CN112668144B - Prediction method for surface subsidence caused by mining of thick surface soil and thin bedrock - Google Patents
Prediction method for surface subsidence caused by mining of thick surface soil and thin bedrock Download PDFInfo
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Abstract
The invention provides a prediction method of surface subsidence caused by mining thick surface soil and thin bedrock, which comprises the following steps from the surface to the bottom: a thick overburden, a thin basement and a coal seam, the prediction method comprising the steps of: 1) establishing a prediction model of surface subsidence caused by coal mining; 2) establishing a prediction model of surface subsidence caused by hydrophobic consolidation of a bottom aquifer; 3) and linearly overlapping the subsidence of the surface subsidence caused by coal mining and the hydrophobic consolidation of the bottom aquifer to obtain a prediction model of the subsidence of the surface subsidence caused by the mining of the thick-surface soil thin bedrock. According to the prediction method, the water-soil coupling effect generated by the influence of coal mining activities on the thick surface soil layer is considered in stratum settlement deformation, and through the solution of a settlement source function and a settlement propagation distribution function, an expression of the surface subsidence amount when the bottom water-bearing stratum is subjected to hydrophobic settlement is obtained, so that a thick surface soil and thin bedrock mining subsidence prediction model and a prediction method thereof are established.
Description
Technical Field
The invention relates to the field of coal mining, in particular to a prediction method of surface subsidence caused by mining of thick surface soil and thin bedrock.
Background
In recent years, as the coal resources of China gradually enter deep mining, the occurrence conditions of thick surface soil and thin bedrock generally appear in the coal resources of Huang-Huai region. According to analysis of a large amount of observation data, the surface subsidence coefficient caused by coal mining activity under thick surface soil and thin bedrock is obviously larger, and the condition that part of mining areas are even larger than 1 occurs; the surface subsidence and horizontal movement range extend far relative to the mining area; deep mines are extremely easy to damage in thick surface soil sections, and the phenomena cannot be reasonably explained according to the conventional mining subsidence theory. The reason is that previous researches are limited to the influence of single coal seam mining on surface subsidence, although some researchers also consider the difference between deformation of a surface soil layer and deformation of a bedrock layer, the researches only distinguish and process the surface soil layer and the bedrock from parameter selection, influence of coal mining activities on the surface soil layer is not considered, water and soil coupling effect generated in the subsidence deformation process of the surface soil layer is not considered, and the characteristics of various media and multi-field coupling effect of thick surface soil and thin bedrock are ignored.
Research and analysis show that along with the mass exploitation of coal resources under thick surface soil and thin bedrock, a large amount of dredging and dropping of bottom water content through a bedrock water flowing fracture zone, the water level is obviously reduced, secondary consolidation and sedimentation occur, and the additional sedimentation and deformation of the ground surface caused by the hydrophobic sedimentation of the bottom water content due to the coal mining effect cannot be ignored. Considering that the bottom aquifer of the thick topsoil belongs to a confined aquifer, the hydrophobic consolidation settlement characteristics of the bottom aquifer are obviously different from the hydrophobicity of the shallow diving stratum. At present, a subsidence prediction model and a prediction method are not available in the aspect of research on the mechanism of stratum subsidence under the combined action of mining of a thick-surface soil thin bedrock coal bed and hydrophobic settlement of confined water at the bottom.
Disclosure of Invention
The invention aims to provide a prediction method of surface subsidence caused by thick surface soil and thin bedrock mining, which can reveal the mining subsidence rule of the thick surface soil and the thin bedrock and the intrinsic mechanism thereof to guide coal mining, is used for preventing and controlling a coal mining subsidence area and ensuring the safety of buildings (structures) in a near mining area, establishes a thick surface soil and thin bedrock mining subsidence prediction model and forms the prediction method.
In order to achieve the above purpose, the invention provides the following technical scheme:
a prediction method for surface subsidence caused by mining of thick surface soil and thin bedrock comprises the following steps from the surface to the bottom: the high-soil-density high-soil-density high-soil-density high-soil-density high-soil-density high-soil-density high-soil-density high-soil-density high-soil-density high-soil-density high-soil-density high-soil-density high-soil-density high-; a solid-liquid two-phase random medium with solid-phase soil particles and confined water is arranged in the bottom water-containing layer; the surface subsidence of the thick surface soil and the thin bedrock is jointly initiated by coal seam mining and hydrophobic consolidation of a bottom aquifer, wherein the prediction method comprises the following steps:
1) establishing a prediction model of surface subsidence caused by coal mining
Any coal bed unit d xi under the condition of a two-dimensional coordinate system2dη2Mining induced subsidence W of arbitrary point A (x, y) of the earth's surfacece(x) Comprises the following steps:
r: the radius of influence of coal seam mining on surface subsidence; d xi2: the horizontal dimension of the coal seam unit; d eta2: the vertical dimension of the coal seam unit;
extending the two-dimensional coordinates into a three-dimensional coordinate system, if the coal seam is horizontal, the coal seam coordinate system o2、ξ2、
The horizontal projection of the horizontal projection is coincident with the o, x and y horizontal projections of the earth surface coordinate system, so that the coal bed unit
Is used to induce subsidence W at any point A (x, y) of the earth's surfacece(x, y) is:
in the inclined coal seam, the maximum sinking amount of the coal seam roof is W0Then over the entire mining range omega2The subsidence of any point A (x, y) on the earth surface caused by inner mining is as follows:
2) establishing a prediction model of surface subsidence caused by hydrophobic consolidation of a bottom aquifer
The subsidence S (x, y, z) of any point of the earth surface caused by hydrophobic consolidation of the bottom aquifer can be determined by a subsidence source function
And sink propagation distribution function
Expressed as:
wherein omega1Is a hydrophobic area of a bottom aquifer;
3) and linearly overlapping the subsidence of the surface subsidence caused by coal mining and the hydrophobic consolidation of the bottom aquifer to obtain a prediction model of the subsidence of the surface subsidence caused by the mining of the thick-surface soil thin bedrock.
