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By Hideki Shimada

In underground coal mines, grouting method is employed in order to reinforce the floor and to control the movement of groundwater into the roadway. However, the seepage and the reinforcement behavior of the grouting material into the floor are not clearly understood. Therefore, grouting is today normally based on empirical relationships and on the experience of the grouting personnel. To assist grouting projects, it must be acknowledged that many of the flow and the hardening processes occurring during grouting so far defy mathematically analysis. From this point of view. this paper discusses the behavior of grouting material, when it is injected into the roadway floor, by means of 3-D Eulerian-Lagragian seepage analysis. Moreover, the effectiveness of reinforcement grouting on the mechanical properties of slaking-prone mine tunnel floor are studied by means of several laboratory tests. Keywords: Mine tunnel floor, Grout, Seepage, Reinforcement

Jan 1, 2002

By Uros Bajzelj

When driving mine roadways in the vicinity of tectonic disturbances and fault zones, sudden outbursts of gas, along with ejections of fine coal, occur. Substantial dynamic changes occur around the roadways in the coal and around the support. The problem has several aspects. Studies have been carried out on the technical analyses of the phenomena which occurred in the Velenje Lignite Mine from 1957 to 1988, The second part of the investigation involves systematic laboratory studies of strength and deformability characteristics of lignite samples and "in-situ" measurements of stress changes during the driving of some roadways. Analyses of events (using the model of limit convergence and the finite element method) showed the possibility of gas outbursts, taking into account the deformability conditions when crossing over from compact lignite to the disturbed region. The rate of advance of roadways and the method of support strongly influence the occurrence of the phenomenon. The preventative measures used in driving roadways under such conditions include trial drilling and the use of blasting instead of machine cutting.

Jan 1, 1992

By Alan Campoli

The Eclipse System was developed by Minova USA Inc. formerly Fosroc Inc. to improve the performance of 5/8-inch deformed rebar fully grouted into a one inch borehole. An 1/8-inch offset bolt head combined with specially formulated Eclipse Lokset resin cartridge results in reduced gloving and increased mixing efficiency. The benefits of the Eclipse System have been demonstrated, under the supervision of MSHA, in Kentucky, West Virginia and Illinois coal mines in partnership with Excel Mining Systems, a leading roof bolt manufacturer. Over 100,000 units have been installed to date. Eclipse system bolts exposed during overcast construction at the Panther Mine of Cumberland Resources displayed an extremely well mixed, uniform resin anchorage over the entire bolt length.

Jan 1, 2003

By Khaled Morsy

In this paper a new method to evaluate the stability of yield pillars was introduced. The evaluation of yield pillar stability was conducted in three steps: (1) Estimation of pillar loading - numerical modeling is a good tool to estimate the pillar loading for most of the geological, geometrical and mining conditions. In this study. finite element technique was used to estimate the state of stress, strain, elastic strain energy and plastic energy, etc. at every point within the pillar. (2) Defining the yield pillar loading zones¬. The proposed method considered the non-uniform stress distribution of yield pillars by dividing the area of the yield pillar into three loading zones, namely core, transition and rib zones. (3) Estimation of stability indicators - an appropriate stability measure was proposed for each loading zone. such as; Core Stability Factor. CSF, Pillar Bump Index, PBI and Rib Instability Index. RIF. A case study of successful and unsuccessful yield pillar application was used to assess the applicability of the proposed method.

Jan 1, 2003

By Khaled Morsy

Most of the available numerical codes simulating the reinforcing effect of fully grouted bolt are accomplished by a series of bar elements which are connected along their length to the host rock by shear springs and sliders. The spring-slider system represents the shear bonding effect between the bolt and the host rock. This paper describes a three dimensional finite element modeling technique for the 3D simulation of fully grouted bolt reinforcement. The proposed technique introduced a physical simulation for the fully grouted bolts. The bolt simulation is composed of a series of beam elements (representing the steel rebar) embedded in brick elements (representing the grout). Because of the complexity of the grout/rock interface, ABAQUS explicit code was used. A modification of the ABAQUS default friction model was conducted to consider the cohesion of the grout/rock interface. The interaction between the grout and the host rock is simulated by the modified friction model. To verify the proposed technique, a simulation of the pull out test we conducted. The results from the simulation were compared with former studies

