In-situ protection method for water body overlying coal seam

Abstract

The present invention discloses a method for in-situ protection of water bodies overlying coal seams. The method comprises injecting a modified slurry into a target stratum located above a coal seam to be mined or being mined and below a target protected water body to form a grouting-reinforced rock layer. A grouting observation hole is drilled downward from the surface to form the target protected water body. The lower end of the grouting observation hole passes through the grouting-reinforced rock layer to the target detached space. A casing is lowered into the grouting observation hole as a grouting observation pipe. Water is injected into the grouting observation pipe to observe the change of the water level in the grouting observation pipe from the surface. If the water level in the grouting observation pipe suddenly drops, it is determined whether to inject filling slurry into the target detached space through the grouting observation pipe based on the development of the detached layer. The rock / soil layer below the target protected water body is grout-reinforced to form a grouting-reinforced rock layer. The detached layer developed below the grouting-reinforced rock layer is quickly grout-filled to prevent mining damage to the target protected water body, thereby protecting the water body overlying the coal seam in situ and reducing surface subsidence.

Description

Technical Field

[0001] The present invention relates to the technical field of water resource protection and mining, and in particular to an in-situ protection method for water bodies overlying coal seams. Background Art

[0002] In recent years, western China has gradually become the primary producer of coal resources. However, this region suffers from an arid climate and low vegetation cover. Shallow surface water (surface water and Quaternary groundwater), a crucial source of water for the region's vegetation, is susceptible to seepage and water level drop due to coal mining, further exacerbating the fragile local ecosystem. Intensive mining can cause large cracks or step-like fissures on the surface, leading to significant groundwater loss, a sudden drop in water levels, and a reduction in soil moisture retention, causing regional vegetation degradation. The impact is particularly pronounced on groundwater-dependent vegetation.

[0003] Clearly, the contradiction between resource development and environmental protection in western China is acute. Addressing water conservation during mining (particularly shallow surface water conservation) is fundamental to ensuring the long-term sustainable development of western mining areas. Therefore, minimizing the loss of surface water and groundwater caused by mining—in other words, in-situ protective mining of overlying water bodies—while maximizing coal resource recovery—has become a crucial challenge urgently needed in my country's ecologically fragile western regions. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to provide an in-situ protection method for overlying water bodies that can minimize the disturbance and damage to the surface ecological environment caused by coal mining.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] A method for in-situ protection of water bodies overlying coal seams comprises the following steps:

[0007] (A) injecting a modified slurry into a target stratum located above a coal seam to be mined or being mined and below a target protected aquifer to form a grouting reinforced rock formation;

[0008] (B) A grouting observation hole is formed by drilling downward from the surface. The lower end of the grouting observation hole passes through the grouting reinforced rock layer to the target separation space. A casing is placed in the grouting observation hole as a grouting observation pipe;

[0009] (C) Inject water into the grouting observation pipe and observe the water level changes in the grouting observation pipe from the surface; the grouting observation hole serves as a monitoring hole for the development of the target delamination space below the grouting reinforced rock layer;

[0010] (D) If the water level in the grouting observation tube drops suddenly, it can be determined that the target delamination space below the grouting reinforced rock layer begins to develop delamination. Based on the delamination development situation, it is determined whether to inject filling slurry into the target delamination space through the grouting observation tube to prevent further delamination development. At this time, the grouting observation hole serves as the grouting hole for filling the delamination in the target delamination space.

[0011] In the above-mentioned in-situ protection method for water bodies overlying coal seams, in step (A), a horizontal borehole is first drilled from the surface into the target stratum, and then a modified slurry is injected into the target stratum through the horizontal borehole.

[0012] In the above-mentioned in-situ protection method for water bodies overlying coal seams, in step (A), the target stratum is a rock stratum or soil stratum with pores or fissures that are conducive to grouting.

[0013] In the above-mentioned in-situ protection method for water bodies overlying coal seams, in step (B), there are more than two grouting observation pipes, at least some of which are arranged perpendicular to the mining working face and perpendicular to the center line of the advancing direction of the mining working face, and the distance between two adjacent grouting observation pipes is less than or equal to the slurry diffusion radius R.

[0014] The above-mentioned in-situ protection method for water bodies overlying coal seams has an R of 80-100m.

[0015] In the above-mentioned in-situ protection method for the water body overlying the coal seam, in step (C), the rate of decrease of the water level in the grouting observation pipe is regularly observed and recorded.

[0016] In the above-mentioned in-situ protection method for water bodies overlying coal seams, in step (D), when the water level drops faster than 0.001 / (πr 2 ) m / s, r is the radius of the grouting observation pipe hole, and filling slurry needs to be injected into the target abscission space immediately.

