Water conservation and disaster reduction methods for calcification-induced diagenesis in Quaternary loose layers

Abstract

The present invention belongs to the field of coal mine water conservation and disaster reduction control, specifically a method for water conservation and disaster reduction of calcified induced diagenesis in the Quaternary loose layer; according to the impact range of underground coal mining on the Quaternary loose layer, the calcified water solution recharge drilling holes and the effect observation drilling holes are reasonably arranged; according to the ion composition and content of the water body stored in the Quaternary loose layer, a reagent aqueous solution of appropriate concentration is prepared; the calcium carbonate precipitation generated by the chemical reaction of groundwater and the calcified water solution is used to reinforce the loose sand / soil particles, promote the diagenesis of the sand / soil body in the corresponding area, and finally form a whole with a certain bearing capacity, prevent the large-scale transmission of the loose layer load, and prevent the occurrence of composite fractures in the key layer, thereby achieving the purpose of groundwater protection and geological disaster prevention and control. The present invention can provide guarantees for water conservation mining and strong mine pressure control in mining areas with thick loose layers and thin bedrock. Its implementation method is simple, safe, environmentally friendly, and highly reliable.

Description

Technical Field

[0001] The present invention relates to a method for groundwater protection and prevention and control of mining-induced geological disasters, and in particular to a method for water conservation and disaster reduction in the field of prevention and control of mining-induced geological disasters such as overall stratum cutting, groundwater leakage, and manifestation of strong underground mine pressure caused by underground coal mining. Background Art

[0002] Coal mining often causes widespread collapse of overburden strata, leading to groundwater loss, significant surface subsidence, and other mining-related damage. Especially in conditions where the Quaternary loose sand / soil layer is thick and the overlying bedrock is relatively thin, the load transfer effect of the loose strata can easily lead to compound fractures in key overburden strata, directly causing the entire overburden to shear off, leading to mining-related geological hazards such as aquifer damage, groundwater loss, surface step collapse, and underground support collapse. Therefore, scientifically reducing the load transfer level of the Quaternary loose strata is crucial for effectively preventing and controlling the occurrence of these problems. Extensive research has shown that if measures are taken to artificially reinforce the Quaternary loose strata and induce the critical load transfer area within it to form a single entity (or local diagenesis), the "diagenetic body" can function as a load-bearing structure, blocking the transmission of overburden loads; thus, the associated geological hazards can be effectively controlled.

[0003] At present, pouring cement, chemical slurry and other solidifying materials are mature technical means for the reinforcement of loose sand / soil, but the large-scale use of these materials has disadvantages such as environmental pollution and high cost. Many studies and engineering practices in the early stage have found that chemical precipitation of calcium carbonate has a similar coagulation effect as the above-mentioned reinforcement slurry. It can aggregate loose sand / soil particles together through the adsorption, growth and scaling process of calcium carbonate crystals, and form a carrier with certain mechanical strength. The microbial induced calcium carbonate deposition (MICP) reinforcement technology, which is currently widely studied at home and abroad, is a typical representative of them. Considering that the Quaternary loose layer is usually hosted by a certain amount of groundwater (generally phreatic aquifers), these groundwaters generally contain a lot of Ca 2+ 、HCO3 - If we can adopt the strategy of inducing CaCO3 precipitation by artificially injecting an aqueous solution of reagents that react with groundwater to form calcium carbonate precipitates, we can leverage their adsorption-consolidation effect to effectively promote the consolidation and diagenesis of loose sand / soil. To this end, it is necessary to develop specialized water conservation and disaster reduction methods for induced diagenesis of loose sand / soil layers based on the migration and load transfer mechanisms of Quaternary loose layers caused by coal mining. Summary of the Invention

