What are the main types of excavation support systems?

Excavation support systems include: (1) Open cut with slopes - simplest, requires space, (2) Sheet piles - interlocking steel sheets, moderate depths, (3) Soldier piles and lagging - H-piles with timber between, economical for stable soils, (4) Secant/tangent pile walls - overlapping concrete piles for water cutoff, (5) Diaphragm walls (slurry walls) - for deep excavations, can be permanent, (6) Soil mixing walls - for moderate depths. Support includes internal bracing, anchors/tiebacks, or top-down construction. Selection considers depth, water, adjacent structures, and permanence.