A method and system for integrated prevention and treatment of hydrogeological hazards of thermally altered rocks

Abstract

The integrated prevention and treatment method of the burned rock water disaster of the present application proposes the concept of combination of resistance and permeation and advanced active prevention and treatment, breaks the thinking stereotype of traditional coal seam roof water disaster independently relying on water drainage and full section curtain interception, and creates a new concept of active comprehensive prevention and treatment of dynamic supply interception, drainage and dry static reserves, and combined use of local bypass flow. The problems of multiple solutions of geophysical prospecting and limitations of drilling are scientifically solved, and for the first time, the fine quantitative delineation of the strong water-conducting burned rock zone is realized from two-dimensional range to three-dimensional water-rich structure. A gravity drainage of an inclined borehole, a roadway catchment, and a gravity flow of a catchment channel form a passive underground water drainage link. The difficulty of drainage and dryness in treating the burned rock water disaster is reduced, and due to the use of the passive underground water drainage link of the gravity flow of the catchment channel, the cost is further reduced. The collected clean water flows into the external clean water warehouse, realizes repeated use, reduces resource waste, and is suitable for large-scale use and promotion in the field of coal mine water disaster prevention and treatment technology.

Description

Technical Field

[0001] This invention belongs to the field of coal mine water hazard prevention and control technology, specifically relating to an integrated prevention and control method for water hazards in burnt rock. Background Technology

[0002] Burnt rock masses are fractured rock masses formed by the spontaneous combustion of coal seams and baking of the surrounding rock. They are widely developed in shallow coal mining areas of the Shaanxi coal base in my country. Compared with normal bedrock, burnt rock masses exhibit significant structural deterioration, with highly developed sintering fractures and pores. These masses often have close hydraulic connections with near-surface water-rich loose layers and surface water bodies, leading to burnt rock water inrush hazards. This severely restricts safe and efficient coal mine production. The "Specifications for the Survey of Hidden Disaster-Causing Factors in Mines" and other regulations issued by the State Administration of Mine Safety have listed burnt rock as a key target for the survey and control of disaster-causing factors in coal mines. Accurate boundary exploration of burnt rock is a crucial prerequisite for coal mine delineation, working face layout, and production efficiency improvement.

[0003] Under this geological structure, when mining the lower coal seam of the already burnt rock strata, the mining directly exposes or disturbs the water-conducting fissures that directly or indirectly expose the strongly water-conducting burnt rock aquifer, which often causes very serious water hazards.

[0004] Due to the wide range and high water content of sintered rocks, existing treatment methods have the following technical limitations:

[0005] 1. Difficulty in drainage: The range of sintered rocks is wide, the water content is high and the permeability coefficient is extremely high (more than 100 times that of normal bedrock), and traditional drilling drainage methods are obviously insufficient.

[0006] 2. For loose media aquifers that are strongly recharged by surface water, a lateral fully enclosed curtain can generally be used for interception and treatment. However, due to the wide range of pyromorphic rocks, the investment scale would be extremely large if a lateral fully enclosed curtain were used for interception.

[0007] 3. Burned rocks are widely developed in shallow coal mining areas of the Shaanxi coal base in my country. The distance between the burned rocks and the underlying unburned normal coal seams is small, and it is generally not possible to leave safe water-proof coal pillars. In many cases, the mining of coal resources under the burned rocks has to be abandoned, resulting in a large waste of resources. Summary of the Invention

[0008] The purpose of this invention is to provide an integrated method and system for preventing and controlling water damage in igneous rocks, so as to solve the problems of high difficulty in drainage, high economic cost and waste of resources in the treatment of water damage in igneous rocks by existing technologies.

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for integrated prevention and control of water hazards in burnt rocks includes the following steps: Step 1: For the target area to be treated, delineate the planar distribution range of the pyrophoric rock in the target area, and then measure the burial depth of the top and bottom plates of the pyrophoric rock. Identify potential water-rich areas of the sintered rocks within the delineated planar distribution area; Pumping tests were conducted in all water-rich areas of the sintered rock to identify the corresponding strong water-conducting zones within these areas. Step 2: Set up a water-cutting curtain at the upstream boundary of the strong water-conducting zone; Step 3: Set up a water collection roadway in the normal coal seam at the bottom of the strong water-conducting zone; Step 4: For the water collection tunnel, a water collection channel is set up on it with a fixed slope, and the bottom slope of the water collection channel is consistent with the slope of the water collection tunnel. The bottom of each of the aforementioned water collection channels is connected to an external clear water reservoir; Step 5: The water-rich area above the strong water-conducting belt is the main drainage area, and the boundary areas at both ends of the intercepting curtain are the bypass control area. Within the main drainage area, multiple main drainage area boreholes are set along the length of the water collection tunnel; Multiple bypass control zone boreholes were set up within the bypass control zone; All the boreholes in the main dredging area and the bypass control area are inclined boreholes, and their final borehole trajectories completely cover the cross-section of the strong water-conducting zone in space. All the borehole outlet pipes of the main dredging area and the bypass control area are connected to the water collection channel, thereby realizing the integrated prevention and control of water hazards to the burnt rock in the target area.

