Study On Law Of Water Sand Inrush Of Mining Damaged N₂ Under Loose Sand Layer

Jurassic coal field in Northern Shaanxi is the key area of coal resources development and utilization in recent years.N₂ laterite is the direct aquifer of Jurassic coal mining under the aquifer of loose sand layer.Due to the large mining intensity and large thickness distribution of the Jurassic coal seam,mining is easy to lead to the damage of the N₂ laterite,and in turn induces water sand inrush disaster.It is very important to research the development process and law of water sand inrush of laterite N₂under the loose sand layer.This article tests and analyzes the physical properties,mechanical properties and microstructure characteristics of N₂ laterite,and studies the relationship between the microstructure and the macro physical properties of N₂ laterite.Through laboratory tests and numerical simulations,the development and evolution characteristics of water sand inrush under different conditions are studied.The main results are as follows:?1?The micro structure of laterite influences its macro properties.Through the analysis of the micro structure of N₂ laterite,the expression of the comprehensive quantitative parameters of the micro structure of laterite is established.Then established an empirical formula between the macro physical properties density,water content of N2 laterite and the microstructure parameters,and an empirical formula between the permeability coefficient and the microstructure parameters.So as to achieve the change of the microstructure and permeability coefficient of the soil sample by measuring the changes of water content and density.?2?Based on the water sand inrush model test results,it shows that water sand inrush in mining damaged N₂ laterite can be divided into two types:attenuation type and growth type.For the attenuation type,the end of water sand inrush is mainly due to the formation of a stress supporting arch in the upper part of the fracture channel,the porosity in the fracture gradually decreases from top to bottom with the development of water sand inrush and approaches the soil around the fracture.During the entire process,the mass flow rate of the exudate and the pore water pressure in the model both increase first and then fluctuate decreasing,and finally tending to a stable change law,while the growth type gradually increases in the last stage.The cumulative total mass of the decaying exudates increases with time as a logarithmic function.The law of the growth type in the early stage is the same,but the linear growth in the later stage.?3?According to the measured water content and density after model test,the microstructure and permeability coefficients of soil samples at different locations of model were calculated using empirical formula.The results show that the closer the distance from the fracture,the more obvious the change of microstructure and the greater the change of permeability coefficient.The shallower the burial depth,the more obvious the change in microstructure and the greater the change in permeability coefficient.However,the microstructure is more affected by the distance from the fracture.The change of microstructure and the increase of permeability coefficient of the growth type are greater than that of the attenuation type.?4?As the the increase of fracture angle,the increase of fracture width and the decrease of soil layer thickness,the longer for the flow velocity in the fracture to reach stability,and water sand inrush is more violent.It is easy to develop into the growth type.However,when the dip angle of the fracture is reduced,the fracture becomes narrower and the thickness of the soil layer increases,the fracture is easily blocked by the solid matter in the water sand inrush and the soil particles carried by the erosion,thereby reducing the probability of water sand inrush disaster.