Water¶
Water can be present at four locations and contribute as either a destabilising or a stabilising action.
Parameters¶
| Parameter | Symbol | Units | Notes |
|---|---|---|---|
| Water unit weight | γw | kN/m³ | default 9.81 |
| Ponded water at toe | Hw | m | external water (lake, valley aquifer) leaning against the slope face |
| Water in the discontinuity | Zw | m | water depth in the joint, generates uplift U on the plane |
| Water in the tension crack | Zt | m | only with TC; generates force V perpendicular to the crack |
| Pressure distribution | – | – | none / triangular max-mid / triangular max-toe / triangular max-at-crack-base |
| Permeable slope | bool | – | connects ponded and joint water hydrostatically |
Force decomposition¶
| Action | Formula | Direction |
|---|---|---|
| Uplift on the failure plane | U = ½·γw·Zw·swet | perpendicular to the plane, pushing the wedge outward |
| Water in the crack | V = ½·γw·Zt² | perpendicular to the crack, pushing the wedge toward the valley |
| Ponded at toe | Up = ½·γw·Hw² | perpendicular to the slope face, pushing back into the wedge (stabilising) |
Pressure distribution¶
The four options control how the pore water pressure varies along the failure plane:
- None — no uplift on the plane (default when Zw = 0)
- Triangular max at mid-height — pressure peaks at L/2, zero at toe and at crest
- Triangular max at toe — pressure peaks at the toe (typical of valley aquifer)
- Triangular max at crack base — pressure peaks at the bottom of the tension crack (typical of perched aquifer)
Permeable slope toggle¶
When enabled, the external ponded water and the joint water are hydraulically connected. Zw is overridden to match Hw, and U/Up are computed consistently to avoid double counting.
On the section¶
- U vector: perpendicular to the failure plane, halfway along O→C
- V vector: perpendicular to the TC, halfway along C→D
- Up vector: perpendicular to the slope face, halfway along O→B
The blue dashed line shows the water level at the toe (Hw) and the water depth in the crack (Zt) is shown by a dashed level on the tension crack.