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By Shiva P. B. Kolli

Surface mining of multiple scams by mountaintop mining methodology is complex in the Appalachian region of West Virginia. Excess spoil from the removal of overburden and interburden is disposed in the adjacent valleys. The valley fills so formed are some of the largest earth constructions, with a relief of 450 ft (137 m) to 650 ft (198 m) and a stretch of 500 ft (152 m) to 2000 ft (610 m). The stability of the valley fills has become an issue of public concern. This paper describes three cases of valley fill slopes. The analysis of each case involved the description of the geo-mechanical properties of different surface and sub-surface layers, and the surface configuration of the slope. Slope stability was carried out using deterministic as well as probabilistic approaches. Based on the analysis, it was found that valley till slopes were stable due to configuration, and the premise that valley fills with great stretch and high volume of spoil tend to be unstable does not hold.

Jan 1, 2001

By Madan M. Singh

Currently longwall coal mining operations require at least 3 entries on both the headgate and tailgate ends because of ventilation and safety requirements. Driving of entries, however, is a slow and costly process. Often it is a bottleneck in longwall development. Single entry gateroads are permitted in Europe and commonly used there. This study entailed ascertaining the feasibility of using a single entry in the United States, without sacrificing safety. This design was conducted for an operating longwall mine in the Black Warrior coalfield in Alabama, An understanding of rock loads and consequent support requirements is prerequisite to the design and successful demonstration of the single entry system. Efforts in this regard were directed at determining center (packwall) support requirements for various single entry widths. Critical to the analysis is knowledge of the nature and extent of side abutment stresses. In collecting geological and geotechnical information relating to the stability of the single entry, Engineers International, Inc. engaged in the following: ? Examination and inspection of the single entry demonstration at the Sunnyside Mine in Utah. Severe ground conditions and unacceptable levels of entry closure were experienced there prior to the tailgate phase. Observations at the mine presented a clear perspective on possible ground control problems for future single entry designs. ? Reconnaissance inspection and classification of roof rock conditions. ? Detailed mapping of roof structure in the areas to be instrumented. ? Installation of convergence stations in the longwall headgate to monitor roof movement during mining. ? Measurement of side abutment stresses in a yield pillar in the area of the convergence measurements. ? Measurements of coal fracture distribution by the detail area method. ? Rock properties determinations of roof, coal, and floor rocks; samples obtained by core drilling. ? Determination of floor bearing capacity by in-situ testing.

Jan 1, 1982

By Liane J. Terrill

A 9O) ft (275 meter) section of a highly fractured beam of halite was mined from the roof of a supported thirteen year old drift at the Waste Isolation Pilot Plant (WIPP). The operation was conducted with a continuous miner and allowed the unique opportunity to collect spatial information on roof beam geology and to observe ground support conditions during the mining advance. Photographs and fracture maps of the mining face document the progress of the operation and the deteriorated condition of the strata. This case study details the drift's excavation and support sequences. the geomechanical response, and the conditions found in the exposed roof beam.

Jan 1, 1997

By Wen H. Su

Multiple seam mining and its associated problems are very serious in Southern West Virginia where poor planning or lack of knowledge in seam interaction often results in complete loss of coal properties. Several measures have been proposed to alleviate the interaction prob¬lems under various multiple seam conditions, but few of them are spec¬ific in terms of mining plan. Two parallel approaches are adopted for this paper. One is field investigation which consists mainly of mine site visits and gathering of data. The other is the two-dimensional finite element simulation of mine workings using the data gathered as input. Two typical cases which represent the past and present multi¬ple seam mining practice in West Virginia were investigated. Much attention is focused on the interaction problems experienced and the important parameters controlling interaction. Several key parameters controlling interaction in multiple seam mining were analyzed. Proper mining plans, by which the interaction problems can be minimized, are proposed for the individual cases after a better understanding of the interaction mechanism was realized through finite element analyses.