Further, in the above prediction method, in the step 2), the sink source function is determined according to the sink source function
Calculating to obtain the three-dimensional unit of the bottom aquifer
The amount of compression set ds due to drainage is located at depth (H-eta) in the two-dimensional coordinate system before the bottom aquifer is drained1) D xi of plane unit1dη1The effective stress between solid-phase soil particles is sigma, and the following calculation formula is satisfied:
σ＝(H-M)γ0+(M-η1)γf-(h-η1)γwformula 5
Wherein eta is1: the distance from any plane unit in the bottom water-containing layer to the bottom of the bottom water-containing layer; gamma ray0: average bulk density, kN/m, of all the earth above the bottom aquifer3；γf: volume weight of saturated soil body in pressure water in bottom water-bearing stratum, kN/m3；γw: volume weight of pressure-bearing pore water in bottom water-containing layer, kN/m3(ii) a h: the height of an initial water head of each point of the bottom aquifer; h: the thickness of the thick topsoil layer; m: the thickness of the bottom aquifer; d xi1: a horizontal dimension of the planar unit; d eta1: a vertical dimension of the planar unit;
the bottom of the bottom aquifer is hydrophobic, the height of the initial water head is reduced by delta h, and the total stress of the overlying surface soil layer is kept constant, so that the pores are formedThe part of the water pressure reduction is converted into solid-phase soil particles to bear, so the depth (H-eta) in the bottom water-containing layer1) D xi plane unit1dη1The effective stress increase of (a) is:
the depth (H-eta) can be obtained by the compaction coefficient formula and consolidation formula of the soil1) D xi of plane unit1dη1At effective stress increment
The compression deformation ds generated under the action of the compression function is the sinking source function of the bottom aquifer plane unit
Wherein e is0: an initial void ratio of the bottom aquifer; cc: a compressibility index of the bottom aquifer.
Further, in the above prediction method, in the step 2), the sinking source function is determined according to the sinking source function
And calculating to obtain the compression deformation ds generated by the hydrophobic property of the bottom aquifer, and calculating to obtain the amount of the surface subsidence caused by the hydrophobic subsidence of the bottom aquifer from the subsidence propagation distribution function, namely:
wherein, Wwe(x) Is the amount of surface subsidence, r (eta), caused by the hydrophobic settlement of any plane unit1) Is eta1The main influence range of the hydrophobic settlement of the bottom aquifer on the earth surface on the level;
radius range-R of hydrophobic consolidation influence throughout the bottom aquiferw～+RwIn addition, any hydrophobic consolidation of planar units produces a small volume compression d xi1ds, ultimate subsidence W of the surface due to hydrophobic consolidation of the bottom aquiferw(x) I.e. the plane unit d xi1dη1Superposition of the effects:
the two-dimensional coordinate system is expanded into a three-dimensional coordinate system, and a hydrophobic settlement coordinate system xi of the bottom aquifer1、o1、
The horizontal projection of the X, O and Y coordinate system coincides with the subsidence W of the X direction of the earth surfacewe(x) And y-direction sinkage Wwe(y) are respectively:
then the bottom aquifer eta1A certain three-dimensional unit at the horizontal position
The hydrophobic consolidation of (a) initiates the subsidence W of any point A (x, y) of the earth's surfacewe(x, y) may be represented as:
then at the top of the bottom aquifer, eta1M with the bottom of the bottom hydrous layer, eta1Radius range of influence of hydrophobic consolidation of the entire bottom aquifer between-0-Rw～+RwIn that any three-dimensional unit generates a slight volume compression
Final subsidence W of earth surface caused by hydrophobic consolidation of bottom aquiferw(x, y) is the superposition of the effects of the above infinitesimal bodies:
further, in the above prediction method, in the step 3), the coal seam mining and the hydrophobic consolidation of the bottom aquifer both induce surface subsidence, and the coal seam mining and the surface subsidence induced by the hydrophobic consolidation of the bottom aquifer are independent of each other, and then the final amount of subsidence of the surface subsidence can be expressed as a result of linear superposition of the surface subsidence induced by the coal seam mining and the surface subsidence induced by the hydrophobic consolidation of the bottom aquifer:
W(x,y)＝Wc(x,y)+Ww(x, y) formula 13.