[0010] The present invention also has the following features: Furthermore, step 1 includes the following sub-steps: Step 11, set the magnetic gradient threshold; A high-precision ground-based gradient magnetic method was used to conduct magnetic gradient tests on the target area. The continuous region where the magnetic gradient ΔT exceeds the magnetic gradient threshold is considered as the potential range of the sintered rock. Measure the burial depth of the top and bottom plates of the pyrophoric rock; Step 12, set the resistivity threshold; Resistivity testing of the potential range of sintered rock was conducted using the ground transient electromagnetic method. The continuous region with resistivity below the resistivity threshold is defined as the water-rich area of ​​the sintered rock; Step 13: Set the inflow threshold and permeability coefficient threshold; Multiple boreholes were drilled in the water-rich area of ​​the sintered rock, and pumping tests were conducted on each borehole to obtain the unit flow rate and permeability coefficient at each borehole point. The borehole locations that simultaneously satisfy the conditions of unit water inflow greater than the water inflow threshold and permeability coefficient greater than the permeability threshold are defined as strong water-conducting points, and multiple strong water-conducting points are obtained. Step 14: Based on multiple strong water-conducting points, perform spatial interpolation on the water-rich area of ​​the sintered rock to obtain multiple similar points with similar geophysical response characteristics to the strong water-conducting points; By sequentially connecting multiple similar points and multiple strong water-conducting points, a strong water-conducting zone is formed.

[0011] Furthermore, in step 2, a water-cutting curtain is set up 50-100m outside the upstream boundary of the strong water-conducting zone; The axis of the cutoff curtain is perpendicular to the strong water-conducting zone of the sintered rock; The root of the cutoff curtain is embedded in the stable water-resistant layer or intact bedrock at the bottom of the loose layer of the target area, and the depth is not less than 5m. The top elevation of the cutoff curtain is more than 2 meters higher than the loose groundwater layer of the target area and lower than the ground surface; The height of the cutoff curtain is no more than 100m, and the thickness is 0.5-1m.

[0012] Furthermore, the vertical distance between the water collection tunnel and the bottom plate of the pyromorphic rock zone mentioned in step 3 is ≥20m; The elevation angle of the water collection tunnel is 5‰ to 8‰.

[0013] Furthermore, the minimum cross-sectional dimensions of the water collection channel mentioned in step 4 are: bottom width ≥ 0.4m and depth ≥ 0.4m.

[0014] Furthermore, in step 5, the spacing between two adjacent main evacuation zone boreholes is 60-100m; The inclination angle of all boreholes in the main evacuation area and the bypass control area is 15°-35°.

[0015] Furthermore, in step 13, the water inflow threshold is 1.0 L / (s·m); The permeability threshold is 50 m / d.

[0016] An integrated monitoring system for the prevention and control of water hazards in calcined rocks includes a flow monitoring module, a water level monitoring module, a water pressure monitoring module, and an early warning module; The flow monitoring module includes flow sensors that are installed one-to-one in each borehole of the main dredging area and the borehole of the bypass control area; The flow monitoring module is used to monitor the real-time flow of each borehole and transmit the flow data to the early warning module; The water level monitoring module includes water level sensors respectively installed in the main dredging area and the bypass control area; The water level monitoring module is used to monitor the real-time water level of the main dredging area and the bypass control area and transmit the water level data to the early warning module; The water pressure monitoring module includes pressure sensors that are installed one-to-one in each borehole of the main dredging area and the borehole of the bypass control area; The water pressure monitoring module is used to monitor the real-time water pressure of each borehole and transmit the water pressure data to the early warning module; The aforementioned early warning module is used for: Receive flow, water level, and water pressure data transmitted from the flow monitoring module, water level monitoring module, and water pressure monitoring module; Set flow rate threshold, water level threshold, and water pressure threshold; An alarm will be triggered if any data exceeds the threshold.

[0017] Furthermore, the flow thresholds include the borehole flow threshold for the main evacuation zone and the borehole flow threshold for the bypass control zone; The borehole flow rate threshold for the main slack disposal area is 5 m³ / h; The borehole flow rate threshold for the bypass control zone is 15 m³ / h.

[0018] Compared with the prior art, the present invention has the following technical effects: (I) The integrated prevention and control method for igneous rock water hazards of this invention proposes a combination of blocking and dredging, along with proactive prevention and control. It breaks through the traditional mindset of relying solely on drainage or full-section curtain interception for coal seam roof water hazards, establishing a new proactive and comprehensive prevention and control concept that combines cutting off dynamic recharge with reducing static storage and intercepting local bypass flow. It scientifically solves the problems of geophysical exploration ambiguity and drilling limitations, achieving for the first time a precise quantitative delineation of highly conductive igneous rock zones from a two-dimensional to a three-dimensional water-rich structure. It constitutes a non-powered underground drainage link: gravity drainage from inclined boreholes – water collection in roadways – gravity-fed water collection channels. This reduces the difficulty of drainage when controlling igneous rock water hazards. The use of a non-powered underground drainage link with gravity-fed water collection channels further reduces costs. The collected clean water flows into an external clean water tank for reuse, reducing resource waste and making it suitable for large-scale use and promotion in the field of coal mine water hazard prevention and control.

[0019] (II) The integrated prevention and control of water hazards in igneous rocks of the present invention digitizes and identifies the water hazard prevention and control effect by defining specific flow rate, water pressure and its rate of change threshold, and rigidly links it with mining production plan, thereby realizing intelligent and dynamic safety guarantee of monitoring-early warning-decision-control, and ensuring the long-term effectiveness of prevention and control. Attached Figure Description

[0020] Figure 1 This is a cross-sectional schematic diagram of the distribution of the water-cutting curtain, water collection tunnel, and boreholes of the present invention; Figure 2 This is a schematic diagram of water hazard in the burnt rock of a shallow coal-bearing area according to one embodiment of the present invention; Figure 3 This is a cross-sectional schematic diagram of a water collection tunnel in one embodiment of the present invention. Detailed Implementation

[0021] It should be noted that, unless otherwise specified, all components in this invention are components known in the prior art.