Jan 1, 1984

By Bruce H. Gardner

This paper describes the application procedure of the Stress Control mine design method. This procedure has evolved over the past 20 years of the practice of this Method in trona, potash, salt, and, most recently, in coal mining. The Stress Control Method of mine design has been defined and amply described in previously-published work (1,2,4) -- likewise, the associated system of in situ instrumentation (3,4) and the computer modelling technique (2,3,4) which are the principal tools of this method. The present paper defines the procedure by which the in situ instrumentation and computer modelling cools are combined in adapting the general concepts of Stress Control to produce site-specific design solutions. This procedure is illustrated by means of case examples from three mines. The Stress Control Method utilizes the geometry of underground excavations, particularly through the time sequence of the creation of yielding pillars, to control stresses. The time sequence is devised such that all the primary stress envelopes are transformed into a single secondary stress envelope, surrounding the group of rooms separated by the yielding pillars. The secondary stress envelope provides protection to the roof and floor boundaries from all the external stresses. This stress relief effect removes the cause of roof and floor failure -- high shear stress in the weakly confined boundaries of underground openings. It thereby replaces artificial support with ground self-support, enabling simultaneous in¬creases in stability and percent recovery. Within limits which are still being explored and extended, the Stress Control Method has proven capable of overcoming the trade-off between stability and extraction ratio which has afflicted conventional mining methods. The application procedure of the Stress Control Method is outlined below in terms of the objectives, structure, and stages of a generic mine rock mechanics program for the site-specific adaptation of the time control yield pillar design technique.

Jan 1, 1984

By Raymond M. Stateham

The Bureau of Mines has developed a portable, lightweight device for determining the integrity of resin-grouted roof bolts. The instrument functions by sending a known pulse of ulstrasonic energy into the bolt and comparing the amount of energy reflected hack with the original measured pulse. Where the bolt is properly bonded or coupled with the rock, the energy passes through the bolt-resin-rock interface and dissipates in the rock. Where the bolt is not properly coupled, the energy is reflected back along the bolt to the instrument. The ratio of reflected energy to the pulse approximates the fraction of the bolt's surface that is improperly bonded. The instrument is easy to use. The operator holds the sensor head of the device firmly over the head of the bolt to be tested, causing the pulse of ultrasonic energy to be imparted to the bolt. The device then listens for reflected energy. This cycle is repeated about 200 times per second until an evaluation of the bolt installation is made and indicated by colored lights in the display window. Bolts having 50% or less of their surface bonded are considered had and cause a red light to he illuminated. Bolts with 50% to 75% of their surface bonded cause a yellow light to be lit and are considered marginal. Bolts having more than 75% of their surface bonded are considered good and cause a green light to be lit. The indicator lamp remains on for about 4 seconds and then goes off, indicating that the instrument is ready for another test.

Jan 1, 1982

By D. L. Price

This paper presents a method of measuring field power consumption of shearers and deriving specific energy consumption versus shearer haulage speed performance curves. A description of a computer program which simulates the cutting action of a shearer drum is presented. A comparison between the field specific energy curves and the computer simulation results is made. The simulation results compare well with the field data where all the coal seam is being cut by the shearer. The computer simulation results give hack-calculated field pick force cutting characteristics, which allow the performance of the shearer to be predicted for other operating conditions, e.g. effect of changes to pick lacing, effect of changing the drum rotational speed, allows the calculation of power requirements for a particular production rate.

Jan 1, 1992

By Thomas Lautsch

After a short description of geology and gateroad roof support technology in the German coalfields the development of roof bolting as primary roof support is presented. Based on geotechnical parameters, different strategies used for roof support at depths of 3,300-4,600 ft. are explained. Strict quality management and a strict monitoring program are part of the entry development. A number of recently finished developments are described such as the introduction of standardized bolts and accelerated resin systems. An outlook of future goals is presented. The paper concludes with a comparison of roof control systems at RAG's mines in the US and Germany.

