Module 13 · Lesson 13.3
One framework
How consolidation, stress history and strength join up.
Why this matters
Critical-state soil mechanics is valuable because it is one consistent picture rather than a collection of separate rules. Seeing how the earlier modules fit into it turns memorised results into understanding — and shows why the same soil parameter appears in a settlement calculation and a strength calculation.
The framework unifies the course:
- Compression (Module 10) is movement along the normal compression line in e–ln p′; the CSL runs parallel to it.
- Stress history / OCR (Module 10) is simply where the soil sits relative to the CSL — heavily overconsolidated means dry of critical, normally consolidated means at or wet of critical.
- Strength (Module 11) — the critical-state strength is (or ); the peak of a dense soil is a bonus from dilation that the framework predicts from how far dry of critical it is.
- Drainage and pore pressure (Module 9) — the sign of the undrained pore-pressure change is set by whether the soil is wet or dry of critical.
One state, relative to one line, ties compressibility, stress history, strength and pore-pressure response together.
Check yourself
In the critical-state framework, what does a soil's overconsolidation ratio correspond to?
Summary
- Compression is movement along the NCL; the CSL runs parallel to it in e–ln p′.
- Stress history / OCR is the soil's position relative to the CSL (dry vs wet of critical).
- Critical-state strength is M (φ′cs); a dense soil's peak is dilation the framework predicts.
- The framework unifies compressibility, stress history, strength and pore-pressure response — a way of thinking, used with judgement.
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