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By C. A. Vining, J. R. Nopola

"Evaporites, such as salt and potash, pose unique problems to ground-support designs not encountered in other rock types. Evaporites are subject to continual creep and no amount of ground support can successfully arrest this process. Common ground-support techniques that are useful for most rock types may reduce the effective life of bolts in evaporite mines and can create unseen hazards. A different approach to ground support must be applied to provide long-term support in areas where high creep rates are present. The goal of effective ground-support designs in these situations is not to contain the rock and prevent it from moving; rather, the ground-support design must be able to move along with the rock and contain any fully detached slabs until additional remediation measures can be undertaken. The most appropriate ground-support designs will consider both the expected movement of the rock and the duration that the area needs to remain accessible.INTRODUCTIONEvaporites, such as salt and potash, pose unique problems to ground-support designs not encountered in other rock types. The factors that must be considered in design stem from the deformation behavior of salt, which can fail in a brittle manner, akin to most rocks, but can also deform in a slow, ductile manner, resembling the stretching and elongation of steel. The deformation behavior of salt has been well established in technical circles where it has been studied for decades (Hardy and Langer, 1984). Much of the research in salt mechanics is related to repository science, specifically at the Waste Isolation Pilot Plant (WIPP) in southwest New Mexico. RESPEC has been continually involved in the WIPP from the initial design considerations (Gnirk, Grams, and Zeller, 1977) to the current day (Keffeler, 2016) and has been able to leverage cutting-edge research of salt mechanics into practical solutions for mining operators. While a detailed description of salt mechanics is not provided in this document, Fossum and Fredrich (2002) include a fine overview of salt mechanics. The following list paraphrases their chapter on basic facts about salt to provide some context for the reader unfamiliar with salt mechanics:"

Jan 1, 2018

By R. Quentin Eades, Kyle Perry

"Surface mines continue to implement highwalls for several reasons, such as increasing recovery, improving margins, and justifying higher stripping ratios. Highwall stability is a complex issue that is dependent upon a variety of mining and geologic factors, and a safe design is necessary for a successful surface operation. To improve highwall stability, it is important to understand the connection between local geology and blasting.Explosives are employed throughout the mining industry for primary rock breakage. There are a number of controlled blasting techniques that can be implemented to improve highwall stability. These include line drilling, smooth wall blasting, trim blasting, buffer blasting, air decking, and presplitting. Each of these techniques have associated advantages and disadvantages. Understanding local geology is necessary for selecting the appropriate controlled blasting technique. Furthermore, understanding the limitations and conditions for successful implementation of each technique is necessary. A discussion of the impact of geologic conditions on highwall stability is provided. Additionally, discussion is provided for the successful incorporation of the controlled blasting techniques listed above, and the associated mining and geologic factors that influence the selection and design of controlled blasting plans. Finally, a new methodology is proposed.INTRODUCTIONExplosives are used throughout the mining industry as the standard for primary rock breakage, a critical part of the mining cycle. In 2015, the U.S.. consumed 2.2 million tons of explosives (Apodaca, 2015). The coal mining industry accounted for the majority of explosive consumption, accounting for approximately 63% of total explosives. The quarrying and nonmetal mining industries accounted for 12% of explosive consumption, and the metal mining industry accounted for 9% (Apodaca, 2015). This constitutes 84% of the explosives used in the U.S. However, the energy released during the detonation process is often in excess of that required to adequately fragment the surrounding rock (Jhanwar and Jethwa, 2000). This excessive energy, along with over confinement and poor blast geometry, will cause damage to the undisturbed rock mass beyond the intended boundary of the blast. This event is known as overbreak or back-break (ISEE, 2011)."

Jan 1, 2018

By Yanfa Gao

Clusters of underground openings were developed around the shaft bottom of Tangshan Mine. They were deep and located in soft rock strata. After development, those openings have been subjected to considerable deformation and damages. A combined supporting method including grouting and bolting, shotcrete lining and brickwork was used. This paper analyzing the theories on which this supporting method was based. A new theory called "Disturbed Creep" was developed for deformation prediction of openings surrounded by strata subjected to stresses close to limiting or failure strength. Keywords ground pressure, deep mine, soft rock, stability control

Jan 1, 2002

By Axel Preusse

This paper shows basic considerations about the prognosis and prediction of surface subsidence and other ground movements in the German hardcoal industry. The following case studies describe experiences collected in projects between university and industry.