Jan 1, 2004

By Klaus Opolony

The German coal industry operates a multi-seam extraction system, with average working depths currently around 1,000 meters. The gate roads serving the longwalls are often used for a second time - a practice which has the advantage of allowing several panels to be extracted with a minimum of roadway drivage work. This preference for re-using gate roads is based on a number of factors: such an arrangement a) prevents the strata pressures in the subsequent panels from being adversely affected by the presence of support pillars, b) helps achieve the target of full mineral extraction and c) allows the roadways to be used for air conditioning and ventilation purposes as part of an advancing longwall system. This paper explains the planning procedure required for a rectangular rockbolted roadway, using as an example a gate road in the 3 meter-thick D2/C seam at Lippe colliery, and describes the subsequent operating experience. Here special attention is focused on modem procedures and techniques for mine roadway planning. The investigation also examines the part played by the mine ventilation system and the available machine technology, which are particularly important parameters for the design of the T-junction areas and support system. Keywords: multiple seam extraction, longwall mining, roadway drivage, roof bolting, roadside pack system, hydraulic frame type support.

Jan 1, 2002

By P. R. Sheorey

Four case studies of special geomining conditions from Indian coalfields are discuss- ed. These cases relate to (a) pillar extraction in two seams simultaneously under a difficult roof (Satpura I and II). (b) depillaring in an inclined seam resulting in rib instability (Sudamdih), (c) depillaring resulting in floor lift and side spalling (Jarangdih) and (d) contiguous pillar extraction under hard incavable strata. Solutions to these problems are given based on rock mechanics principles involving stress analysis, classification techniques, past experience and engineering judgement.

Jan 1, 1988

By Alan A. Campoli

Fosroc continues as a leader in the development of cementitious technology for the mining industry. The considerable expertise accumulated in the development of the Fm cement line has been employed in the development of two pumpable, supplemental roof support systems. The Tekprop system is a unique combination of steel and concrete, specifically designed as a viable alternative to conventional wooden supplementd support. The second system is the Fosroc mineable mi which is a cost competitive variable yield system designed to support longwall ventilation and predriven recovery room entries. Two, separate, ongoing, full scale applications of these systems will be discussed during the inference presentation

Jan 1, 1997

By Sun Henghu

This paper analyses problems associated with cement based technique in metal mines, and provides a new mining technique of packing the tailing sand and water into solidified material. In the new technique, the cementing agent is a solidifying material containing a high percentage of water and tailing sand. The sand and water solidify into the packed body at the same time. The slurry of the packed body varies widely in concentration and suitability for different mining conditions. It consists of two liquid materials, each composed of a cementing agent, tailing sand and water. The thick liquids are transported to the packing place at the same time. Their pumping property is good; they do not solidify or block up the pipe during transportation. At the packing place, the two liquids are evenly mixed. The mixed liquid flattens out well and its solidifying speed is so fast that it solidifies into a packed body within a very short period of time. The compressed strength of the packed body can reach 1.2-5MPa in one day, which satisfies the requirements of different mining conditions. By using the new mining technique, all the tailing sand can be used again in the packed body and it is low in cost and investment. The mechanisation is easy and thus the working efficiency is increased and the use of labour decreased. Contamination problems caused by excess water drainage under the ground are resolved.

Jan 1, 1992

By Syd S. Peng

Full-face shield leg pressures in a longwall panel for a three-month period were collected and analyzed. The pressure data were presented in the following forms: full- panel full-face shield pressure, individual shield pressure, full-face shield pressure, full-panel time-weighted-average pressure, and relationships among setting pressure, final pressure and pressure increment. Although shield pressure varies from shield to shield and from cycle to cycle, the setting pressure and face advance rate do control the 6nal pressure and time-weighted average pressure.

Jan 1, 1997

By Liu Changyou

This paper analyzes experimentally the stress-strain relationship and the characteristics and variation trends of acoustic emission signals of the medium- and high-burst-prone coal/rock fracture process. The precursor and sensitive characteristics of the acoustic emissions when the burst-prone coal/rock fracture occurs were obtained. The characteristic index and the feasibility for predicting rock bursts using acoustic emissions technology were proposed. Keywords: burst-prone coal/rock, acoustic emissions, energy, prediction index

Jan 1, 2003

By Zhang Liandong

Roof control in thick-seam mining has long been a difficult problem in mine design and coal mining. In the early 1980's, through ground control instrumentation and investigation the rules of roof strata movement were determined, based on which the sliding roof bar powered support was properly designed and successfully applied to roof control to thick seam mining with caving. Underground trials in Huating Coal Mine produced satisfying results. The technique is being employed in many Chinese coal mines and won the national price for technical advance.

