Analysis of Reinforcement System (Rock Bolt and Shotcrete) Effect on The Pillars Strength in Underground Mining Using Physical Models Testing in Laboratory (original) (raw)
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Study Of Shape and Inclined Surface Pillar Effect On Strength Of Pillar
PROMINE, 2019
Study of stability and pillar failure mechanism with a variety of methods have been carried with empirical and analytical approach. H. Moomivand dan V.S. Vutukuri in 2008 do to research with physical model of coal cubic with ratio of 0,25 to 10 with surface of pillar is horizontal, this research aims to investigated changes in the ratio of pillar on compressive strength and pillar mine failure mechanism, to study the relationship do the physical modelling with 5 variations of height of 5 cm-40 cm each pillar geometry has 7 variatons inclined surface 0 o-30 o. Samples of the pillar of testing with direction of the axial load on the body pillar until failure. Other than that do to 2D numerical modelling with finite element methods with assisted of software Phase2 (Rockscience). Physical modelling result showed the value of the compressive strength and the strength of pillar will be increased with the increasing ratio of pillars w/h. Effect of change in the inclined surface pillar to the compressive strength and pillar of strength showed no behavioral changes in the compressive strength and the strength of the pillars to change the angle of the surface of the pillar. Changes in strength factor and sigma 1 showed decreasing of the value when the angle of the pillar is increasing even though the changes in the value of the numerical modeling results are not significant.
AN EVALUATION OF THE STRENGTH OF SLENDER PILLARS
Pillars with width to height ratios of less than 1.0 are frequently created in underground hard rock mines. The strength of slender pillars can be estimated using empirically developed equations. However, the equations can provide variable results when the width-to-height ratios approach 0.5. This paper investigates some of the issues affecting pillar strength at low width-to-height ratios in hard brittle rock. The investigation includes an evaluation of empirical pillar strength data presented in the literature and observations of pillar performance in underground limestone mines in the eastern United States, supplemented by numerical modeling in which failure processes and sensitivity of slender pillars to variations in rock mass properties are evaluated. The results showed that the strength of slender pillars is more variable than that of wider pillars. The numerical model results demonstrated the increasing role of brittle rock failure in slender pillar strength. The absence of confinement in slender pillars can result in a fully brittle failure process, while wider pillars fail in a combined brittle and shearing mode. The onset of spalling in slender pillars occurs at or near the ultimate strength, while this is not the case for wider pillars. Slender pillars are shown to be more sensitive to the presence of discontinuities than wider pillars, which can partly explain the increased variability of slender pillar strength. Two examples are presented, which illustrate failure initiation by brittle spalling and the sensitivity of slender pillars to the presence of discontinuities.
Utilizing concrete pillars as an environmental mining practice in underground mines
Journal of Cleaner Production, 2021
Ground control is an integral element of mine design and worker safety. The use of concrete pillars for underground mines is of paramount importance to maintaining the economic and operational security of structures. This paper deals with the use of fiber-reinforced concrete (FRC) as pillars via laboratory and field tests. The strength performance of prepared concrete reinforced with glass, polypropylene and polyacrylonitrile fibers was researched by a mechanical press and a computed tomography (CT) tool. Samples were tested for fiber volume fractions of 0, 0.4, 0.8 and 1.2 wt%, respectively. Results have indicated that, with the addition of fibers, the strength was improved first due to a bridging effect and then decreased due to a pull-out effect. Compared to the reference sample, the absorbed energy prevents FRC from deterioration by mechanisms of matrix cracking, fiber-matrix interface debonding and fiber rupture. The peak strains of FRC linearly rise with increasing fiber. The gray value distribution curves have also good correspondence with 2D CT pore and crack distributions, which reveal that gray value processing could depict the structural behavior of concretes reinforced with or without fiber. Theoretical analyses show that the pillar remains stable for sustainable mining. Besides, the location and size of FRC pillars are suitable for numerical calculations of the trial stope. The findings of this study can offer a key reference for the orebody pillar recovery in underground mines.
