Method for determining fiber modification parameters of filling body based on energy evolution brittleness evaluation

Abstract

This invention provides a method for determining fiber modification parameters of filling materials based on energy evolution brittleness evaluation. The method includes the preparation and curing of standard samples of high-moisture filling materials, unconfined compressive strength testing and energy parameter acquisition, construction of a brittleness calculation model, standardization of brittleness conversion, proposal of a brittleness-ductility transition criterion and a comprehensive brittleness evaluation index, evaluation of the relationship between brittleness and strengthening changes, and reasonable determination of fiber modification parameters and the water-cement ratio of high-moisture materials. This invention solves the problems of lack of energy characterization in filling material brittleness evaluation and reliance on empirical design for fiber modification parameters. It achieves reasonable matching of energy evolution analysis, brittleness quantitative evaluation, and modification parameters, providing a scientific basis for parameter optimization of filling materials in coal mine gob-side retention and filling mining projects. This effectively reduces the risk of brittle failure of filling materials, promotes the application of coal mine gob-side retention and filling mining technologies, and drives green, safe, and efficient coal mining.

Description

Technical Field

[0001] This invention relates to the field of mining technology, and specifically to a method for determining fiber modification parameters of backfill materials based on energy evolution brittleness evaluation. More specifically, it relates to a method for designing and optimizing fiber modification parameters and performance of high-water-content backfill materials in goaf retention and backfill mining projects. Background Technology

[0002] High-water materials have been widely used in coal mine backfilling engineering due to their advantages such as good fluidity, fast setting speed, and adjustable mechanical properties. However, with the increase in mining depth and intensity, traditional high-water material backfills can no longer meet engineering requirements. To address this, researchers have explored incorporating fibers as admixtures into high-water material backfills, achieving modification and optimization of the backfill's mechanical properties through the interaction between the fibers and the matrix.

[0003] However, the brittleness of fiber-modified high-moisture fillers directly affects their safety: excessive brittleness can lead to sudden fracture of the filler under roof pressure, causing overall failure; while excessive toughness (i.e., insufficient brittleness) may result in excessive deformation and loss of load-bearing capacity. Therefore, how to scientifically regulate fiber modification parameters to achieve precise control of filler brittleness has become a critical issue that urgently needs to be addressed.

[0004] While research on the mechanical modification of cement-based materials such as ordinary concrete by fibers is relatively mature, high-water-content materials, as a special type of cement-based material, exhibit significant differences in their high water content characteristics and internal hydration reaction mechanisms compared to traditional cement-based materials. Currently, the regulatory mechanisms of fiber modification parameters (including fiber length, fiber type, and fiber content) and the water-cement ratio of high-water-content materials on the brittleness of infill bodies are still unclear, making it difficult to establish a quantitative correlation between "modification parameters-brittleness-strength". This leads to problems of insufficient or excessive modification in practical engineering, making it impossible to accurately match engineering requirements.

[0005] In addition, existing methods for evaluating the brittleness of fiber-modified high-water-content fillers have significant drawbacks: they rely heavily on single indicators such as "strain magnitude at fracture" and fail to incorporate the energy evolution characteristics of the entire loading process (such as changes in elastic energy accumulation, release, and dissipation). Therefore, they cannot distinguish the essential differences between the "brittleness of the crack initiation stage" before the peak and the "brittleness of the failure propagation stage" after the peak. Based on the above analysis, a method for determining fiber modification parameters of high-water-content material fillers based on energy evolution brittleness evaluation is established, which is of great significance for ensuring safe production in coal mines. Summary of the Invention

[0006] Based on this, this invention proposes a method for determining fiber modification parameters of backfill materials based on energy evolution brittleness evaluation. This invention innovatively reveals the brittle mechanism of fiber-modified high-moisture material backfill materials from an energy evolution perspective, solving the problems of lack of energy characterization in brittleness evaluation and reliance on empirical design for fiber modification parameters in existing technologies. It achieves precise matching between energy evolution analysis, brittleness quantitative evaluation, and modification parameters of the backfill material. This method provides a scientific basis for parameter optimization of fiber-modified high-moisture material backfill materials in coal mine goaf retention and backfilling mining projects, effectively reducing the risk of brittle failure of backfill materials, improving the safety and stability of coal mine backfill materials, and is of great significance for promoting green, safe, and efficient coal mining.

