US 11,313,226 B2 · Internally injected replacement support room-type coal pillar recovery method

Abstract

An internally injected replacement support room-type coal pillar recovery method is provided. During the recovery, the room-type coal pillars with an aspect ratio greater than 0.6 are divided into two parts: reserved coal pillars and pre-mined coal pillars. After the mining of the pre-mined coal pillars, a cemented filling material is injected into a goaf surrounded by the reserved coal pillars, and is stabilized to replace the coal pillars for support, and the reserved coal pillars are recovered. A mechanical model of the reserved coal pillars in a support overburden stage is established based on the Winkler beam theory, to obtain displacement and stress conditions of a roof of the reserved coal pillar in a support stage. A theoretical reserve-width of the reserved coal pillars is obtained according to a first strength theory of the roof and a criterion of ultimate strength of the reserved coal pillars.

An internally injected replacement support room mining coal pillar recovery method, comprising the following steps:

1) dividing a room mining coal pillar into a peripheral reserved coal pillar and an internal pre-mined coal pillar, a reserved coal pillar gap being formed on one side of the reserved coal pillar;
2) stoping the internal pre-mined coal pillar by means of the reserved coal pillar gap;
3) blocking the reserved coal pillar gap after the pre-mined coal pillar is mined, and injecting a cemented filling material into a goaf surrounded by the reserved coal pillar for filling;
and
4) replacing the pre-mined coal pillar for support after the cemented filling material is stabilized, and then recovering the reserved coal pillar,
wherein a width of the reserved coal pillar is calculated by a process below:
a. intercepting a half-plane of the room mining coal pillar for analysis, and setting an overburden stratum acting force on a roof of a mine to be a uniform load q, a foundation coefficient of the reserved coal pillar to be k, a spacing of the adjacent room mining coal pillars to be c, the width of the reserved coal pillar to be b, a width of the pre-mined coal pillar to be a, and then a total width of the room mining coal pillars to be 2(a+b), wherein a differential equation of a deflection curve of each section of the roof in an analyzed area is:
{
EI
⁢
d
4
⁢
ω
1
⁡
(
x
)
dx
4
=
q
⁢
x
∈
[
0
,
a
]
⁢
EI
⁢
d
4
⁢
ω
2
⁡
(
x
)
dx
4
=
q
-
k
⁢
⁢
ω
2
⁡
(
x
)
x
∈
[
a
,
a
+
b
]
⁢
EI
⁢
d
4
⁢
ω
3
⁡
(
x
)
dx
4
=
q
⁢
x
∈
[
a
+
b
,
a
+
b
+
c
]
formula
⁢
⁢
(
i
)
in the formula (i), EI is a flexural rigidity, in N/m;
x is a distance between any point on a foundation surface and a coordinate origin of the half-plane, in m;
and
ω1(x), ω2(x), ω3(x) are deflections of x at sections [0, a], [a, a+b], and [a+b, a+b+c] of the roof, respectively, in m;
b. solving the formula (i), and letting
α
=
k
4
⁢
EI
4
,
to obtain an equation of the deflection curve of the roof:
{
ω
1
⁡
(
x
)
=
q
24
⁢
EI
⁢
x
4
+
d
1
⁢
x
3
+
d
2
⁢
x
2
+
d
3
⁢
x
+
d
4
ω
2
⁡
(
x
)
=
q
k
+
d
5
⁢
e
-
α
⁢
⁢
x
⁢
⁢
cos
⁡
(
α
⁢
⁢
x
)
+
d
6
⁢
⁢
e
-
α
⁢
⁢
x
⁢
⁢
sin
⁡
(
α
⁢
⁢
x
)
+
d
7
⁢
e
α
⁢
⁢
x
⁢
⁢
cos
⁡
(
α
⁢
⁢
x
)
+
d
8
⁢
e
α
⁢
⁢
x
⁢
⁢
sin
⁡
(
α
⁢
⁢
x
)
ω
3
⁡
(
x
)
=
q
24
⁢
EI
⁢
x
4
+
d
9
⁢
x
3
+
d
10
⁢
x
2
+
d
11
⁢
x
+
d
12
formula
⁢
⁢
(
ii
)
in the formula (ii), d1, d2, d3, d4, . . . and d12 are constant coefficients;
and
obtaining parameters d1-d12 according to a model continuity condition and a symmetry boundary condition;
c. solving to obtain an equation of bending moment of the roof:
{
M
1
⁡
(
x
)
=
-
EI
⁢
d
2
⁢
ω
1
dx
2
M
2
⁡
(
x
)
=
-
EI
⁢
d
2
⁢
ω
2
dx
2
M
3
⁡
(
x
)
=
-
EI
⁢
d
2
⁢
ω
3
dx
2
formula
⁢
⁢
(
iii
)
in the formula (iii), M1(x), M2(x), and M3(x) are the bending moments of x at sections [0, a], [a, a+b], and [a+b, a+b+c] of the roof, respectively, in m,
wherein the width b of the reserved coal pillar needs to simultaneously satisfy a first strength theory of the roof and an ultimate strength theory of the coal pillar, namely, simultaneously satisfying that the width b of the reserved coal pillar is greater than or equal to a minimum reserve-width b1 under conditions of the first strength theory of the roof and a minimum reserve-width b2 under conditions of the ultimate strength theory of the coal pillar, specifically as shown in the following steps d and e:
d. simplifying the roof to a simply supported beam with an overburden uniform load q and a support load with the width b1 at the bottom, wherein it is found through analysis that a maximum bending moment Mmax on the roof occurs in one side of a beam span that deviates from a bottom support load and is spaced apart from a model origin by xm=a+b1+3EI·d9/q, and a value thereof is obtained by M3(xm) in the formula (iii), and then a maximum tensile stress of the roof is obtained according to a rectangular beam theory:
σ
max
=
6
⁢
M
max
h
2
formula
⁢
⁢
(
iv
)
in the formula (iv), h is a roof height, in m;
the following formula shall be satisfied according to the first strength theory of the roof, so that the roof is not broken:
σmax≤[σt] formula (v)
in the formula (v), [σt] is an allowable tensile stress of the roof, in MPa;
and
since the spacing c between the adjacent room mining coal pillars and the width 2(a+b) of the room mining coal pillar are known, the minimum reserve-width b1 of the reserved coal pillar under the conditions of the first strength theory of the roof is obtained according to a judgment condition of the formula (iv);
e. making the minimum reserve-width b2 of the reserved coal pillar under the conditions of the ultimate strength theory of the coal pillar satisfy its own non-destruction at the same time, and satisfying according to the ultimate strength theory:
σF≤σp formula (vi)
in the formula (vi), σ is a force acting on the coal pillar, σ=k∫aa+b ω2(x)dx, in m;
F is a safety coefficient, which is 2;
and
σp is an ultimate strength of the reserved coal pillar, in MPa;
calculating the minimum reserve-width of the reserved coal pillar under the conditions of the ultimate strength theory of the coal pillar to be b2 according to the formula (vi);
and
f. finally calculating the minimum reserve-width of the reserved coal pillar to be b=max {b1, b2}.

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Internally injected replacement support room-type coal pillar recovery method

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Internally injected replacement support room-type coal pillar recovery method

Life of this patent

Abstract

Claims5