Experimental Study On Seepage Characteristics Of Granular Accumulation And Mechanism Of Water-Sand Inrush In Mines

Water-sand inrush is a typical mine geological disaster in coal mining in the western part of China.Due to the depletion of mining resources in eastern China and the strategic readjustment of energy reserves,the western region became the focus of the development of carbon resources.With its special geographical location and abundant coal reserves,Shaanxi Yushen mansion has become the most important area for mining coal resource,also the source of "Coal transportation from Weastern to Eastern".However,the special geological characteristics in this area,such as shallow mining depth,thin overburden strata and thick overlying aeolian sand bed near the ground surface rich in groundwater,provide convenient conditions for the occurrence of water-sand inrush and constitute a serious threat to the safety production.Untile now,the urgent problem is mastering themechanism of disaster breed,development and damage,and predicting and taking effective measures in time.The disaster of water-sand inrush is gradually evolving from groundwater seepage.In the pore structure,seepage motion affect sand swarm startup and mixed water-sand migration.The aquifer permeable medium is comprised of loose or consolidated granules with abundant lithology and a relatively complicated granular composition,which leads to a significant difference of permeability,and various flow patterns.Hence,building the relationship between fluid motion and particle swarm transport is one of the major difficulties in this research.Focus on the complex physical phonomeon in the nature wold,laborator experiment is an effective and dependable method.However,the existing mature testing equipments canot satisfy the experimental requirements.Whether the device suit for soil and rock low-speed seepage,or the equipment designed for fracture media seepage with a bit higher speed flow,both canot achieve the aim of large discharge,high flow rate and sand-water mixture flow transport at the same time.Most important of all,the devices mentioned above canot accomplish real-time and accurate split-phases velocities measurement for the mixture water-sand flow.In this study,focuses on the mechanism of disaster breeding and evolvement,in view of the evolution of groundwater seepage resistance,the critical conditions of particle swarm launching and quick sand,and the movement characters of water-sand mixed fluid,the following research works.(1)This study analysis the physical essence of flow resistance in the pore structure based on the capillary model and flow resistance model.The function relationships between structural parameters of porous media against permeability and non-Darcy factor are established.Following this,the influence of the basic parameters of pore structure on the flow resistance characterization parameters,Reynolds numbers and Forchheimer numbers are analysised.The mechanics mechanism of fine particle swarm launching in pores is proposed.(2)Based on the study of seepage resistance model of porous media,the one-dimension two-phase experimental divice is developped,which realizes testing the mixture flow of water and sand seepage,after a large number of practice and tests.This equipment meets the needs of granular packed bed seepage test,and achieve high-precision control and measurement in a wide velocity range,which can mimic the whole process of sand swarm launching and sand-water mixed fluid transporting through the porous skeleton.At the same time,a device for measuring the velocities of split-phase is inventted,which achieve real-time and high-precision measurement of the split-phase velocities of sand-water mixture flow.It provides a powerful technical means for studying the migration characteristics of two-phase flow and the interaction mechanism between the two phases.In addition,it also provides a reference method for similar experimental research.(3)Base on a series laboratory test of fluid flow through granular particle packed beds,the evolution law of seepage in the porous medium under complex boundary conditions is studied and the function relationship between base geometry parameters of pore structure and the structure attribute patameters is estanblished,respecitvely.According to the experimental results,the impact of particle size,particle surface roughness and particle arrangement on the seepage resistance evolution in the pore structure during analyzed.The function relationship between the critical parameters of flow transition and the pore structure parameters is established.(4)In this study,we measured the physical and mechanical property of the aeolian sand.Base on the mechanism analysis of particle swarm startup in pore structure,the particle swarm start up experimental are carry on.The launching mechanism of particle swarm studied from macroscopic and microscopic,respectively.T he necessary conditions of particle swarm starting are qualitatively put forward.The critical flow velocity range of particle swarm startup is tested quantitatively under the laboratory condition.(5)Through a series of experiments,such as fine particle loss test,sand breaking critical and porous skeleton collapse test and high concentration water and sand mixing fluid migration test,the evolution process from the starting of particle swarm to water-snad inrush is simulated,and the interaction,excitation and evolution effect among dreieckig,water,movable sand and porous skeleton,are analyzed.The characteristics of the mechanism and energy conversion and transfer are presented,the necessary conditions for the occurrence of the sand surge are proposed,and the critical flow velocity range of the quick sand inrush under the laboratory conditions is obtained.