Landscape Construction and Hardscape Installation
Domain 6 tests whether you can build a surface that stays flat, drains and lasts. Expect subgrade preparation, base thickness, compaction, edge restraint, retaining-wall drainage and the standards behind them.
The build-up
Pavers on a properly built base: compacted subgrade, geotextile where subgrade is fine-grained, a compacted aggregate base typically 100–150 mm for pedestrian loads (thicker for vehicles), 25 mm of bedding sand, then pavers, joint sand and edge restraint. Compact base in layers of about 100 mm to 95% of Standard Proctor density (ASTM D698); a single thick lift leaves soft spots. Slope pavers at 1.5–2% away from buildings and never rely on joint sand as the drainage path.
Retaining walls
Walls need water release more than brute strength: drain gravel behind the wall, filter fabric between gravel and soil, and weep holes every 1.5–2 m at the base. Bury the first course about 10% of wall height. Batter the face back roughly 25 mm per 300 mm of height. Walls above about 1.2 m, or carrying surcharge, need engineered design, geogrid reinforcement and possibly a permit - do not build tall walls on judgement alone.
Worked example
A 40 m² patio against a house: excavate to 200 mm below finished level, compact subgrade, lay geotextile, place 120 mm base in two lifts and compact each, screed 25 mm sand, lay pavers at 2% fall away from the wall, cut in edge restraint, compact and sweep joint sand. Reasoning: the house side needs positive fall and the base carries the load; the edge stops migration and rutting.
Traps that cost marks
Spreading base in one thick lift. Omitting filter fabric so fines clog the gravel. Using joint sand as drainage. Building a retaining wall with no weep holes or back drainage. Ignoring root zones and buried services before excavation.