Geotechnical Engineering
Geotechnical engineering deals with soil and rock behavior: how the ground carries loads, retains water, and pushes against walls. The exam emphasizes effective stress, earth pressure, bearing capacity, and settlement.
Stress and the Effective-Stress Principle
Total vertical stress at depth is gamma·h. Terzaghi's principle states effective stress sigma' = sigma - u, where u is pore water pressure. Effective stress, not total stress, controls soil strength and compression, so lowering the water table (reducing u) increases effective stress and causes settlement.
Lateral Earth Pressure
Retaining structures feel lateral pressure set by the soil state. Rankine's active coefficient is Ka = tan^2(45 - phi/2) and the passive is its reciprocal. The at-rest coefficient from Jaky's equation is K0 = 1 - sin(phi). The active case gives the least pressure; passive the most.
Weight-Volume Relationships and Bearing
Dry unit weight gamma_d = gamma/(1 + w) removes pore-water weight and gauges compaction against the Proctor optimum. Bearing capacity (Terzaghi) and consolidation settlement determine how much load a foundation can carry and how much it will settle over time.