Geotechnical Engineering carries 13-15% weightage in GATE CE, covering soil mechanics and foundation engineering. Soil mechanics includes phase relationships, index properties, permeability, seepage, compaction, consolidation, and shear strength — all fundamental concepts tested both conceptually and numerically. Foundation engineering covers bearing capacity (Terzaghi, Meyerhof), pile design, earth pressure (Rankine, Coulomb), retaining walls, and slope stability. Terzaghi's consolidation theory and bearing capacity equation are the most important topics.