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CN-121997816-A - Prediction method for diffusion distance of directional drilling grouting slurry in goaf of coal mine

CN121997816ACN 121997816 ACN121997816 ACN 121997816ACN-121997816-A

Abstract

The application provides a prediction method of a directional drilling grouting slurry diffusion distance of a coal mine goaf, which comprises the steps of defining a global coordinate system for an operation scene of the goaf, establishing a three-dimensional numerical model of the goaf, meshing the goaf and a grouting drilling area by adopting a mixed meshing strategy, establishing a three-dimensional space distribution model of goaf porosity and permeability based on an O-shaped ring theory and a key layer theory, introducing a slurry water two-phase flow theory and a level set method of free medium and porous medium flow coupling, establishing a slurry diffusion distance prediction model, taking grouting pressure, slurry dynamic viscosity and porous medium permeability as influencing factors, taking slurry diffusion volume as a response variable, and designing a response surface test of 3 factor and 3 level to obtain an optimal parameter combination of each influencing factor and a prediction result of a corresponding goaf grouting slurry volume fraction. The method provides theoretical basis and engineering support for goaf grouting process parameter optimization and prevention and control of the water damage in the sky.

Inventors

  • BIAN KAI
  • XU WENTAO
  • LI CHONG
  • WANG JIE
  • YANG XIAOFENG
  • WANG YINXI
  • LU CUNJIN

Assignees

  • 河北工程大学

Dates

Publication Date
20260508
Application Date
20260112

Claims (8)