Further, in the above prediction method, before the step 1), a preparation step is further included, and the preparation step specifically includes performing hole drilling coring on the thin bedrock layer and the thick overburden layer from the earth surface, and determining the thickness H of the thin bedrock1The thickness H of the thick surface soil layer and the thickness M of the bottom water-bearing layer, and carrying out a mechanical test on the cored sample to test the average volume weight gamma of all the stratum soil bodies above the bottom water-bearing layer0And the volume weight gamma of the saturated soil body in the pressure water in the bottom aquiferfCompression index C of the bottom aquifercTo initial pore ratio e0(ii) a Monitoring the water level change of the water-bearing stratum at the bottom before and after the coal seam is mined and in the mining process; according to the water level change of the bottom water-bearing stratum, determining an initial water level h before hydrophobic sedimentation of the bottom water-bearing stratum and a stable water level f (xi) after hydrophobic sedimentation of the bottom water-bearing stratum1) (ii) a Calculating a water level drop value according to the water level change of different positions of the bottom water-bearing stratum: Δ h ═ h-f (ξ)1)。
Further, in the above prediction methodProjecting and coinciding the centers of the surface subsidence, the coal seam mining center and the bottom aquifer water-drainage consolidation center on a surface water plane, and establishing a prediction model by adopting a unified coordinate system, wherein the unified coordinate system comprises three coordinate systems of a surface subsidence coordinate system, a coal seam mining coordinate system and a bottom aquifer water-drainage consolidation coordinate system, and the three coordinate systems have the same scale, wherein the surface subsidence coordinate system selects a surface point O which is directly above the center of a goaf as an origin of a horizontal axis x, and the direction of the coal seam from the origin along the horizontal plane is the positive direction of the x axis; an arbitrary point subsidence value W (x) with a surface abscissa of x and a horizontal movement value u (x) are respectively vertically downward and vertically upward from an origin O; the coordinate origin of the bottom aquifer hydrophobic consolidation coordinate system is positioned at the bottom O of the bottom aquifer right above the midpoint of the bottom plate of the run-to goaf1On the abscissa xi1The same direction as the x-axis, the ordinate η1Vertically upwards; the origin of coordinates of the coal seam mining coordinate system is in the middle point O of the bottom plate of the run-out goaf2On the abscissa xi2The same direction as the x-axis, the ordinate η2Vertically upwards.
Further, in the prediction method, the coal seam mining-induced surface subsidence satisfies a traditional probability integration method subsidence model, follows a linear superposition principle, and moves stably due to the coal seam mining-induced surface subsidence volume VSink 2Equal to coal production volume VCoal miningI.e. VSink 2＝VCoal mining(ii) a The bottom aquifer in the hydrophobic consolidation of the bottom aquifer is a confined aquifer, pores in the bottom aquifer are filled with confined water, solid-phase soil particles and confined water in the pores are incompressible and can be regarded as a horizontal homogeneous and isotropic solid-liquid two-phase random medium, and the upper topsoil layer obeys the random medium theory in the hydrophobic consolidation sinking process of the bottom aquifer; the bottom water-bearing layer is a semi-infinite space body, the pore compression caused by hydrophobic consolidation of the bottom water-bearing layer only occurs along the vertical direction, and the compression property of the same kind of soil does not change along with the depth.
Further, in the prediction method, the bottom aquifer belongs to a confined aquifer, the bottom aquifer is hydrophobic to form a virtual falling funnel, the whole bottom aquifer is filled with confined water, the whole bottom aquifer sinks due to hydrophobic consolidation within the influence range of the hydrophobic consolidation, and the stratum compression caused by the hydrophobic consolidation within the virtual falling funnel range of the bottom aquifer is regarded as thickening exploitation.
The analysis shows that the prediction method of the surface subsidence caused by the thick surface soil and the thin bedrock provided by the invention starts from the geological mining characteristics of the thick surface soil and the thin bedrock and the characteristics of various media and multi-field coupling action, considers the water-soil coupling action generated by the thick surface soil layer influenced by coal mining activity into the stratum subsidence deformation, obtains the surface subsidence expression when the bottom water-bearing layer is hydrophobic and subsides through the solution of a subsidence source function and a subsidence propagation distribution function, further establishes the prediction model of the surface subsidence caused by the thick surface soil and the thin bedrock and the prediction method thereof, fills the blank that the surface subsidence prediction model and the prediction method caused by the coal mining and the hydrophobic subsidence of the confined pore water of the bottom water-bearing layer under the geological mining conditions of the thick surface soil and the thin bedrock are not considered at present, and has important theoretical significance for disclosing the internal mechanism of the stratum subsidence specificity under the occurrence conditions of the thick surface soil and the thin bedrock, the method is a basic research for subsequently developing the prevention and control of the subsidence area in coal mining and ensuring the safety of buildings (structures) in a near mining area.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention. Wherein:
fig. 1 is a schematic representation of the co-initiation of surface subsidence by coal seam mining and hydrophobic consolidation of a bottom aquifer in accordance with an embodiment of the present invention.
FIG. 2 is a schematic representation of a model of surface subsidence induced by hydrophobic consolidation of a bottom aquifer according to one embodiment of the present invention;
FIG. 3 is a schematic representation of a three-dimensional coordinate system of a bottom aquifer-induced surface subsidence induced by hydrophobic consolidation according to an embodiment of the present invention;
fig. 4 is a calculation of a surface subsidence according to one embodiment of the present invention.
Detailed Description
The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings. The various examples are provided by way of explanation of the invention, and not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope or spirit thereof. For instance, features illustrated or described as part of one embodiment, can be used with another embodiment to yield a still further embodiment. It is therefore intended that the present invention encompass such modifications and variations as fall within the scope of the appended claims and equivalents thereof.
