What are the main types of retaining walls and their selection criteria?

Retaining wall types: (1) Gravity walls - resist by self-weight, economical for low heights (<3m), (2) Cantilever walls - reinforced concrete L or T shape, most common for medium heights (3-8m), (3) Counterfort walls - triangular braces reduce bending, for heights >8m, (4) Mechanically stabilized earth (MSE) - reinforced soil, economical for large fills, (5) Sheet pile walls - for waterfront, excavation support, (6) Anchored walls - for deep excavations. Selection considers height, soil conditions, water, space constraints, appearance, and cost.