[0022] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0023] like Figure 2 As shown, sintered rocks are widely developed in shallow coal mining areas of the Shaanxi coal base in my country. Firstly, this leads to the significant development of sintered pores and fissures in the surrounding rock mass, forming a special aquifer with significant water conductivity and water-bearing capacity. Secondly, the sintering of the coal seam causes the surrounding rock mass to collapse and cavitate, similar to the caving zones and fault zones with significant water conductivity formed under the disturbance of coal seam mining. Therefore, the structure of the sintered rock and its surrounding rock mass also changes, forming a sintered rock aquifer with strong water conductivity and water-bearing characteristics. The permeability coefficient is generally greater than 100 m / d, and can reach a maximum of 1631.30 m / d, which is more than 100 times the permeability of normal bedrock. At the same time, the sintered rock aquifer formed by the near-surface shallow coal seam sintering is easily replenished by groundwater from the overlying Quaternary water-rich loose aquifer and even surface water, constituting a "replenishment from above and conduction from below" geological structure for water hazards in coal seam mining. Therefore, under this geological structure, when mining the lower coal seam of the already metamorphic rock strata, the mining directly exposes or disturbs the water-conducting fractures that directly or indirectly expose the strongly water-conducting metamorphic rock aquifer, which often leads to very serious water hazard problems. Figure 1 For example, in the Ningtaota Coal Mine, the local water inflow at the working face reached 1200m³ under the influence of sintered rock. 3 / h, causing the working face to be flooded and production to stop, with the water inflow remaining stable at 400m³. 3 Water hazards of this type, such as those occurring at around / h, have severely impacted the safe mining of coal in large mines in the Shennan mining area.

[0024] To address the above-mentioned pain points, this embodiment presents an integrated prevention and control method for water damage to burnt rocks, including the following steps: Step 1: For the target area to be treated, delineate the planar distribution range of the pyrophoric rock in the target area, and then measure the burial depth of the top and bottom plates of the pyrophoric rock. Identify potential water-rich areas of the sintered rocks within the delineated planar distribution area; Pumping tests were conducted in all water-rich areas of the sintered rock to identify the corresponding strong water-conducting zones within these areas. Step 1 specifically includes the following sub-steps: Step 11, set the magnetic gradient threshold; This embodiment does not limit the magnetic gradient threshold. The threshold is adaptively determined by those skilled in the art based on the geological data of the target area and the background field of the work area. As an optional numerical choice, the magnetic gradient threshold range is 70 to 100 nT. The magnetic gradient threshold range of 70–100 nT given in this embodiment is a preferred range.

[0025] In the scenario of spontaneous combustion of coal seams, the baking temperature, duration, and surrounding rock lithology vary in different locations, which leads to uneven content of magnetic minerals generated by spontaneous combustion of coal seams. The magnetic susceptibility is also a variable value that is related to the intensity of spontaneous combustion.

[0026] The threshold range given in this embodiment is 70nT at the lower limit and 100nT at the upper limit. Its range fully covers the magnetic differences caused by uneven burning, avoiding the inclusion of a large number of invalid boundaries due to the threshold being too low or the omission of water-conducting edge areas due to the threshold being too high.

[0027] A high-precision ground-based gradient magnetic method was used to conduct magnetic gradient tests on the target area. The continuous region where the magnetic gradient ΔT exceeds the magnetic gradient threshold is considered as the potential range of the sintered rock. Measure the burial depth of the top and bottom plates of the pyrophoric rock; Step 12, set the resistivity threshold; This embodiment also does not limit the resistivity threshold. The threshold is adaptively determined by those skilled in the art based on the lithology of the target area. This embodiment provides an optional resistivity threshold range of 20 to 15 Ω·m.

[0028] The threshold range given in this embodiment is a preferred range, specifically: In target areas where sintered rocks exist, normal surrounding rocks include unsintered intact sandstone and mudstone, which typically have resistivity ranging from tens to hundreds of Ω·m due to their low porosity and low water content.

[0029] Although the water-poor sintered rock is broken, if it contains no water or has a low water content, the fractured gaps are filled with air, and the resistivity is still relatively high.

[0030] For water-rich sintered rocks, once the fractured voids are saturated with groundwater, the overall resistivity drops sharply to tens or even a few Ω·m due to the presence of soluble salts (ionic conductivity) in the water.

[0031] Therefore, the threshold range given in this embodiment is based on the physical difference between the resistivity of water-bearing sintered rocks and that of surrounding rocks and water-poor sintered rocks, combined with the gradual change in the water-bearing degree of coal seams after sintering, and the calibration basis of the high probability correspondence with the strong water-conducting threshold in engineering practice, and is finally determined as a practical criterion.

[0032] Resistivity tests were conducted on the planar distribution range of sintered rocks using the ground transient electromagnetic method. Ground-based transient electromagnetic method (TEM) is a geophysical exploration technique based on the principle of electromagnetic induction. By passing a pulsed current through a loop (transmitting coil) deployed on the ground, a primary magnetic field is established in the surrounding space. When the current is momentarily cut off, this primary magnetic field induces eddy currents in the underground conductive medium. These eddy currents decay over time, generating a secondary magnetic field. By observing the decay characteristics of this secondary field over time using a receiving coil on the ground, the resistivity distribution of the underground rock strata can be inferred. Because water-bearing fractured rock masses (such as water-rich pyrophoric rocks) have significantly enhanced conductivity, the lower the resistivity, the slower the eddy current decay and the stronger the signal. Therefore, this method can accurately delineate the spatial range of water-rich areas.