As shown in fig. 1 to 4, according to an embodiment of the present invention, there is provided a method for predicting the amount of surface subsidence caused by mining a thick overburden and a thin bedrock. Sequentially from the ground surface to the bottom: the high-soil-density low-soil-density high-soil-density high-soil-density high-soil-density high-soil-density high-soil-density high-soil-density high-soil-density high-soil-density high-soil-density high-soil-density high-soil-density high-density; the bottom water-containing layer is a solid-liquid two-phase random medium with solid-phase soil particles and confined water. The multilayer rock-soil body containing and resisting water layer above the bottom water-bearing layer is equivalent to homogeneous rock-soil body, and the saturated pressure-bearing homogeneous rock-soil body is below the homogeneous rock-soil body.
The surface subsidence is jointly initiated by coal seam mining and bottom water-bearing stratum hydrophobic consolidation, wherein the bottom water-bearing stratum belongs to a confined water-bearing stratum, the bottom water-bearing stratum is hydrophobic to form a virtual falling funnel, the whole bottom water-bearing stratum is filled with confined water, the whole bottom water-bearing stratum is subjected to hydrophobic consolidation subsidence within the influence range of the hydrophobic consolidation, and stratum compression initiated by the hydrophobic consolidation within the range of the virtual falling funnel of the bottom water-bearing stratum is regarded as thickening mining.
The contemplated method comprises the steps of:
1) establishing a prediction model of surface subsidence caused by coal mining
Any coal bed unit d xi under the condition of a two-dimensional coordinate system2dη2Mining induced subsidence W of arbitrary point A (x, y) of the earth's surfacece(x) Comprises the following steps:
r: the radius of influence of coal seam mining on surface subsidence; d xi2: the horizontal dimension of the coal seam unit; d eta2: the vertical size of the coal seam unit;
extending the two-dimensional coordinates to a three-dimensional coordinate system, if the coal seam is horizontal, the coal seam coordinate system o2、ξ2、
The horizontal projection of the horizontal projection is coincident with the o, x and y horizontal projections of the earth surface coordinate system, so that the coal bed unit
Is used to induce subsidence W at any point A (x, y) of the earth's surfacece(x, y) is:
in the inclined coal seam, the maximum sinking amount of the coal seam roof is W0Then over the entire mining range omega2The subsidence of any point A (x, y) on the earth surface caused by inner mining is as follows:
the subsidence of the earth surface caused by coal mining meets the subsidence model of the traditional probability integration method, which can be seen in coal mining subsidence science, Guo growth and the like, page 91, the coal industry Press, 2 nd edition 2016, 7 months. The coal seam mining-induced surface subsidence follows a linear superposition principle, and after the movement is stable, the surface subsidence volume V is caused by the coal seam miningSink 2Equal to coal production volume VCoal miningI.e. VSink 2＝VCoal mining；
The bottom aquifer in the hydrophobic consolidation of the bottom aquifer is a confined aquifer, pores in the bottom aquifer are filled with confined water, the solid-phase soil particles and the confined water in the pores are incompressible and can be regarded as a horizontal homogeneous and isotropic solid-liquid two-phase random medium, and the overlying topsoil layer obeys the random medium theory in the hydrophobic consolidation sinking process of the bottom aquifer;
the bottom aquifer is a semi-infinite space body, namely the compression of soil is carried out under the condition of side limitation, the pore compression caused by hydrophobic consolidation in the bottom aquifer only occurs along the vertical direction, and the compression property of the same kind of soil does not change along with the depth.
2) Establishing a prediction model of surface subsidence caused by hydrophobic consolidation of a bottom aquifer
The subsidence S (x, y, z) of any point of the earth surface caused by hydrophobic consolidation of the bottom aquifer can be determined by a subsidence source function
And sink propagation distribution function
Expressed as:
wherein omega1Is a hydrophobic area of a bottom aquifer;
in step 2), the hydrophobic consolidation of the bottom aquifer is mainly caused by the reduction of the solid-phase soil particle pores due to the increase of the effective stress after the pressure of the confined water (pore water) is reduced. From sink source functions
Calculating to obtain the three-dimensional unit of the bottom aquifer
The amount of compression set ds due to the hydrophobic effect,
in a two-dimensional coordinate system, the bottom aquifer is located at a depth (H-eta) before being drained1) D xi of plane unit1dη1The effective stress between solid-phase soil particles is sigma, and the following calculation formula is satisfied:
σ＝(H-M)γ0+(M-η1)γf-(h-η1)γwformula 5
Wherein eta is1: the distance from any plane unit in the bottom water-containing layer to the bottom of the bottom water-containing layer; gamma ray0: average bulk density, kN/m, of all the earth above the bottom aquifer3；γf: volume weight of saturated soil body in pressure water in bottom water-bearing stratum, kN/m3；γw: volume weight of pressure-bearing pore water in bottom water-containing layer, kN/m3(ii) a h: the height of an initial water head of each point of the bottom aquifer; h: the thickness of the thick topsoil layer; m: the thickness of the bottom aquifer; d xi1: the horizontal dimension of the planar unit; d eta1: the vertical dimension of the planar unit;
h: the height of the initial water head of each point of the bottom aquifer is based on the water head datum plane at the bottom of the bottom aquifer, and the flow speed water head generated by the flow of underground water is ignored.