[0007] This invention analyzes the pre- and post-peak energy evolution of fiber-modified filling materials, constructs a brittleness calculation model considering the pre- and post-peak energy evolution, proposes a brittleness-ductility transition criterion and a comprehensive brittleness evaluation index, establishes the correlation between "modification parameters, brittleness, and strength," and screens parameter combinations that meet the requirements of strength and brittleness of filling materials based on the comprehensive brittleness evaluation index. It determines the optimal fiber modification parameters and water-cement ratio, providing a scientific basis for reducing the risk of brittle failure of filling materials in coal mine goaf retention and filling mining projects.

[0008] In a first aspect, the present invention provides a method for determining fiber modification parameters of infill bodies based on energy evolution brittleness evaluation, comprising: S1. Based on the actual needs of coal mine gob-side roadway retention and backfilling mining projects, design the relevant parameters of standard samples, prepare standard samples of fiber-modified high-moisture material backfill, and further cure them to the corresponding age under standard curing conditions. S2. Unconfined compressive strength testing and energy parameter acquisition, simultaneously acquiring the full stress-strain curve; based on the full stress-strain curve, the peak stress σ is obtained. p Elastic modulus E, residual stress σ r Peak stress corresponds to strain α p and the strain α corresponding to residual stress c The key energy parameters are further calculated using line integrals; these key energy parameters include the total energy U. T Pre-peak elastic energy U e1 Peak dissipation energy U d1 Post-peak release elastic energy U e2 Post-peak dissipation energy U d2 At least one of them; S3. Based on the characteristics of energy accumulation and dissipation in the pre-peak stage and energy release and ductile deformation in the post-peak stage, construct calculation models for pre-peak brittleness D1 and post-peak brittleness D2 based on the key energy parameters in step S2, and perform brittleness standardization conversion. S4. Based on the brittleness standardization conversion in step S3, a brittleness-toughness transition criterion and a comprehensive brittleness evaluation index are proposed to quantify the brittleness and toughness of standard specimens of fiber-modified high-water-content material fillers. S5. Evaluate the relationship between the brittleness and strength of standard samples of high-water-content material fillers with different fiber modifications, use the comprehensive brittleness evaluation index to screen the parameter combination that meets the brittleness requirements, and determine the optimal fiber modification parameters (including fiber type, length, and dosage) and water-cement ratio.

[0009] Preferably, in step S1, the relevant parameters of the standard sample include at least one of the following: fiber type, fiber content, fiber length, fiber diameter, and water-cement ratio.

[0010] Preferably, in step S1, the fiber type is selected from at least one of polypropylene fiber, polyacrylonitrile fiber, and glass fiber (considering fiber crack resistance and dispersion stability).

[0011] Preferably, in step S1, the fiber length is selected from at least one of 3mm, 6mm, 9mm and 12mm, and the fiber diameter is selected from 18μm.

[0012] Preferably, in step S1, the fiber content in the standard sample is selected from at least one of 0%, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5%. The fiber content in the standard sample is the percentage of fiber in the total weight of the standard test.

[0013] Preferably, in step S1, the water-cement ratio in the standard sample is selected from at least one of 1.0, 1.2, 1.5, and 1.8. The water-cement ratio refers to the mass ratio of water to cement in the standard sample.

[0014] Preferably, in step S1, the standard sample size is Φ50mm×100mm, and 3 to 5 samples are prepared for each parameter combination.

[0015] Preferably, in step S1, the curing temperature of the standard sample is 20±2℃, the relative humidity is ≥95%, and the curing period is 7 days.

[0016] Preferably, in step S2, the unconfined compressive strength test is performed using a pressure testing machine.

[0017] Preferably, in step S2, the peak stress σ is obtained based on the full stress-strain curve. p Elastic modulus E, residual stress σ r Peak stress corresponds to strain α p and the strain α corresponding to residual stress c .

[0018] Preferably, in step S2, the loading rate for the unconfined compressive strength test is 0.5 mm / min (simulating the slow sinking of the top plate).

[0019] Preferably, in step S2, the total energy U T The total energy input to the press is the integral value of the total area under the stress-strain curve in the pre-peak stage, and the calculation formula is shown in (1):

[0020] In the formula, σ and ɛ represent stress and strain, respectively; ɛ p This represents the strain corresponding to the peak stress.

[0021] Preferably, in step S2, the pre-peak elastic energy U e1 The elastic strain energy at the peak stress is calculated using the formula shown in (2):

[0022] In the formula, σ p E and E represent peak stress and elastic modulus, respectively.

[0023] Preferably, in step S2, the pre-peak dissipation energy U d1 The difference between the total energy at the peak and the elastic energy before the peak is calculated using the formula shown in (3): .