Pillar stability assessment approach for mechanized and drill and blast excavations
Stability of pillars is essential in achieving maximum safety and economic values in room-and-pillar and block cave mining projects. Today's economic market is motivating underground mining companies to increase development advance rates and enhance their NPVs. There is a drive to move away from the conventional drill-and-blast as the main excavation method to alternative means such as mechanized excavation. The cyclic nature of drill and blast, and its inherent tendency to damage the surrounding excavation rock mass and increase support demand often result in poor advance rates. There is little experience with mechanized or non-explosive excavation methods in hard rock metalliferous underground mining. Therefore, the perceived benefits of mechanized excavation over drill-and-blast must be demonstrated. The application of numerical modeling in rock pillar stability analysis has recently become popular. In this paper a numerical modeling approach has been developed and used to investigate the impact of excavation method on the stability of hard rock rib pillars. Phase 2 , the two-dimensional finite element program was selected for the numerical analysis. The 3D advance of two parallel drifts in mechanized and drill and blast excavations is first modeled using the internal pressure reduction approach. The drill and blast excavation is simulated by assigning lower strength and stiffness properties to a zone adjacent to the excavation boundary representing a blast-induced damaged zone, while no such zone is considered to exist in the case of mechanized excavation. The mechanical properties of rock around the mechanized excavation, and the zone outside the perceived blast damage zone are kept the same, and higher than the blast damaged zone. The impact of excavation method on pillar stability is then assessed using the criteria including the distribution of stresses in the pillar, damage initiation and propagation thresholds, strainburst potential as well as depth of yielding.
Productivity of rock reinforcement: methodology development
Journal of the Southern African Institute of Mining and Metallurgy, 2016
To improve safety for operators and equipment underground, ground support systems (bolts, screens, etc.) are installed in mines to stabilize the rock mass (Hoek, Kaiser, and Bawden, 1995). Important questions to ask when selecting a ground support system include where ground stability problems are located, why they have occurred, how problems should be addressed, and when and how the ground support system should be installed (Hadjigeorgiou and Potvin, 2011). The performance of bolting and screening operations in underground mines is important for both safety and productivity reasons. With greater mine depths and an increasing focus on safety, ground support has become a significant bottleneck in the production process of many mines. Many factors play a role in establishing safe and stable underground structures. Equally, there are several factors to consider in productivity, including the mining method, organization, logistics, mechanization level, and procedures. Today, most mines in Scandinavia have changed from manual to
Geo- Mechanical Properties of Okaba Coal Deposit for Pillar Support System
This paper investigated the Geo-mechanical properties of Okaba Coal deposit for pillar support system in an underground mine, in which the unit weight of sandstone being the roof rock is 2 450 kg/m3, average Uniaxial Compressive Strength (UCS) value for sandstone sample is 58.65 MPa while the coal sample indicated a UCS value of 4.11 MPa. The Rock Quality Designation of sandstone sample is 76 % while that of coal is 35 %. The Rock Mass Rating (RMR) of sandstone is 74 while that of coal is 36. The RMR was used in the system of pillar dimension whose height is 2.6 m, width of 7.8 m and length of 32 m arranged in form of chain along the roadways to support the roof, and the panel is dimensioned to 200 m width and 1200 m length surrounded by roadways of 4 m width. The choice of the pillar dimension is purely based on the fact that it is the only one that satisfies the requirement of factor of safety of 1.6 which is sufficient enough to ensure stability of the roadways in the mine.
Field and simulation study for rock bolt loading characteristics under high stress conditions
2019
Rhomboid shaped coal pillars (35 m x 30 m to 26 m x16 m) were formed by a modified Room and Pillar method below 850 m depth from surface at the CSM mine in the Czech Republic. The pillars were developed in a shaft protective pillar by driving roadways of 3.5-4.5 m in height and 5.2 m in width within Panel V of Seam No. 30. Development of pillars at such great depth is prone to spalling/fracturing (pillar rib dilation) due to redistribution of the high stress regime. The induced stress driven dilation was measured during partial extraction of the coal seam within the shaft protective pillar using rib extensometers. In order to stabilize the pillar ribs, four rows of rock bolts with 2.4 m length were installed into the pillar from all sides at different heights. The immediate roof was also supported by rock bolts at a 1 m grid pattern. Three-way intersections were made to control the deformation of developed pillars and other underground structures. Further, an attempt was made to und...
