A method for treating a goaf by constructing an artificial key layer using waste rock bulk grouting

Abstract

A method for treating goaf by constructing artificial key layer using waste rock granular grouting, comprising the following steps: carrying out geological and measurement investigation; drilling rock sample and carrying out physical and mechanical property test to determine physical and mechanical property parameters of rock sample; investigating blockiness of waste rock granular in goaf, finding out waste rock blockiness distribution rule and porosity in goaf; selecting waste rock granular sample in goaf, carrying out similar material simulation experiment, establishing physical model of artificial key layer, researching seepage rule of waste rock cementation filling, testing mechanical property of cementation filling body; carrying out finite element analysis on artificial key layer; analyzing mechanical characteristics and bearing mechanism of waste rock grouting cementation filling body and surrounding rock coupling body; constructing artificial key layer on site; carrying out waste rock granular cement grouting filling on goaf above artificial key layer; treating goaf below artificial key layer, carrying out residual ore recovery after treatment; carrying out waste rock granular cement grouting filling on goaf below artificial key layer.

Description

Technical Field

[0001] This invention belongs to the field of underground mining technology, and in particular relates to a method for constructing an artificial key layer by grouting waste rock to treat goaf areas. Background Technology

[0002] The overlying hard rock strata in the goaf are prone to fracturing and activity, frequently resulting in roof collapses impacting the working face, and the movement of the hard roof pushing down or crushing props. Roof disasters caused by the instability of the soft and fractured roof are also frequent. Roof instability can easily induce gravity-type rockbursts or mine tremors, and can easily cause safety problems such as pillar instability. Geological disasters on the mine roof pose a huge threat to mine production and the safety of surface structures.

[0003] The critical layer theory is a new theory developed by Academician Qian Minggao based on the masonry rock beam theory. The basic premise of the masonry rock beam theory is that as the mining face advances, the roof rock beams will periodically fracture. The fractured blocks rotate and compress each other, and the horizontal forces between the blocks and the frictional forces generated by their interactions form a beam-like masonry structure, i.e., a masonry beam. The lithology of each layer in coal-bearing strata differs, and each layer plays a different role in the rock mass activity. Some thin, weak layers act as load-bearing layers during activity, while thicker, harder layers act as load-bearing layers. These thicker, harder layers not only bear the weight of their own rock mass but also the weight of the overlying soft rock. These layers, which control all or part of the rock mass activity, are called critical layers. Based on the different fracture mechanisms, critical layers are divided into primary critical layers and subcritical layers. When a critical layer fractures, the subsidence and deformation of all the overlying rock layers are coordinated and consistent; that is, the fracture of a critical layer will cause the entire overlying rock layer to move as a whole, and the fracture of a critical layer will cause the overlying local rock layer to move as a whole.

[0004] The key stratum, as the primary load-bearing stratum, plays a crucial role in controlling the stability of the overlying strata. Failure of the key stratum, especially the main key stratum, will cause rock movement and mine pressure manifestation in the overlying strata, leading to surface subsidence and endangering surface features. Before failure, the key stratum bears the weight of the overlying strata in the form of a slab structure; after fracture, it exists as a masonry beam structure, its structural form reflecting the movement of the strata. Incoordination in movement between key strata leads to delamination within the rock mass. A stratum is considered a key stratum based on its thickness, strength, and load-bearing capacity. In coal-bearing strata mining, the key stratum theory is widely applied to controlling overlying rock movement, gas drainage, prevention of water inrush at the stope floor, mine pressure control in ultra-long fully mechanized longwall mining faces, and mine pressure control in longwall mining face roadways.

[0005] The critical layer theory has been less applied in non-coal mines, primarily in applications such as strengthening anchoring measures. In high-grade precious metal mines, artificial false bottoms are constructed by replacing high-grade pillars with reinforced concrete bottom structures in one or more stopes. In some extremely fractured stopes, for safety reasons, reinforced concrete false roofs or false bottoms are constructed to improve mining recovery rates or ensure the safety of individual stopes. Due to differences in construction purpose and protected objects, artificial false bottoms or roofs differ significantly from artificial critical layers.

