Coal mine cemented filling slurry flowing property requirement design method

Abstract

The invention discloses a coal mine cemented filling slurry flowing property requirement design method which comprises the following steps: respectively designing tests and establishing a database by taking the flowing property and the stability of cemented filling slurry pipeline transportation as research targets; the flow property requirement of the cemented filling slurry in engineering application is comprehensively reflected by utilizing the rheological property index and the settling property index of the cemented filling slurry; the comprehensive flowing property index of the filling slurry with engineering applicability is obtained, and the suitable cemented filling slurry is selected. Through the design of the flowing property requirement of the filling slurry, a design basis can be provided for a mine filling pipeline system, and the situation that the underground filling effect is poor due to unreasonable slurry parameter design is avoided; and pipe blockage and pipe explosion accidents caused by poor fluidity of the slurry can be prevented, and the abrasion of a pipeline system is reduced, so that the stability of the filling slurry in the conveying process is improved, the management of a filling system by mine enterprises is facilitated, and important engineering significance and popularization and application values are realized.

Description

Technical Field

[0001] The invention relates to a design method for flow performance requirements of coal mine cementing filling slurry, and belongs to the scientific research field of mine filling mining. Background Art

[0002] The backfill mining method has been used more and more widely. It has not only improved the resource recovery rate of coal mines and promoted the sustainable development of the coal industry, but also reduced the safety hazards caused by mining activities and effectively controlled the amount of surface subsidence. It is a scientific green coal mining technology. After more than a hundred years of development, backfill mining technology has developed from the early dry backfilling to the current cement backfilling, high-water backfilling and other backfilling methods, and gradually moved towards automation and intelligence to pursue green and efficient mining of coal resources. The slurry used for backfilling starts from the ground backfilling station and is transported to the goaf through the backfilling pipeline pre-laid underground by pumping or gravity conveying, forming a backfilling body with a certain strength to support the surrounding rock. The backfill slurry pipeline transportation ensures the quality and efficiency of underground backfilling, and is one of the key technologies for backfilling mining. In engineering, the flow rate, flow rate and other flow properties of the backfill slurry are generally controlled to control the smooth operation of the pipeline transportation system.

[0003] The flowability of filling slurry is affected by many factors. On the one hand, the flow state of slurry in the pipeline is complex, and the particle grading, particle size and concentration of raw materials will affect the flow of slurry inside the pipeline; on the other hand, due to the complex underground conditions, the inner diameter of the pipeline, pipeline materials, etc. will affect the flowability of slurry. Unreasonable design of flowability parameters will cause segregation and stratification of filling slurry, aggravate the sedimentation of coarse particles, increase the risk of wear on the pipeline wall, reduce the quality of the filling body in the goaf, and in severe cases, cause pipe blockage, pipe burst and other accidents, causing losses to mining companies. At present, engineering generally regards filling slurry as a fluid for research, which has common rheological properties of fluids. However, due to the great differences in the layout of pipelines in different mines, there is a lack of a systematic design method when selecting the flowability parameters of filling slurry. Engineering usually selects and designs based on similar mine conditions or past experience, which reduces work efficiency and lacks the applicability of the method.

[0004] Therefore, studying a scientific design method for the flow performance requirements of cementitious filling slurry has become an urgent problem to be solved. In order to ensure the smooth operation of the filling slurry pipeline transportation, on the one hand, the slurry must be able to flow fully under given pipeline conditions, and the transportation power must exceed the total resistance of the operation; on the other hand, the slurry can be safely transported during the flow process and the aggregate particles do not settle. The present invention carries out research and design from the above two aspects. Through the analysis of the mine pipeline layout and the slurry flow force, the yield stress index is used to characterize the transportation power source and resistance source to meet the slurry flow conditions. At the same time, the concentration stratification index index is defined to characterize the degree of difference in slurry sedimentation, thereby screening out slurry with the required flow performance. Summary of the invention

[0005] In order to overcome the deficiencies in the prior art, the purpose of the present invention is to provide a method for designing the flow performance requirements of coal mine cemented filling slurry. Starting from the fluidity and stability of the filling slurry in the pipeline, the yield stress index is used to determine whether the filling slurry is sufficiently fluid. At the same time, a stratification index index of the slurry concentration is defined to characterize the degree of difference in the settlement of the filling slurry. In this way, a comprehensive flow performance index of the filling slurry with engineering applicability is given, and the filling slurry suitable for the site conditions is selected.

