A design method for flow performance requirements of cemented filling slurry in coal mines

Abstract

The present invention discloses a method for designing the flow performance requirements of cementitious filling slurry for coal mines, comprising the following steps: taking the flow and stability of cementitious filling slurry pipeline transportation as research objectives, respectively designing experiments and establishing a database; using the rheological performance index and sedimentation performance index of cementitious filling slurry to comprehensively reflect the flow performance requirements of cementitious filling slurry in engineering applications; obtaining comprehensive flow performance indexes of filling slurry with engineering applicability, and selecting suitable cementitious filling slurry. The present invention can provide a design basis for the mine filling pipeline system through the design of the flow performance requirements of filling slurry, avoid poor underground filling effect due to unreasonable slurry parameter design; prevent pipe blockage and pipe burst accidents due to poor slurry fluidity, reduce the wear of the pipeline system, thereby improving the stability of the filling slurry during transportation, and facilitate the management of the filling system by mining enterprises, which has important engineering significance and promotion and application value.

Description

Technical Field

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

[0002] The backfill mining method has been increasingly widely used. 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 and green coal mining technology. After more than a hundred years of development, backfill mining technology has evolved from early dry backfilling to today's cemented backfilling, high-water backfilling and other filling methods, and has gradually moved towards automation and intelligence in the pursuit of green and efficient mining of coal resources. The slurry used for backfilling starts from the ground filling station and is transported to the goaf through the pre-laid filling pipeline underground by pumping or gravity, forming a backfill body with a certain strength to support the surrounding rock. Pipeline transportation of filling slurry ensures the quality and efficiency of underground filling and is one of the key technologies of backfill mining. In engineering, the smooth operation of the pipeline transportation system is generally controlled by regulating the flow rate, flow rate and other flow properties of the filling slurry.

[0003] The flow properties of filling slurry are 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 the 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, the pipeline material, etc. will also affect the flow properties of the slurry. Unreasonable design of flow performance parameters will cause the filling slurry to segregate and stratify, 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, lead to accidents such as pipe blockage and pipe burst, causing losses to mining companies. At present, engineering projects generally regard filling slurry as a fluid for research, which has the 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 for selecting the flow performance parameters of filling slurry. Engineering projects usually select and design based on similar mining 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 the 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 solutions:

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

[0008] Step 1: Taking the fluidity and stability of coal mine cemented filling slurry pipeline transportation as the research objectives, experiments were designed to obtain rheological performance indicators reflecting fluidity and sedimentation performance indicators reflecting stability, and a database containing the experimental data was established;

[0009] Step 2: using the rheological performance index and settlement 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: Obtain comprehensive flow performance indicators of filling slurry with engineering applicability through step 2, and select suitable cementitious filling slurry.

[0011] Furthermore, 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 cementitious 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, and c are the concentration quadratic term, linear term parameters, and constant term parameters of the expression of the relationship between the slurry yield stress and concentration respectively.

[0021] Furthermore, the critical delamination index is obtained through the settlement performance test of the cementitious filling slurry, and a fitting model is established for the yield stress and concentration of the cementitious filling slurry based on 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 cementitious filling slurry has a uniform concentration distribution in the horizontal direction of the pipe cross section, while in the vertical direction, the concentration distribution conforms to a linear relationship. An expression model of the slurry concentration and the vertical position is established:

[0025] C=my+n

[0026] Where y = r / R; a rectangular coordinate system is established with the center of the circular pipe 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] Furthermore, the sedimentation column mold includes a column body, and a groove tray is provided on the top of the column body. In one embodiment, the column body of the sedimentation column mold is modified 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 the column top is provided with a square groove tray with a diameter of 10 cm and a height of 3 cm.

[0029] Beneficial effects: The present invention uses multidisciplinary means such as mechanics and rheology to derive coal mine cemented filling slurry pipeline transportation indicators that include performance requirements such as viscosity, yield stress, and stratification index, revealing the flow laws of cemented filling slurry pipeline transportation, and proposing a cemented filling large vertical depth and long distance pipeline transportation performance design theory, providing a theoretical basis for the characterization of coal mine cemented filling slurry flow performance, so that the design of filling slurry transportation indicators can be based on evidence. At the same time, it can provide technical reference for coal mine goaf cemented filling mining work under similar conditions. This method has the advantages of simple design, clear purpose, high efficiency, and wide applicability. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0031] Figure 2 This is a schematic diagram of the sedimentation performance test principle used in 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 between slurry concentration and yield stress. DETAILED DESCRIPTION

[0035] The present invention provides a method for designing the flow performance requirements of coal mine cemented filling slurry. 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, and a yield stress discrimination index is obtained; 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, and a critical stratification index discrimination index is obtained; 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 with reference to the accompanying drawings and embodiments.