[0006] Currently, many mines use the open-cut mining method, failing to leave pillars as designed or neglecting maintenance in the goaf. Roof collapses in the goaf cause instability in the surrounding rock and pillars. The detached ore and rock debris accumulates in the goaf, covering pillars and causing resource loss or difficulty in recovering residual ore. Significant rock movement occurs at the top of the goaf, leading to surface fissures or subsidence. Instability in the pillars endangers underground safety. Some non-coal mines, due to the need to manage goafs or recover residual ore, need to release ore from the original goaf, causing ore and rock movement and redistribution of ground stress. This necessitates measures to control rock movement, protect surface structures, and ensure the safety of underground production before operations commence.

[0007] The critical layer theory is widely applied to coal-bearing strata, while its application in non-coal mines, though less common, shows great promise. Studies have found that deformation of the overlying strata in goaf areas of metal mines still exhibits "three-zone" failure characteristics, such as... Figure 1 As shown, the distribution of the "horizontal three zones" and "vertical three zones," as well as the masonry beams, goaf, and overlying strata, can be observed. According to long-term monitoring data from the Dahongshan Iron Mine, the overlying strata in the goaf exhibit significant collapse zones, fissure zones, and bending deformation zones (Lu Yugen, 2019, Research on the Deformation Law of Overlying Rock Mass Induced by Large-Scale Deep Mining; Hu Xingbao, 2015, Key Technologies for Underground Mining of Metal Deposits). Therefore, the key stratum theory should be more widely applied in the management of goaf and strata control in non-coal mines, especially in soft rock stratabound deposits such as carbonaceous slate, which are gently dipping and have a very similar ore production state to coal mines, offering greater potential for the application of the key stratum theory.

[0008] For example, Chinese patent application number 202110830519.2 proposes a method to mitigate mine pressure in mining areas based on the principle of key layer reconstruction. Zhu Jianming et al. proposed an analysis of the thickness of key layers for artificial filling in goaf areas of small mines. For coal seams damaged by mining methods such as small mines, through field exploration, laboratory tests, and simulation calculations, combined with the distribution of goaf areas, they used drilling grouting to fill the goaf or voids with mechanically stable and low-cost materials, so that it can effectively combine with the surrounding coal body to jointly bear the mining pressure, reduce the mine pressure manifestation during the mining process, and achieve the mining requirements of normal coal seams. Yang Zhenhong et al. analyzed the basic failure forms of the mining roof and the mechanical process of anchor bolt support. Through mechanical model analysis of anchoring key layers, mutation cusp model analysis, and system defect model analysis, they proposed a method for anchoring the mining roof. The key layer theory provides a theoretical basis for the study of anchor bolt support for the roof.

[0009] However, the above applications of the key layer theory are all based on the objective premise that the key layer exists as the main bearing stratum, which is a positive application. Constructing an artificial key layer using the key layer theory when there is no original key layer is a negative application, but such negative applications are only found in a few cases in coal mines. Currently, there are no reported examples of artificial key layers being formed by grouting waste rock. Summary of the Invention

[0010] To address the problems of existing technologies, this invention provides a method for constructing an artificial key layer using waste rock grouting to manage goaf areas. Based on the key layer theory, this method uses waste rock grouting to construct an artificial key layer in non-coal mines to control the movement of overlying rock in goaf areas, ensuring the safety of goaf management. This invention expands the application scope of the key layer theory by being applied to non-coal mines. This invention achieves the reverse application of the key layer theory by constructing an artificial key layer. The filling aggregate used in this invention is waste rock granules, which can be sourced locally, significantly reducing production costs. Furthermore, the artificial key layer uses different filling parameters than the goaf areas above and below it, further saving significant cement material costs and achieving a greater cost advantage. This invention fully utilizes waste rock resources, eliminating the need to transport large amounts of waste rock generated during mining or large amounts of loose waste rock from goaf areas, reducing the environmental damage caused by mining production, and achieving green development in the management of goaf areas.

