Experimental Study On Creep Properties Of Infiltrated Coal

At present,with the rapid development of China's economy,coal demand still maintains the momentum of growth.The waterproof and isolated coal pillars in coal mining are in the state of groundwater infiltration all the year round,and creep phenomenon will occur due to the pressure of the roof plate.As the infiltration time increases,the creep effect will become more and more obvious,and the coal pillar instability may occur.Therefore,the study of creep properties of infiltrated coal has important theoretical and engineering significance.In this paper,the combination of laboratory test and theoretical analysis is used to study the creep properties of coal petrography under different infiltration time and different stress levels The main research contents are as follows:(1)The coal block was taken from the site,processed into an international standard test piece in the laboratory,and the test pieces were divided into six groups.The uniaxial compression test under different infiltration times was carried out to analyze the variation of the uniaxial compressive strength of coal petrography with the infiltration time,trend.It can be seen from the experimental phenomenon that due to the weakening effect of water on coal petrography,the uniaxial compressive strength of coal petrography decreases with the increase of infiltration time,and the rate of strength reduction decreases.After the pore water of the coal petrography is saturated,the pressure difference between the inside and the outside is gradually balanced.(2)Uniaxial compression test of un-wetting coal petrography to obtain uniaxial compressive strength?c,and 30%?c,40%?c,50%?c,60%?c,70%?c,80%?c as six grades of stress Level;then uniaxial creep test under the same stress level and different infiltration time(0 days,1 day,3 days,7 days,15 days,30 days)to analyze the stable creep strain and stable creep of coal petrography The law of variation of strain rate.The results show that with the increase of the infiltration time,the stable creep strain increases;the creep strain rate decreases sharply first,then stabilizes,and finally the brittle fracture occurs.At the initial stage of infiltration,the coal petrography showed three stages of creep at the lower stress level When the stress level developed to 22.2 MPa,the coal petrography infiltrated for 15 days,and four stages of creep occurred.(3)Uniaxial creep tests with the same infiltration time and six different stress levels were carried out to investigate the variation of the time required for accelerated creep and stable creep under the same infiltration time and different stress levels.It is concluded that as the stress level increases,the time required for the coal petrography to reach stable creep and accelerate creep is shorter,and the change of stress level plays a major role in coal petrography deformation.At the initial stage of stress level loading,most of the coal petrography only showed three stages of creep.When the infiltration time reached 15 days,the accelerated creep damage occurred when the coal petrography was at a stress level of 22.2 MPa.(4)According to the creep test results of coal petrography,the creep elastoplastic body is introduced to establish the creep constitutive model of the infiltrated coal petrography.The model can characterize the whole process of coal petrography creep,especially the accelerated creep stage.At the same time,the infiltration effect of water on coal petrography is considered,and the parameters in the constitutive relation are identified.The creep parameters of coal petrography decrease with the increase of stress level and the infiltration time.