Failure characteristics of borehole based on FLAC3D numerical simulation
With the gradual development of coal mining to the deep,the harm of gas over-limit accidents increases.In order to ensure the safety of coal mine production,coal seam gas drilling pre-extraction technology is one of the most effective technologies.Drilling quality had an important influence on the extraction effect.Based on FLAC3Dnumerical simulation software,the characteristics of borehole failure under the influence of different factors were studied.The variation law of coal longitudinal displacement was analyzed.The results show that with the increase of borehole diameter,the longitudinal dis-placement at the top of the borehole increased by 1.10％.The change of the waist side of the borehole was small.The longi-tudinal displacement at the bottom of the borehole was reduced by 17.05％.With the increase of the pressure,the longitudi-nal displacement of the borehole vertex increased by 42.48％.The longitudinal displacement of the waist side of the bore-hole increased by 38.89％.The longitudinal displacement at the bottom of the borehole increased by 38.39％.With the in-crease of loading rate,the maximum longitudinal displacement of drilling vertex was 0.053 mm.The maximum longitudinal displacement of the waist side of the borehole was 0.023 mm.The maximum longitudinal displacement at the bottom of the borehole was 0.005 mm.The borehole diameter,stabilizing pressure and loading rate were negatively correlated with the lon-gitudinal displacement.Through the mechanism analysis of different stages on the stress-strain curve of coal drilling speci-mens,the whole process of borehole instability was clarified.The study provides a theoretical basis for ensuring the safe pre-extraction of coal seam gas.
gas extractiondrilling pre-extractionborehole failure characteristicsstable pressureloading rate
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