Research On The Adaptability Of Drilling Cuttings Method Of Percussion Coal Under Rich Water Conditions

Under the influence of the Luohe Formation aquifers in the coal rock bursts in Binchang and Yonglong mining areas of Shaanxi,it is difficult to clearly reflect the stress state of the coal body by the drilling cuttings volume index,which leads to the failure of the drilling cuttings method and affects the effective monitoring and early warning of the mine rock burst danger.In this paper,the methods of field investigation,data statistics,theoretical analysis,laboratory test and engineering practice are used to study the deterioration of physical and mechanical properties of coal under water-bearing conditions and the mechanical properties,instability and failure of coal samples under triaxial loading drilling conditions.The characteristics,acoustic emission laws,micro-fractures,and energy space-time evolution laws are systematically explored to guide the correction of the cuttings volume index under water-bearing conditions.The main results are as follows:In this paper,based on the elastic-plastic assumption combined with the strain softening and capacity expansion characteristics of the coal under the condition of water content,the analytical formula of the amount of cuttings and the stress of the coal under the condition of water is given by weakening the physical and mechanical properties that affect the parameters of the amount of cuttings.The partial derivative of the mechanical parameters with respect to the amount of drill cuttings is normalized,and it is concluded that the plastic softening coefficient and loose coefficient of the coal body play a decisive role in the value of the drill cuttings.little impact.Triaxial drilling tests were carried out under different stress and water content conditions.The results of sample mechanics and instability failure characteristics show that when the water-bearing coal body is at a higher stress level,the micro-cracks and structural surfaces of the coal body are infiltrated by water,resulting in microstructures.softening,the bonding ability between the structural planes is weakened,and then the phenomenon of slippage and dislocation is obvious under high stress level,and the plastic deformation ability is enhanced.The appearance of the phenomenon is manifested in the significant increase in the time of coal sample compaction stage at the stress level.The results of the space-time evolution of absolute energy during the test show that:under the action of stress,the frequency of dynamic response of coal is positively correlated with water content.Compared with the natural state coal,the elastic energy storage capacity of the sample decreased,the dynamic event incubation process was shortened,and the energy release intensity decreased while the frequency increased,and the absolute energy release time during the test was highly consistent with the stress drop time.The overall spatial distribution of absolute energy is"ellipsoid",with the borehole path as the long axis,showing the characteristics of concentration in the middle and sparse distribution at both ends.Contiguous form distribution.Based on the test cuttings value and absolute energy tomography results,the borehole damage and influence radius were calculated.The actual measurement results of the test drill cuttings show that the amount of drill cuttings in the water-bearing coal body is 2.78 times that of the latter under natural conditions;The amount is 3.48 times that of the latter.And according to the theoretical calculation,compared with the natural state,when the water content is 5.60%,the amount of coal drill cuttings is 1.50～3.20 times that of the latter.It is comprehensively determined that when the water content is(3.7%～5.60%),the correction coefficient H of drill cuttings is 2.10～3.48.