Research On In-situ Stress Measurement Method And Application Based On Kaiser Effect Of Drilling Core

In order to better develop and utilize energy and mineral resources,it is urgent to understand the stress state of rock masses,and in-situ stress measurement is receiving more and more attention.In-situ stress measurement by Kaiser effect method has been widely studied due to its simple operation and low cost,but the problems related to the drilling core Kaiser effect mechanism and application are still not well solved.Thus,in this dissertation,Surrounding in-situ stress measurement,which is based on the Kaiser effect of drilling core,Griffith microcrack model is used.The Kaiser effect direction mechanism of independence is revealed.And then,the effects of cyclic path,cyclic peak load and confining pressure on rock Kaiser effect are explored using laboratory experiments.The reasonable cyclic loading mode and its peak load are proposed,and in-situ stress measurement method is established.Then,based on Byerlee-Anderson theory,the stress accumulation level of rock in mine is analyzed.Based on Hoek-Brown strength criterion,the evaluation index for coal seam overburden is established.Combined with the measured in-situ stress regression model,the characteristics of roof stress field under principal stress deflection and coal seam of repeated mining are studied.Based on the main control factors in strong mine pressure area of mine,prevention technology are proposed,and the mine mining optimization plan is finally formed.The main conclusions are as follows:(1)Secondary loading direction relative deflection angle ? is less than 10°,the relative magnitude of the microcrack critical load is 0.9?1.1,Kaiser effect does not exist independence;? is between 10°?60°,the Kaiser effect of rock is conditional independence.There is a large amount of expansion energy of micro-encapsulated gas in rock.After the stress is relieved,many fine fluid inclusions enclosed inside rock seep,move and phase change over time,producing more microcracks,resulting in less critical load for microcrack cracking during load again,and FR gradually decreases with time.(2)The influence mechanism of high stress on the Kaiser effect is revealed,and the reasonable loading mode of AE-DRA method is proposed.When the peak stress of the first cyele ?p is larger than the previous maximum stress ?hmax,the rock will have further damage and deterioration accumulation based on history irreversible damage memory,which will make rock stress memory different from ?hmax memory,and the FR changes greatly.When ?p is less than or slightly more than ?hmax,the rock interior element body will deform and become unstable,but it will not change the rock crack size,and it has no obvious influence on stress memory of later circulating rock.Different cyclic paths is essentially influence of ?p of the first cycle on rock Kaiser effect.Cyclic loading of load and displacement control is reasonable loading mode for Kaiser effect test by AE-DRA method.The first ?p for coal seam overburden is smaller than the Kaiser effect point stress value,and then the cycle ap does not exceed the expansion point stress value.In triaxial loading,the differential stress and confining pressure corresponding to rock Kaiser effect show a good linear relationship.With increase of cyclic loading times,FR shows a decreasing trend.Under action of low confining pressure,in-situ stress test by Kaiser effect is performed directly under uniaxial loading.(3)The in-situ stress measurement method based on the Kaiser effect of drilling core is established,engineering application has been carried out,and the characteristics of borehole and nearby stress field are obtained.The Kaiser effect test value is compared with the on-site measured values by hollow inclusion,ASR and hydraulic fracturing.The errors are within the reasonable range of the project,and the reliability of the method is verified.(4)The stress accumulation level of coal seam overburden is analyzed,and the stress state evaluation index is established.The friction coefficient of faults in Buertai and Baode coal mines are both about 0.3,which is far less than the lower limit of strike-slip type of fault,and the overall level of stress accumulation is lower.The strength stress ratio index i5 used to evaluate rock mass in these two eoal mines.The former belongs to medium-high in-situ stress field,and the latter belongs to medium in-situ stress field,which is in line with the scene and verifies the reliability of the index.(5)The principal stress deflection has no obvious influence on top coal and basic top principal stress distribution,and has a great influence on the direction.?1 increases as deflection angle increases,and a3 reverses.Walking along the working surface,a stress shell structure is formed above the goaf,and the height is about 90m.Under the tnfluence of overlying coal seam mining,the difference between size and direction of the basic top cal in coal pillar and goaf is greater.The principal direction rotation and ?1 increase,?3 decrease could lead to the expansion of roof crack.(6)The complex mining conditions mainly include simultaneous mining of upper and lower coal seams,dynamic and static loading above goaf and mining process parameters,and composite fracture of the key layer of coal seam overburden in Buertai coal mine.At the same time,the weakly cemented sandstone structure of the Jurassic is loose and the degree of cementation is poor,which leads to strong mineral pressure such as shallow deep deformation and severe patchwork.For strong mine pressure dangerous areas,technologies such as pressure relief blasting and hydraulic fracturing advanced pre-cracking main control rock group can alleviate strong mine pressure.An environmentally friendly blast hole plug is designed for blockage effect,which could achieve multi-level buffer compression burst,extend the action time of the explosion gas,and improve the embrasure blockage effect.Suggestions in the 400m levels mining,the panel alleys axial layout in NS?N30°E,optimization measures are also proposed for mining sequence and strength.