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By V. M. Shick

For practical purposes of the use of information resources in the field of geomechanics and mine surveying with accepted mining technology in mines, the authors have developed the packaged software programs of the survey-geomechanical information system with database objects of mine field. This system enables to execute the graphical representation of workings layout in preset scale, axonometric projection, the zones of higher ground pressure: program packages for calculations of rock pressure manifestations and for selection of suitable support facilities for the permanent, development and active workings and vertical shafts based on the information resources of the State Research Institute of Mining Geomechanics & Mine Surveying (VNIMI). The program packages are applied at coal mines in Russia and in Kazakhstan. The profitable operation of coal mines can be reached only by the combined optimal engineering decisions in mine working's laying-out and their reliability and safety at the stages of their designing and exploitation, and with minimal harm of the environment as well. This problem is being complicated by the fact that today the mining-practicing engineers and designers are ordinarily facing the problem " of an information barrier", when the complexity of controlling systems exceeds the potentialities of traditional management of production practice. Coal mine is a typical representative of complicated systems, because the information about geological structure, physicomechanical properties and stress-strain state of rock mass are of fragmentary character and insufficiently reliable. A mine has a developed network of interrelated workings, by the way, some of them are productive ones being subjected to control to a certain extent, and some of them are abandoned ones being noncontrollable and hazardous in rushes of water, gas, pulp and fire. The ground pressure forces cause the disintegration of rock mass growing with depth. The progress of mining operations constantly changes the geomechanical situation forming the zones of bearing pressure, stress relieving, coal falling, as well as it leads to the pulp movement on the earth surface, breaks the ground water flow, causes deformations and changes in stability of buildings, constructions and natural objects on the earth surface. One should take into account the existence of hazardous zones within the mine field, i.e. the zones of elevated ground pressure, geological dislocations and those ones under natural water reservoirs, ponds, etc. Major coal seams are prone to rock bursts, sudden outbursts, bleeding, endogenic fire. It is obvious, that in practice it is extremely difficult to account for the mentioned above factors in their interrelation.

Jan 1, 1996

By Peter Cain

In response to the appearance of excessive convergence of bolted gateroads in the front abutment zone of retreating coal faces at Phalen Colliery, staff from the CANMET Cape Breton Coal Research Laboratory in Sydney, N.S. initiated a programme of roof profile measurements in the front abutment zone of longwall headgates. The results of these measurements allowed a characteristic deformation curve to be determined for each headgate, and the early identification of areas showing an unstable deformation trend. These areas were then reinforced with supplementary support. The monitoring programme was adopted and enlarged by the rock mechanics staff of the Cape Breton Development Corporation, and has been continuing for a period of approximately two years. A sufficient quantity of data now exists to be able to make an assessment of the effects of a number of mining parameters on the performance of the gateroad in the front abutment zone. The following paper describes the method of measurement, illustrated by typical results, and goes on to relate variations in rate and patterns of movement to geology, interaction, method of support and pre-mining stresses.

Jan 1, 1996

By W. C. Lacy

Stratabound copper ore bodies in thick Proterozoic metamorphosed sedimentary and volcanic rocks at the Tong Kuang Yu Mine in southern Shanxi Province of China were considered as possibly being amenable to block cave mining. Initial evaluation of caving characteristics was based upon old calyx drilling records, limited underground mining experience and geological mapping, a few diamond drill holes and measurements in surface subsidence features. Classification and mapping distribution of rock quality types aided in mine design, prediction of fragment sizing and explosive requirements, cave assist and ground support requirements. Comparison is made between early feasibility predictions and actual mine experience.

Jan 1, 1989

By G. K. Rogers

The portal, which is the near-horizontal, surface point of entry to an underground excavation, can often be an exceedingly difficult area in terms of ground control. Surface and subsurface failures at portals, as discerned during a study involving over 300 case histories, are unfortunately, common. To aid in the engineering evaluation of portals, the Geomechanics Classification System was appended with discontinuity orientation assessment values and support/excavation guidelines. Also, a design model utilizing RMR predicted rock loads in conjunction with half-dome theory is proposed for the most common type of portal failure. Other pertinent comments and recommendations relating to portal stability are included.

