Analysis of the major accident of the roof of the

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Analysis of major accidents in coal mine roof and Research on practical safety technology on site

according to statistics, major safety accidents in coal mines over the years account for 39% of all fatal accidents; Therefore, it is of great significance to curb the occurrence of major accidents by analyzing the causes and laws of major accidents, conducting on-site practical safety technology research, taking targeted preventive measures in management, technology and equipment, and implementing key governance, supervision and monitoring

1 analysis of major accidents in Shandong coal mines (see Table 1)

*: major accidents in coal mines in cities, counties and towns in the table are statistics from 1972 to 2004

from the analysis of Table 1, major accidents prone Majors:

(1) the number of accidents is: roof accounts for 39%, flood accounts for 27%, and gas accounts for 24%

(2) the death toll is: roof accounts for 17%, gas accounts for 40%, and flood accounts for 35%

2 Analysis of major roof accidents and practical management technical measures on the spot

before 1980, coal mines in Shandong province accounted for about 60% of roof accidents, and major accidents such as surface collapse and large roof fall often occurred. The main reasons are "two 2. Unclear speed double closed-loop control": (1) unclear law of roof pressure; (2) The performance and actual support capacity of the pillar are not clear. Therefore, the "two measurements" have been carried out: (1) the mine pressure observation and the floor specific pressure measurement have been carried out to find out the movement law of the overlying strata and the floor failure law of the stope; (2) Conduct pressure test and actual support capacity measurement for pillar maintenance. After ten years of hard work by technicians in the province, great achievements have been made in the "two tests": (1) know well the law of roof pressure and the law of floor failure;; (2) The bursting pressure value of pipe fittings can be effectively detected in the performance and support capacity of the support. On this basis, the top and floor of the main coal seams in the province have been classified, targeted management and technical measures have been taken, and a large number of support reforms have been carried out. Since 1990, the province has put an end to the catastrophic accidents of large roof fall and face collapse, the accidents of sporadic roof knocking have decreased significantly, and the roof accidents in the province have decreased by 30%. However, since 2000, major roof accidents have occurred from time to time in coal mines across the province, and sporadic roof accidents have also occurred frequently. Roof accidents have risen to about 50% of all short-lived accidents;; In 2001, 165 people died in raw coal mines across the province, of which 58 died in roof accidents, accounting for 35%; In 2002, 104 people died in raw coal mines across the province, of which 53 died in roof accidents, accounting for 51%; In 2003, 97 people died in raw coal mines across the province, of which 27 died in roof accidents. The ranking method of the effect is based on the frequency of vocabulary appearance 27 In 2004, 49 people died in raw coal mines across the province, of which 18 died in roof accidents, accounting for 36 7%。

2 . 1 roof accident analysis

(1) time of occurrence: morning shift accounts for 34.8%, middle shift accounts for 26.1%, and night shift accounts for 39.1%. The main reasons for more night shift accidents are that workers have poor rest, lack of concentration, and are easy to ignore the project quality; In addition, the mine leaders worked less at night, relaxing safety management and safety inspection

(2) roof conditions: hard roof slabs such as sandstone are relatively complete and easy to be careless, accounting for 53.6% of all roof accidents; Mud, carbonaceous shale and other relatively broken roof, which are prone to roof leakage and collapse accidents, have attracted attention. Therefore, the accident accounts for only 6%

(3) place of occurrence: the upper and lower ends of the coal mining face and the outlet are the places where roof accidents frequently occur. This is the superposition area of supporting pressure. When moving the head and tail of the transportation machine, a large area of empty roof is caused. In addition, the support density is small at ordinary times, and the quality of special support is poor, resulting in roof fall, accounting for 20%

(4) occurrence process:

① blasting: after blasting in the coal face or after the shearer, the support is not timely, and a large area of empty roof is used to grind coal for a long time. At this time, the measured roof subsidence speed is more than 3 times that of daily, which is very prone to roof separation and collapse, and the roof accident accounts for more than 37%

② pillar retraction: when the pillars are retracted in the coal mining face, the roof activity intensifies, and the roof subsidence speed is 10 times that of daily life. The roof is very easy to follow down and hurt people, and the roof accident accounts for 32%

(5) low support strength: 90% of the roof accidents in the coal mining face are due to the low initial support force of the pillars, the bottom drilling of the soft pillars of the floor, and the low support strength, resulting in the subsidence, separation and caving of the roof

(6) geological structure: because the coal mining face passes through faults and old ketones, the coal seam conditions and the rock properties of the roof and floor change, and special support measures are not taken in time, the occurrence of roof fall accidents accounts for 11 7 %。

(7) heading face: the sinking speed of the roof after heading blasting is twice that of 2m away from the head-on. The front detection beam is not used, the roof is empty, and the first ten sheds are not interlocked and reinforced, resulting in roof falling accidents

(8) at the triple gate and Quad gate at the intersection of the roadway, the bearing pressure is superimposed, and the empty roof area is large. The double lifting shed is not used to strengthen the support, resulting in roof fall accidents

(9) roadway Renovation: do not reinforce and support first, do not support first and then return, resulting in roof fall accident

(10) rockburst: the occurrence of rockburst is mainly related to the mining depth of the mine, the physical and mechanical properties of coal and rock, mining technology and other inducing factors. From 1966 to 2004, a total of 229 destructive rockbursts occurred in Shandong Province, killing 23 people and seriously injuring 44 people

2 . 2 practical technical measures for roof management on site

(1) the coal mining face mainly focuses on "two qualities, three links"

two qualities: ① the quality of the pillar (frame) must be regularly overhauled and pressure tested according to the regulations to ensure that the parts are in good condition; Wood pillars shall be used, and the material must meet the specified requirements; ② The support quality, the pillar must be strong against the mountain, and the support must be neat, stable and connected to the top and bottom plate according to the regulations. Three links: ① pump station pressure, single hydraulic prop must reach 18Mpa, emulsion concentration 1-2%; The fully mechanized support must reach 30 MPa and the emulsion concentration is 3-5%. ② If the bottom plate is soft, wear iron column shoes, and the drill bottom of the column shall not exceed 10cm; ③ Each shift must be rehydrated twice (many times). When raising the column, if the liquid injection is stopped as soon as the movable column touches the top, the initial supporting force is only 55kn/piece. Therefore, when injecting liquid into the pillar, continue to inject liquid for 5S after the convertible top is touched

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