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An investigation of longwall failure using 3D numerical modelling – A case study at a copper mine

Phu Minh Vuong Nguyen

Phu Minh Vuong Nguyen

Glowny Instytut GornictwaKatowice, Poland
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Nguyen, Phu Minh Vuong
, 
Tomasz Olczak

Tomasz Olczak

KHGM Polska Miedz S.A., Polkowice-Sieroszowice mine
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Olczak, Tomasz
 e 
Sywester Rajwa

Sywester Rajwa

Central Mining Institute
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Rajwa, Sywester
  
07 ott 2021
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Categoria dell'articolo: Original Study
Pubblicato online: 07 ott 2021
Pagine: 389 - 410
Ricevuto: 25 nov 2020
Accettato: 08 lug 2021
DOI: https://doi.org/10.2478/sgem-2021-0019
Parole chiave
© 2021 Phu Minh Vuong Nguyen et al., published by Sciendo
This work is licensed under the Creative Commons Attribution 4.0 International License.

Figure 1

Failures in the 5A/1 longwall a) roof falls, b) wall spalling.
Failures in the 5A/1 longwall a) roof falls, b) wall spalling.

Figure 2

Location of the Polkowice-Sieroszowice copper mine.
Location of the Polkowice-Sieroszowice copper mine.

Figure 3

Outline of the A5/1 copper longwall (not to scale).
Outline of the A5/1 copper longwall (not to scale).

Figure 4

Spacing of box crib behind the powered roof support.
Spacing of box crib behind the powered roof support.

Figure 5

Outline of the powered roof support applied in the 5A/1 longwall panel at the set-up stage.
Outline of the powered roof support applied in the 5A/1 longwall panel at the set-up stage.

Figure 6

Location of the convergence points (not to scale).
Location of the convergence points (not to scale).

Figure 7

3D model: a) initial model; b) outline of the 5A/1 longwall panel
3D model: a) initial model; b) outline of the 5A/1 longwall panel

Figure 8

Cable elements (black) and rockbolt elements (blue) in a 3D model.
Cable elements (black) and rockbolt elements (blue) in a 3D model.

Figure 9

Sketch of the LINK-N-LOCK box crib: a) top view, b) dimensions of a single crib.
Sketch of the LINK-N-LOCK box crib: a) top view, b) dimensions of a single crib.

Figure 10

Load-bearing capacity of the LINK-N-LOCK box crib at the height of 2 m with different element lengths.
Load-bearing capacity of the LINK-N-LOCK box crib at the height of 2 m with different element lengths.

Figure 11

The value and distribution of the load-bearing capacity of the powered roof support with pressure of 32 MPa set in the hydraulic legs for an operating height of 2 m.
The value and distribution of the load-bearing capacity of the powered roof support with pressure of 32 MPa set in the hydraulic legs for an operating height of 2 m.

Figure 12

Progress of vertical convergence at: a) headgate, b) tailgate.
Progress of vertical convergence at: a) headgate, b) tailgate.

Figure 13

Failure around the longwall face using the Mohr–Coulomb model.
Failure around the longwall face using the Mohr–Coulomb model.

Figure 14

Displacement around the longwall face using the Mohr–Coulomb model: a) vertical displacement along the tip-to-face distance, b) horizontal displacement along the longwall face.
Displacement around the longwall face using the Mohr–Coulomb model: a) vertical displacement along the tip-to-face distance, b) horizontal displacement along the longwall face.

Figure 15

Failures around the longwall face using the strain-softening model.
Failures around the longwall face using the strain-softening model.

Figure 16

Displacement around the longwall face using the strain-softening model: a) vertical displacement along the tip-to-face distance, b) horizontal displacement along the longwall face.
Displacement around the longwall face using the strain-softening model: a) vertical displacement along the tip-to-face distance, b) horizontal displacement along the longwall face.

Figure 17

Examples of failures that occurred in the 5A/1 longwall: a, b) roof falls, c) wall spalling.
Examples of failures that occurred in the 5A/1 longwall: a, b) roof falls, c) wall spalling.

Figure 18

Plasticity around the longwall face with a) tip-to-face distance of 3 m, b) tip-to-face distance of 1.5 m.
Plasticity around the longwall face with a) tip-to-face distance of 3 m, b) tip-to-face distance of 1.5 m.