[0033] The continuous region with resistivity below the resistivity threshold is defined as the water-rich area of ​​the sintered rock; Step 13: Set the inflow threshold and permeability coefficient threshold; Multiple boreholes were drilled in the water-rich area of ​​the sintered rock, and pumping tests were conducted on each borehole to obtain the unit flow rate and permeability coefficient at each borehole point. In this embodiment, the inflow threshold is q≥1.0 L / (s·m); The permeability threshold is K≥50 m / d; q≥1.0 L / (s·m) means that a continuous large flow of water can be formed; the permeability coefficient (K) characterizes the water permeability of the rock mass itself; A K ≥ 50 m / d exceeds the normal range for common sandstone aquifers, directly quantifying the efficiency of the strong water-conducting channels formed after the fracturing of the igneous rock mass. This ensures that the designated strong water-conducting points pose a large water threat on a macroscopic scale and possess the ability to rapidly conduct hydraulic power and maintain stable recharge on a microscopic scale, providing a scientific criterion that is dually calibrated by hydrogeology and engineering practice.

[0034] The borehole locations that simultaneously satisfy the conditions of unit water inflow greater than the water inflow threshold and permeability coefficient greater than the permeability threshold are defined as strong water-conducting points, and multiple strong water-conducting points are obtained. Step 14: Based on multiple strong water-conducting points, perform spatial interpolation on the water-rich area of ​​the sintered rock to obtain multiple similar points with similar geophysical response characteristics to the strong water-conducting points; The spatial interpolation method used in this step to find similar points is a well-known method in the field. A unit inflow rate q ≥ 1.0 L / (s·m) and a permeability coefficient K ≥ 50 m / d are used as the quantitative thresholds for determining strong hydraulic points. Verified strong hydraulic points are correlated with unverified areas exhibiting similar geophysical (strong magnetic, low resistivity) response characteristics through geostatistical correlation and spatial interpolation. Under the condition of continuous geophysical anomalies and consistent geological genesis (altered rock), the strong hydraulic conductivity of the area between adjacent verification points is inferred, thus achieving a scientific inference from "discrete points" to "continuous zones."

[0035] This continuous zone is a three-dimensional geological unit with clear boundaries, which can be directly used as the core geological basis for optimizing key parts of the water-cutting curtain, designing the trajectory of the water collection tunnel, and locating the target area of ​​the inclined drainage borehole group.

[0036] Within the water-rich area of ​​the sintered rock, the verified strong water-conducting points are correlated with unverified areas that have similar geophysical response characteristics through geostatistical correlation and spatial interpolation, and the delineated areas are used as directional target areas.

[0037] By sequentially connecting multiple similar points and multiple strong water-conducting points, a strong water-conducting zone is formed.

[0038] Step 2: Set up a water-cutting curtain at the upstream boundary of the strong water-conducting zone; A water-cutting curtain is installed 50-100m outside the upstream boundary of the strong water-conducting zone; The axis of the water-cutting curtain is parallel to the strong water-conducting zone of the sintered rock.

[0039] A water-cutting curtain is a curtain-shaped vertical water-cutting body used in this field to block or reduce the flow of groundwater into the foundation pit through the side walls and bottom of the pit and to control the drop of the groundwater level outside the foundation pit. As a further preferred option, the cutoff curtain also meets the following conditions: The wall axis of the water-cutting curtain is perpendicular to the main flow direction of the loose groundwater in the target area, in order to maximize the interception efficiency, and its direction is parallel to the strong water-conducting zone. The base of the cutoff wall must be vertically embedded in the stable impermeable layer or intact bedrock at the bottom of the loose layer, to a depth of not less than 5.0m. This is crucial to ensure vertical rooting of the wall and reduce bottom leakage, achieving a rigid connection with the natural impermeable base.

[0040] The top elevation of the cutoff wall must be at least 2.0m higher than the predicted or measured groundwater level of the loose layer, while being lower than the ground surface, taking into account both overflow prevention and ground safety.

[0041] The total vertical height of the cutoff wall is usually no more than 100m, achieving the optimal balance between effective water interception and engineering economy and feasibility.

[0042] The width (thickness) of the cutoff wall is 0.5-1.0m.

[0043] Step 3: Set up a water collection roadway in the normal coal seam at the bottom of the strong water-conducting zone; The vertical distance between the water collection tunnel and the floor of the metamorphic rock zone is ≥20m; To ensure that subsequent drainage from the inclined boreholes can be collected and flow by gravity without power and to prevent siltation, the elevation angle of the water collection tunnel is 5‰ to 8‰. Construction is carried out uphill at this elevation angle (slope direction pointing towards the main clear water chamber or drainage chamber). This slope is an optimized balance value between hydraulic calculations and equipment transportation requirements.

[0044] The minimum vertical distance between the tunnel roof and the burnt rock zone floor is ≥20m. The intact rock strata serve as a safety barrier against water and pressure, ensuring that the tunnel itself is in a safe harbor and fundamentally avoiding the threat of direct water inrush.

[0045] The minimum horizontal distance between the side of the roadway adjacent to the igneous rock mass and the boundary of the igneous rock zone determined by S1 on the horizontal projection is ≥20m, in order to avoid the risk of lateral runoff or failure of the water-resistant coal and rock pillar.

