Author Contributions
Conceptualisation, L.H., J.C., M.E.; methodology, L.H., J.C., P.F.; software, L.H., J.C., T.P.; validation, L.H., J.C., M.E.; formal analysis, L.H., J.C.; investigation, L.H., M.E.; resources, L.H.; data curation, L.H., T.P., P.F.; writing—original draft preparation, L.H.; writing—review and editing, J.C., M.E.; visualisation, L.H., J.C.; supervision, J.C., M.E. All authors have read and agreed to the published version of the manuscript.
Figure 1.
Study area—Wattstown tip which is south of Wattstown in the county borough of Rhondda Cynon Taf, Wales, and displayed on ESRI world imagery.
Figure 1.
Study area—Wattstown tip which is south of Wattstown in the county borough of Rhondda Cynon Taf, Wales, and displayed on ESRI world imagery.
Figure 2.
Images of Wattstown standard tip. (a) A Google satellite image prior to the landslide (05/2020), (b) a Google satellite image after the landslide (07/2021), (c) delineation of the landslide boundary.
Figure 2.
Images of Wattstown standard tip. (a) A Google satellite image prior to the landslide (05/2020), (b) a Google satellite image after the landslide (07/2021), (c) delineation of the landslide boundary.
Figure 3.
Daily rainfall located at the study area from November 2020 to December 2020 (Met Office Hadley Centre, 2023).
Figure 3.
Daily rainfall located at the study area from November 2020 to December 2020 (Met Office Hadley Centre, 2023).
Figure 4.
Remote-sensing mapping of the Wattstown standard tip prior to the 2020 landslide occurrence. (a) Hillshade map, (b) aspect map, and (c) slope angle map.
Figure 4.
Remote-sensing mapping of the Wattstown standard tip prior to the 2020 landslide occurrence. (a) Hillshade map, (b) aspect map, and (c) slope angle map.
Figure 5.
Methodology of this research, including the input part to collect data for landslide analysis, the methods part of different methods used for landslide analysis, the output part of the final results obtained using these methods, and the validation process using post-landslide satellite images.
Figure 5.
Methodology of this research, including the input part to collect data for landslide analysis, the methods part of different methods used for landslide analysis, the output part of the final results obtained using these methods, and the validation process using post-landslide satellite images.
Figure 6.
Slope models for numerical analysis. (a) A 3D model and 9 monitoring points, (b) a satellite image showing the position of the 9 points, (c) a 2D model constructed along an N–S profile in the 3D model.
Figure 6.
Slope models for numerical analysis. (a) A 3D model and 9 monitoring points, (b) a satellite image showing the position of the 9 points, (c) a 2D model constructed along an N–S profile in the 3D model.
Figure 8.
FS values of the slope angle of 30° (grey line), 35° (red line), and 40° (blue line) in response to different groundwater conditions.
Figure 8.
FS values of the slope angle of 30° (grey line), 35° (red line), and 40° (blue line) in response to different groundwater conditions.
Figure 9.
Results of 2D LE analysis based on the simplified Bishop method, showing FS estimation corresponding to the slip surface. (a) Dry slope, (b) partially saturated slope (regime_1).
Figure 9.
Results of 2D LE analysis based on the simplified Bishop method, showing FS estimation corresponding to the slip surface. (a) Dry slope, (b) partially saturated slope (regime_1).
Figure 10.
FDM modelling result showing the total displacement of a dry slope (regime_1). (a) overview of the modelling result, (b) an N–S cross section of the total displacement contour.
Figure 10.
FDM modelling result showing the total displacement of a dry slope (regime_1). (a) overview of the modelling result, (b) an N–S cross section of the total displacement contour.
Figure 11.
The curves of total displacement at 9 monitoring points when the slope is in a dry condition.
Figure 11.
The curves of total displacement at 9 monitoring points when the slope is in a dry condition.
Figure 12.
FDM modelling result of a partially saturated slope (regime_1). (a) Contour of slope displacement and modelled displacement vectors of the unstable zone, (b) an N–S cross section of the slope displacement contour, (c) close-up image of the N–S cross section showing the geometry of the unstable zone and monitoring points P1, P6, and P8 on the slope.
Figure 12.
FDM modelling result of a partially saturated slope (regime_1). (a) Contour of slope displacement and modelled displacement vectors of the unstable zone, (b) an N–S cross section of the slope displacement contour, (c) close-up image of the N–S cross section showing the geometry of the unstable zone and monitoring points P1, P6, and P8 on the slope.
Figure 13.
The curves of total displacement at 9 monitoring points when the slope is in the regime_1 water condition.
Figure 13.
The curves of total displacement at 9 monitoring points when the slope is in the regime_1 water condition.
Figure 14.
The curves of total displacement at 9 monitoring points. (a) c = 0, (b) c = 20 kPa.
