Experimental Research On Mechanical Properties Of Coal Samples Affected By Water Content

As the depth of the coal mine increases,the problem of high temperature in the mine becomes more serious every day.The use of coal seam cooling water injection can effectively reduce the coal seam temperature,dust removal,and gas prevention.The implementation of water content is of great significance for evaluating coal stability.In this paper,coal seam water injection cooling as the research background.Through theoretical analysis and some laboratory tests,the mechanical properties test,dry-wet cycle test,water immersion test,and rock point load test are carried out on the characteristics of coal and rock mass under different water content conditions.The main contents and results as follows:(1)Through the water absorption test of coal rock,it is concluded that coal rock absorbs water the fastest in the first 24 hours of the initial stage,and the growth rate tends to be stable with the increase of time.Based on the conventional uniaxial compression tests of coal under dry state and different submerged state,the results show that with the increase of water content,the compressive strength and elastic modulus show a downward trend,and the peak strain has a downward trend.At the same time,there is a correlation between the strength reduction coefficient and the size of water content.The continuous increase of water content leads to a decreasing trend of the softening strength reduction coefficient,which decreases from 0.873 on 1d to0.7 on 6d.(2)By performing 1、3、5、7 dry-wetting cycles on the coal samples,in each test stage,the dry quality and saturated quality of the coal and rock were measured,and various physical parameters were calculated and analyzed.It can be concluded that with the increase of the number of dry-wetting cycles,the compressive strength of coal and rock decreases,the peak strength decreases greatly in the early stage,and the peak strength decreases continuously in the later stage,and finally tends to be stable;When the value increases,the number of oblique cracks in the coal rock increases during failure,the failure sound changes from loud noise to low sound,and the failure form gradually evolves from single-slope shear failure to split failure.(3)Carry out point load test for irregular coal rock and coal rock with different moisture content,and obtain mechanical parameters for analysis.The test results show that De2 and failure load P of coal rock in dry state and saturated state change with With the increase of De2 of the damaged coal sample,the damage load P of both the dry state and the saturated state increases continuously.By making a linear fitting curve for the coal samples in the dry state and in the saturated state,it can be found that the fitting coefficient of the fitting curve in the dry state is 0.795,and the fitting coefficient of the fitting curve in the saturated state is 0.648.The conversion relationship between the standard value of point load strength and the uniaxial compressive strength is that the conversion coefficient is taken as 22.59 in the dry state and 24.7 in the saturated state.(4)The failure mode of coal samples under point loading is mainly split failure,most coal blocks are broken into two pieces,and a small number of coal blocks are broken into three pieces.The failure modes of samples under different loading directions are also significantly different.Figure [45] Table [17] Reference [65]...