[0046] Step 4: For the water collection tunnel, set up a water collection channel on it with a fixed slope, and the bottom slope of the water collection channel is consistent with the slope of the water collection tunnel. The bottom of the water collection channels is connected to the external clear water reservoir; The minimum cross-sectional dimensions of the water collection channel are: bottom width ≥ 0.4m and depth ≥ 0.4m.

[0047] As a further preferred option, the water collection channel meets the following conditions: The water collection channel is fixedly located on the upper side of the water collection tunnel (near the tempered rock zone), close to the base of the tunnel wall. Its axis is strictly parallel to the tunnel waistline (with consistent slope) to ensure smooth gravity flow of water.

[0048] This embodiment of the water collection channel is a permanent or semi-permanent engineering facility that simultaneously serves three major functions: water collection, flow diversion, and flow monitoring. Its design must ensure the smooth reception of concentrated water from the borehole opening pipes and visually reflect the flow status at each outlet point, providing data for drainage system operation and hydrological effect assessment.

[0049] Step 5: The water-rich area above the strong water-conducting belt is the main drainage area, and the boundary areas at both ends of the intercepting curtain are the bypass control area. Within the main drainage area, multiple main drainage area boreholes are set along the length of the water collection tunnel; Multiple bypass control zone boreholes were set up within the bypass control zone; All boreholes in the main dredging area and the bypass control area are inclined boreholes, and their final borehole trajectories completely cover the cross-section of the strong water-conducting zone in space. All borehole outlet pipes of the main dredging area and the bypass control area are connected to the water collection channel, thereby achieving integrated prevention and control of water hazards to the burnt rock in the target area.

[0050] This step, building upon the prior pre-emptive interception of dynamic recharge, is a crucial engineering phase involving the proactive drainage of groundwater static reserves and lateral flow around the cutoff curtain in the water-rich pyromorphic aquifer of the coal seam roof. Its core innovation lies in replacing traditional empirical, uniformly distributed borehole drainage with a focused, continuous drainage of the dynamic lateral flow around the cutoff curtain through a cluster of boreholes. This not only effectively releases static reserves but also proactively curbs potential lateral flow.

[0051] The spacing between two adjacent main evacuation zones is 60-100m; The inclination angle of all boreholes in the main evacuation area and the bypass control area is 15°-35°. The core of the method is to define the spatial range, thickness, and water-rich zoning of the strong water-conducting zone, with the two ends of the cutoff curtain as the key areas for bypass flow control, and the pre-set drilling site in the water collection tunnel as the construction platform.

[0052] Along the length of the water collection tunnel, above the core area of ​​the strong water-conducting zone, the main drainage area borehole groups are arranged at intervals of 60-100m, aiming to systematically reduce the static storage of the aquifer. The main drainage area boreholes can be closed in the later stage.

[0053] On the upstream and downstream outer sides of the intersection of the cutoff curtain and the metamorphic rock zone (i.e., the area where bypass flow may occur), borehole groups for bypass control zone are densely arranged at both ends of the water collection tunnel to form a continuous drainage channel and cut off the lateral bypass flow supply path.

[0054] The following is an optional drilling parameter design. The drilling here refers to the general term for the main drainage area drilling and the bypass control area drilling mentioned above. Drilling trajectory parameter design: perpendicular to the long axis of the strong water-conducting zone (i.e. pointing towards the maximum supply direction or perpendicular to the curtain end) to maximize the exposure of water-conducting fractures.

[0055] Drilling inclination angle (elevation angle): Based on the dynamic calculation of the vertical and horizontal distances between the water collection tunnel and the strong water-conducting zone, the borehole is designed to enter the target area with the optimal path, ranging from 15° to 35°.

[0056] Drilling depth and final stratum: The drilling depth must meet two quantitative standards: 1. The drilling length within the igneous zone should be able to control its full thickness (from the upper boundary to the lower boundary); 2. The final drilling point must penetrate at least 5m into the normal rock strata above the top plate of the igneous zone to ensure reliable sealing in non-aquifer sections and prevent communication with other aquifers.

[0057] Drilling structure design: The final hole diameter is not less than φ94mm to meet the needs of large-flow water discharge and possible subsequent deployment of monitoring equipment.

[0058] Drilling casing design: A two-stage casing structure is adopted. The surface casing (orifice casing) utilizes a pre-embedded pipe to penetrate into stable rock strata; the lower section is a filter pipe section, corresponding to the water-rich section of the strong water-conducting zone, with wire mesh wrapped around the filter pipe and filled with filter material; the upper part is the solid pipe and sealing section, which is permanently sealed with cement grout in non-target strata.

[0059] All groundwater from the pyromorphic aquifer drained by gravity from the inclined drainage boreholes is collected in a collection channel. Utilizing the natural slope of the collection channel, the water flows by gravity to a centralized clean water storage tank downstream (it cannot be a sewage storage tank, as this would increase water treatment costs). This clean water can then be directly used for underground production water, achieving water resource recycling.

[0060] Through the systematic construction of steps 2-6 above, a complete, non-powered underground drainage chain is formed, consisting of roadway water accumulation - diversion - channel gravity transport - gravity drainage from inclined boreholes.

