Vacuum Excavation Spoil, Swell, and Tank Fills

ScopeThe individual pothole is small and the day's total is not, and swell is what fills the tank sooner than the arithmetic suggests. Soil excavated from a compacted bank occupies twenty to forty percent more volume loose, and a wet vacuum adds the water used to cut, so the material going into the tank can be well over half again the in-place volume. Planning on bank volume produces a schedule that is optimistic by exactly that margin. A single 8 by 4 ft test pit to 5 ft is 5.93 cubic yards in the bank and 7.70 loose at 30% swell -- 64% OF A TWELVE YARD TANK from one pit. A day of potholing a corridor is thirty keyholes plus the test pits, and the tank fills in the middle of the afternoon a long way from the dump site. DISPOSAL IS THE VARIABLE THAT CHANGES THE NUMBER MOST. Spoil that can go back in the hole is a short cycle; spoil that must be hauled because it is slurry, because it is contaminated, or because the jurisdiction does not permit returning it, is a haul cycle per tank and a completely different day -- which is why the haul time is reported against the fill count rather than left implicit, and why the fills are computed both with and without swell so the difference is visible rather than discovered. Volume arithmetic on prismatic pits. It does not evaluate whether spoil may be returned to the excavation or must be hauled, which is a jurisdictional and contamination question, and it does not address the classification, containment, or disposal of slurry, which in many places is a regulated waste stream. It does not size the vacuum unit, address water supply and pressure for wet cutting, or evaluate the soil's suitability for vacuum excavation. It does not replace exposing a utility as the way to establish its position, nor the one-call notification that must precede any of it. The utility owner, the one-call system, the applicable damage prevention law, and the disposal jurisdiction govern.

Formula or tablebank volume = length x width x depth / 27; loose volume = bank x (1 + swell) plus any water added at 7.48052 gallons per cubic foot; tank fills = loose volume / tank capacity, rounded up.

Source and editionPrismatic volume with an entered swell factor (commonly 20 to 40%) and the water added for wet cutting, by name. The disposal jurisdiction, the utility owner, the one-call system, and the applicable damage prevention law govern.

Free accessVolume arithmetic on the user's own pit dimensions and swell figure; no regulatory waste classification is reproduced.

What governsEstimate. AHJ and licensed professional govern.

API field namespit_length_ft, pit_width_ft, pit_depth_ft, pit_count, swell_pct, water_added_gal, tank_capacity_cy, haul_round_trip_min, bank_cy_each, loose_cy_total, tank_fills, first_pit_tank_pct, haul_time_min

• Swell fills the tank early twenty to forty percent for most soils, plus the water a wet vacuum addsexcavation practice
• Disposal decides the day returnable spoil is a short cycle; hauled slurry is a cycle per tankdisposal jurisdiction
• Potholing does not replace one-call the notification and the owner's marks come firstdamage prevention law