[0011] To achieve the above objectives, the present invention adopts the following technical solution: a method for constructing an artificial key layer using waste rock grouting to treat goaf areas, comprising the following steps:

[0012] Step 1: Determine the characteristics of the goaf, the number of overlying rock layers, the lithology of each layer, the thickness of each layer, and the total thickness of the overlying rock mass through geological and surveying investigations;

[0013] Step 2: Extract ore and rock samples through typical profile drilling, conduct physical and mechanical property tests on the ore and rock samples, and determine the physical and mechanical property parameters of the ore and rock samples;

[0014] Step 3: Investigate the size of the accumulated waste rock in the goaf, and determine the distribution pattern and porosity of the waste rock in the goaf;

[0015] Step 4: Select samples of ore and waste rock in the goaf area, conduct similar material simulation experiments in the laboratory, study the seepage law of waste rock with cementing material, concentration, flow rate and pressure as variables, establish a physical model of artificial key layer, study the seepage law of cemented waste rock backfill, and test the mechanical properties of cemented backfill.

[0016] Step 5: Use finite element software to simulate the artificial key layer, determine the mechanical characteristics of the artificial key layer, and combine the width of the goaf at the actual location of the proposed artificial key layer to determine the thickness and strength index of the artificial key layer.

[0017] Step Six: Analyze the mechanical characteristics and bearing mechanism of the coupled body of the waste rock grouting cemented backfill and the surrounding rock;

[0018] Step 7: Construct the artificial critical layer on-site. The curing time for the artificial critical layer will be determined by the preliminary mechanical tests.

[0019] Step 8: Fill the goaf above the artificial key layer with waste rock grouting.

[0020] Step 9: Treat the goaf area below the artificial key layer, and recover the residual ore after treatment;

[0021] Step 10: Fill the goaf area below the artificial key layer with cement grouting using waste rock.

[0022] In step one, the characteristics of the goaf include the goaf span, pillar length, pillar width, pillar height, and pillar integrity.

[0023] In step two, the physical and mechanical properties of the ore sample include ore density, compressive strength, tensile strength, elastic modulus, Poisson's ratio, cohesion, and internal friction angle.

[0024] In step two, it is also necessary to investigate the rock mass structural parameters, including the degree of rock mass fragmentation, surface characteristics of the structural surfaces, comprehensive structural grade SR and surface condition grade SCR. By using the quantified geological strength index GSI, the value of the empirical parameter mi of the rock mass is determined. The mechanical parameters of the rock mass are calculated by substituting the parameters of the Hoek-Brown empirical criterion into the formula.

[0025] In step three, the block size of the waste rock accumulated in the goaf is obtained by on-site measurement and sieving and grading of mixed samples. The block size distribution pattern is obtained based on on-site investigation, and the porosity is obtained by boiling water method.

[0026] In step four, the similar material simulation experiment includes selecting the granular material to be used for actual granular grouting and filling to form an artificial key layer for grouting and filling simulation experiments. In the experiment, different cement concentrations, different slurry-to-sand ratios, and different waste rock volume percentages need to be controlled for testing. After the sample is formed, the strength of the cemented body is tested until a conclusion is drawn. The similar material simulation experiment also includes sample material preparation and slurry preparation, specimen block preparation and curing, specimen block compressive strength testing, and test result analysis.

[0027] In step five, it is also necessary to analyze the geometric and mechanical characteristics of the upper and lower goaf filling bodies of the artificial key layer using finite element software, and obtain the load distribution of the artificial key layer and the upper and lower goaf filling bodies.

[0028] In step six, the analysis of the mechanical characteristics and bearing mechanism of the waste rock grouting cemented filling body and the surrounding rock coupling body also requires mechanical simulation by constructing a physical model of the artificial key layer in the laboratory before on-site construction, and analysis in combination with the current situation of the surrounding area, until the artificial key layer meets the actual strength requirements.