Jan 1, 1989

By E. C. Westman

Anomalous geologic or stress-induced conditions can create a hazardous working environment for underground miners. Seismic attenuation tomography provides a valuable tool for understanding static and dynamic conditions induced by mining. As a longwall shearer cuts coal, it generates seismic energy. As this energy travels through the rock mass it is attenuated in a manner proportional to the degree of fracturing of the rock mass. By calculating this attenuation at specific locations underground, the degree of fracturing of the rock mass, and hence the relative stress state or material properties can be inferred. The goal of this work has been to create a tool which can be easily used by the mining industry to obtain information about the distribution of stress concentrations or material properties across a broad area in advance of mining.

Jan 1, 1996

By B. Arjang

ABSTRACT: Ground stresses are one of the significant factors in the context of rockbursts and underground instability at some hard rock mines in Canada. Overcoring strain relief measurements using triaxiaI strain eel is were performed at depths between 60 to 1890 m at several mine sites to provide stress data for stability analysis and optimum mine design. Pre-mining ground stress determinations from 64 stress tensor analyses resulted in the following average stress gradients: Maximum horizontal stress. -Hmax - 8.18 - 0.0122 MPa/m depth Minimum horizontal stress. _-,,min - 3.64 - 0.0276 MPa/m depth Average horizontal stress. -11, 5.91 - 0.03-19 MPs m depth Vertical stress. '-, - 0.0266 - 0.008 MPa/m depth The maximum and minimum horizontal compressive stresses. with an average ratio of 1.75 ,0..45. prevail in east--west and northerly directions. respectively. Horizontal compressive stresses in excess of vertical overburden load were determined. indicating large variations in ratios to a depth of about 1000 m with decreasing trend towards depth. From present data. a particular regional zoning for the magnitude and direction of horizontal stress fields cannot be outlined. A common feature at mines with near vertical orebodies is that the maximum horizontal compressive stress acts perpendicular to strike while the minimum horizontal compressive stress is aligned on-strike. The vertical stress components approach the gravitational overburden load.

Jan 1, 1989

By V. M. Shick

With gentle bedding within the zone of support pressure the delamination in roof rocks may occur only on those stratification planes where cohesiveness of rock is close to zero. Unlike this, at dip angles of more than 30-35° disintegration of rock occurs on the surfaces with cohesion up to 5 MPa. Therefore, the delamination in roof rocks at inclined beds is greater than at gently dipping ones. The original disintegration along the pressure fissures with the formation of block structure at inclined strata is not typical, and it may be observed only in roofs with included thick rocks; in this case, the orientation of fractures depends on the angle of seam inclination. Deformation of roof roocks above the mined-out space is determined by anisotropy of layers stiffness (hardness). With the increase of dip angle the own bearing capacity of layers will rise in the direction of strike. It was emphasized that the natural and technological factors are of great importance for rock pressure manifestation in longwalls.

Jan 1, 1996

By Dwayne C. Kicker

This paper introduces the concept of design theory and methodology as applied to rock mechanics for more innovative and efficient design. This is a "frontier" research area in rock mechanics because although design is a fundamental foundation to all engineering branches, very little attention has been paid to this aspect in mining. In discussing the theoretical premise of design, this paper identifies the principles which form the basis of design activity. Also, from a practical viewpoint, the findings from a series of interviews with mine design engineers are presented. These findings lead to the identification of needs arising from overlooked design methodology in practice.

Jan 1, 1989

By W. J. Mcgaughey

A crosshole seismic imaging (tomography) experiment has been carried out in an underground mine in order to delineate waste rock within a massive sulphide ore body. Data comprising 1526 travel time measurements were inverted to yield a compressional wave speed image consistent with, and adding to, knowledge of the extent of the waste inclusions. An effective method of resolving travel time discrepancies measured on reversed ray paths is presented.

