Physical And Mechanical Properties Of Acidified Lamprophyre And Its Influence On Overlying Strata's Movement

Comparing to mine pressure behavior under ordinary roof condition,the mine pressure behavior under hard roof condition is more fierce.When the hanging area of hard roof is larger and is not collapsed,the caving interval is bigger than the ordinary situation.The stress of hard roof is redistributed and nonuniform which absorbs a mass of elastic potential energy.The outburst in crest value of the elastic potential energy can cause damage,even mine earthquake and impact earth pressure to working face and stope.Especially under special thick seam mining condition,the consequence will even worse.The #3-5 thick coal seam which is nearly about 20 m is invaded by gray-yellow layered lamprophyre in the Coal Mine of Datong that forms the hard roof.According to petrological study to lamprophyre,there are a lot of carbonates ingredient in lamprophyre.On account of this condition,the testing program softening of lamprophyre is came up with,which is aimed at reducing the strength of lamprophyre and number of times of rock-burst accident caused by hard roof.The pH and conductivity of acid solution and the mechanical property,scanning electron microscope and numerical simulation model are studied.The damage of lamprophyre mechanical property and structure change in microscopic scales are received.The main research contents are presented as the following ones:(1)According to the real-time monitoring of pH and conductivity after the lamprophyre steeping in acid solution,the reaction stage can be divided into three stages.Rapid-growth stage: in 0~80h,pH value rises rapidly and conductivity reduce quickly.The slow-growth stage: in 80~200h,pH value rises slowly and conductivity reduces slowly.The last is stabilization stage: greater than 200h,pH value rises very slowly and conductivity reduces very slowly which fluctuate in a small scale.(2)In order to explore the mechanical characteristics of uniaxial compression and brazilian tests and study the character before and after steeping in acid solution of lamprophyre,mechanical experiments are designed.The results show that strength deterioration of uniaxial compression and brazilian and the damage of quality are bigger when the pH value is lower.(3)In order to study the microcosmic structure change rule and the change of contact network and the chain of contact force in numerical modeling,the microscopic test,elemental analysis and building of numerical simulation model are designed.The results show that after steeping in acid solution,the number and size of hole on the specimen's surface are bigger while the Celement isdeficient.Comparing to original state,the contact network has obviously bigger destruction when the pH of acid solution is lower.The chain of contact force become bolder which means the balls of numerical modeling model are broke easily.(4)The movement laws of coal and roof before and after softening by acid solution can be studied base on UDEC model.The results show that,the pace of direct top collapsing initially of roof after softening by acid solution reduces comparing with the original state,which pulls down the adverse effect that the roof acts on below coal seam.And in the same excavation step distance,plastic zone,vertical stress and vertical shift extend after softening by acid which means that the lamprophyre roof is easy to damage.