Figure 19

Plasticity around the longwall face with different spacing of the box crib: a) 6.0 m, b) 3.0 m and c) 1.5 m.
Plasticity around the longwall face with different spacing of the box crib: a) 6.0 m, b) 3.0 m and c) 1.5 m.

Figure 20

Plasticity around the longwall face with hydraulic backfilling (sand).
Plasticity around the longwall face with hydraulic backfilling (sand).

Figure 21

Plasticity around the longwall face with different load-bearing capacities of the powered roof support: a) 2600 kN b) 4000 kN.
Plasticity around the longwall face with different load-bearing capacities of the powered roof support: a) 2600 kN b) 4000 kN.

Figure 22

Plasticity around the longwall face with the selected influencing factors combined.
Plasticity around the longwall face with the selected influencing factors combined.

Lithology of rock mass in the A5 region_

Rock mass Rock layer thickness (m)
Anhydrite 157 Roof rocks
Limy dolomite (I) 8
Limy dolomite (I) 9
Compact limy dolomite (II) 1.0
Compact limy dolomite (II) 0.7
Compact limy dolomite (II) 0.5
Dolomite + shale 2.0 Copper deposit
Grey sandstone 4.4 Floor rocks
Red sandstone 200

Mechanical parameters of rock mass adopted for numerical modelling_

Bulk modulus, K (GPa) Shear modulus, G (GPa) Friction angle, θ (°) Cohesion, c (MPa) Tensile strength, Rt (MPa) Density, γ (kg/m3)
Anhydrite 3.60 2.25 34.0 2.40 1.10 2950
Dolomite, limestone upper 2.70 1.84 45.0 2.20 0.93 2750
Dolomite, limestone lower 2.40 1.70 42.0 1.70 0.70 2650
Copper deposit 1.80 1.40 27.0 1.35 0.60 2600
Grey sandstone 1.30 1.10 32.0 1.25 0.50 2200
Red sandstone 0.80 0.70 30.0 1.08 0.45 1900

Cable element and rockbolt element properties_

Rockbolt element Cable element
Rockbolt diameter, m 0.02 Cable diameter, m 0.0155
Young's modulus, GPa 200 Young's modulus, GPa 200
Cross-sectional area, m2 3.14e-4 Cross-sectional area, m2 1.89e-4
Exposed perimeter, m 0.063 Exposed perimeter, m 0.049
Axial tensile yield strength, N 153e3 Tensile yield strength, N 250e3
Normal coupling spring cohesion, N/m 2e6 Grout cohesive strength (force), N/m 190e3
Shear coupling spring 0.5e6 Grout stiffness, 0.4e10
cohesion, N/m N/m/m
Normal coupling spring stiffness, N/m/m 1e10
Shear coupling spring stiffness, N/m/m 40e6

Mechanical parameters of rocks for the strain-softening model_

Bulk modulus, K (GPa) Shear modulus, G (GPa) Friction angle, θ (°) Cohesion, c (MPa) Tensile strength, Rt (MPa) Density, γ (kg/m3) Residual friction angle, θ (°) Residual cohesion, cr (MPa) Residual tensile strength, Rt r (MPa)
Dolomite, limestone lower 2.40 1.70 42.0 1.70 0.70 2650 32 0.7 0.15
Copper deposit 1.80 1.40 27.0 1.35 0.60 2600 22 0.35 0.10

Mechanical parameters of intact rocks in the A5 region_

Bulk modulus, K (GPa) Shear modulus, G (GPa) Friction angle, θ (°) Cohesion, c (MPa) Tensile strength, Rt (MPa) Compressive strength, Rc (MPa) Density, γ (kg/m3)
Anhydrite 21.6 13.5 34 14.5 6.4 92.6 2950
Dolomite, limestone upper (I) 16.07 11.07 45 12.8 5.5 115.5 2750
Dolomite, limestone lower (II) 14.72 10.13 42 10.0 4.2 60.0 2650
Copper deposit 11.27 8.44 27 8.0 3.5 68.0 2600
Grey sandstone 5.12 4.32 32 5.6 2.0 37.0 2200
Red sandstone 3.72 3.36 30 4.8 1.1 25.6 1900

Numerical calculation scenarios_

Factor Original designed parameters Modified parameters
Tip-to-face distance 3.0 m 1.5 m
Average load-bearing capacity 2600 kN 4000 kN
Spacing of box crib Every 6.0 m Every 3.0 m, 1.5 m
Roof control method – hydraulic backfilling (sand) instead of box crib No Yes
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