Jan 1, 2000

By C. P. Mangelsdorf

The success of the Birmingham roof truss (Figure 1) in supporting some difficult roof conditions, particularly in the Illinois coal basin, has given impetus to the development of a number of alternate schemes. These schemes attempt to alleviate two major problems with the Birming-ham truss, namely, the time required for installation and the cost of material. Because of the difficulty of drilling angled holes and the number of different pieces of hardware which must be handled manually, most operators have been unable to install Birmingham trusses in the cycle and have had to schedule truss crews during the maintenance shift or whenever they would not impede production. Due to this delay the truss has traditionally been viewed as a supplemental form of roof support. In fact, the truss might qualify as primary support and replace at least two bolts if it could he installed in the cycle (and MSHA would accept it as an alternate in the roof plan.) [ ] Figure 1. The Birmingham truss. Two attempts to deal with the first difficulty have sought to streamline the truss hardware while preserving the essential character of the Birmingham truss. One of these, by Peabody Coal, is reported elsewhere in these proceedings by C. Bollier. Another is a contract issued by the Bureau of Mines to Bendix Corporation for the development of a machine, particularly suited for use in low coal, which will automate many of the operations currently executed manually. This machine is expected to be ready for field testing by fall of 1982. Once in place, a truss installed by either of these schemes will interact with the roof in the same way as a conventional Birmingham truss. An alternate approach has been proposed by several different manufacturers independently. Although the hardware details differ. the essential idea consists of two angle bolts, the heads of which are connected by a horizontal chord tightened to some pre-determined tension. Figure 2 shows the generalized concept and does not depict any one of the four systems proposed. The advantage of this scheme is that the angle bolts can be installed and tightened in the cycle, and as bolts, immediately satisfy the roof control plan. The horizontal chord can be added later to achieve almost any initial desired roof loading, the limits of which are defined below this scheme is referred to here as the angle-bolt truss. Because of a fundamental difference in the way in which load is transferred between chords, this design does not interact with the roof under subsequent loading in the same manner as a Birmingham truss. The purpose of this paper is to examine this fundamental difference and its consequences. [ ]

Jan 1, 1982

By Y. P. Chugh

The use of wooden supports, supplementary to the primary method of roof control using roof bolts in mines, consumes over 3 million cubic meters of hardwood in the U.S. annually. These supports arc primarily used in the form of cribs and posts. Along with a rapid depletion of high quality timber resources, supplies fluctuate seasonally, costs are escalating rapidly, and product quality is highly variable. Environmental considerations of global climate change put additional pressure on deforestation for utilization of timber for artificial supports. On the other hand, management of coal combustion byproducts (GCBs) from power plants has become a major issue to maintaining a healthy coal industry. The USA currently produces over 100 million tons of CCBs annually and the average cost for their management in the US is about $20/ton. This cost is expected to escalate rapidly with tougher environmental regulations. The principal author has been directing research, development, and demonstration studies for CCBs-based artificial supports and lightweight structural materials in mines for the past seven years and has made significant progress toward commercially viable products. More specifically, first and second generation crib elements and post elements have been developed, characterized analytically, and demonstrated in the field. It is estimated that about 2.5 x 10" tons of fly ash could be utilized for artificial supports in U.S coal mines and this would double if these materials were utilized in non-coal mines as well. The author believes that CCBs-based artificial supports have the potential to replace wooden supports and blocks with better performance and cost competitiveness while managing CCBs in an environmentally sound manner. This paper focuses on the development and field demonstration of CCBs-based artificial supports for use in underground mines, and its pilot scale fabrication facility. Recent analysis results on engineering performance evaluation of the developed crib under various loading conditions using finite element method are presented. The following comments highlight the developments: I ). Engineered artificial supports, crib and post elements, using CCBs as a major constituent, have significant potential for application in mines because their structural performance is significantly better than wooden cribs counterparts. 21. Engineered crib elements provide about 50% larger area for air-flow than a conventional wooden crib. 3). Engineered crib elements are not flammable. 4). Each engineered crib element utilizes about 10 kg of fly ash, about 40 % of the weight of crib element- Therefore, a typical crib 2.0 m high utilizes about 200 kg of fly ash. 5). Each 16.5 cm diameter engineered post utilizes 50 kg of fly ash. 6). Assuming 3.0 million cu. meter of wood consumed for post and crib support systems, it is estimated that about 4 - 5 million tons of fly ash may be utilized for supports fabrication in the USA. 7). An engineered post has excellent post-failure characteristics similar to wood. In addition, the engineered post also has excellent loading and unloading characteristics close to the yield point of about 75% of the ultimate load carrying capacity.

