| At this stage,although the country has put forward the goal of "double carbon",the consumption of coal energy is still at a high level in a short time.In order to achieve the goal of "double carbon" as soon as possible,the coal industry began to make changes from the initial extensive mining to today’s precision mining,effectively avoiding the waste of coal resources.With the mining of coal resources,many mines in China have reached a depth of thousands of meters,and are faced with a series of problems such as high pressure and high gas.In order to reduce the pressure of the working face without wasting coal resources,relevant experts and scholars have proposed the technology of retaining roadways along the goaf.By carrying out deep hole presplitting blasting on the roof of the working face,forced caving is carried out to cut off the stress transmission path of the roof and increase the thickness of the short arm beam for cutting the roof,Effectively reduce the pressure on the roof of the working face,make the roof collapse according to the predetermined plan,and ensure the safety of life and property.The key to the forced caving technology of deep hole presplitting blasting is the selection of blasting parameters.The engineering background of this article is 1452(1)working face of Dingji Coal Mine.The principle of deep hole presplitting blasting was studied and analyzed.According to the actual situation of the working face,the optimization selection of "undercutting" blasting parameters was mainly studied.The numerical simulation and model test were carried out for each parameter,and the following results were obtained:(1)According to the static strain test in the model test,in the loading stage,the test block is under transverse tension,longitudinal compression,and unloading stage,the test block is under transverse compression and longitudinal tension.The dynamic strain test shows that the farther the strain gauge is from the explosive,the longer the time for the stress wave to reach the peak value,and the peak value of the stress wave of each strain gauge also decreases with the increase of the distance.From the analysis of damage caused by explosion,it can be seen that when the distance between blastholes is 8～12 times the diameter of blastholes,the damage caused by explosion is good.When the location of blastholes is relatively concentrated,the energy generated by explosion is relatively concentrated,which will cause serious damage to the weak surface of the test block.When the resistance line is large,the damage to the boundary of the test block caused by explosion is small.Because the upper and lower surfaces of the test block are uneven,when the confining pressure device contacts with it,it will produce stress concentration on the test block,thus affecting the development of damage cracks of the test block after blasting.(2)The numerical simulation software is used to simulate the blast hole spacing of double hole blasting of 40 cm,50cm,60 cm and 70 cm respectively.The final effect of the numerical simulation of double hole blasting is comprehensively analyzed from the effective stress nephogram,the effective stress time history curve and the damage fissure development nephogram of the rock after the explosion.Finally,it is determined that when the blast hole spacing is 60 cm under the condition of no geostress,the cracks between the blast holes just penetrate,and the damage to the surrounding rock mass is small.When the local stress exists,the crack propagation length of double hole blasting is weakened by the ground stress.In the design of actual blasting parameters,the spacing of double hole blasting should be appropriately reduced.(3)Through the research on the principle of gob side entry retaining technology and the comprehensive analysis of the actual situation of 1452(1)working face of Dingji Coal Mine,the deep hole presplitting blasting slit can be carried out on the suspended roof above the working face,cutting off the roof above the goaf,blocking the force transmission path between the roof of the goaf and the roadway roof,and the roof rock of the goaf will cut off the slide along the structural plane of the slit under the periodic weighting,and the collapsed gangue will become the roadway protection body.The roof of the roadway keeps the stability of the roadway under the action of constant resistance,large deformation and high-strength anchor cable support.The specific blasting scheme is divided into three steps: the first step is the deep hole presplitting blasting of the roof within the range of 30 m with the cutting hole inclination of 80 m,which will cause blasting damage between the overlying rock layer of the coal seam at the upper corner of the cutting hole and the overlying rock layer behind the cutting hole.The blasting hole diameter is 94 mm,and the explosive is the three-level coal mine permissible gas drainage water gel cartridge with a high power three-level coal mine permissible water gel explosive.The specification is Φ 63 × 1000 mm ×3300g/piece;Step 2:30 m in front of the cutting hole,80 m inclined,and the thick hard roof within 30 m of the upper layer is subject to ultra deep hole presplitting blasting,which damages the thick hard rock layer.The blasting hole diameter is 94 mm,and the explosive specification is Φ63×1000mm×3300g/piece;The third step is the deep hole presplitting blasting along the slot and the presplitting coupling blasting of the overlying roof.The deep hole presplitting blasting along the slot adopts a blasting hole diameter of 50 mm,a hole spacing of 0.5m,a hole depth of 13 m,and an angle of 75 degrees from the horizontal direction.The explosive is a common Grade III coal mine permissible water gel explosive with a specification of Φ27×430mm×330g/roll,the presplitting blasting of the upper roof adopts the blasting hole diameter of 94 mm,the hole depth of 30-42 m,and the explosive specification is Φ 63 × 1000 mm ×3300g/piece.After deep hole presplitting blasting,the roof pressure and weighting step of the working face are effectively reduced.Figure [60] Table [24] Reference [41]... |
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