Site Construction and Materials
This domain tests materials, base preparation and detailing for hardscape: segmental pavers, concrete, retaining walls, decks and drainage, plus the arithmetic for ordering material.
Base and compaction
Segmental pavers need a compacted aggregate base: typically 4 in for pedestrian loads and 6-8 in for vehicular loads, deeper where frost is a factor, plus about 1 in of bedding sand. Compact base in 2-4 in lifts to about 95% Standard Proctor. Proof-roll the subgrade and remove soft spots.
Concrete and mortar
Exterior slabs are commonly 3.5-4 in thick with a thickened edge, over 4 in of compacted gravel, with isolation joints at structures and control joints spaced at roughly 2-2.5 times the slab thickness in feet. Mortar-set pavers require a concrete base; flexible pavers must never be mortared.
Retaining walls
Segmental block walls above roughly 3-4 ft (verify with local code and soils) need engineered design, geogrid reinforcement, a level compacted base, and free-draining gravel with filter fabric behind the wall.
Worked example
A 300 sq ft patio with a 4 in base: 300 x (4/12) = 100 cu ft, or 3.70 cu yd. Add 15% for compaction and waste: 3.70 x 1.15 = about 4.3 cu yd. Bedding sand at 1 in: 300 x (1/12) = 25 cu ft, about 0.9 cu yd.
Traps
Ordering exactly the geometric volume and running short; mortaring a system designed to stay flexible; omitting drainage and filter fabric behind a retaining wall; laying pavers with no edge restraint; and ignoring the local frost depth.