Method for determining feasibility of water-preserving mining with in-situ protection of floor confined water

A determination method for water-preserving mining with in-situ protection of floor confined water, comprising following steps:

• S1, determining an average distance M between a mining coal seam floor and an aquifer, an average thickness Maqu of the aquifer, an average permeability Kaqu of the aquifer, a working face length Lface, and an advance distance length Ladv;
• S2, detecting to obtain an average depth Mfrac of a mining coal seam floor fracture zone, an average thickness Mi of each rock layer below the fracture zone, an average permeability Ki of each rock layer below the fracture zone, and an equivalent permeability Keq of a layered heterogeneous floor;
• S3, detecting and calculating a total time as ttotal, a water pressure Pi in different time periods within a confined aquifer, and determining a target water pressure Ptarget of a target confined aquifer;
• comparing the detected water pressure Pi of the confined aquifer with the target water pressure Ptarget, and obtaining a water pressure Pexcess of the confined aquifer exceeding the target water pressure Ptarget and a time t, wherein the water pressure Pi of the confined aquifer exceeds the target water pressure Ptarget;
• S4, substituting the target water pressure Ptarget, the water pressure Pexcess, and the time t obtained in the step S3 into a formula
• S
• allow
• =
• K
• a
• ⁢
• q
• ⁢
• u
• μ
• ×
• ∇
• ∫
• 0
• t
• (
• P
• excess
• -
• P
• target
• )
• ×
• L
• face
• ×
• M
• aqu
• ⁢
• dt
• ,
• to obtain an allowable water resource loss Sallow during coal mining;
• wherein μ is a hydrodynamic viscosity coefficient in Pascal-second (Pa·s);
• S5, substituting the water pressure Pi of the confined aquifer obtained in the step S3 and the allowable water resource loss Sallow obtained in the step S4 into a formula
• K
• c
• ⁢
• r
• ⁢
• itical
• =
• S
• allow
• ×
• μ
• ÷
• (
• L
• adv
• ×
• L
• face
• ×
• ∫
• 0
• t
• total
• (
• (
• P
• i
• -
• P
• work
• )
• ÷
• (
• M
• -
• M
• frac
• )
• )
• ⁢
• dt
• )
• ,
• to obtain a critical equivalent permeability coefficient Kcritical of water-resisting rock layers in the mining coal seam floor;
• wherein ttotal is a total detection time in days;
• Kcritical is the critical equivalent permeability coefficient of the water-resisting rock layers in the mining coal seam floor in Darcy (D);
• and Pwork is a working face water pressure in Megapascal (MPa);
• and
• S6, determining feasibility of the water-preserving mining with the in-situ protection of the floor confined water;
• S61, comparing the equivalent permeability Keq of the layered heterogeneous floor obtained in the step S2 with the critical equivalent permeability coefficient Kcritical of the water-resisting rock layers in the mining coal seam floor obtained in the step S5, wherein if Keq>Kcritical, the in-situ protection of the floor confined water may not be achieved after the coal mining;
• and if Keq≤Kcritical, the step S62 is executed;
• and
• S62, substituting the equivalent permeability Keq of the layered heterogeneous floor, the average depth Mfrac of the mining coal seam floor fracture zone, the average distance M between the mining coal seam floor and the aquifer, the working face length Lface, the advance distance length Ladv, and the water pressure Pi of the confined aquifer into a formula Qinflow=Keq÷μ×(Pi−Pwork)÷(M−Mfrac)×Ladv×Lface, to obtain a unit-time water inflow Qinflow over the total time;
• wherein if no continuous period exists with Qinflow≥Qsafe lasting more than 5 days, the in-situ protection of the floor confined water may be achieved;
• and if there is the continuous period with Qinflow≥Qsafe lasting more than 5 days, the in-situ protection of the floor confined water may not be achieved, wherein Qsafe is a safe water inflow for working face mining in cubic meters per day (m3/day).