Method for converting shear strength parameter of tailing sedimentary layer

Abstract

The invention belongs to the technical field of tailing pond design and calculation, and particularly provides a tailing sedimentary layer shear strength parameter conversion method which comprises the following specific steps: step 1, field investigation; step 2, sampling and parameter analysis; the particle size distribution curve, the dry density, the natural density, the maximum void ratio, the minimum void ratio, the permeability coefficient, the cohesive force and the internal friction angle parameter of the tailing sample are obtained; 3, determining in-situ test parameters and correction coefficients; the pore ratio and the standard penetration cohesive force of the in-situ tailing sedimentary body are specifically included; step 4, parameter conversion; converting the cohesive force of the tailings sedimentary layer and converting the internal friction angle of the tailings sedimentary layer. The complete method for calculating the cohesive force and the internal friction angle of the strength parameters of the on-site in-situ tailing sedimentary layer with clear mechanical significance is established, objective strength parameters are provided for stability design of the tailing pond dam, the design error of the tailing pond dam is reduced, and the safety of the tailing pond dam is improved.

Description

[0001] This invention belongs to the field of tailings dam design and calculation technology, and specifically provides a method for converting the shear strength parameters of tailings sediment layers. Background Technology

[0002] Tailings dams are a major hazard source in mines, with over 12,000 existing in my country. In recent years, my country's annual tailings discharge has exceeded 1 billion tons and is increasing year by year, necessitating the construction or heightening of tailings dams. In 2020, the Ministry of Emergency Management proposed that the number of tailings dams nationwide should, in principle, only decrease, to curb non-force majeure dam failures. This has led to a contradiction between the expansion of mining scale and the limited discharge sites, requiring existing tailings dams to be heightened and expanded. However, with the increase in capacity and height, tailings dam failures have become frequent, causing enormous losses.

[0003] Tailings are solid waste generated after mineral processing. After being pumped into tailings ponds, they accumulate over many years to form sedimentary layers. Their hydrophysical properties are complex, and the tailings are in a very slow consolidation state. The paste-like tailings possess both buoyancy and bearing capacity, and their stability affects the safety of the tailings pond. The shear strength parameters (c, φ) of the tailings dam and the accumulated material within the pond are core indicators for assessing the stability of the tailings dam. There are three main methods for determining the strength parameters of the tailings sedimentary layer: first, on-site sampling and laboratory geotechnical testing; however, due to the characteristics of the tailings, the measured results differ greatly from the actual values; second, in-situ testing combined with empirical formulas for estimation; this needs to be combined with laboratory data, but due to the large differences in tailings, it is difficult to propose standard strength parameters; third, the development of in-situ sampling and shear testing equipment to conduct low-disturbance in-situ tests, which is still under exploration.

[0004] Based on a comprehensive analysis of the differences in various aspects of tailings sediment layers, in-situ testing is currently the most objective method for determining strength parameters. However, it is necessary to resolve the correspondence between laboratory geotechnical parameters and in-situ test indices in order to scientifically and objectively determine the strength parameters. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for converting the shear strength parameters of tailings sediment layers, the specific steps of which include: Step 1: On-site investigation; Verify the location, accumulation time, mineral composition, and discharge method of the tailings deposits; Step 2: Sampling and Parameter Analysis; Particle size analysis, density test, compression test, direct shear test and triaxial test were conducted on the tailings samples to obtain the particle size distribution curve, dry density, natural density, maximum void ratio, minimum void ratio, permeability coefficient, cohesion and internal friction angle parameters of the tailings samples; Step 3: Determine the in-situ test parameters and correction factors; Specifically, this includes the porosity and standard penetration cohesion of in-situ tailings deposits; Step 4: Parameter conversion; Calculated cohesion and internal friction angle of tailings deposits.

[0006] Furthermore, in step two, the confining pressure of the triaxial test is set to the pressure at the specimen burial depth.

[0007] Furthermore, in step three, the porosity of the in-situ tailings deposit is: (1); In the formula, e o The in-situ porosity. D ro The relative density for in-situ standard penetration tests; e max The maximum porosity of the tailings is denoted as . e min This represents the minimum void ratio of the tailings.

[0008] Furthermore, in step three, the standard penetration cohesion correction factor is: (2); In the formula, α is the standard penetration cohesion correction factor; N The corrected standard penetration test blow count; m 1. m 2 represents the calculation coefficient; Internal friction angle correction: (3); (4); In the formula, D f D Correction for the internal friction angle caused by in-situ relative density; D f N Correction for the internal friction angle caused by the standard penetration test blow count; D rr The relative density for laboratory geotechnical tests; N b The baseline number of hammer blows; m 3 represents the relative density correction factor; m 4 is the standard penetration correction factor.

