Experimental Study On The Effect Of Particle Size On The Mechanical Properties Of Sandstone

Sandstone is one of the common sedimentary rocks in a large number of engineering constructions.Its mechanical properties are particularly important for engineering safety.In the field of coal mining,sandstone 1s a very common rock type in mining engineering,then its mechanical properties influence all aspects of the coal mining process:Roadway support,the maintenance of roof and floor in working face,and design of protective coal and rock pillars.Therefore,it is of great importance to study how the particle size affects the mechanical properties,failure process and damage forms.This paper was supported by National Natural Science Foundation of China(No.51474134 No.51774194)and the outstanding youth foundation project of Shandong Natural Science Foundation(No.JQ201612).The influence of particle size on the mechanical properties of red sandstone is studied by means of rock mechanics test,micro test and numerical simulation.Two kinds of red sandstone with different particle size were tested by uniaxial tensile test,uniaxial compression test and three axis compression test.After study and analysis,it was found that the red sandstone specimens with fine particle cementation have high uniaxial tensile strength,uniaxial compression strength and tri-axial compressive strength,and the structure of fine granular red sandstone is compact,with low deformation characteristics and loss of bearing capacity.The degree of rock fragmentation is high,the degree of cementation among its internal particles is better than that of coarse grained red sandstone,and the compactness of the specimen is better.The acoustic emission characteristics of two kinds of red sandstone with different particle size were studied by uniaxial compression test and uniaxial cyclic loading and unloading test.It was found that in the process of uniaxial compression,compared with coarser grained red sandstone,the peak strength,modulus of elasticity and peak strain of nne grained red sandstone increased by 23.47%,18.01%,-4.7%respectively.In the process of cyclic loading and unloading,compared with coarser grained red sandstone,the peak strength,modulus of elasticity and peak strain of fine grained red sandstone increase by about 43.64%?16.40%and-1.81%respectively.The microscopic structure of two kinds of red sandstone with different particle size was studied.T Optical microscope,scanning electron microscope and X ray diffract meter test were carried out to analyze the microstructure and mineral composition of the red sandstone.It is found that particle size is the main factor affecting the internal structure and stability of red sandstone.The numerical simulation of two kinds of red sandstone with different granularity was studied.The dynamic response law and mechanical properties of red sandstone under different granularity were simulated by the particle flow nunerical simulation software PFC.It is found that the number of micro cracks and the strain energy index change from sharp drop to slow decline with the increase of the particle size.The peak intensity tends to decrease gradually,and the peak strengjth decreases gradually,too.Fine-grained model specimens had low initial crack stress,and the initiation and development stage of micro cracks started earlier.