[0029] In step eight, the filling between the artificial key layer and the overlying rock layer is carried out by tailings cement filling or waste rock cement grouting filling. When connecting the top, a multiple construction scheme with controlled filling speed or adding a foaming agent is used for the top connection filling.

[0030] In step ten, the filling between the artificial key layer and the goaf floor is carried out by tailings cement filling or waste rock cement grouting. When connecting the roof, a multi-stage construction plan with controlled filling speed or adding a foaming agent is used for roof connection filling.

[0031] The beneficial effects of this invention are:

[0032] The artificial key layer constructed in this invention is the main bearing layer, which is an extension of the key layer theory in the field of non-coal mines, extending the application scope of the key layer theory and providing a new method for the treatment of goaf areas in non-coal mines.

[0033] This invention constructs an artificial critical layer by filling it with waste rock grout, thereby expanding the application scope of critical layer theory by replacing the traditional critical layer.

[0034] The artificial key layer of the present invention is formed by grouting of waste rock with a high ash-sand ratio. Its cemented filling body can bear the weight of the overlying rock strata and the filling body of the goaf, avoid the movement of the overlying rock strata, prevent the surface from collapsing, and thus protect the safety of surface structures and buildings.

[0035] The artificial key layer of this invention uses waste rock grouting with a low ash-sand ratio to fill the upper and lower goaf areas, which reflects the difference between the key layer and the filling of the upper and lower goaf areas. After the upper and lower goaf areas of the key layer are filled, they are connected to the overlying rock mass, which not only controls the movement of rocks, but also saves cement due to the low ash-sand ratio. This not only improves the economy, but also has the characteristics of being green and environmentally friendly.

[0036] This invention forms an artificial key layer by filling waste rock grout. For mines with high rates of roof collapse and waste rock filling in goaf treatment and residual ore recovery operations, it can effectively use the key layer theory to construct a key bearing layer, protect the upper rock strata, avoid the problem of upper rock strata movement caused by stress redistribution after secondary ore discharge, and carry out environmental reconstruction for residual ore recovery. It has the characteristics of strong practicality.

[0037] This invention makes full use of on-site resources, utilizing nearby mining production or on-site caving ore and rock as backfill aggregate, saving material costs for coarse aggregate, reducing waste rock transportation costs, lowering backfill costs, and achieving green mining. Attached Figure Description

[0038] Figure 1 This is a structural model diagram of a masonry beam;

[0039] Figure 2 A schematic diagram of the model distribution of the artificial key layer;

[0040] In the diagram, A—coal wall support zone, B—delamination zone, C—recompacted zone, I—collapse zone, II—fracture zone, III—bent lower layer zone, 1—lower goaf filling body, 2—artificial key layer, 3—upper goaf filling body, 4—overlying rock strata of the goaf, q—force of topsoil on bedrock. Detailed Implementation

[0041] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0042] A method for treating goaf areas by constructing an artificial key layer using waste rock grouting includes the following steps:

[0043] Step 1: Determine the characteristics of the goaf, the number of overlying rock layers, the lithology of each layer, the thickness of each layer, and the total thickness of the overlying rock mass through geological and surveying investigations; among which, the characteristics of the goaf include the goaf span, pillar length, pillar width, pillar height, and pillar integrity;

[0044] Step Two: Extract ore and rock samples through typical profile drilling, and conduct physical and mechanical property tests on the ore and rock samples to determine their physical and mechanical property parameters. These parameters include ore density, compressive strength, tensile strength, elastic modulus, Poisson's ratio, cohesion, and internal friction angle. Additionally, it is necessary to investigate the rock mass structural parameters, including the degree of rock fragmentation, surface characteristics, comprehensive structural grade (SR), and surface condition grade (SCR). Using the quantified geological strength index (GSI), determine the empirical parameter mi value for the rock mass. Substitute these parameters into the formula according to the Hoek-Brown empirical criterion to calculate the mechanical parameters of the rock mass.

