Geotechnical Engineering
Soil behaves differently from every other engineering material because part of it is water that can leave, slowly. These topics animate the phases, the pressures between them, and what happens when the water is squeezed out.
Start from the beginning →8 topics you can watch now, 14 still to come.
Soil as a material
The three-phase model, and the index properties built on it.
- Weight-volume relationships
- Particle size distribution and sieve analysis
- Atterberg limits and consistency
- Soil classification systems
- Compaction and the Proctor test
Permeability and seepage
Water moving through the gaps, and the pressure it carries.
- Laboratory and field permeability tests
- Flow net construction step by step
Stress and consolidation
Effective stress, and why settlement takes years.
- Effective StressOne equation, and most of the subject's failures. Quicksand, liquefaction and rain-triggered landslides are all the same event seen from different angles.
- Consolidation and SettlementThe water takes the load first because it cannot escape, and hands it over across decades. Watch the two bands trade while the total never changes.
- Boussinesq and Westergaard stress distribution
- Sand drains and preloading
Shear strength
The strength that decides whether the ground holds.
- Triaxial test interpretation
- Critical state soil mechanics
Earth pressure and foundations
What the theory is for.
- Earth Pressure and Retaining WallsA load that depends on how the structure responds to it — millimetres of movement halve the pressure, and water behind the wall doubles it.
- Bearing Capacity and FoundationsWalk a marker up the load-settlement curve to failure, then back to the safe load — where settlement, not strength, usually decides the answer.
- Slope StabilityWatch one factor-of-safety marker walk down as rain, a toe excavation and a rapid drawdown each take their share.
- Coulomb wedge analysis
- Pile groups and negative skin friction
- Site investigation and SPT correlations
About Geotechnical Engineering
Geotechnical engineering deals with the one structural material nobody gets to specify. Steel arrives with a certificate; soil is already on site, variable across a few metres, and its behaviour depends heavily on the water inside it.
That is why the three-phase model comes first. Soil is solids, water and air together, and most of its mechanical behaviour follows from the proportions. The decisive idea is effective stress: strength depends not on total load but on the load carried by the grain-to-grain contacts, so raising the water pressure weakens the soil without adding any load at all.
Everything applied follows from there. Shear strength decides whether a slope stands. Bearing capacity decides what a foundation can carry. Seepage decides where water travels and what it carries with it. Consolidation decides how much a structure settles, and over what timescale — sometimes decades.
What to know first
- Fluid Mechanics, particularly pressure and seepage
- Strength of Materials for the shear-strength material
Where it gets used
- Judging whether a foundation type suits the ground beneath it
- Understanding slope failures after heavy rain as effective-stress events
- Reading a site investigation report and knowing what governs the design