Figure 1
![Location of the Cao Son open pit coal mine [37].](https://sciendo-parsed.s3.eu-central-1.amazonaws.com/64737a0a4e662f30ba53f8b8/j_sgem-2022-0019_fig_001.jpg?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Credential=AKIA6AP2G7AKOUXAVR44%2F20251206%2Feu-central-1%2Fs3%2Faws4_request&X-Amz-Date=20251206T085625Z&X-Amz-Expires=3600&X-Amz-Signature=c23f31f993f54112c9c916c0aea38ef07743fad3de64dbafb2b9d77f2e9d717f&X-Amz-SignedHeaders=host&x-amz-checksum-mode=ENABLED&x-id=GetObject)
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Change of FoS value and size of the slope failure surface with different scenarios of UG operation by 2025_
| Slope in 2025 | FoS value | |||
|---|---|---|---|---|
| Before UG | After UG | |||
| Scenario I | Scenario II | Scenario III | ||
| Left slope wall | 1.75–2.0 | 1.75–2.0 | 1.5–1.75 | 1.75–2.0 |
| Right slope wall | >2.5 | >2.5 | >2.5 | 2.0–2.25 |
Mechanical properties of rock mass in the studied region [33]_
| Type of rock mass | Bulk modulus K (GPa) | Shear modulus G (GPa) | Cohesion c (MPa) | Fiction angle φ (°) | Tensile strength σt (MPa) | Density ρ (kg/m3) |
|---|---|---|---|---|---|---|
| Mudstone | 2.31 | 1.54 | 1.87 | 30 | 1.34 | 2620 |
| Claystone | 2.23 | 1.34 | 2.05 | 26 | 1.14 | 2600 |
| Anthracite | 2.17 | 1.36 | 2.14 | 27 | 1.22 | 1500 |
| Conglomerate | 4.76 | 3.57 | 3.23 | 28 | 2.27 | 2510 |
| Sandstone | 3.91 | 2.46 | 3.56 | 28 | 1.96 | 2600 |
Strength parameters of the fault in the studied region [33]_
| Strength parameters | Friction angle (°) | Cohesion (kPa) | Tensile strength (kPa) |
|---|---|---|---|
| Value | 12–20 | 3.4–4.4 | 0 |
Hypotheses for calculating thickness of the caved zone_
| Author, year | Thickness of caved zone |
|---|---|
| Peng and Chiang, 1984 [38] | (2–10)t |
| Bai et al., 1995 [39] | 100t/(c1g+c2) |
| Mazurkiewicz et al., 1997 [40] | t/(kr−1) |
| Heasley, 2004 [41] | (10–18)t |
| Biliński, 2005 (simplified) [42] | (nkst)/(0.05Rc0.5+0.02) |
| Wang et al., 2017 [43] | (3–4)t |