[0004] Purpose of the invention: In order to overcome the deficiencies in the prior art, the present invention provides a method for water conservation and disaster reduction through calcification-induced diagenesis of the Quaternary loose layer. According to the impact range of underground coal mining on the Quaternary loose layer, the calcified water solution recharge boreholes and effect observation boreholes for inducing calcium carbonate precipitation are rationally arranged; according to the ion composition and content of the water body stored in the Quaternary loose layer, a reagent aqueous solution of appropriate concentration is prepared; the calcium carbonate precipitation generated by the chemical reaction between groundwater and the calcified water solution is used to reinforce the loose sand / soil particles, promote the diagenesis of the sand / soil in the corresponding area, and ultimately form a whole with a certain bearing capacity, preventing the large-scale transfer of the loose layer load and preventing the occurrence of composite fractures in the key layer, thereby achieving the purpose of groundwater protection and geological disaster prevention and control.

[0005] Technical solution: To achieve the above-mentioned purpose, the water conservation and disaster reduction method of the Quaternary loose layer calcification induced diagenesis of the present invention comprises the following steps: before coal seam mining, whether the key layer of the overburden in the mining area has composite fracture is calculated based on the key layer theory to determine whether the corresponding area needs to construct a calcified water solution re-injection borehole; if the key layer has composite fracture, calcified water solution re-injection boreholes and effect observation boreholes are constructed on the corresponding surface within a certain range within and outside the mining area; a suitable calcified water solution is prepared according to the ionic composition and content of the water stored in the Quaternary loose layer and injected from the calcified water solution re-injection borehole; the calcium carbonate precipitate generated by the chemical reaction of the calcified water solution re-injected into the loose layer with groundwater is used to consolidate and induce diagenesis of the loose sand / soil particles, so that they form a whole with a certain bearing capacity, thereby preventing the large-scale transfer of the loose layer load and preventing the key layer from composite fracture, thereby achieving the purpose of groundwater protection and geological disaster prevention and control.

[0006] The specific steps are as follows:

[0007] a. Before coal seam mining, determine the mining area where compound fracture occurs in the key overburden strata;

[0008] b. For mining areas where composite fractures occur in key overburden strata, determine the horizontal and vertical extent of the corresponding Quaternary loose strata that require induced consolidation and diagenesis;

[0009] c. Construction of calcified water solution recharge drilling in the plane range corresponding to the surface where the Quaternary loose layer needs to be induced to consolidate and diagenesis;

[0010] d. Prepare a calcified water solution based on the ionic composition and content of the water stored in the Quaternary loose layer, and inject the calcified water solution into the loose layer through the recharge borehole;

[0011] e. During the recharging process of the calcified aqueous solution, calcium carbonate precipitates are produced and continuously adsorbed on the surface of loose sand / soil particles, effectively condensing and consolidating the loose sand / soil particles, gradually forming a load-bearing whole with a certain mechanical strength, thereby blocking the transmission of overlying loads.

[0012] Preferably, in step b, the planar range of the Quaternary loose layer that needs to be induced to consolidate and diagenesis is the coal mining area where compound fracture occurs in the overburden key layer plus the D+h range extending outward from the boundaries of the mining area, wherein D is the bedrock influence range caused by mining in the mining area, and h is the thickness of the Quaternary loose layer.

[0013] Preferably, in step b, the vertical range in which the Quaternary loose layer needs to be induced to consolidate and diagenesis is (0.5-0.8) h upward from the top interface of the bedrock.

[0014] Preferably, in step c, the calcified water solution recharge borehole is a vertical borehole constructed from the surface, with a final hole depth of h, and a casing is arranged in the calcified water solution recharge borehole, and the casing in the range of (0.5-0.8) h above the bottom of the hole is a flower pipe.

[0015] Preferably, in step c, the calcified water solution recharge boreholes are arranged in an array in strike and dip with spacing set within the plane range where the Quaternary loose layer needs to be induced to consolidate and diagenesis.

[0016] Preferably, in step c, the distance between the outermost calcified aqueous solution recharge borehole and the plane boundary line of the Quaternary loose layer that needs to be induced to consolidate and diagenesis is less than 150m.

