Module 15 · Lesson 15.3
What governs, and what is missing
Finding the critical case, the missing information, and the next course.
Why this matters
Interpretation is not only about what the data says — it is about spotting the critical case among several, and being honest about what you do not yet know. The most valuable output of an interpretation is often a clear statement of the governing mechanism and the information still needed to pin it down.
Try it
Scenario interpreter
Which considerations govern this ground and project? Select them, then check — and see which course carries it into design.
Scenario
How to decide
- Loading or unloading? Clay (undrained short-term) or sand (drained)?
- Is stability the concern, or settlement, or seepage?
- Design itself belongs to a later course — this identifies what governs.
Select the governing considerations, then press Check.
Two habits mark good interpretation:
- Identify the governing case. Loading or unloading? Short-term or long-term? Strength or serviceability? Often one mechanism dominates and the rest are secondary — find it, and design against it, while checking the others do not become critical.
- State what is missing. A ground model is built on a few boreholes and tests (Module 3); its weakest points are the assumptions between them. Naming the missing information — a groundwater level not monitored long enough, an undrained strength not measured, a fissure network not sampled — turns a hidden risk into a managed one, and points to the next investigation.
Check yourself
A structure applies a sustained load to soft clay. Stability is fine in every case, but the client is worried about long-term settlement. Which is the governing consideration?
Practice
A clay layer 4 m thick with e₀ = 1.0 and Cc = 0.4 has its effective stress raised from 40 to 120 kPa (normally consolidated). Estimate the primary settlement, in mm.
Summary
- Good interpretation identifies the single governing case among several and designs against it.
- It also states what information is missing, turning hidden risk into a managed one and directing further investigation.
- This course builds understanding up to — but not including — design.
- Foundations, retaining structures and slopes are carried into design by later Queensferry courses that build on this one.
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