Figure 14.
The curves of total displacement at 9 monitoring points. (a) c = 0, (b) c = 20 kPa.
Figure 15.
Results of sensitivity analysis associated with the cohesion of colliery spoil. (a) c = 0, (b) c = 20 kPa, (c) N–S cross section of the cohesionless modelling result, (d) N–S cross section of the 20 kPa modelling result.
Figure 15.
Results of sensitivity analysis associated with the cohesion of colliery spoil. (a) c = 0, (b) c = 20 kPa, (c) N–S cross section of the cohesionless modelling result, (d) N–S cross section of the 20 kPa modelling result.
Figure 18.
The curves of total displacement at 9 monitoring points. (a) φ = 10%, (b) φ = 30%.
Figure 18.
The curves of total displacement at 9 monitoring points. (a) φ = 10%, (b) φ = 30%.
Figure 19.
Results of sensitivity analysis associated with the porosity of colliery spoil. (a) φ = 10%, (b) φ = 30%, (c) N–S cross section of the 10% porosity modelling result, (d) N–S cross section of the 30% porosity modelling result.
Figure 19.
Results of sensitivity analysis associated with the porosity of colliery spoil. (a) φ = 10%, (b) φ = 30%, (c) N–S cross section of the 10% porosity modelling result, (d) N–S cross section of the 30% porosity modelling result.
Figure 20.
UKCP18 daily precipitation projection of a 5 km grid located in the study area from 1 July 2024 to 31 December 2028.
Figure 20.
UKCP18 daily precipitation projection of a 5 km grid located in the study area from 1 July 2024 to 31 December 2028.
Table 1.
Colliery spoil properties characterised by their variations from minimum to maximum values with the summary of references.
Table 1.
Colliery spoil properties characterised by their variations from minimum to maximum values with the summary of references.
Soil Property | Mean | Minimum | Maximum | Reference |
---|
Unit weight (KN/m3) | 19 | 17 | 21 | [37,41,42,43,44,45,46] |
Friction angle (°) | 37 | 32 | 42 |
Cohesion (KPa) | 10 | 0 | 20 |
Porosity (%) | 20 | 10 | 30 |
Table 2.
Soil properties for the colliery tip and underlying natural slope for LE numerical analysis.
Table 2.
Soil properties for the colliery tip and underlying natural slope for LE numerical analysis.
| Friction Angle | Cohesion | Tensile Strength | Porosity |
---|
Colliery tip | 37° | 1 × 104 Pa | 0 | 20% |
Natural slope | 40° | 1 × 105 Pa | 5 × 104 Pa | 10% |
Table 3.
Strength and deformability properties of colliery spoil and natural slope used for FDM modelling.
Table 3.
Strength and deformability properties of colliery spoil and natural slope used for FDM modelling.
| Friction Angle | Cohesion | Tensile Strength | Bulk Modulus | Shear Modulus |
---|
Colliery spoil | 37° | 1 × 104 Pa | 0 | 1.67 × 108 Pa | 0.77 × 108 Pa |
Natural slope | 40° | 1 × 105 Pa | 5 × 104 Pa | 8.33 × 108 Pa | 4 × 108 Pa |
Table 4.
FS estimation in various hydrogeological conditions by using different LE methods, including the simplified Bishop method, simplified Janbu method, and Spencer method.
Table 4.
FS estimation in various hydrogeological conditions by using different LE methods, including the simplified Bishop method, simplified Janbu method, and Spencer method.
Method | Dry Slope | Partially Saturated Slope (Regime_1) |
---|
Simplified Bishop | 1.471 | 1 |
Simplified Janbu | 1.28 | 0.897 |
Spencer | 1.464 | 1.019 |
Table 5.
The number of events that the amount of single-day precipitation exceeds specific thresholds from 1 July 2024 to 31 December 2028.
Table 5.
The number of events that the amount of single-day precipitation exceeds specific thresholds from 1 July 2024 to 31 December 2028.
| | 2024 | 2025 | 2026 | 2027 | 2028 |
---|
| |
---|
50–60 mm | 1 | 2 | 3 | 3 | 1 |
60–70 mm | 1 | 1 | 1 | 0 | 1 |
≥70 mm | 1 | 1 | 0 | 0 | 1 |
Table 6.
The number of events that the amount of three-day accumulative precipitation exceeds specific thresholds from 1 July 2024 to 31 December 2028.
Table 6.
The number of events that the amount of three-day accumulative precipitation exceeds specific thresholds from 1 July 2024 to 31 December 2028.
| | 2024 | 2025 | 2026 | 2027 | 2028 |
---|
| |
---|
100–115 mm | 0 | 0 | 1 | 2 | 1 |
115–130 mm | 0 | 1 | 0 | 0 | 0 |
≥130 mm | 0 | 0 | 0 | 1 | 0 |