[0009] Furthermore, in step four, the calculated cohesion of the tailings sediment layer is: (5); In the formula, c o For in-situ cohesion; c r For cohesion in laboratory geotechnical tests; k Permeability coefficient; e o The in-situ porosity. e r The void ratio is from laboratory geotechnical tests. α is the standard penetration cohesion correction factor.

[0010] Furthermore, in step four, the converted internal friction angle of the tailings sediment layer is: (6); In the formula, f o This refers to the in-situ internal friction angle at the site. f r This refers to the internal friction angle measured in laboratory geotechnical tests.

[0011] The beneficial effects of using this invention are: Establish a complete and mechanically meaningful calculation method for the strength parameters of in-situ tailings sediment layers, namely cohesion and internal friction angle, to provide objective strength parameters for the stability design of tailings dams, reduce design errors of tailings dams, and improve the safety of tailings dams. Attached Figure Description

[0012] Figure 1 This is a flowchart of the present invention; Figure 2 This is a particle size distribution diagram of copper tailings. Detailed Implementation

[0013] The present invention will now be described in detail with reference to the accompanying drawings.

[0014] Reference Figure 1 A method for converting shear strength parameters of tailings deposits, the specific steps of which include: Step 1: On-site investigation; The specific investigation should include verifying the location, time, mineral composition, and discharge method of the tailings deposits.

[0015] Step 2: Sampling and Parameter Analysis; Tailings samples were taken from different exploration depths, packaged, and transported. Particle size analysis, density test, compression test, direct shear test and triaxial test were conducted on the tailings samples to obtain the particle size distribution curve, dry density, natural density, maximum void ratio, minimum void ratio, permeability coefficient, cohesion and internal friction angle parameters of the tailings samples; In the triaxial test, the confining pressure is set to the pressure at the depth of the specimen burial.

[0016] Step 3: Determine the in-situ test parameters and correction factors; Porosity of in-situ tailings deposits: (1); In the formula, e o The in-situ porosity. D ro The relative density for in-situ standard penetration tests; e max The maximum porosity of the tailings is denoted as . e min This represents the minimum void ratio of the tailings.

[0017] Standard penetration cohesion correction factor: (2); In the formula, α is the standard penetration cohesion correction factor; N The corrected standard penetration test blow count; m 1. m 2 represents the calculation coefficient; Internal friction angle correction: (3); (4); In the formula, D f D Correction for the internal friction angle caused by in-situ relative density; D f N Correction for the internal friction angle caused by the standard penetration test blow count; D rr The relative density for laboratory geotechnical tests; N b The baseline number of hammer blows; m 3 represents the relative density correction factor; m 4 is the standard penetration correction factor.

[0018] Step 4: Parameter conversion; Equivalent cohesion of tailings deposits: (5); In the formula, c o For in-situ cohesion; c r For cohesion in laboratory geotechnical tests; k Permeability coefficient; e o The in-situ porosity. e r The void ratio is from laboratory geotechnical tests. α is the standard penetration cohesion correction factor.

[0019] The converted internal friction angle of the tailings deposit layer is: (6); In the formula, f o This refers to the in-situ internal friction angle at the site. f r This refers to the internal friction angle measured in laboratory geotechnical tests.

[0020] Establish a complete and mechanically meaningful calculation method for the strength parameters of in-situ tailings sediment layers, namely cohesion and internal friction angle, to provide objective strength parameters for the stability design of tailings dams, reduce design errors of tailings dams, and improve the safety of tailings dams.

[0021] Example 1

[0022] Reference Figure 1 A copper tailings dam is located in a seasonally frozen area. It is a flat tailings dam, covering an area of ​​approximately 6.7 km². 2 The initial design of the dam was 1195m long, about 54m high, about 8m wide at the top, and the upstream-downstream slope ratio was about 1:2.5. It was a permeable rockfill dam; above it was a 7-stage rockfill dam.

[0023] A method for converting the shear strength parameters of tailings deposits is applied to correct the data. The specific process is as follows: On-site investigation; The tailings dam discharges copper tailings using a paste discharge process. In actual operation, paste discharge is used in summer, while high-concentration tailings water is used in other seasons. The dam has been in operation for 15 years.

[0024] Reference Figure 2 In copper tailings, particles with a diameter of 100-1000 μm (sand size) account for 60% of the volume, particles with a diameter of 10-100 μm (coarse particles) account for 25%, particles with a diameter of 1-10 μm (fine particles) account for 13%, and the remaining 2% are 0.1-1 μm (submicron) particles. D[4,3] and D[3,2] are 152.6 and 17.2 respectively, with a large difference between the two values, indicating that the material has irregular particle shape and uneven particle size distribution; Dv(90) value is 320.5, indicating that the overall particle size is relatively coarse. The SiO2 content in copper tailings reaches the highest at 68.4%, and the main chemical components from largest to smallest are SiO2 > Fe2O3 > CaO > Al2O3 > MgO.