[0061] An integrated monitoring system for the prevention and control of water hazards in calcined rocks includes a flow monitoring module, a water level monitoring module, a water pressure monitoring module, and an early warning module; The flow monitoring module includes flow sensors that are installed one-to-one in each borehole of the main evacuation area and the borehole of the bypass control area; The flow monitoring module is used to monitor the real-time flow rate of each borehole and transmit the flow rate data to the early warning module; The water level monitoring module includes water level sensors installed in the main dredging area and the bypass control area, respectively; The water level monitoring module is used to monitor the real-time water level in the main evacuation area and the bypass control area and transmit the water level data to the early warning module; The water pressure monitoring module includes pressure sensors that are installed one-to-one in each borehole of the main dredging area and the borehole of the bypass control area; The water pressure monitoring module is used to monitor the real-time water pressure of each borehole and transmit the water pressure data to the early warning module; The early warning module is used for: Receive flow, water level, and water pressure data transmitted from the flow monitoring module, water level monitoring module, and water pressure monitoring module; Set flow rate threshold, water level threshold, and water pressure threshold; An alarm will be triggered if any data exceeds the threshold.

[0062] This step is the final verification and dynamic management of the water control effect of the entire process from S1 to S6. Its core innovation lies in the establishment of a dynamic safety assurance system that is driven by real-time monitoring data, judged by quantitative safety thresholds, and controlled by the coordinated regulation of mining activities. This system enables intelligent control of the entire process of water hazard prevention and control from "project completion" to "sustainable effect, controllable risk, and coordinated production".

[0063] It is constructed through a point-line-surface three-dimensional monitoring system.

[0064] Point monitoring: Monitor the real-time flow rate (Q) and water pressure (P) of each drainage borehole, and calculate its attenuation curve and unit inflow (q).

[0065] Line monitoring: Focus on monitoring the water level difference between the upstream and downstream of the curtain cutoff wall to verify its long-term effectiveness; monitor the water level dynamics along the water collection tunnel and in the observation wells of the bypass control area.

[0066] Surface monitoring: Draw isobaric (pressure) maps of the aquifers in the pyromorphic rocks of the entire mining area to visually demonstrate the shape, range, and stability of the drainage funnels.

[0067] As an optional implementation method, this embodiment further provides a graded early warning standard: Warning status (requires optimization and adjustment): When the stable flow rate of any main drainage area borehole is >5 m³ / h, or the stable flow rate of any bypass control area is >15 m³ / h, or the water level shows a rising trend, the system will issue a warning. The cause needs to be analyzed and optimization measures such as borehole repair need to be prepared.

[0068] Safe condition (mining permitted): The following conditions must be met simultaneously: a. The borehole flow rate in all main evacuation areas is ≤5 m³ / h and the daily drop variation is <5%.

[0069] b. The borehole flow rate in all bypass control zones is ≤15 m³ / h and the daily drop variation is <3%.

[0070] Only when this state is reached can it be considered that the aquifer is in a safe and controllable low-pressure state.

[0071] By rigidly linking water condition monitoring results with mining and production plans, proactive safety assurance can be achieved.

[0072] Only after the aforementioned "safety status" has been assessed and met can a mining permit be issued for the underlying or adjacent working faces. During mining operations, all drainage boreholes must maintain continuous drainage to preserve the low-pressure state of the aquifer. The mining face must be equipped with effective drainage capacity. The monitoring system operates continuously throughout the mining process. If the data exceeds the "safety status" threshold, an early warning will be immediately activated, and measures such as adjusting the drainage volume, increasing monitoring frequency, or temporarily restricting mining can be taken as needed, forming a dynamic management closed loop of "monitoring-assessment-control-remonitoring" to ensure safety throughout the entire cycle.

[0073] The following is a more specific example: In a coal mine in northern Shaanxi, the main coal seam (4-2 coal seam) is locally shallowly buried. The overlying Jurassic Yan'an Formation strata have formed a large area of ​​transmuted rock due to spontaneous combustion of ancient coal seams. This transmuted rock mass is extremely fragmented, with well-developed pores, and receives strong lateral recharge from the overlying Quaternary loose aquifer, forming a highly water-conducting transmuted rock zone. This zone directly threatens the safe mining of the underlying coal seam. Traditional surface vertical borehole drainage methods, due to their low efficiency, high cost, and inability to control the recharge source, have failed to effectively solve the problem, resulting in the long-term inability to safely recover coal resources in this area.

[0074] To address the aforementioned challenges, the method described in this embodiment has been systematically applied in the mine.

[0075] First, a high-precision gradient magnetic method was used to delineate the magnetic anomaly zone with ΔT > 120 nT, clarifying the planar distribution range of the sintered rock to be approximately 0.35 km², with the top plate buried at a depth of 30-80 m. Subsequently, ground transient electromagnetic scanning (TEM) was conducted within the magnetic anomaly zone, delineating a continuous low-resistivity anomaly zone of approximately 0.18 km² with resistivity < 15 Ω·m, which was interpreted as a water-rich area.

[0076] Verification boreholes (ZK1, ZK2, and ZK3) were drilled at three low-resistivity anomaly centers. Core sampling revealed extremely fractured rock masses, with RQD values ​​generally below 20%. Pumping test results showed: ZK1 borehole q = 1.5 L / (s·m), K = 65 m / d; ZK2 borehole q = 1.8 L / (s·m), K = 80 m / d; ZK3 borehole q = 1.2 L / (s·m), K = 55 m / d. All borehole parameters met the "strong water conduction point" threshold (q ≥ 1.0, K ≥ 50).

[0077] Based on the combined results of magnetics, TEM, and drilling, and through spatial interpolation, a highly hydroconductive metamorphic rock zone with a length of approximately 650m, a width of 80-150m, and an average thickness of approximately 25m was finally delineated, serving as the geological basis for all subsequent engineering designs.