Revista Facultad de Ingeniería, 2019
Pillar replacement in mining works is a technique of using the pillars that are part of the support structures having a high degree of mineralization, which attracts economic interest. The technique consists of replacing the support pillars of the mineral matrix that contain appreciable and beneficial quantities of mineral by artificial pillars that provide geomechanical structure to the operations, generating support and safety benefits greater than or equal to those provided by the original pillars and thus maximizing the intrinsic economic value of the available rock in the operation. Based on the literature regarding design techniques for the assembly of pillars used in underground gold mining, daily and continuous field inspections were conducted for two months, taking the necessary data for the proposed design following ISRM standards for data collection. The proposed pillars must consider a set of operational economic requirements and meet the geomechanical performance requir...
Some new developments in the design of pillars in salt mining
The new pillar design method by Hou/Lux takes up the theoretical statements. and experiences for the determination of the short-term load bearing capacity of pillars and the necessary safety coefficients already to be found in the methods by Menzel and Uhlenbecker. However, it also follows up on and integrates discoveries of continuum damage mechanics, which are subjectively regarded as essential and promoting, into the field of salt mechanics. Furthermore, the probabilistic safety concept for taking account of the uncertainties resulting from scattering, calculation processes and imponderables, used in the fields of foundation engineering and constructive engineering, is integrated into the design concept. This procedure can be used to determine the short-term load bearing capacity of pillars. the time-dependent load bearing capacity of pillars. the permissible pillar load in conjunction with a failure probability, the necessary rheological safety coefficient, the probabilistic safety coefficient for the uncertainties resulting from scattering, calculation processes and imponderables as well as the necessary safety coefficient for the pillar design and for the safety analysis of existing pillar systems. A first practice-oriented application is presented here.
The Effect of Weak Layers on Pillar Performance in South African Chrome and Platinum Mines
Generally pillars in the Southern African hard rock tabular underground mining environment are designed using either empirical pillar design formulae or numerical modelling (analytical) methods utilizing the Hoek-Brown failure criterion. However, none of the pillar design methodologies employed takes cognizance of weak layers either within the pillar material or in the immediate foundation of the pillar. Over the past few years, the presence of a weak layer either within the pillar material or within the immediate foundation of the pillar has resulted in the closure of one platinum mine (Everest Mine), closure of one chrome mine (Wonderkop Chrome) and large-scale instability in a couple of chrome and platinum mines in South Africa and Zimbabwe. A study has been initiated to better understand the failure mode and strengths of the pillars where pillar failure associated with weak layers occurred. Owing to the infancy of the study into the failed pillar strength and failure mechanism, the purpose of this paper is to highlight the circumstances that led to the collapse of mining sections and a shaft, and the difficulty associated with designing pillars in the Southern African chrome and platinum mining operations. 1 INTRODUCTION Southern African chrome and platinum mines generally operate at shallow to intermediate depths (surface to an approximate average depth of 700 metres below surface). Except for Northam Platinum, which is the deepest operating platinum mine in Southern Africa utilizing backfill for regional stability, all the operations make use of pillars to ensure local and regional stability for the on-reef excavations. Pillar performance requirements vary with some operations making use of crush pillars, one operation making use of yielding pillars and others making use of stable pillars. Not all operations use the same methodology for pillar design, despite the operations typically being in close proximity to one another. Most operations make use of a typical Hedley-Grant type power formula, or some variation thereof, whilst another operation has made use of numerical modeling utilizing the Hoek-Brown failure criterion. However, both these methods make use of a number of assumptions regarding the rock mass strength and pillar loading mechanisms. A number of operations have been adversely affected, from a stability point of view, owing to inappropriate assumptions being made whilst determining the pillar strengths. These operations are typically the shallower operations (average depth approximately 240 metres below surface). The case presented in this paper is one where there is a layer of weak material within the pillar material.