Jan 1, 2004

By Russell C. Frith

This paper presents recent findings concerning longwall caving mechanisms relating to Australian mining conditions and their effect upon longwall support requirements and behaviour. The findings arc based on a program of intensive hydraulic support monitoring in a variety of Australian mining conditions coupled with geotechnical observations. Results from the study illustrate periodic weighting cycles of varying severity and these are related to the overlying geology in terms of the strength of individual strata units, their thickness and proximity to the longwall extraction. Several different caving mechanisms are identified which contribute to periodic weighting cycles. The importance of recognising weighting cycles in relation to the operation of the longwall face will be discussed in detail. Longwall support design methods are critically examined in relation to the case histories of the monitoring program. The applicability of the said design methods to Australian coal mining conditions is discussed and an outline of design considerations to facilitate productive longwalling is presented. Overall, the paper only "scratches the surface" of the work currently being undertaken by ACIRL in this area, and the findings of that work.

Jan 1, 1992

By Rene Rodriguez

Sandstone paleo-channels encountered during coal mining operation can significantly slow down the advance in mining, and often completely shut-down coal mine production, with consequent extensive economic losses to the mine operator. Definition of the encountered channel usually involves intensive drilling; vertically from the surface and/or horizontally from underground vantage points. Coal operators with limited resources often resort to exploration by extending mine faces toward the channel. Both drilling and underground mining exploration are prohibitively expensive and usually provide only partial information about the location, size and shape of the sandstone channel. A low cost alternative which can also provide a more comprehensive picture of the channel is the application of Underground High Resolution Seismic Methods (UHRSM) developed and successfully tested by GECOH Exploration. UHRSM applies surface seismic reflection technology rotated as needed (usually 90 degrees) to accommodate the faces of the exposed channel, coal rib, or coal in front of the inclusion (sandstone channel, etc.). This entails placing high frequency seismic sources and geophones horizontally across these exposed faces. Refraction and reflection events from the front and back of the channel are isolated, analyzed and inverted, to calculate the channel's location and geometry. This paper presents a summary of the geophysical exploration technique and two case history examples where it was applied. In the first case, the accuracy of the technique was verified through subsequent mining. Mining is yet to commence in the second case. Both cases were applied to room-and-pillar nines where the irregular rib lines significantly extended the data processing effort. This suggests that UHRSM will find the easiest application when used along straight rib lines, but that is not a requisite to the application. The UHRSM should find ready application in longwall mining to delineate sandstone channels and other non-coal inclusions in the middle of the panels or ahead of the gate road faces.

Jan 1, 1994

By Wolfgang Schott

The propagation velocity of in-seam seismic (ISS ) waves depends on frequency which is also known as dispersion. This dispersion is not only determined by the thickness of the coal seam and its dirt hand content (i.e. thickness and position), but also by the rock type and its condition (soft or compact) above and below the coal. A coal panel completely surrounded by roadways was investigated using the in-seam seismic transmission survey technique. Along the roadways the immediate roof was either sandstone and shale- The seam thickness varied between 1.20 m (sandstone in the roof) and 1.40 m (shale in the roof) and a fault system (normal faults) crossed the panel with a total throw of about the seam thickness. Below this coal seam another coal scam with a thickness of about 80 cm exists. Its interval shown by exploratory drilling changes from about 60 cm to more than 6 m (scam splitting). Tomographic inversion was applied to the dispersion of the measured ISS waves and velocity distributions were calculated at frequencies found to he most sensitive to changes in the seam thickness and the distance to the coal seam below. By correlating the velocity distributions with known values along the roadways approximate distributions of the coal seam thickness and the seam splitting within the panel were produced. The mining of the coal panel had already been finished and comparison was made between the survey results and the actual situation as far as it was documented. Prediction by the seismic survey was partly in good agreement with the actual held conditions or showed at least the same trends.