[0078] Advanced partial curtain wall construction: Based on the upstream boundary of the delineated strong water-conducting zone and the direction of groundwater flow in the loose layer (SW→NE), a straight underground continuous wall was designed and constructed approximately 80m outside its upstream side boundary (located on top of the unburned bedrock).

[0079] The cutoff wall axis is perpendicular to the runoff direction, with a length of 340m (the mining area is 240m long, with each end extending 50m outwards), a wall thickness of 0.8m, a depth of 58-62m (embedded in bedrock to a depth of 5.5-6.0m), and the top of the wall is 2.5m above the water level.

[0080] After the completion of the cutoff wall, the water level in the downstream (burnt rock side) observation well dropped by about 1.8m in three months, while the upstream water level remained basically stable, which preliminarily verified the wall's effective interception effect on lateral recharge.

[0081] Construction of water collection tunnel: The water collection tunnel is located in the underlying stable fine sandstone layer, about 25m below the bottom plate of the strong water-conducting zone (meeting the vertical distance ≥ 20m) and about 30m horizontally (meeting the horizontal distance ≥ 20m).

[0082] A water collection tunnel with a length of 280m, a net width of 4.2m, a net height of 3.5m, and a slope of 7‰ was constructed. High-strength anchor mesh shotcrete + anchor cable combined support was adopted. A drilling site was set up every 50m, and φ133mm orifice pipes were pre-buried and high-pressure gate valves were installed.

[0083] A concrete collection channel with a cross-section of 0.4m × 0.4m and a slope of 7‰ was constructed on the water collection tunnel. A Parshall flume was installed every 50m and connected to an automatic monitoring system.

[0084] Main drainage holes: Four sets (a total of eight) of inclined boreholes are arranged along the roadway, with a spacing of about 70m and an inclination angle of 25°-30°. The final boreholes penetrate more than 5m into the normal rock strata above the top of the metamorphic rock zone, accurately revealing the highly water-conducting section.

[0085] Bypass control boreholes: At both ends of the tunnel, four inclined boreholes were drilled at the curtain wall head to form a control barrier. All boreholes were equipped with standard borehole control devices, and the outlet pipes were uniformly connected to the water collection channel.

[0086] The water collection channel connects to two-stage sedimentation tanks and a filtration device. The treated clean water flows by gravity into a 600m³ underground clean water tank, and is then supplied to the underground mining face for dust control, equipment cooling, and other purposes through dedicated pipelines, achieving closed-loop recycling of water resources. During operation, the average daily water recovery and reuse volume is approximately 450m³, with a recycling rate exceeding 75%.

[0087] In the initial stage of drainage, the maximum flow rate of a single borehole reached 25 m³ / h. After three months of continuous decline, the flow rate of all boreholes gradually decreased and tended to stabilize.

[0088] When the monitoring data meets the following conditions: 1. The flow rate of the main dredging orifice is <5 m³ / h and the daily variation is <5%; 2. The flow rate of the bypass control orifice is <12 m³ / h and the daily variation is <2%; 3. The water level in the entire area drops below the safety level and forms a stable funnel, the system determines that it has reached a "safe state".

[0089] Under safe conditions (mining permitted), the water level / pressure of the sintered rock aquifer has dropped below the design safe mining standard, and the water pressure / level is stable. The flow rate of all main drainage boreholes is ≤5 m³ / h with a daily drawdown variation of <5%. The flow rate of all bypass control boreholes is ≤15 m³ / h with a daily drawdown variation of <3%.

[0090] Based on the "safe condition" assessment, the mine initiated safe mining of the working face beneath the strong water-conducting zone (mining length 200m, less than the controlled roadway length). During mining, the drainage system operated continuously, and monitoring data remained stable, ensuring safe production throughout the entire mining cycle.

[0091] This embodiment of the integrated prevention and control method for igneous rock water hazards proposes a combination of blocking and drainage, along with proactive prevention. It breaks through the traditional mindset of relying solely on drainage or full-section curtain interception for coal seam roof water hazards, establishing a new proactive and comprehensive prevention and control concept that combines cutting off dynamic recharge, reducing static storage capacity, and intercepting local bypass flow. It scientifically solves the problems of geophysical ambiguity and drilling limitations, achieving for the first time a precise quantitative delineation of highly conductive igneous rock zones from a two-dimensional to a three-dimensional water-rich structure. It constructs a non-powered underground drainage link: gravity drainage from inclined boreholes – water collection in roadways – gravity-fed water collection channels. This reduces the difficulty of drainage when controlling igneous rock water hazards. The use of a non-powered underground drainage link with gravity-fed water collection channels further reduces costs. The collected clean water flows into an external clean water tank for reuse, reducing resource waste and making it suitable for large-scale application and promotion in the field of coal mine water hazard prevention and control.

