Experimental Study On Mechanical Properties Of Infiltrated Coal And Its Constitutive Relation

In mining engineering,the coal seam water injection process and the waterproof isolation coal pillar retention involve the interaction of water and coal.This paper takes a raw coal from a mine in northern Shaanxi as a sample to carry out the experimtental study on the mechanical properties of the infiltrated coal,determine the stress threshold point of the infiltrated coal,construct the constitutive relationship of the infiltrated coal,and comprehensively analyze the influence of the water-rock action on the mechanical properties of the coal.Provide theoretical support for safe and efficient mining.The main research contents are as follows:Firstly,through the water immersion test and mechanical properties test of coal,the stress-strain curve and mechanical characteristic parameters of coal under different immersion time are obtained.Before the coal is s.aturated,the campaction and linear elastic phase of the stress-strain curve of the uniaxial compression test gradually become steeper with the increase of the immersion time;after saturation,the compaction and linear elastic phase of the stress-strain curve gradually increase with the immersion time.Slow down.Before saturation,the compressive strength,tensile strength and elastic modulus of the measured coal increase with the increase of the immersion time:after saturation,the compressive strength,tensile strength and elastic modulus decrease with the increase of the immersion time.Secondly,the stress threshold points of the infiltrated coal is determined by the tangent mspethed,the acouemic emission method and the strain measurement method respectively,and the advantages and disadvantages of vardous methods are discussed.Ths results show that the tangent method can quickly obtain the range of stress threshold points,but can not obtain the determined value;the acoustic emission method can determine the stress threshold point of the short-term(15 days)infiltrated coal,but can not accurately determine the coal immersion time longer than 15 days.The stress threshold point;the strain measurement method determines that the stress threshold point is less affected by subjective factors and can be solved by programming.Finally,the compressive deformation of saturated coal is divided into two processes:microcrack deformation and coal matrix deformation through closed stress threshold points.Based on the statistical damage and non-coordination deformation theory of rock,an infiltrated coal considering the microcrack closure effect is constructed.The segmented constitutive model discusses the influence of model parameters on damage variables and verifies the model by saturated coal uniaxial compression test data.The results show that the theoretical curve agrees well with the experimental results.