The bottom of the bottom aquifer is hydrophobic, the height of the initial water head is reduced by delta H, and as the total stress of the overlying surface soil layer is kept constant, the part with reduced pore water pressure is converted into solid-phase soil particles to bear, so the depth (H-eta) in the bottom aquifer1) D xi plane unit1dη1The effective stress increase of (a) is:
the depth (H-eta) can be obtained by the compaction coefficient formula and consolidation formula of the soil1) D xi of plane unit1dη1At effective stress increment
The compression deformation ds, ds infinitesimal consolidation compression deformation generated under the action, the compression function of which is the sinking source function of the bottom aquifer plane unit
Wherein e is0: initial void ratio of the bottom aquifer; cc: compression index of the bottom aquifer. The compaction coefficient formula is
The formula of consolidation is
In the formula, av: the bottom aquifer compaction factor; e.g. of the type0: initial pore ratio of the bottom aquifer; Δ e: a change in the bottom aquifer porosity ratio;
effective stress increment of the bottom aquifer; Δ si: the deformation of the bottom aquifer under a certain level of effective stress increment; Δ ei: change in the void ratio of the bottom aquifer at a certain level of effective stress increment; e.g. of the type0i: the bottom aquifer pore ratio before a certain level of effective stress increment; hi: the bottom hydrous layer thickness before a certain effective stress increment.
According to the random medium theory, the plane unit d xi in the plane problem1dη1The surface subsidence caused by the compression subsidence of the hydrophobic consolidation is the surface subsidence propagation distribution function caused by the hydrophobic consolidation of the bottom aquifer.
In step 2), sink source function is settled according to
Calculating to obtain the compression deformation ds generated by the hydrophobic bottom aquifer, and calculating to obtain the surface subsidence caused by the hydrophobic subsidence of the bottom aquifer by the subsidence propagation distribution function, namely:
wherein, Wwe(x) Is the amount of surface subsidence, r (eta), caused by the hydrophobic settlement of any plane unit1) Is eta1The main influence range of hydrophobic settlement of a bottom aquifer on the earth surface on the horizontal level;
and after calculating a tiny compression amount, the subsidence propagation distribution function is transferred to the surface, namely, the transfer amount of the subsidence source function to the surface is calculated.
Radius of influence range-R of hydrophobic consolidation of whole bottom aquiferw～+RwInternal, i.e. RwIs the radius of influence of the hydrophobic consolidation of the bottom aquifer, and the hydrophobic consolidation of the planar unit between the top of any bottom aquifer and the bottom of the bottom aquifer generates a tiny volume compression d xi1ds, ultimate subsidence W of the surface due to hydrophobic consolidation of the bottom aquiferw(x) I.e. the plane unit d xi1dη1Superposition of the effects:
a two-dimensional coordinate system is expanded into a three-dimensional coordinate system, and a hydrophobic settlement coordinate system xi of a bottom aquifer1、o1、
The horizontal projection of the X, O and Y coordinate system coincides with the subsidence W of the X direction of the earth surfacewe(x) And y-direction sinkage Wwe(y) are respectively:
then the bottom aquifer eta1A certain three-dimensional unit at the horizontal position
The hydrophobic consolidation of (2) induces the subsidence W of any point A (x, y) on the surfacewe(x, y) may be represented as:
then at the top of the bottom aquifer, eta1M with the bottom of the bottom hydrous layer, eta1Radius of influence range-R of hydrophobic consolidation of the entire bottom aquifer between-0w～+RwIn that any three-dimensional unit generates a slight volume compression
Final subsidence W of earth surface caused by hydrophobic consolidation of bottom aquiferw(x, y) is the superposition of the effects of the above infinitesimal bodies:
3) and linearly overlapping the subsidence of the surface subsidence caused by coal mining and hydrophobic consolidation of the bottom aquifer to obtain a prediction model of the subsidence of the surface subsidence caused by mining the thick surface soil and the thin bedrock.
In the step 3) of the process,
the coal seam mining and the bottom water-bearing stratum hydrophobic consolidation both cause surface subsidence, the surface subsidence caused by the coal seam mining and the bottom water-bearing stratum hydrophobic consolidation are independent of each other, and then the final subsidence amount of the surface subsidence can be expressed as the linear superposition result of the surface subsidence caused by the coal seam mining and the surface subsidence caused by the bottom water-bearing stratum hydrophobic consolidation:
W(x,y)＝Wc(x,y)+Ww(x, y) formula 13
Preferably, a preparation step is further included before step 1), the preparation step specifically includes,
drilling and coring the thin bedrock stratum and the thick surface soil layer from the earth surface to determine the thickness H of the thin bedrock1The thickness H of the thick surface soil layer and the thickness M of the bottom water-bearing layer, and carrying out a mechanical test on the cored sample to test the average volume weight gamma of all the stratum soil bodies above the bottom water-bearing layer0And the volume weight gamma of the saturated soil body in the pressure water in the bottom aquiferfBottom aquiferCompression index CcTo initial pore ratio e0；
Monitoring the water level change of a water-bearing stratum at the bottom before and after the coal seam is mined and in the mining process; the water level change of the bottom water-bearing stratum before and after the coal seam is mined and during the mining process can be monitored through the hydrological observation holes close to the similar coal seam or the overlying strata of the similar coal seam in the adjacent mining area.