Jan 1, 2003

By Robert C. Speck

Floor heave or deformation of the mine floor into the mine opening is a problem which has plagued coal mines in this country and others. In mining areas where room and pillar mining is practiced, floor heave generally occurs when the stress applied to the floor material by a coal pillar exceeds the bearing capacity of the floor strata. When the floor strata beneath the coal pillar fail, the pillar moves downward and displaces the material under it. This material, in turn, moves outward and upward into the mine opening (Figure 1). As the underlying materials fail, the load supported by the coal pillar may be transferred to adjacent pillars. If these are marginally stable, they too may become overloaded and push into the floor. Thus, floor heave can spread through a large portion of the mine in a progressive manner. As the pillars push into the floor, differential movement and flexure of the roof strata may cause them to weaken and fail, resulting in subsidence of the ground surface above the mine. This paper describes the problem as it was manifested in the Zeigler Coal Company No. 5 and Murdock room and pillar coal mines near Murdock, Illinois, and reports the results of a U. S. Bureau of Mines- sponsored study conducted by the University of Missouri-Rolla. During the course of the study, floor heave in the two mines hindered the transportation of men, machines, and coal to and from the working mine-face, interrupted ventilation plans, drastically increased roadway maintenance costs, intensified safety and strata control problems, destroyed large pieces of equipment, and, several times, pre- vented access to otherwise minable coal resources. The ultimate objective of the study was to develop one or more simple procedures to allow detection of a potential floor heave problem during the exploration phase of mine design--before initiation of production mining.

Jan 1, 1981

By Richard C. Repsher

The U.S. Bureau of Mines has developed a method and device designed to detect lose rock material in underground mines. The technology is designed to be an aid to mine workers in detecting hazardous roof conditions in underground mines which can complement or replace the traditional roof sounding techniques where the miner relies on experience to determine whether rock conditions are sound. The leading cause of accidents and fatalities in underground mines is falls of lose rock pieces or rock slabs from the mine roof. The device is an electronic roof sounding device that acoustically determines the integrity of mine rock. In previous research the Bureau of Mines found that loose rock, when impacted, vibrates at a much lower frequency than intact rock material. A major problem in determining rock stability using this technique has been the repeatability of the matt signal. This difficulty baa been greatly reduced in the current design by measuring the power spectra contained in two separate frequency bands of the signal produced by striking the rock in question. The ratio of the energy contained in each band is computed. This process minimizes any striking force differences, producing accurate, repeatable results for solid rock as well as loose, drummy material. The prototype has been successfully- tested in a variety of underground environments including coal, uranium, molybdenum, silver and salt. The technology has been investigated by the U.S. Mine Health and Safety Administration and the Department of Energy for use in detecting detached tunnel lining areas in nuclear repositories. The paper will discuss the technique, applicable results, and future applications.

Jan 1, 1990

By Kenneth Rigsby

Black Mountain Resources' Highlands Mine No. I is a full extraction room and pillar operation located in Harlan County, Kentucky. Black Mountain extracts the 0.9 to 1.1 meter (36- to 42-inch) thick Owl Scam that is situated 60 to 70 meters (200 to 235 ft) above the longwall panels of the abandoned Arch No. 37 Mine, in the 3.4 meter (I I ft) thick Harlan Scam. In the areas where full extraction has taken place, the overburden above the Owl Seam ranges from 60 to 430 meters (200 to 1,400 ft). A short room and pillar panel was developed above an extracted longwall panel to test the selected pillar size, to evaluate support systems, and to verify the shape of the subsidence profile over the recovery end of the depleted longwall panel. It is over the recovery end that Highlands Mine No. I would access the Owl Seam reserves that exist above the No. 37 Mine. Black Mountain selected pillars sizes to be employed above the longwalls based on the ability to fully extract a pillar employing extended cuts. After a mechanical testing program was completed and mine behavior and top disturbance were observed in the test panel, John T. Boyd Company (BOYD) verified pillar stability and designed support systems. BOYD previously designed No. 37 Mine's gate pillars and studied subsidence and gob formation over its longwall panels; this effort aided the analysis of overburden movement and pillar integrity at Highlands Mine No. 1.

