Study On Failure Mechanism And Protection Measures Of Fan-Shaped Holes Brow Line Of Broken Orebody

The sublevel caving has been widely used in underground mines with its unique mining advantages,and in recent years it has also been gradually applied to the mining of broken orebody,but many problems have arisen when the method is used in broken orebody,for example,brow line damage has become a key problem that seriously limits the successful use of the sublevel caving in broken orebody.In the western No.2 mining area of Longchou Mine of Jinchuan Group,the ore rock is relatively crushed,and there is a serious problem of brow line damage when using sublevel caving for recovery,which greatly affects the normal production of the mine.In order to solve the problem of brow line damage in the caving stope of the western No.2 mining area and to provide technical reference for mines applying the sublevel caving under similarly broken orebody conditions,the following studies were done in this paper.Firstly,in view of the serious problem of brow line damage in the western No.2 mining area,combined with on-site research and relevant mine data,it is determined through theoretical analysis that,in addition to the factor of broken orebody,the unreasonable charging parameters of fan-shaped medium-deep holes and the unreasonable location of the initiation point are the main influencing factors of brow line damage.Secondly,for the main influencing factors of brow line damage in the western No.2 mining area,the mechanism of brow line damage under two extreme charging parameters,namely dense charging at the orifice(no charge length of 2m～3m at the orifice)and large area of no charge at the orifice(no charge length of 6m～8m at the orifice),was investigated by combining theoretical analysis,theoretical calculation and numerical simulation study,and it was concluded that when the charging at the orifice is too dense,the explosive energy at the orifice.When the orifice is too densely charged,the concentration of explosive energy at the orifice will lead to serious damage to the brow line;when the orifice is not charged over a large area,the reflection of stress waves propagating to the free surface of the drift will also lead to serious damage to the brow line,breaking the traditional perception that increasing the length of the uncharged orifice is beneficial to the protection of the brow line.At the same time,the research results show that the explosive energy distribution of these two charging parameters is very uneven,and there is a very obvious phenomenon of explosive energy concentration and explosive energy lack,which has a great impact on the integrity of the brow line.In addition,numerical simulation and theoretical analysis methods to study the damage mechanism of the brow line under the hole initiation modes,the results show that the density coefficient of fan-shaped holes from the bottom of the hole to the orifice gradually increased,so that the same section in the hole initiation modes under the larger amount of initiation charge,easily lead to the large explosive energy at the mouth of the hole,causing brow line damage.Finally,in order to solve the serious problem of brow line damage,through theoretical analysis and numerical simulation analysis method proposed to optimize the charging parameters,the use of hole bottom initiation,take the brow line reinforcement program and optimize the number of holes and other measures,where the optimization of the charging parameters mainly follow the principle of uniform distribution of explosive energy,that is,the charge is full of gun hole charging orifice distance in accordance with 20 times the diameter of the pillar package to determine the rest of the gun hole without charge The length of the remaining holes is determined by the sum of the unloaded length corresponding to the limit distance of ore damage between adjacent loaded holes and the distribution range of cracks at the end of the cylindrical charge.The field engineering test shows that the brow line protection measures proposed in this paper can effectively protect the brow line,after taking the brow line protection measures,the brow line damage length improved from 2.2m～4.4m to about 0.4m at present,the damage height improved from 1m～2m to only the roof support body is damaged at present,and the average recovery rate of the drift improved from 55%～66% under the severe damage of the brow line to 72%～89% at present.