11.1 Sitework: Surveying, Excavation & Grading

Site Layout and Surveying

Before any earth is moved, the building must be located on the lot accurately. Surveying establishes both horizontal position and vertical elevation. Two reference systems anchor the work:

• Benchmarks — permanent, surveyed points of known elevation. The contractor establishes at least one onsite benchmark and protects it from disturbance for the life of the project. All vertical measurements (finish floor, grading, utilities) trace back to this benchmark.
• Batter boards — temporary horizontal frames set back from the building corners, usually 3–4 feet above grade. Once footings are excavated, corner stakes are lost, so layout strings are transferred to batter boards to preserve the building line. The strings can be re-plumbed and re-measured at any time.

Setbacks are the minimum horizontal distances from property lines to the building, set by the local jurisdiction's zoning ordinance and the 2018 IBC (International Building Code) for fire separation distance. Setbacks must be verified before excavation; a misplaced footing is expensive to fix.

Quick Answer: Establish a protected benchmark for vertical control and batter boards for horizontal layout before excavating; verify setbacks against zoning and the 2018 IBC.

Excavation and Grading

Excavation removes soil to create the building footprint, footings, and utility trenches. Grading reshapes the ground surface for drainage and access. Two rough grades are common: rough grade (bulk earthwork to within 6 inches of final) and fine grade (finished elevation before placing base or slabs).

The building pad must be elevated so that surface water drains away from the foundation. The 2018 IBC requires positive drainage away from the foundation — surface water must be directed away from the building, typically with a slope of at least 1/2 inch per foot for the first 10 feet away from the foundation wall.

Soil Types and Bearing Capacity

Soil-bearing capacity determines footing width and depth. The 2018 IBC Table 1806.2 lists presumptive bearing values for common soil classes:

When the bearing capacity is questionable or the soil is not in the IBC table, a geotechnical investigation with borings and lab testing is required.

Compaction

Compaction increases soil density and reduces future settlement. Fill placed under floors or slabs must be compacted to at least 90% of the maximum dry density determined by the Proctor test (ASTM International D698 standard, or D1557 modified). Lifts are generally limited to 8 inches loose depth for cohesive soils and 12 inches for granular soils. Each lift is tested before the next is placed. Field density is checked with a nuclear gauge or sand cone.

Trenching for Utilities

Utility trenches carry water, sewer, gas, electric, and communication lines. Trench bottom must be firm and uniform; soft spots are over-excavated and backfilled with compacted granular material. Bedding (sand or crushed stone) cushions the pipe. Minimum cover depths are specified by code and utility — typically 12 inches for electric and 18–24 inches for water and gas, but local jurisdictions may require more.

Excavation Safety: OSHA 29 CFR 1926 Subpart P

Trenching is one of construction's deadliest operations. OSHA (Occupational Safety and Health Administration) 29 CFR Part 1926 Subpart P governs excavations and requires:

1. Competent person — someone capable of identifying existing and predictable hazards and authorized to stop work. The competent person inspects every excavation daily and after every rainstorm or hazard-increasing event.
2. Protection for trenches 5 feet or deeper — one of three systems:
   • Sloping — cutting the trench walls back at a safe angle. Maximum allowable slopes: 0.75H:1V (53°) for Type A; 1H:1V (45°) for Type B; 1.5H:1V (34°) for Type C.
   • Shoring — a support system such as hydraulic cylinders, screw jacks, or timber shoring that braces the trench walls.
   • Shielding — a trench box that protects workers from cave-ins but does not prevent wall collapse.
3. Spoils, equipment, and material must be kept at least 2 feet from the trench edge to prevent surcharge loads from collapsing the wall.
4. Egress — a ladder, ramp, or stairway within 25 feet of every worker in trenches 4 feet or deeper.

OSHA Soil Classification for Excavations

Quick Answer: A trench 5 feet or deeper requires sloping, shoring, or shielding, and a competent person must inspect it daily and after rain.

Erosion Control and Site Drainage

Erosion control keeps sediment on site. A Stormwater Pollution Prevention Plan (SWPPP) is required for projects disturbing one acre or more under the EPA Construction General Permit. Common best management practices (BMPs) include silt fence, inlet protection, stabilized construction entrances, and temporary seeding. Site drainage manages both surface and subsurface water. Surface drainage uses grading to direct runoff away from the foundation. Subsurface drainage uses footing drains (perforated pipe at footing level, surrounded by washed stone and filter fabric) to carry groundwater away from the foundation wall.