[0006] To achieve the above object, the present invention adopts the following technical solution:

[0007] A method for designing flow performance requirements of coal mine cementing filling slurry comprises the following steps:

[0008] Step 1, taking the fluidity and stability of coal mine cementing filling slurry pipeline transportation as the research objectives, respectively designing experiments to obtain rheological performance indicators reflecting fluidity and sedimentation performance indicators reflecting stability, and establishing a database containing experimental data;

[0009] Step 2, using the rheological performance index and the sedimentation performance index of the cementitious filling slurry to comprehensively reflect the flow performance requirements of the cementitious filling slurry in engineering applications;

[0010] Step 3, obtaining the comprehensive flow performance index of the filling slurry with engineering applicability through step 2, and selecting the appropriate cementitious filling slurry.

[0011] Further, the cementitious filling slurry is considered to be a Bingham fluid.

[0012] Furthermore, the rheological performance index of the cementitious filling slurry is characterized by a yield stress discrimination index, which satisfies the following conditions:

[0013]

[0014] Where τ0 is the yield stress; P e is the maximum pumping pressure; Pg is the gravity acting on the slurry; K is the resistance coefficient; L is the pipe length; D is the pipe diameter; v is the slurry flow rate; k and u are the parameters of the mathematical characterization model of the slurry yield stress and viscosity, respectively.

[0015] Furthermore, the yield stress discrimination index is obtained by testing the cementing filling slurry with a rotational rheometer, and a fitting model is established for the yield stress and viscosity of the filling slurry based on the test results, which is expressed as:

[0016] τ0=kμ+u

[0017] Here, μ is the viscosity.

[0018] Furthermore, the settlement performance index of the cementitious filling slurry is characterized by a critical stratification index discrimination index, which satisfies the following conditions:

[0019]

[0020] Where SI0 is the critical delamination index; τ0 is the yield stress; τ W max is the maximum shear stress of the slurry at the boundary layer; m and n are the parameters of the expression of slurry concentration and position respectively; a, b, c are the concentration quadratic term, linear term parameters and constant term parameters of the expression of the relationship between slurry yield stress and concentration respectively.

[0021] Furthermore, the critical delamination index discrimination index is obtained through the test of the settlement performance of the cementitious filling slurry, and a fitting model is established for the yield stress and concentration of the cementitious filling slurry according to the test results, which is expressed as:

[0022] τ0=exp(aC 2 +bC+c)

[0023] Where C is the concentration of cementitious filling slurry.

[0024] Furthermore, the cementing filling slurry has a uniform concentration distribution in the horizontal direction of the pipe cross section, and in the vertical direction, the concentration distribution conforms to a linear relationship, and an expression model of slurry concentration and vertical position is established:

[0025] C=my+n

[0026] Wherein, y=r / R; a rectangular coordinate system is established with the center of the circular pipe cross section as the origin, then r is the distance from a certain position of the slurry to point 0, which is positive above the 0 axis and negative below it; R is the pipe radius; the value range of y is [-1,1].

[0027] Furthermore, the settling performance test of the cementitious filling slurry is carried out by using a settling column mold.

[0028] Further, the sedimentation column mold includes a column body, and a groove tray is arranged on the top of the column body. In one embodiment, the column body of the sedimentation column mold is transformed from a syringe with an inner diameter of 6.8 cm and a length of 26 cm, with a total capacity of 500 ml, and a square groove tray with a diameter of 10 cm and a height of 3 cm is arranged on the top of the column.