Jan 1, 2000

By Anthony Lannacchione

There has been a persistent need to forecast roof falls so that miner's exposure to hazardous underground environments can be minimized. Several monitoring techniques have been developed and are used today with varying levels of acceptance in the mining industry. This paper examines the potential for monitoring microseismic emissions activity as a means of forecasting roof falls. The use of this activity to forecast roof falls has drawn only limited attention, resulting in a lack of published field performance data. This deficiency is being partially addressed by analyzing data obtained during longwall mining at Moonee Colliery in 1998. The Moonee data base contains a wealth of information concerning roof fall forecast parameters and the seismic alarm criteria used to develop these forecasts. Four seismic alarm criteria were developed and used by Moonee with varying degrees of success. Roof falls were forecasted 73% of the time with average forecast times of 54 minutes. Ninety percent of the predicted roof falls had a warning time, i.e., the time between warning and roof fall event, of greater than 1 minute. The fraction of forecasted roof falls decayed logarithmically as a function of warning time, until only 20% of events were predicted more than 100 minutes prior to roof falls. False alarms occurred in 50% of the warnings. Many of the false alarms were quickly followed by a cessation in mining which could have temporarily halted the on-going failure process. If mining had continued immediately after the false alarms, a roof fall may have occurred soon after. The microseismic activity collected .from Moonee Colliery demonstrates that techniques to forecast roof rock instabilities in underground mines are possible.

Jan 1, 2005

By M. V. Kurlenya

The experience of application of geomechanical investigations for substantiation of extraction of undermined ore deposit in the north of Siberia is discussed. The finite element method was used for forecasting the state of massif during the development of mining works. The results of calculations were compared with the experimental data of observations in situ for evaluation of authenticity of numerical modelling.

Jan 1, 1990

By S. N. Zhow

China has at least 200 collieries suffering from the problem of instantaneous outbursts of coal and gas. The strong outbursts often occurred in active tectonic lanes and areas of high stress concentration. In this paper, the author describes some characteristics of the strong outbursts and analyses the effects of ground stress, gas pressure and the properties of coal in outbursts.

Jan 1, 1987

By Binchuan Zhang

The combined reinforcement system (CRS) combines the strengths of roof' bolting, resin-anchored cable bolt, and chemical grouting to effectively control the deformation of the strata surrounding an extremely poor entry. It is easy to implement and fast in installation. It is one of the systems that are suitable for the reinforcement and maintenance of extremely poor entries.

Jan 1, 2001

By G. Bucelluni

An essential element of truss bolt installation requires machines to angle a hole in the top of approximately 39° to 45° from its vertical axis. Parameter which inherently effect the drill position are: height, width of truss, physical size of mast, and whether single or dual mast bolting is utilized. The combination of these facets govern the installation procedures required for the bolting cycle. The following illustration with written explanation will demonstrate this concept. See Figure #1. [ ] This model assumes certain fixed criteria which corresponds to a dual mast drill design and a set 41° drill angle. Using the derived formula, the maximum possible seam height for both masts to touch the bottom can be calculated for any given condition by substituting by the appropriate bolt spread distance. [ ] In a high seam application where the mast touching the bottom was considered a requirement, the proposed model demonstrates the advantage of single mast drilling. See Figure #2. [ ]

Jan 1, 1982

By Li-min Liu

The Semi-Analytical method can be used to solve a variety of problems in geomechanics and civil engineering. When it comes to layered rock strata and rock masses, it is superior to all other analytical methods. This paper presents the application of a 3-D semi- analytical method to 3-D surface subsidence and stress analysis caused by mining. In this semi-analytical method the layered elements and triangular elements ate used alternatively. Their displacement pattern, strain mahix, elastic matrix, stiffiness matrix, load matrix and stress matrix are presented. A numerical simulation program based on the semi-analytical method bas been developed using Fortran 90. This program is suitable for subsidence prediction and stress analysis of mom and pillar mining, strip longwall and mechanized longwall mining methods. It is applicable to all geological conditions and mining methods. Comparing with the finite method, this method reduces significantly the number of simultaneous equations to be solved and the amount of data preparation. It not only reduces the computer memory, but also runs faster and cost less. Key Words Semi-analytical method, surface subsidence, stress analysis, layered element, triangular prism element