Claims

1. A method for integrated prevention and control of water hazards in burnt rock, characterized in that, Includes the following steps: Step 1: For the target area to be treated, delineate the planar distribution range of the pyrophoric rock in the target area, and then measure the burial depth of the top and bottom plates of the pyrophoric rock. Identify potential water-rich areas of the sintered rocks within the delineated planar distribution area; Pumping tests were conducted in all water-rich areas of the sintered rock to identify the corresponding strong water-conducting zones within these areas. Step 2: Set up a water-cutting curtain at the upstream boundary of the strong water-conducting zone; Step 3: Set up a water collection roadway in the normal coal seam at the bottom of the strong water-conducting zone; Step 4: For the water collection tunnel, a water collection channel is set up on it with a fixed slope, and the bottom slope of the water collection channel is consistent with the slope of the water collection tunnel. The bottom of each of the aforementioned water collection channels is connected to an external clear water reservoir; Step 5: The water-rich area above the strong water-conducting belt is the main drainage area, and the boundary areas at both ends of the intercepting curtain are the bypass control area. Within the main drainage area, multiple main drainage area boreholes are set along the length of the water collection tunnel; Multiple bypass control zone boreholes were set up within the bypass control zone; All the boreholes in the main dredging area and the bypass control area are inclined boreholes, and their final borehole trajectories completely cover the cross-section of the strong water-conducting zone in space. All the borehole outlet pipes of the main dredging area and the bypass control area are connected to the water collection channel, thereby realizing the integrated prevention and control of water hazards to the burnt rock in the target area.

2. The integrated prevention and control method for water hazards in ignited rock as described in claim 1, characterized in that, Step 1 includes the following sub-steps: Step 11, set the magnetic gradient threshold; A high-precision ground-based gradient magnetic method was used to conduct magnetic gradient tests on the target area. The continuous region where the magnetic gradient ΔT exceeds the magnetic gradient threshold is considered as the potential range of the sintered rock. Measure the burial depth of the top and bottom plates of the pyrophoric rock; Step 12, set the resistivity threshold; Resistivity testing of the potential range of sintered rock was conducted using the ground transient electromagnetic method. The continuous region with resistivity below the resistivity threshold is defined as the water-rich area of ​​the sintered rock; Step 13: Set the inflow threshold and permeability coefficient threshold; Multiple boreholes were drilled in the water-rich area of ​​the sintered rock, and pumping tests were conducted on each borehole to obtain the unit flow rate and permeability coefficient at each borehole point. The borehole locations that simultaneously satisfy the conditions of unit water inflow greater than the water inflow threshold and permeability coefficient greater than the permeability threshold are defined as strong water-conducting points, and multiple strong water-conducting points are obtained. Step 14: Based on multiple strong water-conducting points, perform spatial interpolation on the water-rich area of ​​the sintered rock to obtain multiple similar points with similar geophysical response characteristics to the strong water-conducting points; By sequentially connecting multiple similar points and multiple strong water-conducting points, a strong water-conducting zone is formed.

3. The integrated prevention and control method for water hazards in burnt rock as described in claim 2, characterized in that, In step 2, a water-cutting curtain is set up 50-100m outside the upstream boundary of the strong water-conducting zone; The axis of the cutoff curtain is perpendicular to the strong water-conducting zone of the sintered rock; The root of the cutoff curtain is embedded in the stable water-resistant layer or intact bedrock at the bottom of the loose layer of the target area, and the depth is not less than 5m. The top elevation of the cutoff curtain is more than 2 meters higher than the loose groundwater layer of the target area and lower than the ground surface; The height of the cutoff curtain is no more than 100m, and the thickness is 0.5-1m.

4. The integrated prevention and control method for water hazards in burnt rock as described in claim 3, characterized in that, The vertical distance between the water collection tunnel and the bottom plate of the pyromorphic rock zone mentioned in step 3 is ≥20m; The elevation angle of the water collection tunnel is 5‰ to 8‰.

5. The integrated prevention and control method for water hazards in ignited rock as described in claim 4, characterized in that, The minimum cross-sectional dimensions of the water collection channel mentioned in step 4 are: bottom width ≥ 0.4m and depth ≥ 0.4m.

6. The integrated prevention and control method for water hazards in ignited rock as described in claim 5, characterized in that, In step 5, the spacing between two adjacent main evacuation zone boreholes is 60-100m; The inclination angle of all boreholes in the main evacuation area and the bypass control area is 15°-35°.

7. The integrated prevention and control method for water hazards in burnt rock as described in claim 2, characterized in that, In step 13, the inflow threshold is 1.0 L / (s·m); The permeability threshold is 50 m / d.

8. A monitoring system for the integrated prevention and control of water hazards in burnt rock, characterized in that, It includes a flow monitoring module, a water level monitoring module, a water pressure monitoring module, and an early warning module; The flow monitoring module includes flow sensors that are installed one-to-one in each borehole of the main dredging area and the borehole of the bypass control area; The flow monitoring module is used to monitor the real-time flow of each borehole and transmit the flow data to the early warning module; The water level monitoring module includes water level sensors respectively installed in the main dredging area and the bypass control area; The water level monitoring module is used to monitor the real-time water level of the main dredging area and the bypass control area and transmit the water level data to the early warning module; The water pressure monitoring module includes pressure sensors that are installed one-to-one in each borehole of the main dredging area and the borehole of the bypass control area; The water pressure monitoring module is used to monitor the real-time water pressure of each borehole and transmit the water pressure data to the early warning module; The aforementioned early warning module is used for: Receive flow, water level, and water pressure data transmitted from the flow monitoring module, water level monitoring module, and water pressure monitoring module; Set flow rate threshold, water level threshold, and water pressure threshold; An alarm will be triggered if any data exceeds the threshold.

9. The integrated prevention and control effect monitoring system for water hazards in burnt rock as described in claim 8, characterized in that, The flow thresholds include the borehole flow threshold for the main evacuation zone and the borehole flow threshold for the bypass control zone; The borehole flow rate threshold for the main slack disposal area is 5 m³ / h; The borehole flow rate threshold for the bypass control zone is 15 m³ / h.

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