[0017] The technical solution of the present invention achieves the following beneficial technical effects:

[0018] After obtaining the spatial conduction mechanism of mining under high-intensity mining disturbance and the evolution law of overburden damage, an attempt was made to cut off the propagation path of mining damage. Based on the time effect of overburden mining conduction, a preliminary concept was proposed to reinforce and transform the rock stratum by grouting, artificially shape the key layer, and then quickly grout the developed stratum in the transformed rock stratum during the slow closure process to block the damage caused by mining to surface water, loose aquifers, roof bedrock aquifers and old empty water bodies, protect the overlying water body of the coal seam in situ, and effectively reduce surface subsidence.

[0019] Make full use of the lag time of the development and closure of the delamination space at the bottom interface of the rock / soil layer during the mining space conduction process, and carry out timely delamination grouting and filling to prevent the mining space and mining deformation from continuing to develop toward the surface, effectively block the damage of mining to the overlying rock / soil structure, prevent the loss of overlying water bodies and surface subsidence, so as to achieve in-situ protection of overlying water bodies and minimize the disturbance and damage of coal mining to the surface ecological environment.

[0020] Especially for the in-situ protection of shallow surface water (surface water and loose layer water), since the rock / soil layer grouting transformation and separation grouting are located in the shallow rock / soil layer (less than 100 meters underground), the grouting depth is shallow, which greatly reduces the grouting hole engineering volume, and the grouting pressure is small, which will effectively improve the treatment efficiency and reduce the engineering cost.

[0021] When targeting bedrock water-bearing bodies without an obvious key layer below, select a rock layer with strength close to that of the key layer, further increase its strength through grouting, shape it into the key layer, and then grout the developed separation layer below it; for bedrock water-bearing bodies with a key layer below, directly perform separation layer grouting. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of grouting reinforcement of rock / soil layer formed by grouting reinforcement of rock layer according to the present invention;

[0023] Figure 2 Schematic diagram of rock / soil layer grouting reinforcement and transformation - separation layer grouting filling.

[0024] The reference numerals in the figure are as follows: 1-coal seam; 2-target protected water-bearing body; 3-grouting reinforcement rock layer; 4-grouting observation pipe; 5-target separation space; 6-mining working face. DETAILED DESCRIPTION Example

[0025] In order to reduce the loss of overlying water caused by coal seam mining, this embodiment, after obtaining the mining space conduction mechanism and the evolution law of overlying rock damage under high-intensity mining disturbance, cuts off the propagation path of mining damage. Based on the time effect of overlying rock mining conduction, a method is proposed to select a rock / soil layer below the overlying water body of the mined coal seam for grouting reinforcement to form a grouting reinforced rock layer, artificially shape the key layer, and then quickly grouting and filling the detached layer of the grouting reinforced rock layer during the delayed closure process (see Figure 2 ) to prevent mining from damaging the overlying rock formations and target protected water bodies.

[0026] (A) A modified slurry is injected into a target stratum located above a coal seam 1 to be mined or currently being mined and below a target protective water body 2 to form a grouting-reinforced rock stratum 3. The target stratum is a rock or soil stratum with pores or fractures that are conducive to grouting.

[0027] First, a horizontal borehole is drilled from the surface into the target formation, and then the modified slurry is injected into the target formation through the horizontal borehole.

[0028] In order to reduce the impact on the surface ecological environment, overburden delamination grouting technology is a commonly used technical means to reduce surface losses. This technology uses ground drilling to inject grouting into the overburden delamination area, intervenes in the activity state of the overburden in advance, artificially forms overburden structure and filling and compaction bearing area, and then controls the development of overburden cracks and ground subsidence process, achieving effective control of mining collapse, thereby reducing surface settlement and reducing the impact on ground buildings.

[0029] However, with the long-term, continuous and high-intensity mining of coal resources, the mining depth of coal seams is getting deeper and deeper, and the depth of key layers in the overlying rock strata is also getting deeper and deeper. Generally, grouting reinforcement is required at key layers 300-400 meters underground.

[0030] In this example, after studying the spatial conduction mechanism of mining under high-intensity mining disturbance and the evolution of overburden damage, we proposed pre-grouting reinforcement of the rock / soil layer beneath the overlying water body. When designing grouting for detached layers, the critical layer theory is generally used to determine the appropriate grouting layer location.

[0031] If the target protected water body is shallow water (surface water and loose layer water), a comprehensive analysis of the depth of shallow water resources and key layer theory is conducted to determine that the grouting layer is less than 100 meters underground near the surface.

[0032] Therefore, this embodiment proposes to perform horizontal drilling in the rock / soil layer below the target protected water body 2 and perform pre-grouting reinforcement to form a key layer - the grouting reinforced rock layer 3.

[0033] If the target protected aquifer is a bedrock aquifer without an obvious key layer, select a rock layer below the bedrock aquifer with a strength close to that of the key layer, and further increase its strength by drilling horizontal boreholes and grouting to shape it into a key layer. Then, grouting is performed on the abscission layer developed below it. For bedrock aquifers with a key layer below, abscission grouting can be performed directly.

