| In underground engineering,with coal mining and coal face,large thin layer thickness of soft rock roadway roof forming instability of large area,easy happening caving is closely related to the long-term effects of groundwater,rock with water will occur a series of physical and chemical action between lead to damage of rock mass structure,mechanical properties,degradation,so the water rock interaction has important engineering significance.In this paper,the gob retention of 1901 working face of Xintian Coal Mine is taken as the research background.Through field observation,it is found that the strength weakening caused by the hydrolysis of thin layered mudstone roof is closely related to the nature of leached water.Thus,static and dynamic immersion tests of p H=5,p H=7and p H=9 are carried out to obtain the hydrolysis law of thin layered mudstone.Combined with macro and meso analysis,XRD diffraction analysis and arc tensile strength test,the characteristics of density,fracture development,component change and strength weakening of thin layered mudstone specimens under p H=5,p H=7 and p H=9 were obtained,and the static soaking hydrolytic characteristics of thin layered mudstone under p H=5,p H=7 and p H=9 were clarified.The relationship between mineral composition change and strength weakening under the hydrolysis of thin layered mudstone at p H=5,p H=7 and p H=9 was discussed.The main conclusions are as follows:(1)Under the same soaking time,the hydrolytic salinity,mass loss and saturated water content of thin layered mudstone granular rock sample and intact rock sample are all p H=5>p H=9>p H=7,and the granular rock sample is2-4mm>4-6mm>6-8mm>8-10mm>10-12 mm.(2)The dynamic and static hydrolytic salinity of thin layered mudstone has an exponential relationship with the density difference of the specimen.Under the condition of p H=5,the stability time of dynamic hydrolytic salinity is later than that of static 0-2D,and the average cumulative dynamic salinity is 240.60% higher than that of static.(3)Interbedding and intra-bedding fissures appear in the thin-layered mudstone soaked in both dynamic and static water environments.The interbedding fissures are located on the side of the specimen,while the intra-bedding fissures are located on the top and bottom of the specimen.The change rates of the interbedding and intra-bedding fissures have a quadratic polynomial relationship with the cumulative salinity.(4)Under the microscope,there are white crystal lines,white mineralization points,spot-like white crystals and gold mineralization points in both dynamic and static specimens.The changes of mineralization points in dynamic and static specimens are stable after 2d and 3D,respectively.The fracture development of the dynamic p H=5specimen was stable after 2-6d,and that of the static p H=5 specimen was stable after4-8d.The fracture stability of the dynamic specimen was earlier than that of the static specimen on average 2d.(5)Weakening of the reaction of albite and(iron)dolomite,disappearance of the hydrolysis of palygorskite and water absorption are the main reasons for the strength reduction of the thin layered mudstone.The tensile strength and strain of the original rock specimens are 76.07% and 70.57% higher than that of the specimens with static p H=5.Higher than 489.65%,362.85%,287.98% of dynamic p H=5,p H=7,p H=9 and16.03%,45.61%,27.29%,respectively.Based on the results of laboratory test,theoretical analysis and engineering field,the stress change caused by the subsidence of the roof of thin layered mudstone is1.95% different from that in laboratory.There is a difference of 1.03% between the actual roadway surrounding rock and the laboratory results,and the theory is consistent with the practice,which can provide a theoretical basis for roof and floor water control and surrounding rock strengthened support in Xintian Coal mine and similar geological conditions.There are 66 figures,26 tables and 101 references. |
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