According to the water level change of the bottom water-bearing stratum, determining the initial water level h before hydrophobic sedimentation of the bottom water-bearing stratum and the stable water level f (xi) after hydrophobic sedimentation of the bottom water-bearing stratum1)；
Calculating a water level drop value according to water level changes at different positions of the water-bearing stratum at the bottom: Δ h ═ h-f (ξ)1)。
In the prediction method for the subsidence amount of the surface subsidence caused by the mining of the thick surface soil and the thin bedrock, the projection of the center of the surface subsidence, the center of the mining of the coal bed and the center of the hydrophobic consolidation of the water-bearing stratum at the bottom are superposed on the surface water plane, a prediction model is established by adopting a unified coordinate system,
the unified coordinate system comprises three coordinate systems of a surface subsidence coordinate system, a coal seam mining coordinate system and a bottom aquifer drainage consolidation coordinate system, the three coordinate systems have the same scale, wherein,
the surface subsidence coordinate system selects a surface point O which is directly above the center of the goaf as an origin of an abscissa axis x, and the direction of the coal seam from the origin along a horizontal plane is taken as the positive direction of the x axis; an arbitrary point subsidence value W (x) with a surface abscissa of x and a horizontal movement value u (x) are respectively vertically downward and vertically upward from an origin O;
the coordinate origin of the bottom aquifer hydrophobic consolidation coordinate system is positioned at the bottom O of the bottom aquifer right above the midpoint of the bottom plate of the run-to goaf1On the abscissa xi1The same direction as the x-axis, the ordinate η1Vertically upwards;
the origin of coordinates of a coal seam mining coordinate system is in the middle point O of the bottom plate of the run-out goaf2On the abscissa xi2The same direction as the x-axis, the ordinate η2Vertically upwards.
Examples
According to the prediction method of the surface subsidence caused by the mining of the thick surface soil and the thin bedrock, the following methods are known: the average thickness of the coal seam is 2.5m, the mining depth of the coal seam is 800m, and the thickness H of the thin bedrock1200M, the thickness of the overlying thick surface soil layer is H-600M, the thickness of the bottom water-containing layer is M-80M, and the influence radius R of hydrophobic consolidationw1000m, and a working face length L of 200 m. The coal seam average thickness and the working face trend length are combined to form the mining range omega of the coal seam2Namely the coal seam mining range.
The water level before the bottom aquifer is drained is-300 m, the water head of the bottom aquifer is reduced by 50m due to drainage, H is H (600) -300, the-300 is the distance from the water head of the bottom aquifer to the ground surface, and the negative sign represents that the water head is lower than the ground surface. Compression index CcInitial void ratio e of 0.400.6, average bulk density gamma of all the earth above the bottom aquifer0＝18kN/m3Volume weight gamma of saturated soil body in pore water in bottom aquiferf＝20kN/m3Volume weight of pore water in bottom aquifer gammaw＝9.81kN/m3。
And solving the steps in sequence to obtain the predicted results of the surface subsidence under the geological mining condition and the hydrophobic bottom, as shown in figure 4.
When the coal seam mining effect is considered independently, the maximum value of the subsidence of the surface subsidence is 1.416m, and the subsidence of the surface subsidence ranges from minus 440m to 440m in the radius range of 10 mm; when the coal seam mining and the hydrophobic consolidation of the bottom aquifer are considered to act together, the maximum value of the subsidence of the surface subsidence is 2.537m, and the radius range of the subsidence of the surface subsidence being 10mm is-1340 m. Analysis shows that the maximum value of the surface subsidence under the combined action of coal seam mining and bottom aquifer hydrophobic consolidation is far larger than the maximum value of the surface subsidence under the coal seam mining action, the surface subsidence coefficient under the combined action is larger than 1, and the range of the surface subsidence under the combined action of 10mm is obviously larger than the range of the surface subsidence under the traditional surface subsidence theory under the coal seam mining action.
Analysis shows that the surface subsidence coefficient of the thick surface soil and the thin bedrock is obviously increased at the moment, the surface subsidence range is far extended relative to a mining area, and the establishment of the prediction model of the surface subsidence amount in the mining of the thick surface soil and the thin bedrock reveals the internal mechanism of the stratum subsidence particularity under the occurrence condition of the thick surface soil and the thin bedrock, so that the basic research of preventing and controlling the subsidence area in the coal mining and ensuring the safety of buildings (structures) in the near mining area is carried out subsequently.
From the above description, it can be seen that the above-described embodiments of the present invention achieve the following technical effects:
the method for predicting the surface subsidence caused by mining the thick surface soil and the thin bedrock is based on the geological mining characteristics of the thick surface soil and the thin bedrock and the characteristics of various media and multi-field coupling action, takes the water-soil coupling action generated by the thick surface soil layer influenced by coal mining activities into the stratum subsidence deformation, obtains the surface subsidence expression when the bottom aquifer is subjected to hydrophobic settlement through solving the subsidence source function and the subsidence propagation distribution function, further establishes the thick surface soil and the thin bedrock mining subsidence prediction model and the prediction method thereof, fills the blank that the surface subsidence prediction model and the prediction method which are jointly caused by the coal mining and the water-hydrophobic settlement of the confined pore of the bottom aquifer under the geological mining conditions of the thick surface soil and the thin bedrock are not considered at present, and has important theoretical significance for disclosing the internal mechanism of the stratum subsidence specificity under the occurrence conditions of the thick surface soil and the thin bedrock, the method is a basic research for subsequently developing the prevention and control of the subsidence area in coal mining and ensuring the safety of buildings (structures) in a near mining area.