Jan 1, 1989

By James J. Scott

Dynamic rock anchors are interior fixtures developed by the author which promise to be a revolutionary development in the field of ground control. The fixtures are designed to be placed in the ground with modern roof bolting equipment, such as the type used in the American coal mining industry. They are composed of a plastic form- able anchor tube which serves to fasten a buttress deformed rod which is thrust and turned into the plastic and in turn clamps the roof plate to the rock surface. Plastic tubes 10 to 16 inches in length provide sufficient anchorage to exceed the yield strength of steel rods 5/8, 3/4 or' 7/8 inches in diameter. This paper presents field testing and early work done on the device over the last seven years. Results of pull tests, creep tests, laboratory testing in concrete, and field testing under natural rock conditions demonstrate the uniqueness and effectiveness of this new support system. A second development which uses the dynamic rock anchor in conjunction with a resin cartridge to provide a stiffer anchorage system is also discussed. These products will be manufactured and marketed by Ingerso-11-Rand Co. under the trademark of DYNA-ROK and DYNA-ROK PLUS anchors.

Jan 1, 1989

By X. S. Tan

This paper deals with the analysis of stress condition on the interface between two types of floor rock materials when the vertical stress is larger, or when the horizontal stress is larger in a rectangular opening. It indicates that the floor Failure and the failure stress of floor rocks are closely related. It also demonstrates that a larger horizontal stress is one of the most important factors in increasing the potential for floor rock failure and floor heave.

Jan 1, 1990

By Barry Voight

The law [ ] where [ ] is a measurable quantity such as strain and A and cu are empirical constants, describes the behavior of materials in terminal stages of failure under conditions of approximately constant stress and temperature. Applicable to intact rock and rock masses, the relation may be extended to conditions of variable stress and cyclic stress, and may be used to predict time to failure. Applications in rock mechanics include slope and excavation stability and various topics in ground control.

Jan 1, 1989

By L. J. Lorig

Much of the present knowledge about caving behavior of rock masses has been obtained from empirical observations. Additional notions about caving have been developed through inferences derived from two-dimensional finite element analyses. These analyses have indicated that a combination of one low-angle set of fractures and one nearly vertical set of fractures is the optimum fracturing configuration for ease of cavability of an orebody. This paper presents the results of two- and three-dimensional distinct element analyses which draw different conclusions than those reported from finite element studies. The distinct element method is selected far analysis of cavability because this method treats the rock mass as an assemblage of rock blocks which may interact individually, The results of the analyses are compared to a documented case history which involved a groundfall of 80,000 tons of ore in a 160-foot high pillar. The mechanics associated with these results are-explained in terms of simple static stability analysis of wedges. The propensity for orebody caving is primarily a function of the number of joint sets or potential "release" surfaces in the orebody. This mechanism is influenced by the bounding weak discontinuities, and intact strength of rock material.

Jan 1, 1989

By Jeffrey M. Listak

This report describes a study, conducted jointly by BethEnergy Mines Inc. and the Bureau of Mines, to assess the effects of longwall front abutment loading on various supplemental support materials utilized in a predriven recovery room. The purpose of the predriven recovery room is to reduce longwall equipment transfer time by eliminating the premove preparation associated with conventional recovery methods. In addition, the room provides a large area in which face salvage equipment can maneuver. Results of four recovery-room study areas show the progression and influence of the front abutment on the longwall panel and supports and their subsequent behavior. The best performance (i. e. the support that most facilitated recovery) of support material was achieved through the use of a concrete mixture which had a sand content of 35 percent by volume. The longwall transfer time was reduced by 30 percent which translates to a production advantage of 37,000 raw tons of coal per panel.

Jan 1, 1989

By Raymond A. Mazzoni

Over the last twenty years, roof support technology has made numerous advances since the original wedge and slotted bolts of the 1950's. By comparison, the roof supports used today are more complex and specialized than the supports used in the past, providing mines with a varied selection of supports from which to choose. As a result, when problems with supports are encountered, it is more difficult to determine whether it is the result of geological changes, poor installation practices, or malfunctioning supports. Recognizing this problem, MSHA's Roof Control Division of the Pittsburgh Safety and Health Technology Center, has undertaken the task of publishing a guide for trouble¬shooting problems encountered with roof support systems. The purpose of this guide is to provide a logical sequence to resolving the most common problems encountered with roof supports. The objective of this paper is to introduce this guide to the mining industry as well as provide insight into the evolution of the guide from its beginnings as rudimentary charts to its more comprehensive present format as a practical guide for use by the mining commu¬nity.