[0017] Preferably, in step c, an effect observation borehole is also constructed.

[0018] Preferably, in step c, the effect observation borehole is a vertical borehole constructed from the ground surface, and the effect observation borehole is arranged at the four corners of the plane range boundary line where the Quaternary loose layer needs to be induced to consolidate and diagenesis, and the final hole depth is h; the hole wall of the effect observation borehole is closed with casing at a depth of 0.5h below the ground surface, and other sections are protected with flower pipes.

[0019] Preferably, in step d, the injection pressure should be greater than the submerged water head pressure of the loose layer, but not exceed the water head pressure corresponding to the thickness of the loose layer.

[0020] Preferably, in step d, if the Quaternary loose layer water is rich in Ca 2+ , then the calcified aqueous solution is made of CO3 2- Aqueous solution prepared by mixing chemical reagents with deionized water, CO3 2- The concentration can be compared with the groundwater Ca 2+ Sufficient precipitation reaction occurs to set.

[0021] Preferably, in step d, if the Quaternary loose layer water Ca 2+ If the concentration is low or there is basically no water in the loose layer, prepare the Ca 2+ and CO3 2-At the same time, two water pipes are set in the calcified water solution recharging borehole to the bottom of the hole, which are used to inject the calcium-containing 2+ and CO3 2- The calcified water solution enters the Quaternary loose layer.

[0022] Preferably, the method further comprises step f. testing the calcification diagenesis effect through effect monitoring drilling.

[0023] Preferably, in step f, if the water level in the effect monitoring hole cannot be restored to the original groundwater level, the recharge volume of the calcified aqueous solution is reduced until no water accumulates in the effect monitoring borehole after pumping, and then the recharge of the calcified aqueous solution is stopped.

[0024] Preferably, the method further includes step g. constructing a core drilling hole for the diagenetic effect of the Quaternary loose layer within the plane range where the consolidation and diagenesis of the Quaternary loose layer needs to be induced, coring the drilling section from the drilling depth of less than 0.5h to the top interface of the bedrock, observing the integrity and mechanical strength of the core, and if the uniaxial compressive strength of the core is lower than the set value, continuing to inject the calcified water solution; until the compressive strength reaches the set value.

[0025] Preferably, in step g, a Quaternary loose layer diagenetic effect core drilling hole is constructed near the effect monitoring hole.

[0026] Beneficial Effects: Based on the migration and load transfer mechanism of the Quaternary loose stratum caused by coal mining, the present invention fully considers the ionic composition and content of the water stored in the Quaternary loose stratum, and specifically carries out the layout of calcified water solution recharge drilling, effect observation drilling, and the preparation of calcified water solution. Calcium carbonate precipitates generated by the chemical reaction of the calcified water solution with groundwater are used to consolidate and shape the loose sand / soil particles in the Quaternary loose stratum, thereby forming a calcified diagenetic body of a certain thickness within the range of the Quaternary loose stratum affected by mining. This effectively blocks the downward transmission of large amounts of overlying loads and avoids compound fractures in key overburden layers. This not only significantly reduces the development height of water-conducting fissures and prevents shallow groundwater loss, but also reduces the intensity of mine pressure at the underground mining face, achieving the dual purposes of water conservation and disaster reduction. Its use method is scientific and reliable, safe, environmentally friendly, and highly practical.

[0027] Compared with the existing technology, it has the following advantages:

[0028] (1) Calcium carbonate precipitates generated by the chemical reaction between calcified aqueous solution and the water storage of the Quaternary loose layer are used to cement and solidify the loose sand / soil particles. The calcium carbonate precipitates are easily adsorbed on the surface of the sand / soil particles, which neither pollutes the groundwater nor is easily eroded by groundwater flow. The loose layer forms a bearing entity with a certain mechanical strength, effectively blocking the transmission of a large amount of overlying loads, avoiding compound fracture of the key overburden layer, and achieving the dual effects of water conservation and disaster reduction;

