hydraulic backfill can limit rock mass deformation and disintegration in the mining field where remnants have been left. It may also reduce stress concentration inside or in the vicinity of a remnant, increase its stability, as well as prevent and reduce seismic and rockburst hazards. Hydraulic backfill as a local support stabilizes the geomechanical situation in the mining field.

Time-Dependent Behavior of Rock Materials

Understanding the geomechanical behavior of a geological model is still an on-going challenge for engineers and scientists. More challenges arise when considering the long-term behavior of rock materials, especially when exposed to environments that enable time-dependent processes to occur and govern overall behavior. The latter is essential in underground projects such as nuclear waste repositories. The lifespan can exceed one million years or other openings where the project’s lifetime and sustainability are the critical design parameter. In such cases, progressive rock mass deformation that can lead to instabilities, time-dependent overloading of support and delayed failure are considered the product of time-dependent phenomena. Understanding and predicting the overall impact of such phenomena aims to achieve design optimization, avoiding dlivery delays and thus cost overruns. This chapter provides more insight into the time-dependent behavior of rocks. Simultaneously, the emphasis is given to investigating and analyzing creep deformation and time-dependent stress relaxation phenomenon at the laboratory scale, and in-depth analyses are presented. This work further develops the understanding of these phenomena, and practical yet scientific tools for estimating and predicting the long-term strength and the maximum stress relaxation of rock materials is presented. The work presented in this chapter advances the scientific understanding of time-dependent rock, and rock mass behavior increases the awareness of how such phenomena are captured numerically and lays out a framework for dealing with such deformations when predicting tunnel deformations.

A method to determine the relative importance of geological parameters that control the hydraulic erodibility of rock

The most common methods used to evaluate the potential hydraulic erosion of rock are index-based methods, which correlate the force of flowing water and the capacity of a rock to resist erosion. This capacity is evaluated using erodibility indices, which combine a set of specific geological parameters. Nonetheless, there exists no clear consensus in regard to the relative importance assigned to the geological parameters. Our study proposes (i) a review of the existing index-based methods used to evaluate the hydraulic erodibility of rock, and (ii) a method to determine the relative importance of the geological parameters governing the erodibility of rock. The developed approach relies on a large data set of case studies providing details of unlined spillways subjected to erosion. We demonstrate that the analyzed geological parameters can be classified according to their relative importance—from highest to lowest—as follows: (1) joint shear strength, (2) nature of the potentially eroding surface, (3) rock block volume, (4) joint opening, (5) rock block's shape and orientation relative to flow direction, and (6) the rock mass deformation module. This ordering of the relative importance of the geological parameters agrees largely with previously established orderings that were based on field observations.