Jan 1, 1997

By Victor V. Nazimko

Long term stability of the pillars that have been remained after R&P extraction causes postponed subsidence. To prevent unforeseen subsidence and to diminish postponed subsidence 25-50% new method for its control has been developed by the author. It supposes to use drilling and blasting technology and other original approaches. New method has been fulfilled through the holes being drilled from the surface or from the active underground openings. Explosives had been charged into the holes and were blasted. This had increased bulking factor dramatically and prevented natural caving of the strata. Physical scale modeling corroborated efficiency of the new approach. The bulking factor has grown from 0.0623 to 0.1185 and surface subsidence has been diminished from 1.1 m to 0.2 m or 5.5 times.

Jan 1, 1996

By David Forrester

Subsidence beneath the land surface has traditionally been monitored using the most accurate surveying methods of the day. Over the several hundred years of subsidence investigation, these techniques have improved, and thus the accuracy of subsidence measurements has improved. In circumstances where the subsiding surface is masked by water or rock, novel methods must be developed. This method describes the recent successes of subsidence monitoring using advanced bathymeric techniques in the Sydney Coalfield. In order to obtain subsidence profiles above submarine coal extractions, seafloor bathymetry surveys, run before and after mining, have shown that subsidence profiles can be detected, despite the primitive nature of some of the trials. Very recently, there have been considerable advances in this field, associated with the availablity of high-powered personal computers to control data collection and analyse the results. The recent surveys described in this paper have demonstrated the considerable potential for such methods. This paper describes bathymetric subsidence monitoring developed in the Sydney Coalfield, illustrated with some typical results, and summarizes the findings of the research leading to the development of subsidence design criteria specific to the Sydney Coalfield.

Jan 1, 1996

By F. Ziaie

Line electrical resistivity method using physically infinite distance between current line electrodes is proposed to determine the location of mine workings. In this method at least three line electrodes are used. One of the current electrodes is used as a sinkhole electrode while the other two are used for different activiations of line electrodes when the survey area is between one of the line electrodes and outside the other one. The resistivity profiles perpendicular to the current line electrodes for different activation of electrodes is plotted versus the distance of the midpoint of the measuring potential electrodes. The anomaly due to presence of any locally lateral resistivity variation (e.g. mining cavity) will represent itself as peak or trough depending on resistivity contrast between the source of the anomaly and surrounding medium. Physical simulation of the proposed model was conducted by using a tank model in the laboratory. The results of experiments appear to be consistent with the theoretical model. Experiments for different depths and different spacial locations of the simulated cavities appeared to be successful for locating the depth and size of the cavity.

Jan 1, 1989

A model was developed to facilitate secondary tailgate support selection based on analysis of over 100 case studies, compiled from two different surveys of operating longwall coal mines in the United States. The ALPS (Analysis of Longwall Pillar Stability) program was used to determine adequacy of pillar design for the successful longwall case histories. A relationship was developed between the secondary support density necessary to maintain a stable tailgate entry during mining and the CMRR (Coal Mine Roof Rating). This relationship defines the lower bound of secondary support density currently used in longwall mines. The model used only successful tailgate case history data, with adequate ALPS SF according to the CMRR for each case. This model facilitates mine design by predicting secondary support density required for a tailgate entry depending on the ALPS SF and CMRR, which can result in significant economic benefits.

Jan 1, 1996

By Shosei Serata

The application of conventional rock mechanics methods to complex ground is very difficult. Yet. In most underground mining, the ground is complex. Therefore. conventional methods are not only difficult to apply but are also generally ineffective in improving underground operations. Similarly, conventional rock mechanics instrumentation has not significantly contributed to improvement of mining practice. Rock mechanics instrumentation in underground mining operations is often considered to be" merely an expensive nuisance. A new system of mine instrumentation is changing this traditional view. The new instrumentation method, called the SPDR method, was originally devised by Dr. Shosei Serata to meet the specific requirement of establishing the Stress Control Method of mining upon a solid quantitative foundation. This instrumentation method has contributed substantially to the widespread success of Stress Control mining under widely varying ground conditions in different types of underground mines (1.2.3.4). The instrumentation method provides an effective means for optimizing Stress Control mining patterns, simultaneously achieving reduction in production costs and substantial improvements in safety (5). The principles and methods of the new instrumentation method are described below, with field examples.

Jan 1, 1986