[0029] (2) The selected calcified aqueous solution can not only chemically react with groundwater to generate calcium carbonate precipitates and consolidate loose sand / soil particles, but also regulate the pH and hardness of groundwater to a certain extent, effectively improving the groundwater quality;

[0030] (3) The determination of water conservation and disaster reduction methods for the calcification-induced diagenesis of the Quaternary loose layer that can adapt to different mining conditions can provide guarantees for water conservation mining and strong mine pressure control in mining areas with thick loose layers and thin bedrock. The implementation method is simple, safe, environmentally friendly and highly reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a plan view of the arrangement of the calcified water solution recharge drilling holes and the effect observation drilling holes of the present invention;

[0032] Figure 2 The present invention Figure 1 AA cross-section diagram.

[0033] In the figure: 1-calcified water solution recharge borehole, 2-effect observation borehole, 3-diagenetic effect core drilling hole. DETAILED DESCRIPTION

[0034] The embodiments of the present invention are further described below with reference to the accompanying drawings:

[0035] like Figure 1-2 As shown, the water conservation and disaster reduction method of calcification-induced diagenesis of the Quaternary loose layer of the present invention comprises the following steps: before coal seam mining, whether a composite fracture occurs in the key layer of the overburden in the mining area is calculated based on the key layer theory to determine whether a calcified water solution re-injection borehole needs to be constructed in the corresponding area; if a composite fracture occurs in the key layer, a calcified water solution re-injection borehole 1 and an effect observation borehole 2 are constructed on the corresponding surface within a certain range within and outside the mining area; a suitable calcified water solution is prepared according to the ionic composition and content of the water stored in the Quaternary loose layer and injected from the calcified water solution re-injection borehole 1; the calcium carbonate precipitate generated by the chemical reaction of the calcified water solution re-injected into the loose layer with groundwater is used to consolidate and induce diagenesis of the loose sand / soil particles, so that they form a whole with a certain bearing capacity, thereby preventing a large amount of load transfer in the loose layer and preventing composite fracture in the key layer, thereby achieving the purpose of groundwater protection and geological disaster prevention and control.

[0036] The specific steps are as follows:

[0037] a. Before coal seam mining, the key layer location and fracture characteristics are determined by drilling columns of geological holes at different locations in the mining area based on key layer theory. This determines the mining area where compound fractures of the overburden key layer occur. For mining areas where compound fractures occur in key layers, a calcified water solution re-injection borehole 1 and a calcified water solution re-injection borehole 2 are arranged. For mining areas where layer-by-layer fractures occur in key layers, no relevant drilling is required.

[0038] b. For mining areas where composite fractures occur in key overburden strata, determine the horizontal and vertical extent of the corresponding Quaternary loose strata that require induced consolidation and diagenesis;

[0039] The plane range of the Quaternary loose layer that needs to be induced to consolidate and diagenesis is the coal mining area (working face mining range) where the overburden key layer undergoes composite fracture plus the D+h range extending outward from the boundaries of the coal mining area, where D is the bedrock impact range caused by mining in the coal mining area, and h is the thickness of the Quaternary loose layer; when the mining coal seam burial depth H≤500m, When H>500m,

[0040] The vertical range of the Quaternary loose layer that needs to be induced to consolidate and diagenesis is (0.5-0.8) hours upward from the top interface of the bedrock;

[0041] c. Construction of drilling holes 1 for calcified aqueous solution recharge and observation of the effect of drilling holes 2 in the plane range corresponding to the surface where consolidation of the Quaternary loose layer is to be induced;

[0042] The calcified water solution recharge borehole 1 is a vertical borehole constructed from the surface, with a final hole depth of h. A PVC casing is laid in the calcified water solution recharge borehole 1, and the casing within the range of (0.5-0.8) h above the bottom of the hole is a floral pipe. The calcified water solution recharge borehole 1 starts at the center of the plane range where the Quaternary loose layer needs to be induced to consolidate and diagenesis, and is arranged in an array at intervals of 150-200 m in strike and dip within the plane range where the Quaternary loose layer needs to be induced to consolidate and diagenesis, and the outermost calcified water solution recharge borehole 1 is less than 150 m away from the boundary line of the plane range where the Quaternary loose layer needs to be induced to consolidate and diagenesis.