[0024] Preferably, in step S2, the elastic energy U is released after the peak. e2 The difference between the elastic energy at the post-peak stage and the elastic energy at the peak stage is calculated using the formula shown in (4):

[0025] In the formula, σ r This represents residual stress.

[0026] Preferably, in step S2, the post-peak dissipation energy U d2 The integral value of the total area under the stress-strain curve in the post-peak stage is calculated using the formula shown in (5):

[0027] In the formula, ɛ c This represents the strain corresponding to the residual stress.

[0028] Preferably, in step S3, Pre-peak brittleness D1: Pre-peak dissipation energy U d1 and pre-peak elasticity U e1 The ratio is calculated using the formula shown in (6): .

[0029] Preferably, in step S3, post-peak brittleness D2: post-peak dissipation energy U d2 Post-peak release elastic energy Ue2 The ratio is calculated using the formula shown in (7): .

[0030] Preferably, in step S3, the calculation and normalization conversion methods for each brittleness are as follows: Normalized pre-peak brittleness D F and the brittleness after the standardized peak D B The calculation formulas are shown in (8) and (9):

[0031] Standardization conversion achieves a unified evaluation range for pre- and post-peak brittleness, unifying brittleness to the 0-2 range.

[0032] Preferably, in step S4, the brittle-toughness transition criterion is: the standardized brittleness degree 1 is the critical point of the brittle-toughness transition, 0~1 is the evaluation standard for obvious toughness characteristics, and 1~2 is the evaluation standard for obvious brittleness characteristics.

[0033] Preferably, in step S4, when the fiber content is between 0.2% and 0.3% and the water-cement ratio is between 1.2 and 1.5, the comprehensive brittleness evaluation index D is concentrated at 1.0, forming a parameter range for the transition between brittleness and toughness.

[0034] Preferably, in step S4, the comprehensive brittleness evaluation index D is as shown in formula (10): .

[0035] Preferably, in step S5, the pre-peak and post-peak brittleness of standard samples of fiber-modified high-water-content material fillers are calculated according to formulas (6) and (7), and the standardized pre-peak and standardized post-peak brittleness of standard samples of fiber-modified high-water-content material fillers are calculated according to formulas (8) and (9). Finally, the comprehensive brittleness evaluation index is calculated according to formula (10), and reasonable fiber modification parameters and water-cement ratio are determined considering whether the strength meets the requirements.

[0036] Preferably, in step S5, the strength requirements include (a) strength > 10 MPa, (b) strain > 0.065 and (c) comprehensive brittleness index D > 1, and reasonable fiber modification parameters and water-cement ratio are determined.

[0037] Beneficial effects This invention discloses a method for determining fiber modification parameters of filling materials based on energy evolution brittleness evaluation. The method includes the preparation and curing of standard samples of fiber-modified high-moisture material filling materials; unconfined compressive strength testing and energy parameter acquisition of fiber-modified high-moisture material filling materials; construction of a brittleness calculation model considering the pre- and post-peak energy evolution law; standardized conversion of brittleness to achieve a unified brittleness evaluation interval; proposing a brittleness-ductility transition criterion and a comprehensive brittleness evaluation index; and evaluating the brittleness and strengthening changes of standard samples of fiber-modified high-moisture material filling materials, thus achieving reasonable... The invention determines the fiber modification parameters and the water-cement ratio of high-moisture materials. It solves the problems of lack of energy characterization in the evaluation of the brittleness of backfill bodies and the reliance on empirical design for fiber modification parameters in existing technologies. It achieves energy evolution analysis, brittleness quantification evaluation, and reasonable matching of modification parameters for fiber-modified high-moisture material backfill bodies. This provides a scientific basis for parameter optimization of fiber-modified high-moisture material backfill bodies in coal mine gob-side retention and backfilling mining projects, effectively reducing the risk of brittle failure of backfill bodies. It is conducive to the promotion and application of gob-side retention and backfilling mining technologies in coal mines, and promotes green, safe, and efficient coal mining.