[0029] Beneficial effects: The present invention adopts the means of multidisciplinary intersection such as mechanics and rheology to obtain the coal mine cementing filling slurry pipeline transportation index including performance requirements such as viscosity, yield stress and stratification index, reveal the flow law of cementing filling slurry pipeline transportation, and propose the cementing filling large vertical depth and long distance pipeline transportation performance design theory, which provides a theoretical basis for the characterization of the flow performance of coal mine cementing filling slurry, so that the design of filling slurry transportation index has a basis to follow. At the same time, it can provide technical reference for the cementing filling mining work in coal mine goaf under similar conditions. This method has the advantages of simple design, clear purpose, strong efficiency and wide applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a design flow chart of the flow performance index of the filling slurry according to the present invention;

[0031] Figure 2 It is a schematic diagram of the sedimentation performance test adopted by the present invention;

[0032] Figure 3 It is a schematic diagram of pipeline cross-section division;

[0033] Figure 4 is the relationship between yield stress and Bingham viscosity;

[0034] Figure 5 This is the relationship diagram between slurry concentration and yield stress. DETAILED DESCRIPTION

[0035] The present invention provides a method for designing the flow performance requirements of cemented filling slurry in coal mines. A mathematical characterization model of the yield stress and viscosity of the cemented filling slurry is obtained by a rotational rheometer test of the cemented filling slurry to obtain a yield stress discrimination index; a mathematical characterization model of the yield stress and stratification index of the cemented filling slurry is obtained by a sedimentation performance test of the cemented filling slurry to obtain a critical stratification index discrimination index; and a comprehensive flow performance index of the filling slurry is obtained from the two indices.

[0036] The present invention will be further explained below in conjunction with the accompanying drawings and embodiments.

[0037] Example

[0038] The design process of the flow performance index of the cementing filling slurry of the present invention is as follows: Figure 1 The principle of the sedimentation performance test is as shown in Figure 2 The schematic diagram of pipeline cross-section division is shown in Figure 3As shown, the specific design steps are described through the following embodiments.

[0039] In this embodiment, the total pipeline length of a coal mine cement filling slurry transportation system is 2909.7m, the vertical depth of the filling pipeline riser is 497m, and the cumulative vertical depth is 781m, which belongs to a large vertical depth and long distance pipeline transportation system. In the process of slurry transportation, there are scientific problems such as unclear flow field and pressure distribution inside the pipeline and unclear slurry concentration distribution. The design process of flow performance indicators is as follows:

[0040] (1) Filling material: Coal gangue is used as filling aggregate, cement and fly ash are used as binder, certain additives are added to activate the fly ash, and water is added in a certain proportion to form a slurry with certain fluidity. The designed test plan is shown in Table 1.

[0041] Table 1 Test mix ratios for cementitious filling material transportation performance

[0042]

[0043]

[0044] The filling slurries of various proportions were subjected to rotational rheometer tests and sedimentation tests, and the respective results were obtained and summarized.

[0045] (2) According to the test results of the rotational rheometer, the relationship between the yield stress and viscosity of the filling slurry is as follows: Figure 4 shown.

[0046] The yield stress of Bingham fluid has a linear relationship with viscosity, where the modified determining exponent R 2 is 0.993, and the fitting formula is as follows:

[0047] τ0=kμ+u (Formula 1)

[0048] In this embodiment,

[0049] τ0=195.23761μ+6.53319 (Formula 2)

[0050] (3) To ensure that the filling slurry flows fully, the condition that the power source of the conveying is greater than the resistance source is met, which can be expressed as:

[0051] P e +P g ≥KLi (Formula 3)

[0052] Among them, the pipeline resistance loss i is:

[0053]

[0054] Combining equations 1, 3, and 4, we can get the expression of yield stress discrimination index:

[0055]

[0056] (4) According to the conditions of this coal mine example, the yield stress judgment index is:

[0057]

[0058] Where τ0 is the yield stress, Pa; v is the average flow velocity in the pipeline, m / s; P e is the power that the pump can provide, Pa; P g Power provided by gravity, Pa; D1, D2, …, D n is the diameter of the segmented pipeline, m; L1, L2, ..., L n is the length of the segmented pipeline, m; K is the local resistance coefficient, generally 1.05 to 1.1. According to the parameters of the mine filling system and the slurry data, the maximum allowable yield stress is calculated to be 219.8Pa.