[0025] sampling; The design borehole spacing is 60.0 meters and the borehole depth is 85m.

[0026] Soft soil samplers were used to collect tailings samples at different exploration depths, which were then packaged and transported to ensure that the core recovery rate met the specifications and to reduce soil sample disturbance.

[0027] Parameter analysis; Particle size analysis, density test, compression test, direct shear test and triaxial test were conducted on the tailings samples. In the triaxial test, the confining pressure is set to the pressure at the specimen burial depth. The particle size distribution curve, dry density, natural density, maximum void ratio, minimum void ratio, permeability coefficient, cohesion and internal friction angle of the sample were determined.

[0028] Standard penetration tests were conducted in situ at the survey points, and the standard penetration test blow count was recorded. The blow count was then corrected according to the Code for Geotechnical Investigation (GB 50021). Taking the F7 exploration point as an example, (1) Tailings ③, at 1.65-1.95m, N=1.0 blow; at 3.65-3.95m, N=3.7 blow; (2) Tailings ④, at 8.65-8.95m, N=5.0 blows; at 13.15-13.45m, N=3.8 blows; (3) Tailings ⑤, at 17.15-17.45m, N=4.3 blows; at 19.15-19.45m, N=4.9 blows; at 21.65-21.95m, N=9.8 blows; at 33.65-33.95m, N=5.6 blows; (4) Tailings ⑥, at 36.65-39.95m, N=11.2 blows; (5) Tailings ⑦, at 44.65-44.95m, N=13.3 blows; at 50.15-50.45m, N=14.7 blows.

[0029] The porosity of the in-situ tailings sediments at the site; Taking the F7 exploration point as an example, the in-situ porosity of the tailings is calculated using formula (1). e o The results are as follows: (1) Tailings ③, at 1.65-1.95m, e o =0.813; at 3.65-3.95m, e o =0.794; (2) Tailings ④, at 8.65-8.95m, e o =0.761; at 13.15-13.45m, e o =0.776; (3) Tailings ⑤, at 17.15-17.45m, e o =0.740; in the range of 19.15-19.45m, e o =0.732; in the range of 21.65-21.95m, e o =0.678; at 33.65-33.95m, e o =0.733; (4) Tailings ⑥, at 36.65-39.95m, e o =0.693; (5) Tailings ⑦, at 44.65-44.95m, e o =0.609; at 50.15-50.45m, e o =0.602.

[0030] Standard penetration cohesion correction factor; Select m 1 = 0.04 m 2=0.96. Taking the F7 exploration point as an example, the standard penetration cohesion correction factor α is calculated using formula (2), and the calculation results are as follows: (1) Tailings ③, at 1.65-1.95m, α =0.960; in the range of 3.65-3.95m, α =1.012; (2) Tailings ④, at 8.65-8.95m, α =1.024; in the range of 13.15-13.45m, α =1.013; (3) Tailings ⑤, at 17.15-17.45m, α =1.018; in the range of 19.15-19.45m, α =1.024; in the range of 21.65-21.95m, α =1.051; at 33.65-33.95m, α =1.029; (4) Tailings ⑥, at 36.65-39.95m, α =1.057; (5) Tailings ⑦, at 44.65-44.95m, α =1.064; at 50.15-50.45m, α =1.068.

[0031] Correction value for internal friction angle; m 3 = 0.15° / % ~ 0.25° / % m 4 = 2.0°~3.0°, taking exploration point F7 as an example, it is selected with a preference for safety. m 3 = 0.15° / %, m 4 = 2.0°. The correction value of the internal friction angle is calculated using formulas (3) and (4), and the calculation results are as follows: (1) Tailings ③, at 1.65-1.95m, D f D =0.037°, D f N =-0.191°; at 3.65-3.95m, D f D =0.070°, D f N =0.419°; (2) Tailings ④, at 8.65-8.95m, D f D =0.079°, D f N =-2.197°; at 13.15-13.45m, D f D =0.067°, D f N =-2.746°; (3) Tailings ⑤, at 17.15-17.45m, D f D=0.069°, D f N =-2.499°; at 19.15-19.45m, D f D =0.073°, D f N =-2.238°; at 21.65-21.95m, D f D =0.102°, D f N =-0.851°; at 33.65-33.95m, D f D =0.073°, D f N =-1.971°; (4) Tailings ⑥, at 36.65-39.95m, D f D =0.100°, D f N =-0.584°; (5) Tailings ⑦, at 44.65-44.95m, D f D =0.106°, D f N =-0.241°; at 50.15-50.45m, D f D =0.109°, D f N =-0.040°.