Jan 1, 2002

By David L. Kuck

This paper describes a system for providing structural, support in underground mines, employing water ice for pillars. packwalls and brattices. It consists of a refrigeration brine chiller, brine circulation system, and disposable plastic containers. The system provides for the timely freezing of uniform ice pillars, and for ice maintainance and/or melting on demand. Unique, useful ice properties include: expansion upon freezing, resilience to dynamic loads, and plasticity. Ice will not dilute or contaminate coal or ore. Economic advantages include: 1) lower labor and material costs (water can be piped to the ice pillar site through mine-water, spray-water, or drill-water lines); 2) replacement or supplementation of timber. concrete or other roof support equipment; and 3) potential use of ice brattices as ventillation control; and 4) conversion of ice bratices to ice pillars upon retreat. See Figure . A safety advantage for personnel and equipment is that ice pillars can be placed in hazardous sites, by remote control, if neccessary, without human entry. All filling, freezing and melting operations can be controlled from a safe distance.

Jan 1, 1987

By James M. Tennant

In the mid 1970's, American Electric Power significantly expanded its internal coal production. This involved opening several large mines in seams that had never been mined on a large commercial scale before. One of the mines opened was the Martinka No. 1 Mine which is located approximately five miles southeast of Fairmont. The mine was originally designed for room and pillar mining with continuous miners but was later modified to permit the utilization of longwalls and continuous miners for entry development. The coal seam to be mined was the Lower Kittanning which averages fifty-six inches. In order to successfully mine this seam, it required that the mine design recognize the effect caused by the dip of the seam which averages four percent to the Northwest with a maximum of sixteen percent for short distances and a relatively low cover. In fact, seventy-four percent of the reserves have cover of less than four hundred feet. Also, the core hole data indicated that the immediate roof varied from zero to eighteen feet of shale with two to forty-five feet of sandstone overlying the shale.

Jan 1, 1982

By Venkata S. Vutukuri

Compressive strength of cylindrical specimens of a model material and sandstone with various diameter/height (d/h) ratios was determined in unconfined compression tests. It was observed that the compressive strength increases with increase in d/h ratio. Triaxial compression tests were also conducted on the specimens of the same materials with a d/h ratio of about 0.47. It was observed that the axial stress at failure increases with increase in confining pressure. A very interesting correlation was found between the effect of d/h ratio on compressive strength in unconfined compression tests and the effect of confining pressure on axial stress at failure in triaxial tests. The relationships between d/h ratio and confining pressure, s3 in MPa are:- For model material - s3 = -0.95 + 1.7957*(d/h) 0.7883. For sandstone - s- (-0.4554 + 0.9888* (d/h) 1.0355. The correlation coefficients for these equations are 0.9997 and 1. These equations are valid for d/h ratios of up to 10.

Jan 1, 1993

By J. A. Nemcik

Although floor failure at longwall faces has been traditionally associated with a soft floor, in many csses floor buckling has been observed just ahead of the longwall supports, despite the floor being a competent rock The floor failure is associated with the presence of weak bedding planes in the floor and the movement of strata towards the goaf opening. This paper presents the principles of the floor failure based on numerical modelling and field observations and outlines the practical approach to estimate the risks involved with floor failure.

Jan 1, 1995

By John C. Stankus

The success of cable bolts for mine ground control have been well documented in papers presented at this conference too numerous to reference. Cable bolts have proven effective over the years mainly utilized in the form of supplemental support. Some limited work has been conducted on the use of cable bolts as primary support This work has been mainly confined to the West and the bolts utilized were of a non- tensioned type MSHA requirements for primary support have been that the bolt system he tensioned or if non-tensioned, then fully encapsulated with resin. Many operators are now interested in using cable bolts as primary support Further, despite the enormous success of cable bolts, there have been questions raised about the longevity and corrosion characteristics of the cable itself particularly for long tern applications. To improve the corrosion characteristics of cable bolts, galvanized cable has been used for some applications However. although improving the corrosion resistance of cable, galvanized cable for mine ground control does not provide complete protection under certain types of situations and mine environments. Realizing a need for a cable bolt that can be used for primary support and provides consistent installed tension, complete corrosion protection, and a fast installation, Keystone Mining Services. LLC (KMS), an affiliate of Jennmar Corporation, has developed the INSTáL CableOx system. This paper will detail the development and specifics of this system including two underground case studies