[0037] Example

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

[0039] In this example, the total pipeline length of a coal mine cemented filling slurry conveying system reached 2909.7 meters, the vertical depth of the filling pipeline riser reached 497 meters, and the cumulative vertical depth reached 781 meters. This is a large vertical depth and long-distance pipeline conveying system. The slurry conveying process faces scientific challenges such as unclear flow field and pressure distribution within the pipeline and unclear slurry concentration distribution. The flow performance index design process is as follows:

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

[0041] Table 1 Test mix ratios for cementitious filling materials’ transport 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 (Equation 1)

[0048] In this embodiment,

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

[0050] (3) To ensure sufficient flow of the filling slurry, the condition to be met is that the power source of the conveying is greater than the resistance source, 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 obtain the expression of the yield stress discrimination index:

[0055]

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

[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, in meters; K is the local resistance coefficient, generally ranging from 1.05 to 1.1. Based on the parameters of the mine filling system and the slurry data, the maximum allowable yield stress is calculated to be 219.8 Pa.

[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 bound 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 15mm; C τ is the shear resistance coefficient. For ideal smooth spherical particles, its value is 1, and for non-spherical particles, it is 1.2 to 2. Based on this engineering condition, the minimum value for coarse slurry particles to prevent accumulation and pipe clogging can be calculated to be 45.8 Pa.

[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 judged.

[0064] (7) The stratification index SI is a dimensionless parameter that reflects the uniformity of particle concentration distribution in the fluid. It is a parameter used to evaluate the degree of stratification of high-concentration cementitious filling slurry during pipeline transportation. It reflects the sedimentation difference 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 radical needs to be selected with a positive or negative sign based on 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 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 from 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 formulas, we can get the stratification index discrimination index

[0084]

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

[0086] Table 2 Test results parameters

[0087]

[0088] Substituting into Equation 16, we can calculate that the critical stratification index of mix 9 is 0.335, and the critical stratification index of mix 15 is 0.341. According to the test results of the settlement test, the stratification index of mix 9 is 0.25, and the stratification index of mix 15 is 0.24, both 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 principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for designing the 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 cemented filling slurry pipeline transportation as the research objectives, experiments were designed to obtain rheological performance indicators reflecting fluidity and sedimentation performance indicators reflecting stability, and a database containing the experimental data was established; Step 2: using the rheological performance index and settlement performance index of the cementitious filling slurry to comprehensively reflect the flow performance requirements of the cementitious filling slurry in engineering applications; The settlement performance index of the cementitious filling slurry is characterized by a critical stratification 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; a, b, and c are the concentration quadratic term, linear term parameter, and constant term parameter of the expression of the relationship between slurry yield stress and concentration, respectively; Step 3: Obtain comprehensive flow performance indicators of filling slurry with engineering applicability through step 2, and select suitable 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 fill slurry is considered to be a Bingham fluid.

3. The 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 by a rotational rheometer test of the cemented 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. The method for designing flow performance requirements of coal mine cementing filling slurry according to claim 1, characterized in that: The critical delamination index is obtained through the settlement performance test of the cementitious filling slurry, and a fitting model is established for the yield stress and concentration of the cementitious 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.

6. A method for designing flow performance requirements of coal mine cementing filling slurry according to claim 5, characterized in that: The cementitious filling slurry has a uniform concentration distribution in the horizontal direction of the pipe cross section, while 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 Where y = r / R; a rectangular coordinate system is established with the center of the circular pipe 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].

7. The method for designing flow performance requirements of coal mine cementing filling slurry according to claim 5, characterized in that: The settling performance test of the cementitious filling slurry is carried out by using a settling column mold.

8. A method for designing flow performance requirements of coal mine cementing filling slurry according to claim 7, 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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