[0038] This invention proposes a brittleness calculation model and standardized conversion method based on the pre- and post-peak energy evolution law, constructs a brittleness-ductility transition criterion and a comprehensive brittleness evaluation index, and realizes the differentiation and unified quantitative evaluation of brittleness in the crack initiation and failure propagation stages throughout the entire loading process of high-water-content material filling bodies. It fills the gap in the existing technology of brittleness evaluation of high-water-content material filling bodies that lacks energy characterization and cannot establish the correlation between modification parameters, brittleness, and strength. Through the fiber modification parameters and water-cement ratio of high-water-content materials determined by this method, the technical problem of fiber modification parameters of high-water-content material filling bodies relying on empirical design and being prone to insufficient or excessive modification is solved. It effectively reduces the safety risks caused by brittle failure or excessive deformation of high-water-content material filling bodies, which is of great significance to promoting the development of green mining and safe and efficient mining technologies in coal mines. It has significant technical value, economic and social benefits and broad prospects for promotion. Attached Figure Description

[0039] Figure 1 This embodiment provides a schematic diagram of the working face excavation project along the goaf and a columnar section of the top and bottom rock strata. Figure 2 This is a flowchart illustrating the preparation and curing process of fiber-modified high-water-content material filler samples provided in this embodiment. Figure 3 The diagram shows the calculation of various energy parameters of the fiber-modified high-water-content material filler provided in this embodiment; Figure 4 The fiber type provided in this embodiment is polypropylene fiber, with a fiber content of 0.3% and a fiber length of 6 mm. The stress-strain curve of the high-water material filling body with a water-cement ratio of 1.5 is shown in the figure. Figure 5This embodiment provides a diagram illustrating the variation patterns of various brittleness indices based on energy evolution. Figure 6 This is a graph showing the brittleness and strength variations of high-water-content fillers with different fiber modification parameters provided in this embodiment. Figure 7 The diagram shows the deformation of the surrounding rock in the high-water-content material filling body with reasonable fiber modification parameters provided in this embodiment. Figure 8 This is a flowchart illustrating the method for determining fiber modification parameters of fillers based on energy evolution brittleness evaluation provided in this embodiment.

[0040] Terminology Explanation Certain embodiments of the invention will now be described in detail, examples of which are illustrated by the accompanying structural and chemical formulas. The invention is intended to cover all alternatives, modifications, and equivalents, all of which are included within the scope of the invention as defined in the claims. Those skilled in the art will recognize that many similar or equivalent methods and materials can be used to practice the invention. The invention is by no means limited to the methods and materials described herein. In the event that one or more of the incorporated documents, patents, and similar materials differ from or contradict this application (including, but not limited to, defined terminology, application of terminology, described techniques, etc.), this application shall prevail.

[0041] It should be further appreciated that certain features of the invention, for clarity, have been described in multiple independent embodiments, but may also be provided in combination in a single embodiment. Conversely, various features of the invention, for brevity, have been described in a single embodiment, but may also be provided individually or in any suitable sub-combination.

[0042] Unless otherwise stated, all technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. All patents and publications related to this invention are incorporated herein by reference in their entirety.

[0043] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0044] In the following content, all numbers disclosed herein, whether or not they use words such as "approximately" or "about," are approximate values. The value of each number may vary by 1%, 2%, 5%, 7%, 8%, 10%, 15%, or 20%. Whenever a number with a value of N is disclosed, any numbers with values ​​of N+ / -1%, N+ / -2%, N+ / -3%, N+ / -5%, N+ / -7%, N+ / -8%, N+ / -10%, N+ / -15%, or N+ / -20% will be explicitly disclosed, where "+ / -" indicates addition or subtraction. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention in any way. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of this disclosure. Such structures and techniques have also been described in many publications.

[0046] All reagents used in this invention can be purchased commercially or prepared by the methods described in this invention.

[0047] The engineering background of this embodiment: A mine mainly mines the No. 3 coal seam. The 1305 working face has a dip length of 210m and a strike length of 1200m. The average mineable thickness of the coal seam is 5.5m. It is a stable coal seam with a dip angle of 3°~5° and an average dip angle of 4°. The northern part of the working face is the goaf of the 1303 working face, and the southern part is the 1307 working face. The 1305 working face haulage roadway is left along the goaf and used as the return air roadway for the 1307 working face. The schematic diagram of the mining project of the 1305 working face is shown below. Figure 1 As shown in Figure A, the columnar section of the top and bottom strata of the 1305 working face is as follows: Figure 1 As shown in Figure B, based on the production geological conditions of the 1305 working face, the mining situation of adjacent working faces, and the lithology and rock mechanics parameters, the support resistance of the high-water-content material roadway backfill in the 1305 working face transport roadway was determined to be 20MN / m. The width of the roadway backfill was set at 2.0m and the height at 4m. The compressive strength of the roadway backfill in the goaf-retention roadway during the stable bearing stage (7 days after construction) should be greater than 10MPa. To adapt to the rotation and subsidence of the key roof block, the strain value corresponding to the peak stress of the roadway backfill should be greater than 0.065. During the implementation of the goaf-retention roadway in the 1305 working face transport roadway, a high-water-content material backfill without fiber was used (water-cement ratio 1.8). Due to the insufficient toughness (excessive brittleness) of the roadway backfill, local cracking occurred under the slow subsidence of the roof, resulting in severe roadway deformation, frequent repairs, and seriously affecting the mining succession of the working face.