[0045] Step 3: Investigate the size of the accumulated waste rock in the goaf, and determine the distribution pattern and porosity of the waste rock in the goaf. The size of the accumulated waste rock in the goaf is obtained by on-site measurement and sieving and grading of mixed samples. The distribution pattern of the size is obtained from on-site investigation. The porosity is obtained by boiling in water.

[0046] Step 4: Select granular rock samples from the goaf and conduct similar material simulation experiments in the laboratory to study the seepage law of granular rock with cementing material, concentration, flow rate, and pressure as variables. Establish a large-scale (1:100) physical model of the artificial key layer, study the seepage law of cemented backfilling of waste rock, and test the mechanical properties of the cemented backfill. The similar material simulation experiment includes selecting granular materials (such as cement, waste rock, water, sand, tailings, etc., which are the same or similar materials) to be used for actual granular grouting and backfilling to form the artificial key layer for grouting and backfilling simulation experiments. In the experiment, different cement concentrations, different slurry-to-sand ratios, and different waste rock volume percentages need to be controlled for testing. After the sample is formed, the strength of the cemented body is tested until a conclusion is drawn. The similar material simulation experiment also includes sample material preparation and slurry preparation, specimen block preparation and curing, specimen block compressive strength testing, and test result analysis.

[0047] Step 5: Simulate the artificial key layer using finite element software such as Flac3d to determine its mechanical characteristics. Combined with the width of the goaf at the actual location of the proposed artificial key layer, determine its thickness and strength parameters. Furthermore, analyze the geometric and mechanical characteristics of the goaf filling material above and below the artificial key layer using finite element software to obtain the load distribution between the artificial key layer and the upper and lower goaf filling materials. The model is shown below. Figure 2 As shown;

[0048] Step Six: Analyze the mechanical characteristics and bearing mechanism of the waste rock grouting cemented backfill and the surrounding rock coupling body; among them, the analysis of the mechanical characteristics and bearing mechanism of the waste rock grouting cemented backfill and the surrounding rock coupling body also requires mechanical simulation by constructing an artificial key layer physical model in the laboratory before on-site construction, and analysis in combination with the current situation of the surrounding site, until the artificial key layer meets the actual strength requirements.

[0049] Step 7: Construct the artificial critical layer on-site. The curing time for the artificial critical layer will be determined by the preliminary mechanical tests.

[0050] Step 8: Fill the goaf above the artificial key layer with waste rock grouting; the filling between the artificial key layer and the overlying rock layer is carried out by tailings cement filling or waste rock grouting. When connecting the top, a multi-stage construction plan with controlled filling speed or filling agents such as foaming agents are used for the connection filling.

[0051] Step 9: Treat the goaf area below the artificial key layer, and then recover the residual ore. This can ensure the safety of the top during the recovery of the residual ore.

[0052] Step 10: Fill the goaf area below the artificial key layer with waste rock grouting; the filling between the artificial key layer and the goaf floor is carried out by tailings cement filling or waste rock grouting. When connecting the roof, a multi-stage construction plan with controlled filling speed or filling agents such as foaming agents are used for roof connection filling.

[0053] The solutions described in the embodiments are not intended to limit the scope of patent protection of this invention. All equivalent implementations or modifications that do not depart from the scope of this invention are included in the patent scope of this case.