  1. 1. The method for predicting the diffusion distance of directional drilling grouting slurry in a goaf of a coal mine is characterized by comprising the following steps: S1, defining a global coordinate system aiming at a working scene of a goaf, establishing a three-dimensional numerical model of the goaf, and simultaneously meshing the goaf and a grouting drilling area by adopting a mixed meshing strategy; s2, based on an O-shaped ring theory and a key layer theory, establishing a three-dimensional space distribution model of the goaf porosity and the permeability; S3, a slurry-water two-phase flow theory and a level set method of free medium and porous medium flow coupling are introduced, and a slurry diffusion distance prediction model is established so as to simulate the displacement process of the goaf directional drilling grouting slurry on underground water; S4, taking grouting pressure, slurry dynamic viscosity and porous medium permeability as influencing factors, taking slurry diffusion volume as a response variable, and designing a response surface test of 3 factors and 3 levels, so as to obtain an optimal parameter combination of each influencing factor and a prediction result of the volume fraction of the grouting slurry in the corresponding goaf.
  2. 2. The method according to claim 1, wherein S1 specifically comprises: S11, taking an intersection point of the middle part of the junction of the goaf and the stope working surface and the top plane of the bottom plate as a coordinate origin, setting the direction along the trend and pointing to the deep part of the goaf as an x-axis positive direction, setting the direction along the trend and pointing to the return air side as a y-axis positive direction, and setting the direction along the vertical direction of the top plane of the bottom plate and pointing upwards as a z-axis positive direction, thereby defining a global coordinate system; S12, setting the trend length, the trend width and the vertical height of the goaf three-dimensional numerical model; s13, in order to describe the distribution characteristics of the O-shaped ring with relatively compact middle part and crack development around, two concentric and coaxial elliptic boundaries are established in an xy plane and stretched along the z axis direction to form an elliptic cylindrical surface, so that the goaf is divided into a compaction stable region, a load influence region and a natural accumulation region from inside to outside; S14, adopting a short-distance pinnate branch hole mode, arranging a horizontal main hole along the trend in the middle of the goaf, sequentially arranging branch holes from the starting point along the trend at equal intervals of 50m, expanding the left side and the right side in a staggered manner, keeping a small included angle between each branch hole and the main hole and pointing to two side roadways, and explicitly modeling the main hole and the branch hole in a model by using a cylindrical channel with the radius of 0.074 m; S15, the goaf main body adopts a free tetrahedron grid, the grouting drilling area is mapped through an inlet circular surface and axially swept to generate regular hexahedral units, and boundary layer grids are arranged at the hole wall to refine the near-wall flow field.
  3. 3. The method of claim 1, wherein the three-dimensional spatial distribution model of goaf porosity is established in S2 by: S21, based on an O-shaped ring theory and a key layer theory, respectively establishing a distribution model of the goaf porosity along the directions of an x axis, a y axis and a z axis as follows: on a goaf y=0 tangential plane, along the x-axis direction, the porosity phi x shows a change trend from the top cutting line to the open-cut eye position, wherein the change trend is that the porosity phi x is firstly reduced and then increased, and the whole approximately symmetrical distribution is as follows: ; wherein phi x is the porosity in the x-axis direction on the section of the goaf y=0, D is the trend length of the goaf, m, x is the trend distance from a certain point in the goaf to the stope face, m; On the goaf x=0 section, the porosity change coefficients phi ' y are approximately symmetrically distributed along y=0, and when extending from the middle of the working surface to the direction of the air inlet lane and the air return lane, phi' y increases along with the increase of |y| as follows: ; Wherein phi' y is the change coefficient of the porosity along the y-axis direction, is dimensionless, W is the goaf trend width, m, y is the coordinate value of a certain point in the goaf along the y-axis direction, m; In the xy-plane along the z-axis, the porosity variation coefficient φ' z satisfies the following piecewise functional relationship: ; Wherein, the ; Wherein phi' z is the change coefficient of the porosity along the z-axis direction, z is the coordinate value of a certain point in the goaf in the z-axis direction, m, a 1 、a 2 、b 1 、b 2 is the length of a long half shaft and a short half shaft of two ellipses of the compaction stable region and the load influence region, m, f (x, y) is the normalized space position coefficient, and the value range is (0, 1) and is used for describing the relative position of any point (x, y) in the load influence region relative to the boundaries of the inner ellipse and the outer ellipse, so that the smooth transition of the porosity in space is realized. S22, using the product of phi x 、φ' y and phi' z to represent the three-dimensional space continuous distribution equation of the porosity phi in the goaf is as follows: 。
  4. 4. a method according to claim 3, wherein in S2 a three-dimensional spatial distribution model of goaf permeability is established by: s23, by fitting a change curve of porosity and permeability of the porous medium, establishing an exponential relation equation of the porosity and the permeability of the porous medium as follows: ; Wherein, kappa is the permeability of the porous medium, m 2 , phi is the porosity of the porous medium, and the dimension is not provided; s24, obtaining a three-dimensional space continuous distribution equation of the goaf permeability kappa based on the three-dimensional space continuous distribution equation of the goaf inner porosity phi, wherein the three-dimensional space continuous distribution equation is as follows:
  5. 5. The method of claim 1, wherein S3 specifically comprises: s31, defining the sum of the volume fractions of water and slurry to be 1: ; Wherein S i is the volume fraction of the phase (water or slurry), N is the phase number, when N=2, the two-phase flow is represented, at this time, S 1 、S 2 is the volume fraction of the water and the slurry respectively and satisfies S 1 +S 2 =1; s32, describing the flow of the slurry in the goaf free medium by using a transient incompressible Navie-Stokes equation: ; wherein ρ is the fluid density, kg/m 3 , u is the velocity vector, m/s, p is the pressure, pa, I is the identity matrix, dimensionless, μ is the hydrodynamic viscosity, pa.s, F is the volumetric force vector, N/m 3 ; s33, describing the flow of the slurry in the porous medium by using an incompressible brinkman equation: ; in the formula, Is porous medium porosity, dimensionless, kappa is porous medium permeability, m 2 , beta is Forchheimer coefficient, 1/m, considering that the grouting flow rate is low, ignoring inertia term ; S34, tracking the interface of the free medium and the porous medium by adopting a level set method, and smoothing the density and viscosity mutation at the interface.
  6. 6. The method of claim 1, wherein the evolution equation of the level set function for tracking the interface of the free medium and the porous medium in S34 is expressed as: ; in the formula, Is a smooth step function of 0 in one phase and 1 in the other phase, gamma is the reinitialization parameter, m/s, epsilon 1s is the interface thickness control parameter, m; Smoothing the density and viscosity abrupt change at the interface by the following formula: ; Wherein ρ 1 、μ 1 is the density and dynamic viscosity of the groundwater, and ρ 2 、μ 2 is the density and dynamic viscosity of the slurry.
  7. 7. The method of claim 1, wherein the simulation process satisfies the following basic assumption: (1) The slurry is an isotropic, incompressible continuous medium; (2) The dynamic viscosity of the slurry only changes with time, and the dynamic viscosity of different positions at the same moment is the same; (3) Slurry flow is mainly laminar flow, and turbulence can occur only in local areas near grouting holes; (4) The slurry diffusion mode is complete displacement diffusion, and the mixing of water and slurry at the slurry-water phase interface is not considered; (5) The side wall meets the non-slip boundary condition; (6) Before grouting, the goaf is in a single water phase saturated state and is in hydrostatic balance, and the initial pore water pressure is set according to hydrostatic pressure distribution.
  8. 8. The method of claim 1, wherein the initial conditions of the slurry diffusion distance prediction model are set as follows: Assuming that goaf pores are completely filled with underground water and are in a hydrostatic balance state before grouting, setting pore water pressure to 0MPa at an altitude Z 0 communicated with the atmosphere, and enabling initial pore water pressure to meet a hydrostatic pressure distribution relation: ; Wherein ρ 1 =1000kg/m 3 is the density of groundwater, g=9.81 m/s 2 is the gravitational acceleration, and the gravitational acceleration direction is in negative agreement with the vertical coordinate; The boundary conditions of the slurry diffusion distance prediction model are set as follows: The horizontal main hole opening arranged along the roadway is used as a grouting inlet, a specified pressure boundary condition is applied to the boundary, grouting pressure takes an engineering actual grouting pressure value, an open-cut hole communicated with the goaf is used as an outlet, a specified pressure boundary of 0MPa is applied to the position to represent a free outflow condition communicated with the atmosphere, and impermeable boundary conditions are uniformly adopted for the rest outer boundaries.