The above is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made to the present invention by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (8)
1. A method for predicting the surface subsidence caused by mining thick surface soil and thin bedrock is characterized by that,
sequentially from the ground surface to the bottom: the high-soil-density high-soil-density high-soil-density high-soil-density high-soil-density high-soil-density high-soil-density high-soil-density high-soil-density high-soil-density high-soil-density high-soil-density high-soil-density high-; a solid-liquid two-phase random medium with solid-phase soil particles and confined water is arranged in the bottom water-containing layer;
the surface subsidence of the thick surface soil and the thin bedrock is triggered by coal mining and hydrophobic consolidation of a bottom water-bearing stratum together, wherein,
the prediction method comprises the following steps:
1) establishing a prediction model of surface subsidence caused by coal mining
Any coal bed unit d xi under the condition of a two-dimensional coordinate system2dη2Mining induced subsidence W of arbitrary point A (x, y) of the earth's surfacece(x) Comprises the following steps:
r: the radius of influence of coal seam mining on surface subsidence; d xi2: the horizontal dimension of the coal seam unit; d eta2: the vertical dimension of the coal seam unit;
extending the two-dimensional coordinates into a three-dimensional coordinate system, if the coal seam is horizontal, the coal seam coordinate system o2、ξ2、
The horizontal projection of the horizontal projection is coincident with the o, x and y horizontal projections of the earth surface coordinate system, so that the coal bed unit
Is used to induce subsidence W at any point A (x, y) of the earth's surfacece(x, y) is:
in the inclined coal seam, the maximum sinking amount of the coal seam roof is W0Then over the entire mining range omega2The subsidence of any point A (x, y) on the earth surface caused by inner mining is as follows:
2) establishing a prediction model of surface subsidence caused by hydrophobic consolidation of a bottom aquifer
The subsidence S (x, y, z) of any point of the earth surface caused by hydrophobic consolidation of the bottom aquifer can be determined by a subsidence source function
And sink propagation distribution function
Expressed as:
wherein omega1Is a hydrophobic area of a bottom aquifer; eta1: the distance from any plane unit in the bottom water-containing layer to the bottom of the bottom water-containing layer; hydrophobic sedimentation coordinate system xi of bottom water-bearing layer1、o1、
The depth (H-eta) can be obtained by the compaction coefficient formula and consolidation formula of the soil1) D xi of plane unit1dη1At effective stress increment
The compression deformation ds generated under the action of the compression function is the sinking source function of the bottom aquifer plane unit
Wherein e is0: an initial void ratio of the bottom aquifer; cc: a compressibility index of the bottom aquifer;
according to the sink source function
And calculating to obtain the compression deformation ds generated by the hydrophobic property of the bottom aquifer, and calculating to obtain the amount of the surface subsidence caused by the hydrophobic subsidence of the bottom aquifer from the subsidence propagation distribution function, namely:
wherein, Wwe(x) Is the amount of surface subsidence, r (eta), caused by the hydrophobic settlement of any plane unit1) Is eta1The main influence range of the hydrophobic settlement of the bottom aquifer on the earth surface on the level;
3) and linearly overlapping the subsidence of the surface subsidence caused by coal mining and the hydrophobic consolidation of the bottom aquifer to obtain a prediction model of the subsidence of the surface subsidence caused by the mining of the thick-surface soil thin bedrock.
2. The prediction method according to claim 1,
in the step 2), the sink source function
Calculating to obtain the three-dimensional unit of the bottom aquifer
The amount of compression set ds due to the hydrophobic effect,
in a two-dimensional coordinate system, the bottom aquifer is located at a depth (H-eta) before being drained1) D xi of plane unit1dη1The effective stress between solid-phase soil particles is sigma, and the following calculation formula is satisfied:
σ＝(H-M)γ0+(M-η1)γf-(h-η1)γwformula 5
Wherein eta is1: the distance from any plane unit in the bottom water-containing layer to the bottom of the bottom water-containing layer; gamma ray0: average bulk density, kN/m, of all the earth above the bottom aquifer3；γf: volume weight of saturated soil body in pressure water in bottom water-bearing stratum, kN/m3；γw: volume weight of pressure-bearing pore water in bottom water-containing layer, kN/m3(ii) a h: the height of an initial water head of each point of the bottom aquifer; h: the thickness of the thick topsoil layer; m: the thickness of the bottom aquifer; d xi1: a horizontal dimension of the planar unit; d eta1: a vertical dimension of the planar unit;
the bottom of the bottom aquifer is hydrophobic, the height of the initial water head is reduced by delta H, and as the total stress of the overlying surface soil layer is kept constant, the part with reduced pore water pressure is converted into solid-phase soil particles to bear, so the depth (H-eta) in the bottom aquifer1) D xi plane unit1dη1The effective stress increase of (a) is:
3. the prediction method according to claim 2,
in the step 2) described above, the step of,
radius range-R of hydrophobic consolidation influence throughout the bottom aquiferw～+RwIn addition, any hydrophobic consolidation of planar units produces a small volume compression d xi1ds, ultimate subsidence W of the surface due to hydrophobic consolidation of the bottom aquiferw(x) I.e. the plane unit d xi1dη1Superposition of the effects:
the two-dimensional coordinate system is expanded into a three-dimensional coordinate system, and a hydrophobic settlement coordinate system xi of the bottom aquifer1、o1、
The horizontal projection of the X, O and Y coordinate system coincides with the subsidence W of the X direction of the earth surfacewe(x) And y-direction sinkage Wwe(y) are respectively:
then the bottom aquifer eta1A certain three-dimensional unit at the horizontal position
The hydrophobic consolidation of (a) initiates the subsidence W of any point A (x, y) of the earth's surfacewe(x, y) may be represented as:
then at the top of the bottom aquifer, eta1M with the bottom of the bottom hydrous layer, eta1Radius range of influence of hydrophobic consolidation of the entire bottom aquifer between-0-Rw～+RwIn that any three-dimensional unit generates a slight volume compression
Final subsidence W of earth surface caused by hydrophobic consolidation of bottom aquiferw(x, y) is the superposition of the infinitesimal effects:
4. the prediction method according to claim 3,
in the step 3) described above, the step of,
and (2) surface subsidence is caused by coal mining and the hydrophobic consolidation of the bottom aquifer, the coal mining and the surface subsidence caused by the hydrophobic consolidation of the bottom aquifer are independent, and the final subsidence amount of the surface subsidence can be expressed as the linear superposition result of the surface subsidence caused by the coal mining and the surface subsidence caused by the hydrophobic consolidation of the bottom aquifer:
W(x,y)＝Wc(x,y)+Ww(x, y) formula 13.