Claims

1. A method for constructing an artificial key layer using waste rock grouting to treat goaf areas, characterized in that... Includes the following steps: Step 1: Determine the characteristics of the goaf, the number of overlying rock layers, the lithology of each layer, the thickness of each layer, and the total thickness of the overlying rock mass through geological and surveying investigations; Step Two: Extract ore and rock samples through typical profile drilling, conduct physical and mechanical property tests on the ore and rock samples, and determine the physical and mechanical property parameters of the ore and rock samples. The physical and mechanical property parameters of the ore and rock samples include ore and rock density, compressive strength, tensile strength, elastic modulus, Poisson's ratio, cohesion, and internal friction angle. It is also necessary to investigate the rock mass structural parameters, including the degree of rock mass fragmentation, surface characteristics of structural surfaces, comprehensive structural grade SR, and surface condition grade SCR. Through the quantified geological strength index GSI, determine the value of the empirical parameter mi of the rock mass, and substitute the parameters into the formula according to the Hoek-Brown empirical criterion to calculate the mechanical parameters of the rock mass. Step 3: Investigate the size of the accumulated waste rock in the goaf, and determine the distribution pattern and porosity of the waste rock in the goaf; Step 4: Select samples of ore and waste rock in the goaf area, conduct similar material simulation experiments in the laboratory, study the seepage law of waste rock with cementing material, concentration, flow rate and pressure as variables, establish a physical model of artificial key layer, study the seepage law of cemented waste rock backfill, and test the mechanical properties of cemented backfill. Step 5: Use finite element software to simulate the artificial key layer, determine the mechanical characteristics of the artificial key layer, and combine the width of the goaf at the actual location of the proposed artificial key layer to determine the thickness and strength index of the artificial key layer. Step Six: Analyze the mechanical characteristics and bearing mechanism of the coupled body of the waste rock grouting cemented backfill and the surrounding rock; Step 7: Construct the artificial critical layer on-site. The curing time for the artificial critical layer will be determined by the preliminary mechanical tests. Step 8: Fill the goaf above the artificial key layer with waste rock grouting. Step 9: Treat the goaf area below the artificial key layer, and recover the residual ore after treatment; Step 10: Fill the goaf area below the artificial key layer with cement grouting using waste rock.

2. The method for constructing an artificial key layer using waste rock grouting to treat goaf areas according to claim 1, characterized in that: In step one, the characteristics of the goaf include the goaf span, pillar length, pillar width, pillar height, and pillar integrity.

3. The method for constructing an artificial key layer using waste rock grouting to treat goaf areas according to claim 1, characterized in that: In step three, the block size of the waste rock accumulated in the goaf is obtained by on-site measurement and sieving and grading of mixed samples. The block size distribution pattern is obtained based on on-site investigation, and the porosity is obtained by boiling water method.

4. The method for constructing an artificial key layer using waste rock grouting to treat goaf areas according to claim 1, characterized in that: In step four, the similar material simulation experiment includes selecting the granular material to be used for actual granular grouting and filling to form an artificial key layer for grouting and filling simulation experiments. In the experiment, different cement concentrations, different slurry-to-sand ratios, and different waste rock volume percentages need to be controlled for testing. After the sample is formed, the strength of the cemented body is tested until a conclusion is drawn. The similar material simulation experiment also includes sample material preparation and slurry preparation, specimen block preparation and curing, specimen block compressive strength testing, and test result analysis.

5. The method for constructing an artificial key layer using waste rock grouting to treat goaf areas according to claim 1, characterized in that: In step five, it is also necessary to analyze the geometric and mechanical characteristics of the upper and lower goaf filling bodies of the artificial key layer using finite element software, and obtain the load distribution of the artificial key layer and the upper and lower goaf filling bodies.

6. The method for constructing an artificial key layer using waste rock grouting to treat goaf areas according to claim 1, characterized in that: In step six, the analysis of the mechanical characteristics and bearing mechanism of the waste rock grouting cemented filling body and the surrounding rock coupling body also requires mechanical simulation by constructing a physical model of the artificial key layer in the laboratory before on-site construction, and analysis in combination with the current situation of the surrounding area, until the artificial key layer meets the actual strength requirements.

7. The method for constructing an artificial key layer using waste rock grouting to treat goaf areas according to claim 1, characterized in that: In step eight, the filling between the artificial key layer and the overlying rock layer is carried out by tailings cement filling or waste rock cement grouting filling. When connecting the top, a multiple construction scheme with controlled filling speed or adding a foaming agent is used for the top connection filling.

8. The method for constructing an artificial key layer using waste rock grouting to treat goaf areas according to claim 1, characterized in that: In step ten, the filling between the artificial key layer and the goaf floor is carried out by tailings cement filling or waste rock cement grouting. When connecting the roof, a multi-stage construction plan with controlled filling speed or adding a foaming agent is used for roof connection filling.

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