[0043] The effect observation borehole 2 is a vertical borehole constructed from the ground surface. The effect observation borehole 2 is arranged at the four corners of the plane boundary line of the Quaternary loose layer that needs to be induced to consolidate and diagenesis. The final hole depth is h. The borehole wall of the effect observation borehole 2 is sealed with a casing from a depth of 0.5h below the ground surface, and the other sections are protected with a flower pipe.

[0044] d. Prepare a suitable calcified water solution based on the ionic composition and content of the water stored in the Quaternary loose layer. Inject the calcified water solution into the loose layer through the recharge borehole 1. The injection pressure should be greater than the submerged water head pressure of the loose layer, but should not exceed the water head pressure corresponding to the thickness of the loose layer to ensure that the calcified water solution can be injected into the loose layer without outflow.

[0045] If the Quaternary loose layer water is rich in Ca 2+ , then the calcified aqueous solution is made of CO3 2- Aqueous solution prepared by mixing chemical reagents with deionized water, CO3 2-The concentration can be compared with the groundwater Ca 2+ If the Quaternary loose layer stores water Ca 2+ If the concentration is lower than 500mg / L or there is basically no water in the loose layer, prepare the Ca 2+ and CO3 2- At the same time, two water pipes are set in the calcified water solution recharging borehole 1 to the bottom of the hole, which are used to inject the calcium-containing 2+ and CO3 2- The calcified aqueous solution enters the Quaternary loose layer;

[0046] e. During the recharging process of the calcified aqueous solution, calcium carbonate precipitates are generated and continuously migrate and diffuse from the bottom of the calcified aqueous solution recharging borehole 1 to the periphery. During the diffusion process, they are continuously adsorbed on the surface of loose sand / soil particles, while also adsorbing other precipitates and wrapping them layer by layer. This effectively condenses and consolidates the loose sand / soil particles, gradually forming a load-bearing whole with a certain mechanical strength, thereby preventing the transmission of overlying loads;

[0047] f. Perform a pumping test on the effect monitoring borehole 2 at intervals of 1-2 weeks; if the water level in the effect monitoring hole 2 cannot be restored to the original groundwater level, reduce the amount of recharge of the calcified aqueous solution until the effect monitoring borehole 2 is no longer pumped and water accumulates, then stop recharge of the calcified aqueous solution;

[0048] g. Within the plane range where the Quaternary loose layer needs to be induced to consolidate and diagenesis, and near the effect monitoring hole 2, a Quaternary loose layer diagenetic effect coring borehole 3 is constructed, and the drilling section from the drilling depth of less than 0.5h to the top interface of the bedrock is cored to observe the integrity and mechanical strength of the coring. If the uniaxial compressive strength of the core is lower than 2-5MPa, it is necessary to continue the injection of calcified aqueous solution; thereafter, drilling and coring tests are carried out at intervals of 2-3 weeks until the compressive strength exceeds 2-5MPa. The construction position of the next diagenetic effect coring borehole 3 is near the construction position of the previous diagenetic effect coring borehole 3.

[0049] The present invention is not limited to the above-mentioned optimal implementation mode. Anyone can derive other various forms of methods under the inspiration of the present invention. However, any technical solution that is the same or similar to that of the present application falls within the scope of protection of the present invention.