[0032] Equivalent cohesion of tailings deposits; Taking the F7 exploration point as an example, the equivalent cohesion value of the tailings sediment layer is calculated using formula (5), and the calculation results are as follows: (1) Tailings ③, at 1.65-1.95m, c o =8.45 kPa; in the range of 3.65-3.95 m, c o =8.91 kPa; (2) Tailings ④, at 8.65-8.95m, c o =11.78 kPa; in the range of 13.15-13.45 m, c o =11.65 kPa; (3) Tailings ⑤, at 17.15-17.45m, c o =14.46 kPa; in the range of 19.15-19.45 m,c o =14.53 kPa; in the range of 21.65-21.95 m, c o =14.93 kPa; at 33.65-33.95 m, c o =14.61 kPa; (4) Tailings ⑥, at 36.65-39.95m, c o =15.85 kPa; (5) Tailings ⑦, at 44.65-44.95m, c o =17.87 kPa; in the range of 50.15-50.45 m, c o =18.04 kPa.

[0033] Calculation of internal friction angle for tailings deposits; Taking the F7 exploration point as an example, the converted internal friction angle value of the tailings sediment layer is calculated using formula (6), and the calculation results are as follows: (1) Tailings ③, at 1.65-1.95m, f o =1.35°; at 3.65-3.95m, f o =1.99°; (2) Tailings ④, at 8.65-8.95m, f o =12.38°; at 13.15-13.45m, f o =11.82°; (3) Tailings ⑤, at 17.15-17.45m, f o =13.07°; between 19.15 and 19.45 m, f o =13.34°; at 21.65-21.95m, f o =14.75°; at 33.65-33.95m, f o =13.60°; (4) Tailings ⑥, at 36.65-39.95m, f o =16.82°; (5) Tailings ⑦, at 44.65-44.95m, f o=17.87°; at 50.15-50.45m, f o =18.07°.

[0034] The above content is only a preferred embodiment of the present invention. For those skilled in the art, many changes can be made in the specific implementation and application scope based on the concept of the present invention. As long as these changes do not depart from the concept of the present invention, they all fall within the protection scope of the present invention.

Claims

1. A method for converting shear strength parameters of tailings sediment layers, characterized in that, The specific steps include: Step 1: On-site investigation; Verify the location, accumulation time, mineral composition, and discharge method of the tailings deposits; Step 2: Sampling and Parameter Analysis; Particle size analysis, density test, compression test, direct shear test and triaxial test were conducted on the tailings samples to obtain the particle size distribution curve, dry density, natural density, maximum void ratio, minimum void ratio, permeability coefficient, cohesion and internal friction angle parameters of the tailings samples; Step 3: Determine the in-situ test parameters and correction factors; Specifically, this includes the porosity and standard penetration cohesion of in-situ tailings deposits; Step 4: Parameter conversion; Calculated cohesion and internal friction angle of tailings deposits.

2. The method for converting shear strength parameters of tailings sedimentary layers according to claim 1, characterized in that: In step two, the confining pressure of the triaxial test is set to the pressure at the specimen burial depth.

3. A method for converting shear strength parameters of tailings sedimentary layers according to any one of claims 1 or 2, characterized in that: In step three, the porosity of the in-situ tailings deposit is: (1)； In the formula, e o The in-situ porosity. D ro The relative density for in-situ standard penetration tests; e max This represents the maximum void ratio of the tailings. e min This represents the minimum void ratio of the tailings.

4. The method for converting shear strength parameters of tailings sedimentary layers according to claim 3, characterized in that: In step three, the standard penetration cohesion correction factor is: (2)； In the formula, α is the standard penetration cohesion correction factor; N The corrected standard penetration test blow count; m 1. m 2 represents the calculation coefficient; Internal friction angle correction: (3)； (4)； In the formula, D φ D Correction for the internal friction angle caused by in-situ relative density; D φ N Correction for the internal friction angle caused by the standard penetration test blow count; D rr The relative density for laboratory geotechnical tests; N b The baseline number of hammer blows; m 3 is the relative density correction factor; m 4 is the standard penetration correction factor.

5. The method for converting shear strength parameters of tailings deposits according to claim 4, characterized in that: In step four, the equivalent cohesion of the tailings sediment layer is: (5)； In the formula, c o For in-situ cohesion; c r For cohesion in laboratory geotechnical tests; k Permeability coefficient; e o The in-situ porosity. e r The void ratio is from laboratory geotechnical tests. α is the standard penetration cohesion correction factor.

6. The method for converting shear strength parameters of tailings deposits according to claim 5, characterized in that: In step four, the converted internal friction angle of the tailings sediment layer is: (6)； In the formula, φ o This refers to the in-situ internal friction angle at the site. φ r This refers to the internal friction angle measured in laboratory geotechnical tests.

Images