[0048] Example 1 like Figure 8 As shown in the figure, this embodiment provides a method for determining fiber modification parameters of infill bodies based on energy evolution brittleness evaluation, which specifically includes the following steps: (1) Preparation and curing of fiber-modified high-water-content material filling samples To systematically study the effects of fiber parameters and water-cement ratio on the mechanical properties of high-water-content filling materials and to determine the optimal material proportioning scheme, this experiment selected polypropylene fiber as the modifying material. The experimental parameters were designed using the controlled variable method. The specific scheme and preparation and curing process are as follows: Experimental parameter design: The fiber type was fixed as polypropylene fiber, with fiber lengths of 3mm, 6mm, and 9mm, fiber content of 0%, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5%, and water-cement ratio of 1.0, 1.2, and 1.5.

[0049] Experimental preparation procedure: Accurately weigh the high-moisture material powder, polypropylene fiber, and water according to the above parameter combination. First, thoroughly dry-mix the fiber and powder evenly, then add the corresponding proportion of water and stir until the slurry is uniform and free of lumps. Next, slowly pour the slurry into a standard cylindrical mold with a diameter of 50mm × 100mm. During the pouring process, use a vibrator to gently vibrate and vent air to ensure the sample is dense and free of pores. Finally, smooth the surface of the mold and cover it with plastic wrap to prevent moisture evaporation. To ensure the reliability of the experimental data, three samples were prepared in parallel for each parameter combination.

[0050] Curing condition control: Place the cast specimens along with the molds into a standard curing chamber. Strictly control the curing environment parameters: temperature 20±2℃, relative humidity 96%, and continue curing for 7 days. After curing, remove the specimens from the molds for later use. Specimen preparation and curing are as follows: Figure 2 As shown.

[0051] (2) Unconfined compressive strength test and energy parameter calculation Unconfined compressive strength tests were conducted on specimens of different ages using a compression testing machine. The loading rate was set to 0.5 mm / min. Stress-strain curves were simultaneously acquired, and the total energy (Us) was calculated using curve integration. T ), pre-peak elasticity (U e1 ), peak dissipation energy (U d1 Post-peak release elastic energy (U) e2 Post-peak dissipation energy (U) d2 The calculation models for each energy parameter are as follows: Figure 3 As shown, Figure 3 A illustrates how the total energy (U) can be obtained from the full stress-strain curve. T and post-peak dissipation energy (U d2 The curve integral interval of ) Figure 3 B illustrates the extraction of the pre-peak dissipated energy (U) from the full stress-strain curve.d1 ), pre-peak elasticity (U e1 The integration method of ) Figure 3 C illustrates the extraction of post-peak elastic energy (U) from the full stress-strain curve. e2 The integration method of ).

[0052] The following example uses a sample of a high-water-cement material with polypropylene fiber, a fiber content of 0.3%, a fiber length of 6 mm, and a water-cement ratio of 1.5 to demonstrate the calculation process.

[0053] 1) Basic test data, the full stress-strain curve of the specimen is as follows: Figure 4 As shown, the peak stress σ of this specimen p =11.9MPa, elastic modulus E=0.46GPa, residual stress σ r =9.5MPa, peak stress corresponds to strain α p =0.074, residual stress corresponds to strain α c =0.195; 2) Total Energy (U) T ), calculated using formula (1),

[0054] By integrating the pre-peak stress-strain curve using Origin software, U is obtained. T =463.55kJ; 3) Pre-peak elasticity (U e1 ), calculated using formula (2),

[0055] 4) Peak dissipation energy (U d1 ), calculated using formula (3),

[0056] 5) Post-peak release of elastic energy (U e2 ), calculated using formula (4),

[0057] 6) Post-peak dissipation energy (U d2 ), calculated using formula (5),

[0058] By integrating the post-peak stress-strain curve using Origin software, U is obtained. d2 =1209.68kJ.

