Module 15 · Lesson 15.2
Worked interpretations
Two problems taken end to end through the framework.
Why this matters
The framework is best learned by using it. Here are two contrasting problems — a loading on soft clay and an excavation in water-bearing sand — each carried through the same sequence, showing how the modules interlock and how the governing case flips between them.
Worked example
Interpretation 1 — embankment on soft clay
Given
- 5 m of soft, saturated clay over dense sand; water table at the surface
- Clay: water content w = 45%, Gs = 2.70
- A wide embankment will add Δσ ≈ 60 kPa at the surface
Find
Read the problem through the framework: state, effective stress at mid-depth, the governing stability case, and the deformation to expect.
Assumptions
- Clay fully saturated (S = 1); wide load so 1-D conditions; drained final state.
Worked example
Interpretation 2 — excavation in water-bearing sand
Given
- A deep excavation in clean sand with the water table well above formation level
- Water seeps into and up through the base of the excavation
Find
Read the problem through the framework and identify the governing hazard.
Assumptions
- Clean sand, so essentially always drained; steady seepage towards the excavation.
Practice
For the soft clay of Interpretation 1 (w = 45%, Gs = 2.70, S = 1), confirm the void ratio e.
Summary
- The same framework reads opposite problems: a loading on clay vs an unloading in sand.
- Loading on clay: undrained short-term stability, then slow consolidation settlement.
- Excavation in sand: drained, with seepage and piping/heave the governing hazard.
- Classification → effective stress → drainage → strength/deformation makes the governing case clear.
This is educational material. It uses simplified examples to teach principles, and must not be relied on for real design or safety-critical decisions. Module overview and checkpoint