7D Retaining Walls and Excavation

Erosion and sediment control keeps disturbed soil on the site and out of storm drains, ditches and neighboring property while construction is under way and until vegetation is established. Under the federal Clean Water Act, any project that disturbs one acre or more needs coverage under a construction stormwater permit and a written plan, commonly called a SWPPP, and many cities set lower thresholds. The physical work is simple and unglamorous: silt fence trenched in along the downhill perimeter, a stone construction entrance so trucks do not track mud onto the road, protection around every inlet, check dams in ditches, and erosion control blanket or hydroseed on slopes. What most owners underestimate is the maintenance: controls have to be inspected after every rain of a quarter inch or more and repaired, and inspectors write violations for torn fence and full silt traps, not for missing paperwork.

Excavation contractors dig and move earth for foundations, basements, utilities, pools and site cuts. Most residential jobs run on a mini or mid-size excavator paired with a skid steer and a dump truck; larger cuts bring in a dozer or scraper. The price depends less on the size of the hole than on what is in the ground: clay, ledge rock, high groundwater and buried utilities all slow the machine down and change the hauling math. Before the bucket touches dirt the site needs an 811 utility locate, and any trench deeper than five feet needs a protective system under OSHA rules.

Foundation contractors build the part of the structure that carries everything above it into the ground: spread footings below frost depth, stem walls or basement walls, monolithic and slab-on-grade foundations, and pier or grade beam systems where soils are poor. The work follows the stamped plans and the geotechnical report, and it is inspected at fixed points, usually the open footing trench with rebar in place before the pour, then again before the slab and before backfill. Frost depth sets the footing bottom, from about twelve inches in the Gulf states to four feet or more across the northern tier. Waterproofing or dampproofing, a footing drain and free-draining backfill are what keep a basement dry, and they are cheapest to do right while the wall is still exposed.

Retaining walls hold back soil where a grade change is too steep to slope, and they fail for one reason far more than any other: water. A wall that lasts has a compacted crushed-stone base, a perforated drain pipe at the heel, clean gravel backfill behind the wall face, and geogrid layers tied into the backfill on anything tall. Segmental concrete block is the most common residential system and can be built by a landscape contractor up to about four feet; above that, or wherever a driveway, slope or structure sits above the wall, an engineer's design is required by most codes and the wall becomes structural work. Poured concrete and reinforced masonry walls are used for tall cuts and tight sites, boulder walls for rural and natural-look projects, and pressure-treated timber for budget walls with a shorter life.

Site preparation is the package of work that turns a lot into a place a builder can start. On a typical job that means clearing vegetation, stripping and stockpiling topsoil, cutting or filling to the pad elevation, compacting fill in lifts, cutting in a temporary driveway, and installing the silt fence and gravel entrance the stormwater inspector expects to see. The scope shifts with the ground: a flat suburban infill lot may take two days, while a sloped wooded parcel with poor soil can run weeks and involve undercutting and replacing unsuitable material. Site prep contractors typically coordinate with the surveyor who sets the corners and the geotechnical engineer who signs off on compaction.