Landscape Construction and Hardscape Installation
Layout and subgrade
Set grades and string lines from benchmarks before digging. Excavate to the designed depth, proof-roll and compact the subgrade, and remove soft spots. Poor subgrade is the root cause of most paver and wall failures.
Segmental pavers
Place geotextile where subsoil is fine grained, then install aggregate base in lifts of two to four inches, compacting each lift to about 95 percent of maximum density. Bedding sand is screeded about one inch thick; pavers are laid tight, cut cleanly at edges, restrained with an edge restraint spiked into the base, and joint sand is swept in and compacted. Slope the finished surface for drainage.
Concrete and walls
Use air-entrained concrete in the 4,000 psi range for freeze-thaw exposure in Oregon, with control joints at regular intervals and proper curing. Retaining walls need a compacted leveling pad, a battered face, drainage gravel behind the block, filter fabric, an outlet, and geogrid where the design calls for it. Footings must bear below frost depth. Walls above about four feet, or walls carrying surcharge, generally require engineered design and a permit.
Worked example
A 10 foot by 30 foot patio at two percent slope falls about six inches across the long dimension: 30 x 0.02 = 0.6 feet.
Traps: skipping base compaction, using masonry sand as base, and building a wall without drainage.
Rule of thumb: build walls with a one inch setback per foot of height unless designed otherwise.