Jan 1, 2003

By James H. Fletcher

Much data and experience has been accumulated, especially in the last 5 or 6 years, to show that modern roof trusses, both of the Birmingham type and the bolt-and-channel type, perform well to support certain kinds of coal mine roof. For some time now, roof trusses of the Birmingham type have been effective in controlling thick shale roof, which tends to sag and fall over a period of about eight weeks. These falls leave dame-shaped cavities which are reminiscent of the pressure arch theory of roof failure. Lately there has also been significant interest in supporting some longwall panel entries with channel and-bolt systems. These systems utilize two vertical center bolts and two 45 degree end bolts through a heavy gage channel. Both types of truss systems have long bolts, which require 8 to 9 Foot holes on a 45 degree angle, and point anchor resin bolts, which utilize a 2 or 3 foot rebar grouted in a thin annulus of polyester resin. Consequently, many coal mining people have been impressed with the very good anchorage characteristics and tensionability features of these systems. However, the same people have been proportionately dismayed to find that very often the most difficult part of introducing a trussing program to a mine is deciding on the machine specifications which determine the truss installation rate. The purpose of this paper is to indicate aspects of truss bolter design and use which are not shared by roofbolter design and its vertical pattern of bolts. Of the two types of drill units conventionally accepted, arm feed units and mast units, only one 15 judged suitable. While the arm feed unit offers low collapsed height with a long drill feed length, a great attribute for low seam use, it has not lent itself to being rolled over to a 45 degree angle. One reason for this inability is that many items which are conventionally mounted on the arm feed unit cannot be allowed to rotate with the unit. These items include drilling controls, tool Cray, lights, canopy or safety post, panic bar, and stab jack(s). If these items were independent of the arm feed drilling unit, they would have to be out of the way of the boom arms, links, and feed cylinder as the unit moves. To ease this problem, the arm feed unit can be made very short and even mounted across the machine. However, the resulting short feed length is undesirable. Several short drill steel extensions are required to drill a relatively long hole, making this procedure time-consuming as well as increasing the likelihood of drilling a crooked hole. Another reason for abandonment of the arm feed unit is that a very stiff drill guide (or "centralizer") is required to start the hole. Using the mast tilt control, the roof bolter operator will force the bit against the roof and will rotate the bit without feeding to cut sideways into the roof to form a hole face. Omission of this step often results in the skidding of the bit toward the rib. To date, no such sturdy drill guide has been designed for an arm feed drill unit. The mast style unit has been the most successful design for angle drilling. It is easily rolled over to a 45 degree angle or to 90 degrees and, on single head models, often has been made to roll through 180 degrees. The mast style is compact, in plain view and is easily fitted with heavy duty manual or hydraulically operated drill guides. It can be mounted directly on a machine chassis, or onto a swinging boom, or onto a slider arrangement in a broad variety of configurations which will accommodate controls, tool trays, stab and roof support jacks, lights, canopies, and panic bars. The only significant difficulty with mast drilling units occurs in lower mining heights when desirable low mast height is accompanied by undesirable short feed length. While the lead extension in the drill string can be as large as the mining height will allow, a short feed length will permit only the use of shorter middle extensions and drivers, and perhaps will. require the use of two different length wrenches. The associated problem is the relatively short distance from the drillhead to the drillguide. This distance is further shortened when raising the drillhead to get the bit to the roof. One might keep longer lead extensions on the machine; drill a vertical pocket for the bit, starting the angle hole at this pocket; or modify the mast. If the mast is made so that the distance from the drillhead to the drillguide remains constant while the mast extends, after which the drillhead travels up the mast, the shorter mast can be made to start the hole more easily. However, short teed length will still result in longer drilling time. It is obvious from these points that a proper choice of mast is simply the highest one which will be moved easily in the given mining height. This, of course, goes against the grain of most experienced coal mining people who realize that a relatively small decrease in mining height can create a problem correctable only with the purchase and installation of shorter masts. If the mining

