Causes Of Mine Collapse.docx

Causes of Mine Collapse A mining accident is an accident that occurs during the process of mining minerals. Thousands of miners die from mining accidents each year, especially in the processes of coal mining and hard rock mining. Mining accidents can have a variety of causes, Gas Leakage Slope Collapse Flooding/ water leakage Mechanical error Use of Improper Explosives Poor workmanship

Methods of avoiding mine collapse Lining type 1. Natural support in rock

Field of application 1. Limited to competent rock in low in situ stress conditions 2. Commonly adopted in several metalliferous and evaporite deposit mining conditions

2. Rock 1. Mechanical anchor bolts reinforcement applied in hard rock mining conditions 2. Full column bonded bolts used in weaker rock conditions to promote stability. 3. Suitable for rectangular roadways and rooms in systematic pillar mining 4. Used as a surcharge support in conjunction with steel sets 5. Truss bolting applicable to competent roof beams 6. Suited to longwall retreat mining roadways and face developments

Operational features 1. Rare in UK coal mines although used in some shaft bottom locations 2. In some hard rock mines, mesh is installed using rock bolts to prevent spalling and detachment of slabs/ blocks although the bolts are not necessarily recognised as constituting a support system in such conditions 1. Large range of bolt types has been developed to cater for a wide range of mining problems and geological conditions eg, Swellex bolts, split sets, cable bolting etc. 2. Often used in conjunction with meshing and/or shotcrete in friable roof conditions 3. Major worldwide mine tunnel support method 4. Non-column bonded bolts can be prone to corrosion problems as well as installation and performance problems.

3. Steel sets

1. Found favour in European 1. Steel possesses favourable post coal mines where they have not yield behaviour in that the steel been limited by depth below the section does not usually completely surface and where extensive rupture under high loading but allows yield zones form a plastic hinge to form; although this 2. Suited to advance Iongwall reduces the support's strength, it mining where rock bolt does not usually result in complete applications have not been failure under normal mining feasible deformations 3. Steel sets provide successful 2. Support system behaviour depends support in most conditions on ancillary items such as connecting involving long term large scale plates, struts and stilting deformations arrangements to suit particular 4. Rigid and yielding versions strata conditions have been successfully employed 3. Adaptable to a wide range of opening profiles

4. Concrete supports

1. Segmental, monolithic and shotcrete supports have all found application in the mining size industry confined 2. Monolithic concrete widely in construction of shafts of and shaft bottom areas remote from mining induced stresses 3. Benefits from stability induced by the shaft pillar 4. Easily adapted to large crosssections 5. Segmental linings have found limited use in European coal mines repair

1. Segmental concrete supports are relatively difficult to handle and transport due to their weight and which can cause problems in spaces as exists in mine tunnels used 2. Highly dependent on the standard backfilling for correct operation which can be difficult in fractured rock masses 3. Monolithic concrete easier to transport but does not contain a significant amount of yield once constructed, thereby giving limited applications 4. Concrete supports can cause work difficulties if they fail, due to their large mass and physical size

5. Shotcrete

1. Shotcrete used in mining as a temporary support if required and to control rock mass deterioration by sealing from the mine air 2. Fibre reinforced concrete is finding increased application to support in conditions of poor quality rock and blocky rock where rock bolting is deemed inappropriate due to the size of the fractured material

1. Shotcrete has found limited use in mining due to scheduling difficulties with large numbers of working areas 2. It is now recognised as a low cost effective support medium which is suitable for a variety of rock conditions with or without supplementary support systems

