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Project brief
A precast concrete manhole section lowered by crane chains into an excavation shored with steel trench boxes

Calculator · Sheet T-203

Trench excavation calculator

Trench volume with vertical walls in a trench box or sloped walls, plus bedding, pipe displacement, backfill and spoil.

Trench excavation · Sheet T-203Metric
m
m
m
H per 1V
0 = vertical (trench box or shoring).
mm
mm
mm
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Estimates only. Check quantities against the drawings and your supplier before ordering.

STA 0+120How it works

Trench cross-section area = depth × (bottom width + slope × depth); volume = area × length. Bedding and embedment are the granular zone from the trench bottom to the stated depth above the pipe crown, minus the pipe’s own area. Backfill is the rest of the trench above the embedment zone. Loose spoil applies the material’s swell ratio to the full excavation.

STA 0+240Assumptions and sources

Swell ratios per bank cubic metre as published in the field manual3333. The calculator does not add over-excavation, benching steps, manhole bell holes or trench-box clearance; allow for them separately.

Worker protection

Protective systems are required beyond 1.2 m in most provinces and 1.5 m in Alberta and Manitoba; engineer-designed support is required beyond set depths1212. See trench safety by province.

Questions people ask

How do you calculate trench volume?

Multiply the trench cross-section area by its length. For vertical walls the area is depth × width; for sloped walls it is depth × (bottom width + slope × depth).

How deep can a trench be without shoring?

In Ontario, British Columbia, Saskatchewan and the Atlantic provinces, protection is required when a worker enters a trench deeper than 1.2 m1; in Alberta the trigger is 1.5 m2.

How much bedding does a pipe need?

That is set by the pipe material and the owner’s specification (bedding class). Enter the bedding and embedment depths from your spec; the calculator returns the volume.

Sources

  1. O. Reg. 213/91 Construction Projects, Part III Excavations (ss. 222-242)Government of Ontario (e-Laws) · consolidation current to 2026-09-21
  2. Alberta OHS Code (Alta Reg 191/2021), Part 32 Excavating and TunnellingGovernment of Alberta (OHS legislation search) · retrieved 2026-09-24
  3. FM 5-434 Earthmoving Operations, Chapter 1, Tables 1-1 and 1-2U.S. Department of the Army (field manual; hosted copy on GlobalSecurity.org) · FM 5-434 (2000)