Jan 1, 1982

By C. C. White

Much benefit can be achieved by a mining company and a manufacturer if both parties can communicate effectively with each other and assist in product development; mutually beneficial ideas and products will develop. This communication can best be achieved if both parties have the opportunity of having on their respective staffs, specialists whose function is to improve the use of products used in mine development. Although a great wealth of roof control knowledge has long existed among mine operators, until recently there was not an abundance of joint development of roof control material by manufacturers and mine operators. This was perhaps due, in past lean years, to the preoccupation of mine management with other overwhelming problems that arise in mining. Manage¬ment had little time for the lengthy process of product development. Until recently, only a few of the largest mining companies had fulltime personnel devoted to roof control. A bolt manufacturer who is invited to work with an operator's roof control people in developing new material is lucky indeed in that he learns what is wanted and he acquires the benefit of the operator's knowledge and experience. He has only to come up with a satisfactory product at an acceptable price - which is not always easy: The development of new products is usually costly and time consuming, and many new products fall by the wayside. In the case of point anchors, however, this product is here to stay. The advantage of point anchors over mechanical anchors is now a proven fact. This advantage is due to less bleed off and higher ultimate load capacity of the resin point anchors. Point anchored bolts have proven to be superior to fully grouted bolts in many areas. We at Birmingham Bolt Company are fortunate in that we have been involved in joint efforts to develop point anchors with several coal companies from whom excellent advice and direction was received. It is appropriate to mention before continuing that the use of point anchors began in the 1960's in Europe and became widespread only recently in the United States. They fall in two categories, point anchors and combination point anchors. These categories have been defined by the Bureau of Mines as follows: (1) point anchors having 24" of grouted length and (2) combination anchors having 24" or more of grouted length. In the present nomenclature, all are anchored with resin or some sort of cementing compound between the rebar or tensioned element and the wall of the hole. The latest development includes an expansion shell as well as rebar, the purpose of the expansion shell being to facilitate installation without the delay necessary in use of types that require a waiting periond for setting of the resin before tightening. (See figures #1 and #2.

Jan 1, 1982

By Herryal Z. Anwar

In recent years, many both mining and civil engineering projects are developed in the area which may be categorized unstable, such as fractured and jointed rocks or "water sensitive rocks". For example, in underground coal mining, in which the floor strata normally consist of weak shale, the problem that may arise in roadway is floor heaving. In this case cement injection in borehole appears to be an economically effective method in order to make roadway more stable. This method may be also applied in the projects in which the constructions are laid on fractured and jointed rock. Nevertheless, the successful cement injection is much dependent on the water-cement ratio and the injection technique. This paper discusses the application of cement grouting to improve the ground stability in longwall mining, the laboratory experimentation of cement grouting and the method of floor injection.

Jan 1, 2000

By Jamal Hematian

Understanding the behaviour of rocks in a high horizontal stress field, such as that in Australia, is critical when analysing the stability of underground structures. This paper addresses the significance of the post-failure behaviour of rocks on the stability of underground structures which are under the influence of a high horizontal stress field. The research work was conducted through a combination of numerical modelling, laboratory testing and field investigation. A number of 2-D FE model of roadways were constructed based on the data obtained from laboratory testing and field investigations. The models were then analysed using three different solution techniques; simple linear-elastic, non-linear elastic-plastic and elastic-plastic with consideration of post-failure behaviour (softening model). Results indicated that the post-failure behaviour of rocks significantly influence the stress and displacement patterns around the roadway. The stress and displacement patterns as well as the extent of the yield zone around the roadway predicted by the softening model were in good agreement with that from the field study. Based on the results of the study, an appropriate support system has been suggested to govern the stability of roadways.

Jan 1, 1994