[0059] (3) Calculation of brittleness and comprehensive brittleness evaluation index Taking a sample with a water-cement ratio of 1.5, a fiber content of 0.3%, and a fiber length of 6 mm as an example, the brittleness index of the filling body was calculated. The pre-peak brittleness D1 was calculated using formula (6), and the post-peak brittleness D2 was calculated using formula (7), respectively.

[0060] Standardized pre-peak brittleness D F The standardized pre-peak brittleness D is calculated using formula (8). B The calculations are performed using formula (9), as follows:

[0061] The comprehensive fragility evaluation index D is calculated using formula (10).

[0062] Figure 5 This study presents the variation characteristics of brittleness indices. These indices rely solely on pre-peak and post-peak energy characteristics, making them more suitable for brittleness analysis of high-water-content material infills under different fiber modification parameters and water-cement ratios. Depending on the engineering objective, pre-peak, post-peak, or combined indices can be analyzed. When focusing on the crack resistance of the infill, the pre-peak brittleness index D is used. F When considering the stability of the filling material after failure, post-peak brittleness D is used. B When a comprehensive balance of brittleness and toughness is required, a comprehensive index D is used. These indices make the brittleness analysis of fillings more flexible and adaptable.

[0063] (4) Analysis of the brittle-ductile transition characteristics of fillers under different fiber modification parameters The above tests and calculations were repeated for samples with all parameter combinations, and the results are as follows. Figure 6 As shown, the brittleness-ductility transition law of the infill body under different fiber modification parameters and water-cement ratios is analyzed.

[0064] 1) Analysis of the brittle-ductile characteristics before the peak For the standardized pre-peak brittleness D F Filler D under different parameter combinations F The values ​​range from 0.32 to 1.85, with the fiber content of the filling material being 0. F A value below 1 indicates a brittle range, meaning that the energy input from the outside during the pre-peak stage is mostly stored as releasable elastic energy, with a relatively small proportion of energy used for damage such as pre-peak crack propagation and ductile deformation. Figure 6 B and Figure 6 D shows that as the fiber content increases, D F It shows a significant increasing trend. When the fiber content reaches 0.3% or higher, sample D... FWhen the value exceeds 1, the region enters a range where toughness characteristics are prominent. This is because the incorporation of fibers improves the compactness of the internal structure of the filler, reduces primary porosity and microcracks, and the crack-blocking effect of fibers in the pre-peak stage makes the energy dissipation process more complete. More input energy is used for the interfacial interaction between fibers and the matrix and for inhibiting the development of microcracks, resulting in enhanced pre-peak toughness characteristics.

[0065] 2) Post-peak brittle-ductile characteristics analysis Figure 6 A and Figure 6 B shows that, unlike the pre-peak characteristics, the standardized post-peak brittleness of the filling material under all parameter combinations is D. B All values ​​are greater than 1, falling within the toughness range, and generally showing an increasing trend with increasing fiber content. In the post-peak stage of unfiber-infused fillers, crack propagation and penetration are not constrained by fibers; energy is mainly consumed in interparticle frictional slippage and fracture surface slippage, resulting in relatively concentrated energy release. However, with the addition of fibers, the bridging effect of the fibers restricts further crack propagation, requiring more external energy input post-peak to drive sustained ductile deformation of the filler. The post-peak dissipated energy U... d2 A significant increase, leading to D B As the value increases, the toughness characteristics become more pronounced.

[0066] Figure 6 A and Figure 6 C shows that, at the same fiber content, the water-cement ratio has a significant effect on post-peak brittleness and toughness. As the water-cement ratio increases from 1.0 to 1.8, the filler D... B The value increased from 1.63 to 1.95 because, under high water-cement ratio conditions, the hydration reaction inside the filling material was insufficient, leading to increased porosity and a higher residual elastic energy U after peak stress. e2 The reduced storage capacity, slower energy release rate, decreased post-peak external force input, relatively enhanced toughness characteristics, and increased water-cement ratio weaken the load-bearing capacity of the filling material, leading to a change in the balance between post-peak energy release and dissipation.

[0067] 3) Comprehensive transformation law of brittleness and toughness The comprehensive brittleness evaluation index D comprehensively reflects the brittleness and toughness characteristics before and after the peak. Its value first increases and then decreases with increasing fiber content, and increases with increasing water-cement ratio. The minimum D value of the filler with 0% fiber content and water-cement ratio of 1.0 is 0.45 (obvious brittleness characteristics), while the maximum D value of the polypropylene fiber modified filler with 0.3% fiber content and water-cement ratio of 1.8 is 1.70 (obvious toughness characteristics).