Description

Prediction method for diffusion distance of directional drilling grouting slurry in goaf of coal mine Technical Field The application belongs to the technical field of mine water damage prevention and control, and particularly relates to a prediction method for a diffusion distance of directional drilling grouting slurry in a goaf of a coal mine. Background During coal mine shutdown, there are still large quantities of coal mines in production around the abandoned mine. These abandoned mines not only have a significant impact on regional groundwater systems, but their empty waters also pose a potential water inrush threat to nearby produced coal mines. Meanwhile, the top plate of the goaf collapses to cause the overlying stratum to sink and gradually conduct to the ground to form ground subsidence. In the sedimentation process, a large number of cracks are generated in the stratum due to uneven stress. These cracks become channels for groundwater to flow. The aquifer blocked by the rock stratum is communicated with the goaf, groundwater more easily floods into the goaf, the water burst risk is improved, and then regional environmental problems are induced, and even the safety of ground buildings and infrastructure is threatened. Statistical analysis of coal mine safety accidents in the last 20 years shows that water damage is one of five disasters of the coal mine, and becomes a second approximate disaster factor next to gas accidents, thereby seriously threatening the coal mine safety production and the life safety of practitioners. Although the water disaster prevention and control work of coal mines in China has been actively progressed in recent years, water disaster accidents still occur continuously, and the duty ratio of the water disaster in the sky is increased, which shows that weak points still exist in the links of the exploration, the treatment and the monitoring of the water in the sky at present. Based on the method, a grouting method is often adopted in mining engineering to displace aquifer water, the aquifer is transformed into a relative water-resisting layer, and water guide channels such as primary cracks, faults, collapse columns and the like in the stratum are plugged and reinforced, so that the purposes of water damage management and stratum stability are achieved. However, under different working conditions, the migration, diffusion range and law of the level Kong Jiangye are difficult to predict uniformly or accurately, engineering practice is dependent on field experience, and the engineering practice has a certain blindness. A great deal of theoretical, model and experimental researches are carried out by students in the fields of slurry diffusion rules and characteristics, and rich results are obtained. However, the existing research focuses on the grouting slurry diffusion mechanism under the condition of karst fracture aquifers such as Ore limestone and the like and the complete rock mass of a coal seam bottom plate, and in contrast, the research results on the directional drilling slurry migration and diffusion characteristics in the extremely heterogeneous and strong anisotropic crushing medium of the goaf formed by mining are still limited. Disclosure of Invention Therefore, the application aims to provide a prediction method for the diffusion distance of directional drilling grouting slurry in a goaf of a coal mine, which can provide theoretical basis and engineering support for goaf grouting process parameter optimization and prevention and control of water damage in the sky. The application provides a prediction method for the diffusion distance of directional drilling grouting slurry in a coal mine goaf, S1, defining a global coordinate system aiming at a working scene of a goaf, establishing a three-dimensional numerical model of the goaf, and simultaneously meshing the goaf and a grouting drilling area by adopting a mixed meshing strategy; s2, based on an O-shaped ring theory and a key layer theory, establishing a three-dimensional space distribution model of the goaf porosity and the permeability; S3, a slurry-water two-phase flow theory and a level set method of free medium and porous medium flow coupling are introduced, and a slurry diffusion distance prediction model is established so as to simulate the displacement process of the goaf directional drilling grouting slurry on underground water; S4, taking grouting pressure, slurry dynamic viscosity and porous medium permeability as influencing factors, taking slurry diffusion volume as a response variable, and designing a response surface test of 3 factors and 3 levels, so as to obtain an optimal parameter combination of each influencing factor and a prediction result of the volume fraction of the grouting slurry in the corresponding goaf. 2. The method according to claim 1, wherein S1 specifically comprises: S11, taking an intersection point of the middle part of the junction of the goaf and the stope working surf