Assessment Of Rock Mass Geology Condition Based On Drilling Parameters Of Gas Drainage Boreholes And Its Application

The most common method of gas control in coal mining is drainage gas with drilling holes,therefore,a lot of in-seam boreholes and cross-measure boreholes are need to be constructed in the gas mines.During gas extraction,low gas concentration in gas drainage is an engineering problem restricting the extraction efficiency.However,one of the key problems is how to determine the reasonable sealing depth of boreholes.If the sealing position of borehole is too deep,the blind area of gas extraction will be appeared.But,If the sealing position of borehole is too shallow,air will enter the boreholes from the surface of the roadway,that will reduce the gas concentration.Therefore,it is necessary to obtain the zone of damage and the distribution of stress in surrounding rock for determining the reasonable borehole sealing position,which is still a lack of widely implemented technology at present.The response of drilling rig is closely related to the state of rock in coal mines.In the process of drilling,workers can predict the state of rock according to the response of drilling rig.But at present,the acquisition of such information is mainly dependent on the quality and experience of construction staff,which will inevitably lead to incomplete and unreliable information acquisition.Therefore,in this paper,a drilling parameter recorder was designed to monitor drilling process,and the drilling process of gas drainage holes in III1011 working face of Haizi coal mine had been monitored.Based on the monitoring data,the relationship between the geological condition of the rock mass and the operating parameters of the drilling rig was analyzed,and a method for determining the rational sealing position of the gas extraction borehole was proposed.The main achievements of this paper are as follows.?1?A drilling parameter recorder was designed for hydraulic drilling rig based on the analysis of the structure of hydraulic drilling rig.It was composed of data collection,control system and power supply system.Data collection consists of pressure sensor,hall sensor and displacement sensor.Control system is core of a drilling parameter recorder.It has the function of recording,displaying and processing for drilling parameters.The battery system provides electric energy.It mainly composes of NiMH battery.?2?The drilling parameters of gas drilling holes were collected by drilling parameter recorder.It is analyzed that relationship between the stress state of the rock mass and the operating parameters of the drilling.The results showed that the idle pressure of drilling rig increases with the increase of drilling depth,and which features a rapid increase at the certain depth from the roadway wall.The state of abnormal drilling was analyzed by rotation pressure and characteristics of displacement.?3?The numerical simulation software FLAC^3D is used to simulate the drilling process and roadway excavation for grasping the causes what idle pressure is rapid increase.The distribution of stress,permeability and gas pressure along the direction of the boreholes is obtained.The results showed that plastic deformation and gas pressure are mainly reason for increasing idle pressure,and position of stress concentration can be determined by the change of the idle pressure.?4?The numerical simulation of the seepage process of gas extraction different sealing depth is carried out to study the effect of gas extraction for different sealing depth,and to determine the reasonable sealing depth.Two parameters,namely seepage resistance and equivalent seepage velocity,are proposed to measure the difficulty of air seepage based on Darcy's law.The seepage process of gas along boreholes direction and vertical boreholes direction is analyzed.The result showed that the depth of sealing should be slightly higher than area of stress concentration,and the area can be determined by the idle pressure.Stress concentration is located in the zones where is around 14 m from the roadway wall in the test site of Haizi coal mine.The proposed reasonable sealing depth is 16 m.In the field,the sealing depth is16 m,and it works well.