[0068] Further analysis revealed a distinct parameter threshold for the brittle-ductile transition of the filling material, such as... Figure 6As shown, when the fiber content is between 0.2% and 0.3% and the water-cement ratio is between 1.2 and 1.5, the comprehensive brittleness evaluation index D is concentrated around 1.0, forming a parameter range that marks the transition between brittleness and toughness. The modification parameters regulate the energy evolution and brittleness-toughness state of the material. When the parameter combination crosses this threshold range, the energy distribution pattern (the ratio of elastic energy storage to dissipation) of the filling material changes, and the brittleness-toughness characteristics change significantly.

[0069] (5) Parameter optimization and screening Based on the engineering requirements: strength > 10 MPa, strain > 0.065, and comprehensive brittleness index D > 1, a reasonable combination of fiber modification parameters was finally selected for the high-water-content material filling body. The fiber type is polypropylene fiber, the fiber content is 0.3%, and the water-cement ratio of the high-water-content material is 1.5. The comprehensive brittleness index D of the filling body obtained by the fiber modification parameters of this high-water-content material filling body is 1.63, which is within the safe range of toughness. The strength is 11.9 MPa, and the strain corresponding to the peak stress is 0.074. Before the peak, it is mainly weakly brittle, and after the peak, it is mainly strong and tough. It meets the comprehensive requirements of "crack resistance-bearing capacity-deformation coordination" for the filling body of the goaf retention.

[0070] (6) On-site engineering application verification Fiber-modified high-water-content material slurry was prepared according to the above parameters and poured into the roadway side filling using an underground pumping system. Field application results showed that during the stable bearing stage (7 days after construction) of the roadway side filling in the goaf retention roadway, no local cracking or brittle fracture occurred, and the integrity was good. The convergence of the roof and floor plates in the goaf retention roadway stabilized at 497 mm, the deformation of the solid coal face was 205 mm, and the deformation of the roadway side filling was 48 mm, meeting the roadway usage requirements. This effectively solved the problem of severe roadway deformation and frequent repairs caused by insufficient toughness of the non-fiber-added filling, verifying the scientific validity and engineering applicability of the parameter determination method. The deformation of the surrounding rock after the on-site implementation of the goaf retention roadway is as follows: Figure 7 As shown. From Figure 7 The surrounding rock deformation diagram shows that as the distance from the working face increases, the deformation of the roadway filling, the deformation of the solid coal side, and the approach of the roof and floor first increase and then tend to stabilize. When the distance from the working face is 120m, the maximum deformation of the roadway filling is 48mm, the maximum approach of the roof and floor is 497mm, and the maximum deformation of the solid coal side is 205mm. The deformation of the surrounding rock in the goaf-retained roadway is within the expected range.

[0071] The method of this invention has been described through preferred embodiments. Those skilled in the art will readily be able to modify or appropriately alter and combine the methods and applications described herein within the scope, spirit, and context of this invention to implement and apply the technology of this invention. Those skilled in the art can refer to the content herein to appropriately improve process parameters. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included within the scope of this invention.

Claims

1. A method for determining fiber modification parameters of filling materials based on energy evolution brittleness evaluation, characterized in that, include: S1. Based on the actual needs of coal mine gob-side roadway retention and backfilling mining projects, design the relevant parameters of standard samples, prepare standard samples of fiber-modified high-moisture material backfill, and further cure them to the corresponding age under standard curing conditions. S2. Unconfined compressive strength testing and energy parameter acquisition, with simultaneous acquisition of the full stress-strain curve; Based on the full stress-strain curve, the peak stress σ is obtained. p Elastic modulus E, residual stress σ r Peak stress corresponds to strain α p and the strain α corresponding to residual stress c The key energy parameters are further calculated using line integrals; these key energy parameters include the total energy U. T Pre-peak elastic energy U e1 Peak dissipation energy U d1 Post-peak release elastic energy U e2 Post-peak dissipation energy U d2 At least one of them; S3. Based on the characteristics of energy accumulation and dissipation in the pre-peak stage and energy release and ductile deformation in the post-peak stage, construct calculation models for pre-peak brittleness D1 and post-peak brittleness D2 based on the key energy parameters in step S2, and perform brittleness standardization conversion. S4. Based on the brittleness standardization conversion in step S3, a brittleness-toughness transition criterion and a comprehensive brittleness evaluation index are proposed to quantify the brittleness and toughness of standard specimens of fiber-modified high-water-content material fillers. S5. Evaluate the relationship between the brittleness and strength of standard specimens of high-water-content fillers with different fiber modifications, use the comprehensive brittleness evaluation index to screen the parameter combination that meets the brittleness requirements, and determine the optimal fiber modification parameters and water-cement ratio.

