Petrologic Studies On Mechanical Properties Of Sedimentary Rocks Of Jurassic Coal Measures In Shendong

Shendong mining area is a large modern mining area among the world,and its coal production has reached 1.2×10~9t annually,accounting for 6%of the national coal production.However,compared with other domestic mines,Shendong mining area has typical geological characteristics,such as shallow burial,thin bedrock and thick loose layer.These special geological conditions lead to several serious dynamic hazards,including the overall cutting of coal roof and stent destroyed.Therefore,this paper takes the main coal mines of Shendong mining area as the research objects,including Bulianta,Daliuta and Buertai coal mines.On the basis of collecting and analyzing the geological data,geophysical exploration and drilling data in the study area,the geological characteristics of the main coal roof in Shendong mining area are studied by using numerical simulation,examination and statistics of rock,XRD and SEM,rock mechanics test,ultrasonic velocity measurement and mathematical statistics.The conclusions are as follows:(1)Coal-bearing strata of Jurassic in Shendong mine area were developed in a large terrestrial basin.Because of the influence of sedimentary environment,the sedimentary lithology,lithofacies and their combinations in the coal measures are obvious differences,and the stresses of rocks show significant anisotropy in space.During mining process,the worse stability of coal roof,caused by the serious heterogeneity,lead to the movement,breaking regularity and periodic pressure complicated.(2)From the macroscopic view,there are many weak structural surfaces in sandstones of the main coal seam roof,including beddings,lithology interfaces,cracks and erosion surfaces.On the surfaces,there are a large amount of carbon debris,carbonized trunks and plant leaf fossils.However,the mudstone is a homogeneous block and has a high degree compactness.There are less weak structural surfaces and biological disturbance traces in the mudstone.(3)The sandstone structure is loose in Shendong mine area.In mineral composition of sandstones,quartz content is predominant,followed by feldspar,debris,mica and organic matters.The uniaxial compressive strength and elastic modulus of sandstones increase with the increase of quartz content;on the contrary,the trend is decreasing with the increase of feldspar and organic matter contents.The uniaxial compressive strength and elastic modulus are decreasing with the increase of the particle size and non-uniform coefficient of sandstones,meanwhile the acoustic velocity is decreasing.The structure of mudstones is compact.In mineral composition of mudstones,quartz content is dominant,followed by clay minerals and feldspar.The uniaxial compressive strength and elastic modulus of mudstones are increasing with the increase of quartz contents,whereas,that are decreasing with the increase of clay minerals content.