Mining exposes workers to lethal amounts of energy. The energies in underground mines are in states of motion or stored in moving shafts and gears; electricity; the mine roof, rib or sides of the tunnel; hydraulic cylinders; and more. An unexpected release of this energy can equal disaster. These energies must be controlled at all times and in all situations. Unfortunately, our controls are not always up to the task. Gas leakage event apparently involved the methane gas accumulating into the explosive range and an ignition source. Mine roofs collapse for many reasons, such as fault lines in the strata, inadequate bolting or other mechanical controls, inadequate pillar size or improper mining methods. Mines blow up when methane gas accumulations go undetected or inundate a mine quickly before power can be cut or the area can be ventilated. Investigations into these recent mining disasters have not been completed, so the basic or root causes cannot be known yet. To prevent incidents in mining, both large and small, is no easy task. In underground mines, stored energy in the form of earth surrounds the worker. Miners work in a confined space that has the potential to collapse on them at any time, despite efforts to maintain the integrity of the roof, ribs and floor of the void in which they work. The challenge to identify and control hazards in this workplace is unequaled. Mine safety begins with commitment. Management must commit to preventing accidents by providing adequate resources for the identification and control of hazards. All mines must integrate safety into everything they do. There is no magic bullet to prevent injuries and loss. But it's essential to have commitment: -- To prevention, vigilance and excellence in workplace examinations. -- To safe work practices and procedures. -- To controlling the hazards associated with the worker, the equipment, material and the environment. A former supervisor of mine was fond of saying, "Plan for the exception, and expect it to happen." Perhaps for mining, this goes double. The miners who perished at Upper Big Branch were killed instantly. There was no opportunity for them to evacuate or take refuge. The miners at the San Jose copper mine might have escaped back in August had all escape routes been maintained properly. Companies must embrace an aggressive culture of safety prevention first and foremost and also incorporate a program of mine emergency response that is second to none.

How is methane detected and controlled? Large fans circulate air in mines to provide ventilation to the working areas. These fans operate to dilute the methane to well below explosive levels (5-15%). Monitors installed on mining machines deactivate the machine when the methane concentration reaches 1%. Mines with excessive methane can remove the gas prior to mining by drilling drainage holes.

How is methane controlled from mined-out areas? Coal mines generally have active mining zones and areas that were previously mined. These mined-out areas can be abandoned areas that are no longer ventilated and are separated from the active mining areas by explosion-resistant structures called seals. Seals are designed to contain an explosion within the abandoned area. Longwall mining is an example in which an "active" mined-out area called a "gob" is created behind the advancing panel extraction. This gob area becomes a reservoir for methane gas to collect, and may be difficult to fully ventilate because the overburden has collapsed and filled this area full of broken rock fragments. In this case, ventilation of the working face is critical to restrict the migration of methane from the gob and dilute that which escapes into the working area.

What is done to prevent coal dust explosions? Underground coal mining produces finely divided coal dust that deposits throughout the mine and serves as a source of combustible material for coal dust explosions. Limestone powder, known as rock dust, is spread throughout the mine workings on a regular basis. This rock dust serves to inert the coal dust when applied in the proper proportion. When explosions do occur, the dispersed limestone powder absorbs the heat generated from the explosion and will either stop the chain reaction or reduce the intensity of the explosion. It is critical that this inertization practice of rock dusting be consistent with the mining process. Even a thin layer of additional coal dust deposited on a previously rock dusted area can restore the explosive condition.

Room and pillar (variant of breast stoping), also called pillar and stall,[1] is a mining system in which the mined material is extracted across a horizontal plane, creating horizontal arrays of rooms and pillars. The ore is extracted in two phases. In the first, "pillars" of untouched material are left to support the roof overburden, and open areas or "rooms" are extracted underground; the pillars are then partially extracted in the same manner as in the "Bord & Pillar method". The technique is usually used for relatively flat-lying deposits, such as those that follow a particular stratum.

The room and pillar system is used in mining coal, iron and base metals ores, particularly when found as manto or blanket deposits, stone and aggregates, talc, soda ash andpotash. [2] The key to successful room and pillar mining is in the selection of the optimum pillar size. In general practice, the size of both room and pillars are kept almost equal, while in Bord & Pillar, pillar size is much larger than bord (gallery). If the pillars are too small the mine will collapse, but if they are too large then significant quantities of valuable material will be left behind, reducing the profitability of the mine.[2] The percentage of material mined varies depending on many factors, including the material mined, height of the pillar, and roof conditions; typical values are: stone and aggregates 75 percent, coal 60 percent, and potash 50 percent.