A branch of soil mechanics
Unsaturated Soil Mechanics
Most construction happens above the water table, in soil that holds both air and water. Classical soil mechanics treats ground as either dry or fully saturated. This free learning pathway is about what happens in between: why it matters for safe, economical and sustainable design, and how to recognise, read and use it in practice.
Why it is its own branch
The ground is rarely just dry or saturated
Classical soil mechanics was built on soil whose pores are full of water. That assumption is powerful and, for strength, usually on the safe side. But much of the ground we build in, on and with is unsaturated: compacted fills, embankments, the upper metres of most sites, and large areas of tropical, arid and semi-arid ground. There, water is held under tension, called suction, and it changes with every wet and dry spell.
Ignoring it can waste resources
Designing as if the ground were always saturated can be overly conservative: more support, more material and more carbon than the ground actually needs while suction is present.
Ignoring it can also miss the real problem
Some soils collapse or swell when they get wetter. Here the danger comes from losing suction, and a design that never thinks about the change in water can be unsafe, not conservative.
Understanding unsaturated soil helps you judge both: when suction is helping you, how long you can rely on it, and when wetting is the thing to design for.
The pathway
Four courses, one step at a time
Each course builds on the one before. Start at Course 1, even if you know some soil mechanics: it sets up the ideas and the way of reasoning used in everything that follows.
When does unsaturated behaviour matter, what is suction, and how does weather become an engineering problem? Three lessons, about 4 hours, with an assessment.
Open nowHow suction is measured, how to read a soil-water characteristic curve with confidence, and how retention links to permeability. Three lessons, about 4½ hours, with an assessment.
Open nowTurn laboratory and field evidence into a defensible engineering recommendation, with clear assumptions and uncertainty.
Coming nextChoose field and laboratory tests and monitoring, and design an investigation around the decision it must support.
Coming nextWho it is for: anyone working with soil above the water table, including research students, designers, contractors, laboratory staff and engineers who want to go beyond the saturated textbook case. A basic understanding of soil mechanics helps, but each idea is explained from the start.
Sign up free to start
Enter your first name and email, and Course 1 opens straight away. You only need to do this once on each device, and your progress is saved in your browser.
You are signed up on this device. Pick up where you left off.
Invite me to teach, speak or mark
I run talks, short courses and workshops on unsaturated soil mechanics for universities, research groups, professional bodies and engineering teams, and I mark written assessments. If this pathway would suit your group, get in touch or see speaking.
This pathway reflects my own research, teaching and general practice. It is independent of any employer or client, and all examples are fictional. Lessons are for learning only: on real projects, follow current codes of practice and the advice of a qualified engineer.