Study On The Permeability Characteristics Of Ion-type Rare Earth Weathered Granite Under Cyclic Impact Loading

Based on the National Natural Science Foundation of China(No.51404111),based on the low leaching efficiency of the low-permeability ion-type rare earth ore weathering layer,this paper proposes to use the stress wave generated by small-quantity air-spaced blasting to change the internal pore structure of the rock mass.The method of optimizing the permeability of ore body,using SHPB device system to simulate the propagation process of explosive stress wave in ore body,combined with GDS-VIS triaxial rheometer to analyze the change law of permeability of rock sample before and after cyclic impact,the main research results as follows:(1)The effective porosity,wave velocity measurement and static uniaxial compression test of ion-type rare earth weathering layer granite rock samples were carried out.The effects of effective porosity of rock samples on the characteristics of stress and strain curves under wave velocity and uniaxial compression were analyzed.The compressive strength of the rock sample decreases with the increase of the effective porosity of the rock,indicating that the effective porosity can reflect the damage condition before the rock sample is subjected to the load.The larger the effective porosity,the less the number of fragments after the damage is damaged.It is consistent with the law that the longitudinal wave velocity decreases with the increase of its effective porosity.Under the dry state,the wave velocity of the rock sample is less than the saturated state.(2)Using the SHPB device system to carry out cyclic impact on the rock sample,the effective porosity change law,deformation characteristics and rock fragmentation mode of the rock sample before and after the cyclic impact are studied.The results show that the effective porosity of the rock sample is 6 m.The speed of /s increases directly after the impact of the cycle,and it shows a trend of decreasing first and then increasing after the impact load of 4 m/s and 5 m/s.As the number of constant-speed cyclic shocks increases,the rock sample’s resistance to impact gradually decreases,and this phenomenon continues until the rock sample is completely damaged.(3)Regardless of whether the rock sample is subjected to constant velocity cyclic impact or stepwise loading cyclic impact,the stress-strain curve of the rock sample will show four typical deformation stages and a "rebound" phenomenon will occur before the rock sample is damaged.When the single impact velocity is large enough,the main crack in the rock sample can be directly expanded to exhibit a distinct splitting and breakage mode,and the splitting direction is more parallel with the axial direction.During the constant velocity cyclic impact load,the number of fragments after the rock sample is damaged The impact velocity is proportional to the inverse of the initial effective porosity of the rock sample.(4)Based on the GDS-VIS triaxial rheometer device system,the permeability of the rock samples before and after the cyclic impact was measured,and the influence of effective porosity on the permeability of the rock samples was analyzed.When the permeation test conditions are the same,the permeability of the rock sample increases with the increase of the effective porosity.However,the uncertainty of the internal pore opening direction and the pore size will lead to the increase of the porosity of the rock sample and the decrease of the permeability.Small phenomena,even the phenomenon that the permeability of rock samples of similar porosity differ greatly,but the effective porosity can directly affect the permeability of rock mass.(5)The constant velocity impact of 4 m/s and 5 m/s will increase the permeability of the rock sample first and then weaken,and the 6 m/s constant velocity impact will continuously optimize the rock sample permeability to the rock.Damaged.The gradual loading cyclic impact is better than the initial value after the secondary impact(5 m/s).In addition,after each impact,the permeation test will make the fluid seepage channel more obvious,and the impact speed increases with the step-by-step loading.The effect of rock sample augmentation is also more obvious.The larger the initial effective porosity of the rock sample,the more the internal pore distribution is more likely to change.At the same time,the effect of the rock sample under the subsequent impact load is also closely related to the initial effective porosity.The larger the initial effective porosity,the subsequent impact load.The effect of lower osmosis is more obvious.