2. The determining method according to claim 1, characterized in that, In step S1, the relevant parameters of the standard sample include at least one of the following: fiber type, fiber content, fiber length, fiber diameter, and water-cement ratio.

3. The determining method according to claim 2, characterized in that, In step S1, the fiber type is selected from at least one of polypropylene fiber, polyacrylonitrile fiber and glass fiber; In step S1, the fiber length is selected from at least one of 3mm, 6mm, 9mm and 12mm, and the fiber diameter is selected from 18μm; In step S1, the fiber content in the standard sample is selected from at least one of 0%, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5%. In step S1, the water-cement ratio in the standard sample is selected from at least one of 1.0, 1.2, 1.5 and 1.8; In step S1, the standard sample size is Φ50mm×100mm, and 3 to 5 samples are prepared for each parameter combination.

4. The determining method according to claim 2, characterized in that, In step S1, the curing temperature of the standard sample is 20±2℃, the relative humidity is ≥95%, and the curing period is 7 days.

5. The determining method according to claim 1, characterized in that, In step S2, the unconfined compressive strength test is performed using a compression testing machine; In step S2, the peak stress σ is obtained based on the full stress-strain curve. p Elastic modulus E, residual stress σ r Peak stress corresponds to strain α p and the strain α corresponding to residual stress c ; In step S2, the loading rate for the unconfined compressive strength test is 0.5 mm / min.

6. The determining method according to claim 1, characterized in that, In step S2, the total energy U T The total energy input to the press is the integral value of the total area under the stress-strain curve in the pre-peak stage, and the calculation formula is shown in (1): In the formula, σ and ɛ represent stress and strain, respectively; ɛ p This represents the strain corresponding to the peak stress. In step S2, the pre-peak elastic energy U e1 The elastic strain energy at the peak stress is calculated using the formula shown in (2): In the formula, σ p E and E represent peak stress and elastic modulus, respectively; In step S2, the pre-peak dissipation energy U d1 The difference between the total energy at the peak and the elastic energy before the peak is calculated using the formula shown in (3): In step S2, the elastic energy U is released after the peak. e2 The difference between the elastic energy at the post-peak stage and the elastic energy at the peak stage is calculated using the formula shown in (4): In the formula, σ r This is residual stress; In step S2, the post-peak dissipation energy U d2 The integral value of the total area under the stress-strain curve in the post-peak stage is calculated using the formula shown in (5): In the formula, ɛ c This represents the strain corresponding to the residual stress.

7. The determining method according to claim 1, characterized in that, In step S3, Pre-peak brittleness D1: Pre-peak dissipation energy U d1 and pre-peak elasticity U e1 The ratio is calculated using the formula shown in (6): ； In step S3, post-peak brittleness D2: post-peak dissipation energy U d2 Post-peak release elastic energy U e2 The ratio is calculated using the formula shown in (7): ； In step S3, the calculation and normalization conversion methods for each brittleness are as follows: Normalized pre-peak brittleness D F and the brittleness after the standardized peak D B The calculation formulas are shown in (8) and (9): Standardization conversion achieves a unified evaluation range for pre- and post-peak brittleness, unifying brittleness to the 0-2 range.

8. The determining method according to claim 1, characterized in that, In step S4, the criterion for the transition between brittleness and toughness is as follows: the standardized brittleness degree of 1 is the critical point for the transition between brittleness and toughness, 0~1 is the evaluation standard for obvious toughness characteristics, and 1~2 is the evaluation standard for obvious brittleness characteristics. In step S4, the comprehensive fragility evaluation index D is as shown in formula (10): 。 9. The determining method according to any one of claims 1 to 8, characterized in that, In step S5, the pre-peak and post-peak brittleness of standard samples of fiber-modified high-water-content material fillers are calculated according to formulas (6) and (7), and the standardized pre-peak and standardized post-peak brittleness of standard samples of fiber-modified high-water-content material fillers are calculated according to formulas (8) and (9). Finally, the comprehensive brittleness evaluation index is calculated according to formula (10), and the reasonable fiber modification parameters and water-cement ratio are determined by considering whether the strength meets the requirements.

10. The determining method according to claim 9, characterized in that, In step S5, the strength requirements include (a) strength > 10 MPa, (b) strain > 0.065 and (c) comprehensive brittleness index D > 1, in order to determine reasonable fiber modification parameters and water-cement ratio.

Images