[0034] By drilling and grouting the rock / soil layer of the target protected water body to prevent seepage and reinforce it, the mechanical strength and anti-seepage capacity can be significantly improved.

[0035] (B) A grouting observation hole is formed by drilling downward from the surface. The lower end of the grouting observation hole passes through the grouting reinforced rock layer 3 to the target separation space 5. A casing is lowered into the grouting observation hole as a grouting observation pipe 4.

[0036] There are two or more grouting observation pipes 4, at least some of which are arranged perpendicular to the mining working face 6 and perpendicular to the centerline of the mining working face 6's advancement direction. The spacing between two adjacent grouting observation pipes 4 is less than or equal to the slurry diffusion radius R, which is 80-100m.

[0037] (C) Water is injected into the grouting observation pipe 4 and the water level change in the grouting observation pipe 4 is observed from the surface; the grouting observation hole serves as a monitoring hole for the development of the target delamination space 5 below the grouting reinforced rock layer 3.

[0038] It is necessary to regularly observe and record the rate of water level drop in the grouting observation pipe 4.

[0039] (D) If the water level in the grouting observation pipe 4 drops suddenly, it is determined whether to inject filling slurry into the target abscission space 5 through the grouting observation pipe 4 according to the development of the abscission layer to prevent the abscission layer from developing further. In this case, the grouting observation hole serves as the grouting hole for filling the abscission layer in the target abscission space 5.

[0040] When the water level drops faster than 0.001 / (πr 2 ) m / s (r is the radius of the borehole of the drilling and grouting observation pipe 4), it is necessary to immediately inject filling slurry into the target absorptive space 5.

[0041] By fully utilizing the lag time for the development and closure of the delamination space at the bottom interface of the rock / soil layer during the mining space conduction process, timely delamination grouting and filling can be carried out to prevent the mining space and mining-induced deformation from continuing to develop toward the surface. This effectively blocks mining damage to the shallow surface rock / soil structure, prevents overlying water leakage and surface subsidence, and achieves in-situ protection of the overlying water body, minimizing the disturbance and damage to the surface ecological environment caused by coal mining. This is especially true for the protection of surface water and groundwater. Since the grouting transformation of the rock / soil layer and the delamination grouting are located in shallow rock / soil layers (less than 100 meters underground), the grouting depth is shallow, greatly reducing the number of grouting holes and the grouting pressure, which will effectively improve treatment efficiency and reduce project costs.

[0042] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the claims of this patent application.

Claims

1. A method for in-situ protection of water bodies overlying coal seams, characterized in that: The steps include: (A) injecting a modified slurry into a target stratum located above a coal seam (1) to be mined or being mined and below a target protected aquifer (2) to form a grouting reinforced rock stratum (3); first, drilling a horizontal borehole from the surface into the target stratum, and then injecting the modified slurry into the target stratum through the horizontal borehole; (B) drilling downward from the surface to form a grouting observation hole, the lower end of the grouting observation hole passes through the grouting reinforcement rock layer (3) to the target separation space (5), and a casing is placed in the grouting observation hole as a grouting observation pipe (4); there are two or more grouting observation pipes (4), at least part of which is perpendicular to the mining working face (6) and perpendicular to the center line of the advancing direction of the mining working face (6), and the distance between two adjacent grouting observation pipes (4) is less than or equal to the slurry diffusion radius R; (C) injecting water into the grouting observation pipe (4) and observing the water level change in the grouting observation pipe (4) from the surface; the grouting observation hole serves as a monitoring hole for the development of the target delamination space (5) below the grouting reinforced rock layer (3); (D) If the water level in the grouting observation pipe (4) suddenly drops, it can be determined that the target delamination space (5) below the grouting reinforced rock layer (3) begins to develop delamination. According to the delamination development situation, it is determined whether to inject filling slurry into the target delamination space (5) through the grouting observation pipe (4) to prevent the delamination from further developing. At this time, the grouting observation hole serves as a grouting hole for filling the delamination in the target delamination space (5).

2. The in-situ protection method for water bodies overlying coal seams according to claim 1, characterized in that: In step (A), the target stratum is a rock or soil stratum with pores or cracks that are conducive to grouting.

3. The in-situ protection method for water bodies overlying coal seams according to claim 1, characterized in that: R is 80-100m.

4. The in-situ protection method for water bodies overlying coal seams according to claim 1, characterized in that: In step (C), the water level drop rate in the grouting observation pipe (4) is regularly observed and recorded.

5. The in-situ protection method for water bodies overlying coal seams according to claim 4, characterized in that: In step (D), when the water level drops faster than 0.001 / (πr 2 ) m / s, r is the radius of the grouting observation tube (4) hole, and it is necessary to immediately inject filling slurry into the target abscission space (5).

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