5. The prediction method according to claim 1,
before the step 1), a preparation step is also included, and the preparation step specifically comprises,
drilling and coring a thin bedrock layer and a thick surface soil layer from the earth surface, and determining the thickness H of the thin bedrock1The thickness H of the thick surface soil layer and the thickness M of the bottom water-bearing layer, and carrying out a mechanical test on the cored sample to test the average volume weight gamma of all the stratum soil bodies above the bottom water-bearing layer0And the volume weight gamma of the saturated soil body in the pressure water in the bottom aquiferfCompression index C of the bottom aquifercTo initial pore ratio e0；
Monitoring the water level change of the water-bearing stratum at the bottom before and after the coal seam is mined and in the mining process;
according to the water level change of the bottom water-bearing stratum, determining an initial water level h before hydrophobic sedimentation of the bottom water-bearing stratum and a stable water level f (xi) after hydrophobic sedimentation of the bottom water-bearing stratum1)；
Calculating a water level drop value according to the water level change of different positions of the bottom water-bearing stratum: Δ h ═ h-f (ξ)1)。
6. The prediction method according to claim 1,
the projections of the center of the surface subsidence, the center of the coal seam mining and the center of the bottom water-bearing stratum hydrophobic consolidation are superposed on the surface water plane, a unified coordinate system is adopted to establish a prediction model,
the unified coordinate system comprises three coordinate systems of a surface subsidence coordinate system, a coal seam mining coordinate system and a bottom aquifer drainage consolidation coordinate system, the three coordinate systems have the same scale, wherein,
the surface subsidence coordinate system selects a surface point O which is arranged right above the center of the goaf as an origin of an abscissa axis x, and the direction of the coal seam from the origin along a horizontal plane is in the positive direction of an x axis; an arbitrary point subsidence value W (x) with a surface abscissa of x and a horizontal movement value u (x) are respectively vertically downward and vertically upward from an origin O;
the coordinate origin of the bottom aquifer hydrophobic consolidation coordinate system is positioned at the bottom O of the bottom aquifer right above the midpoint of the bottom plate of the run-to goaf1On the abscissa xi1The same direction as the x-axis, the ordinate η1Vertically upwards;
the origin of coordinates of the coal seam mining coordinate system is in the middle point O of the bottom plate of the run-out goaf2On the abscissa xi2The same direction as the x-axis, the ordinate η2Vertically upwards.
7. The prediction method according to claim 1,
the coal seam mining-induced surface subsidence satisfies the traditional probability integration method subsidence model, follows the linear superposition principle, and moves stably due to the coal seam mining-induced surface subsidence volume VSink 2Equal to coal production volume VCoal miningI.e. VSink 2＝VCoal mining；
The bottom aquifer in the hydrophobic consolidation of the bottom aquifer is a confined aquifer, pores in the bottom aquifer are filled with confined water, solid-phase soil particles and confined water in the pores are incompressible and can be regarded as a horizontal homogeneous and isotropic solid-liquid two-phase random medium, and the upper topsoil layer obeys the random medium theory in the hydrophobic consolidation sinking process of the bottom aquifer;
the bottom water-bearing layer is a semi-infinite space body, the pore compression caused by hydrophobic consolidation of the bottom water-bearing layer only occurs along the vertical direction, and the compression property of the same kind of soil does not change along with the depth.
8. The prediction method according to claim 1,
the bottom aquifer belongs to a confined aquifer, the bottom aquifer is hydrophobic to form a virtual falling funnel, the whole bottom aquifer is filled with confined water, the whole bottom aquifer sinks due to hydrophobic consolidation within the influence range of the hydrophobic consolidation,
the formation compression induced by hydrophobic consolidation within the virtual falling funnel of the bottom aquifer is considered thickening mining.
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