Claims

1. A method for water conservation and disaster reduction in calcification-induced diagenesis of Quaternary loose layers, characterized by: The following steps are involved: a. Before coal seam mining, determine the mining area where compound fracture occurs in the key overburden strata; b. For mining areas where composite fractures occur in key overburden strata, determine the horizontal and vertical extent of the corresponding Quaternary loose strata that require induced consolidation and diagenesis; c. Construction of calcified water solution recharge drilling in the plane range corresponding to the surface where the Quaternary loose layer needs to be induced to consolidate and diagenesis; d. According to the ion composition and content of the Quaternary loose layer water, prepare a calcified water solution and inject it into the loose layer through the calcified water solution recharge borehole; if the Quaternary loose layer water is rich in Ca 2+ , then the calcified aqueous solution is made of CO3 2- Aqueous solution prepared by mixing chemical reagents with deionized water, CO3 2- The concentration can be compared with the groundwater Ca 2+ If the Quaternary loose layer stores water Ca 2+ If the concentration is low or there is basically no water in the loose layer, prepare the Ca 2+ and CO3 2- At the same time, two water pipes are set in the calcified water solution recharging borehole to the bottom of the hole, which are used to inject the calcium-containing 2+ and CO3 2- The calcified aqueous solution enters the Quaternary loose layer; e. During the recharging process of the calcified aqueous solution, calcium carbonate precipitates are produced and continuously adsorbed on the surface of loose sand / soil particles, effectively condensing and consolidating the loose sand / soil particles, gradually forming a load-bearing whole with a certain mechanical strength, thereby blocking the transmission of overlying loads; f. Test the calcification diagenesis effect through the effect monitoring borehole. If the water level in the effect monitoring hole cannot be restored to the original groundwater level, reduce the recharge rate of the calcification solution until the effect monitoring hole no longer accumulates water after pumping, and then stop the recharge of the calcification solution; g. Within the plane range where the Quaternary loose layer needs to be induced to consolidate and diagenesis, construct core drilling holes for the Quaternary loose layer diagenesis effect, and take cores from the drilling section with a depth of less than 0.5h to the top interface of the bedrock. Observe the integrity and mechanical strength of the cores. If the uniaxial compressive strength of the cores is lower than the set value, continue to inject the calcified water solution until the compressive strength reaches the set value.

2. The water conservation and disaster reduction method according to claim 1, characterized in that: In step b, the planar range of the Quaternary loose layer that needs to be induced to consolidate and diagenesis is the coal mining area where composite fracture occurs in the overburden key layer plus the D+h range extending outward from the boundaries of the mining area, where D is the bedrock influence range caused by mining in the mining area, and h is the thickness of the Quaternary loose layer.

3. The water conservation and disaster reduction method according to claim 1 or 2, characterized in that: In step b, the vertical range of the Quaternary loose layer that needs to be induced to consolidate and diagenesis is the range of (0.5-0.8) h upward from the top interface of the bedrock.

4. The water conservation and disaster reduction method according to claim 1, characterized in that: In step c, the calcified water solution recharge boreholes are arranged in an array in strike and dip with spacing set within the plane range where the Quaternary loose layer needs to be induced to consolidate and diagenesis, and the outermost calcified water solution recharge borehole is less than 150m away from the boundary line of the plane range where the Quaternary loose layer needs to be induced to consolidate and diagenesis.

5. The water conservation and disaster reduction method according to claim 1, characterized in that: In step c, the calcified water solution recharge borehole is a vertical borehole constructed from the surface, with a final hole depth of h. Casing is arranged in the calcified water solution recharge borehole, and the casing within the range of (0.5-0.8)h above the bottom of the hole is a flower pipe, and h is the thickness of the Quaternary loose layer.

6. The water conservation and disaster reduction method according to claim 1, characterized in that: In step c, an effect observation borehole is also constructed. The effect observation borehole is a vertical borehole constructed from the ground surface. The effect observation borehole is arranged at the four corners of the plane range boundary line where the Quaternary loose layer needs to be induced to consolidate and diagenesis, and the final hole depth is h; the hole wall of the effect observation borehole is closed with casing at a depth of 0.5h below the ground surface, and other sections are protected with flower pipes, and h is the thickness of the Quaternary loose layer.

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