Jan 1, 2000

By Kikuo Matsui

In a difficult economic environment, the coal mines in Japan have been making extensive efforts in order to survive by rationalizing the mining operations. Introduction of a new longwall mining system is one of these efforts to establish the rational production structure. In the high production longwall mining system, gateroads should be developed rapidly and maintained effectively during their lifetime. Strata bolting support system has been employed in the gateroads to raise their stability levels and reduce their maintenance cost. However, excessive gatemad closure caused by longwall mining is still occurring, impeding the passage of equipment, personnel transportation, and ventilation air in the longwall panels. This paper describes the development system of gateroads and proposes a new mining method to control the excessive roadway closure problem.

Jan 1, 1995

By Dieter Wittenberg

The successful extension of the applications in which rockbolts can be used in the German coalmining industry is, because of the very great raining depth combined with a high degree of stress in the native rock, only possible on the basis of a comprehensive quality management system. The quality assurance system consists of material tests on the individual component parts of a rockbolt, of test rig trials of installed rockbolts, of suitability tests underground and of measures for quality assurance during roadway drivage. Only on the basis of exact knowledge of the way in which installed rockbolts function in the underground and possible sources of error and faults can quality assurance be guaranteed during roadway drivage.

Jan 1, 2000

By Archie Richardson

Periodic weighting of longwall supports occurs during retreat ofthe face under certain geologic conditions. Strong stratain the immediate and main roof tend to cantilever over the gob, weighting the supports periodically. The distance between weighting peaks, as well as the intensity ofperiodic weighting, is determined by the suength and thickness of roof members, their location relative to the seam, the frequency of joinling, and characteristics of the gob. In this paper the effects of varying several of these variables ate investigated using block modeling. The models are calibrated against a published case history of periodic weighting in the Pittsburgh Seam. It is concluded that block modeling is a useful tool for correlating measured support pressure histories with expected modes of strata behavior in the roof, with potential for predicting shield behavior in new geologic enviromnents.

Jan 1, 1998

By Kewal K. Kohli

An investigation was performed to determine the sequence of events which caused the 1987 surface subsidence and related damage to several homes in Walker County, Alabama, USA (see Figure 1). Surface affects compared to mine maps indicated the subsidence to be mine related. However, two coal seams had been worked under this area. The upper seam, the American seam ranged from 250 to 280 feet beneath the surface in the area in question. It was mined-out before 1955 by room-and-pillar method leaving in place narrow-long pillars to support the overburden strata, and abandoned in 1955. The lower seam, the Mary Lee seam, ranged from 650 to 700 feet beneath the surface. The Mary Lee seam had been abandoned in 1966 and subsequently became flooded. The dewatering of the Mary Lee seam workings in 1986 caused the submerged pillars to be exposed to the atmosphere. Due to multiple seam mining and the fact that workings had been inundated then dewatered, a subsurface investigation ensued to determine the sequence and ultimate cause of surface subsidence. Core sample tests with fracture analysis in conjunction with "down-the-hole" TV camera inspections provided necessary information to determine that the subsidence started in the lower seam and progressed through the upper coal seam to the surface. Evidence from the investigation program established that dewatering of the lower seam workings caused the marginally stable support pillars and the roof to collapse. This failure triggered additional subsidence in the upper seam which broadened the area of the influence at the surface.

Jan 1, 1992

By John J. Bowders

The stability of surface slopes undergoing subsidence due to longwall mining was investigated to examine the effect the subsidence had on the stability of the slopes. Stability analyses were performed on all slopes along both longitudinal and transeverse sections of the longwall panel before and after subsidence. Both finite- and infinite-slope analyses were performed with both drained and undrained cases. The results indicated that the changes in the stability of slopes due to subsidence were insignificant for the cases analyzed. Although significant lateral ground movements were recorded, these were not attributed to slope failure. Explanations for these movements are presented in the paper.

Jan 1, 1988