[0059] (5) After obtaining the maximum allowable yield stress, the critical yield stress parameter can be used to derive the yield stress range of the filling slurry. In this embodiment, the lower limit of the yield stress required for the particles to "not settle" is conservatively analyzed from the perspective of the force on the gangue particles themselves, using the following formula:

[0060]

[0061] Among them, ρ p is the density of coarse aggregate, kg / m 3 ; ρ is slurry density, kg / m 3 ; d is the particle size of gangue, here it is taken as 15mm; C τ is the shear resistance coefficient, which is 1 for ideal smooth spherical particles and 1.2 to 2 for non-spherical particles. Based on this engineering condition, the minimum value of 45.8 Pa for coarse slurry particles to prevent pipe blockage can be calculated.

[0062] Therefore, the yield stress range of the filling slurry is 45.8≤τ0≤219.8Pa.

[0063] (6) Based on the previous mechanical property test and experimental results, combined with the yield stress discrimination index, the No. 9 and No. 15 filling slurry ratios were preliminarily selected, and the delamination index was then determined.

[0064] (7) The stratification index SI is a dimensionless parameter that reflects the uniformity of particle concentration distribution in a fluid. It is a parameter used to evaluate the degree of stratification of high-concentration cementitious filling slurry during pipeline transportation. It reflects the difference in sedimentation of slurries with different particle sizes under the action of gravity.

[0065]

[0066] Among them, C max , C min , C avg They are the maximum allowable concentration, minimum concentration and average concentration of slurry respectively;

[0067] From the analysis of the previous rheological test data, it can be seen that the slurry yield stress is positively correlated with the slurry concentration, such as Figure 5 shown.

[0068] The correlation expression between slurry yield stress and concentration is obtained as follows:

[0069]

[0070] Where C is the slurry concentration; a, b, and c are the concentration quadratic term, linear term, and constant term parameters, respectively. Solving equation 9 yields

[0071]

[0072] Since C is the concentration of the high-concentration cementitious filling slurry, in Formula 10, the coefficient before the root formula needs to be selected with a positive or negative sign according to the actual situation.

[0073] (8) The relationship between the layered concentration and position of 16 groups of orthogonal test ratios in the sedimentation test was fitted, and it was found that the slurry concentration distribution conformed to the linear equation, indicating that under the extreme condition of pipeline transportation for a sufficiently long time, the slurry concentration decreased linearly from top to bottom. Therefore, a two-variable linear equation was used to characterize the concentration change in the vertical direction of the pipeline.

[0074] C=my+n (Formula 11)

[0075] Among them, m and n are the parameters of the fitting equation; y = r / R, r is positive above the origin of the pipeline and negative below it, so the value range of y in the pipeline section is [-1,1].

[0076] (9) The maximum allowable concentration, minimum concentration and average concentration of the slurry required by formula (8) in this embodiment are

[0077]

[0078] C min =m+n (Formula 13)

[0079]

[0080] (10) Under Bingham fluid conditions, the shear stress of the slurry pipe wall is obtained by the Buckingham equation

[0081]

[0082] Among them, τ W is the shear stress of the pipe wall, Pa; τ0 is the yield stress, Pa; v is the average flow velocity in the pipeline, m / s; D is the pipe diameter, m.

[0083] (11) Combining the above equations, we can get the stratification index discriminant index

[0084]

[0085] Among them, a, b, and c are obtained by fitting 16 sets of orthogonal test data, which are 339.45, -455.13, and 136.18, respectively. The yield stress and viscosity of the No. 9 and No. 15 mixes are obtained by rotational rheometer testing, and the minimum concentration is obtained by sedimentation test results, as shown in Table 2.