Jan 1, 1990

By Ezzeddin Bakhtavar

There are several geotechnical challenges and risks inherent in the interaction between the open-pit and block cave mining environments. This is especially true when they have to work simultaneously for a short time, as well as when only the caving operation is continued. Some of these challenges and risks include the induced zones of stress due to the large and deep open-pit, instability of the slope, instability of the crown pillar and water inflows, subsidence, and sometimes instability of the main accesses to the block cave portion of the mine. These challenges usually occur due to cave propagation. In this paper, these geotechnical challenges and associated risks have been studied and discussed. It was concluded that the majority of the mentioned geotechnical risks could be decreased, and often eliminated, by considering the appropriate dimensions of a stable crown pillar, especially in simultaneously working open-pit and block caving operations.

Jan 1, 2011

At any given lime, the tidal force subjects massive regions to a spatially uniform load. The deformation of any large structure due to these forces is proportional to the elastic properties of the structure. In this aspect, the tidal force applies a load in a manner similar to that of a large-scale testing machine. Any anomalies in the measured tidal response must reflect alterations in the average elastic response of the massive structure. In the present work, tidal tilt measurements obtained in the wall of a large dam are used to infer changes in the response of the dam to applied loads. In particular, it is found that the dam response has changed by approximately 13 percent, on average, for two monitoring periods separated by 5 years. It is possible that these changes were produced by the different volumes of water in the dam for the monitoring periods. The tidal measurement technique can also be applied to monitor changes in the average structural response of large underground and surface masses relevant to coal and metal mines.

Jan 1, 1992

By Vasundhara

Underground coal mining in soft floor environments has often led to strata control problems ranging from small scale issues such as floor heave which disrupts traffic and ventilation, rib spalling and induced fractures in pillars, through to large scale instability and long term subsidence. Past investigations of the problems encountered in Newcastle Coalfields of New South Wales, Australia, have revealed that the soft floor unit comprises of claystone which is very sensitive to moisture. It is prone to swelling, reduction in stiffness and loss of strength in the presence of moisture. Long term stability of mine panels in such an environment is governed by the extent of deterioration of the floor strata. The paper reports the field investigations conducted at Cooranbong Colliery to assess the extent of softened floor zone in the roadway and under a pillar.

Jan 1, 2001

By Graham Daws

The introduction of UK rock bolting technology has been applied in many large underground coal mines around the world. This paper explains the methods that have been applied for its successful introduction and discusses several case studies. It does not give fine detail but is intended to allow decision makers to gain a basic understanding of the method used to introduce rock bolting to a mine.

Jan 1, 2011

By Russell C. Frith

Risk-based roadway roof support design is now a critical part of the Australian Coal Industry. Safe and efficient mining demands that roof support be tailored to the prevailing geotechnical conditions and coal mining legislation in New South Wales, Queensland, and Tasmania is clear in requiring that formalized roof support design be undertaken. The assumption of dead-load suspension of an otherwise unstable roof has been used in roadway roof support design for many years. However longevity does not necessarily translate into either a best or even reasonable practice in the current industry, particularly when pro-active strata management systems are now routinely used and reinforcing support design methods are available. The paper discusses why the assumption of dead-load suspension is fundamentally incorrect in almost all instances when pro-active or reinforcing roof support is applied and how it can easily result in misleading and potentially under-designed roof support systems under various circumstances. The commonly used design methodology of balancing the installed axial capacity of long tendons with the assumed ?weight? of a future roof fall is summarized, and several fundamental flaws are identified. The critical area of selecting the design Factor of Safety is also discussed in detail. Accepting that under certain circumstances the roof of a roadway will require it to be ?suspended?, suggestions are given for how a robust support system can be developed, designed and applied.

Jan 1, 2011

By Song Guo

This paper will present the roof bolting finite element model developed at Jennmat Corporation used to study the control mechanism of the tensioned bolt system in the laminated roof with a large horizontal stress. In addition, it will discuss general support concepts pertaining to the tensioned bolt system which are derived 6om a series of studies in conjunction with the authors' working experience and extensive research efforts over the years.

Jan 1, 1997

By Joachim Leonhardt

Hundreds ofbolt-indicators were already used successfully in the German deep hard coal-mines to increase the safety and economy. The bolt-indicator offers the simple possibility to show roof-bolt (anchor-) loads. to indicate weak points as well as to optimize the anchor density and the dimension: The bolt-indicator is mushroom shaped and consists of coated metal. It is inserted between the anchor plate and the flanged nut. The loads appearing at the anchor are transferred to the bolt- indicator and can be recognized visually at the cylindrical part by the amount of the surface coating. Examples are used to clarify the application aims, operation and usage of the bolt-indicator and its yielding advantages in practice.

Jan 1, 2001

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