2018 Tailings and Mine Waste Conference

Transcription

1 2018 Tailings and Mine Waste Conference Improved Methodology for TSF Capacity Prediction October 1, 2018 Gordan Gjerapic, Golder Associates, Inc. Dobroslav Znidarcic, University of Colorado at Boulder

2 Outline Three-dimensional considerations of seepage and compression Large strain deformation during deposition and closure Variable production rate and complex geometries Robust numerical approach Mass balance and water balance errors 2

3 Numerical Models H I S T O R I C A L P E R S P E C T I V E Gibson et al. (1967) large strain consolidation theory One-dimensional models Schiffman et al. (1992) ACCUMV Yao and Znidarcic (1997) CONDES Fox and Berles (1997) CS2 GWP Software (1999) FSConsol 3

4 Numerical Models 2D and 3D C O M M E R C I A L M O D E L S U S E D F O R T S F C O N S O L I D AT I O N Programs supporting large strain consolidation approach FLAC and FLAC3D TM - ITASCA Consulting Group PLAXIS, PLAXIS3D Plaxis BV => Bentley Systems, Inc. SVOFFICE TM 5 SVFLUX SVSOLID, SoilVision => Bentley Systems, Inc. 4

5 Simplified Consolidation Approach 3D D O M I N A N T S E E PA G E A N D C O M P R E S S I O N M E C H A N I S M S TSF modelling using a series of one dimensional columns (Gjerapic et al. 2008) Consolidation dominated by seepage in vertical direction Applicable to most TSF geometries and boundary conditions SoilVision => Pseudo 3D large-strain consolidation (under development as of May 2018) 5

6 Improved Methodology P R A C T I C A L I M P L I C AT I O N S Develop solutions for rapid assessment of TSF capacity Negligible vertical strains during the filling process Fully consolidated tailings (apply analytical solutions) TSF filling starting with the deepest column and continuing by filling horizontal layers at higher elevation (e.g. FSConsol approach) TSF filling using a series of one-dimensional vertical columns (Gjerapic et al. 2008) => computationally efficient and relatively easy to implement 6

7 Upper and Lower Bound N U M E R I C A L M O D E L S Horizontal Layers: n V total = i=1 H i H i 1 A i 7

8 Upper and Lower Bound N U M E R I C A L M O D E L S Vertical Columns: V total = n i=1 A LBi H LBi 8

9 Does it Matter? TA I L I N G S V S. F O U N D AT I O N C O M P R E S S I B I L I T Y 9

10 How to Determine Calculation Errors? M A S S C O N S E R VAT I O N t න Q s τ dτ = ρ dry,avg V TSF t 0 Total Mass of Solids = Avg. Dry Density of Tails x TSF Volume t න 0 Q s τ dτ = G s ρ w Total Mass of Solids = n i=1 A LBi H i solids Mass Density of Solids x Volume of Solids in Individual Columns 10

11 Mass (Mt) Example F I L L I N G S C E N A R I O Case 1 => 30,000 t/day for 10 years Case 2 => On-off filling (1yr + 1yr) see paper Case Time (year) 11

12 Height (m) Case 1 Results Time Settlement M A S S C O N S E R VAT I O N FSConsol FILLCON - Tallest Column Incompressible Tailings (U=0%) Instantaneous Consolidation (U=100%) Time (year) 12

13 Height (m) Case 1 Void Ratio Profiles at 10 years 90 FSConsol 75 Column 1 60 Column 2 45 Column 3 30 Column 4 Column Void Ratio (-) 13

14 Height (m) Case 1 Avg. Void Ratio Profiles at 10 years FSConsol Column 1 Layer Filling Model Column Filling Model Void Ratio (-) 14

15 Height (m) Case 1 Void Ratio Profiles at 16 years FSConsol Column 1 Column 2 Column 3 Column 4 Column Void Ratio (-)

16 Height (m) Case 1 Avg. Void Ratio Profiles at 16 years FSConsol Column 1 Layer Filling Model Column Filling Model Void Ratio (-) 16

17 Mass Balance Error Mass Balance Errors Horizontal Layer Approach -70% -60% -50% -40% -30% -20% -10% 0% Year 10 Year 16 Year 20 Year 30 Error - Using Average Solids Content/ Density Error - Integrated Void Ratio Profile 17

18 Mass Balance Error Mass Balance Errors Vertical Column Model -0.70% -0.60% -0.50% -0.40% -0.30% -0.20% -0.10% 0.00% Year 10 Year 16 Error - Using Average Solids Content/ Density Error - Integrated Void Ratio Profile 18

19 More things should not be used than are necessary William of Ockham Everything should be made as simple as possible, but not simpler Albert Einstein 19

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