[0086] Table 2 Test results parameter table

[0087]

[0088] Substituting into formula 16, the critical stratification index of mix No. 9 is 0.335, and the critical stratification index of mix No. 15 is 0.341. According to the test results of the settlement test, the stratification index of mix No. 9 is 0.25, and the stratification index of mix No. 15 is 0.24, both of which are within the critical range.

[0089] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for designing flow performance requirements of coal mine cementing filling slurry, characterized by: The following steps are involved: Step 1, taking the fluidity and stability of coal mine cementing filling slurry pipeline transportation as the research objectives, respectively designing experiments to obtain rheological performance indicators reflecting fluidity and sedimentation performance indicators reflecting stability, and establishing a database containing experimental data; Step 2, using the rheological performance index and the sedimentation performance index of the cementitious filling slurry to comprehensively reflect the flow performance requirements of the cementitious filling slurry in engineering applications; Step 3, obtaining the comprehensive flow performance index of the filling slurry with engineering applicability through step 2, and selecting the appropriate cementitious filling slurry.

2. A method for designing flow performance requirements of coal mine cementing filling slurry according to claim 1, characterized in that: The cementitious filling slurry is considered to be a Bingham fluid.

3. A method for designing flow performance requirements of coal mine cementing filling slurry according to claim 1, characterized in that: The rheological performance index of the cementitious filling slurry is characterized by the yield stress discrimination index, which meets the following conditions: Where τ0 is the yield stress; P e is the maximum pumping pressure; P g is the gravity acting on the slurry; K is the resistance coefficient; L is the pipe length; D is the pipe diameter; v is the slurry flow rate; k and u are the parameters of the mathematical characterization model of the slurry yield stress and viscosity, respectively.

4. A method for designing flow performance requirements of coal mine cementing filling slurry according to claim 3, characterized in that: The yield stress discrimination index is obtained through the rotational rheometer test of the cementing filling slurry, and a fitting model is established for the yield stress and viscosity of the filling slurry based on the test results, which is expressed as: τ0=kμ+u Here, μ is the viscosity.

5. A method for designing flow performance requirements of coal mine cementing filling slurry according to claim 1, characterized in that: The settlement performance index of the cementitious filling slurry is characterized by a critical stratification index discrimination index, which satisfies the following conditions: Where SI0 is the critical delamination index; τ0 is the yield stress; τ Wmax is the maximum shear stress of the slurry at the boundary layer; m and n are the parameters of the expression of slurry concentration and position respectively; a, b, c are the concentration quadratic term, linear term parameters and constant term parameters of the expression of the relationship between slurry yield stress and concentration respectively.

6. A method for designing flow performance requirements of coal mine cementing filling slurry according to claim 5, characterized in that: The critical delamination index is obtained through the settlement performance test of the cementing filling slurry, and a fitting model is established for the yield stress and concentration of the cementing filling slurry based on the test results, which is expressed as: τ0=exp(aC 2 +bC+c) Where C is the concentration of cementitious filling slurry.

7. A method for designing flow performance requirements of coal mine cementing filling slurry according to claim 6, characterized in that: The cementing filling slurry has a uniform concentration distribution in the horizontal direction of the pipe cross section, and in the vertical direction, the concentration distribution conforms to a linear relationship. An expression model of slurry concentration and vertical position is established: C=my+n. Wherein, y=r / R; a rectangular coordinate system is established with the center of the circular pipe cross section as the origin, then r is the distance from a certain position of the slurry to point 0, which is positive above the 0 axis and negative below it; R is the pipe radius; the value range of y is [-1,1].

8. A method for designing flow performance requirements of coal mine cementing filling slurry according to claim 6, characterized in that: The settling performance test of the cementitious filling slurry is carried out by means of a settling column mould.

9. A method for designing flow performance requirements of coal mine cementing filling slurry according to claim 8, characterized in that: The sedimentation column mold comprises a column body, and a groove tray is arranged on the top of the column body.

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