Calculate cut volume, fill volume, and truck loads for trenches, foundation pits, basement excavations, and sloped sites. Includes soil swell and shrinkage factors for accurate earthwork quantity estimates.
Standard drainage trench: 0.45–0.6m wide
For irregular shapes, break into rectangles and sum.
Use average depths from site survey levels.
Standard tipper truck: 4–8 m³. Check your supplier.
Extra for over-excavation and irregular edges.
The basic formula for rectangular excavations is Volume = Length × Width × Depth. For a standard drainage trench 20m long, 0.6m wide, and 1.5m deep: V = 20 × 0.6 × 1.5 = 18 m³ of bank (in-situ) material. However, once excavated, soil swells and occupies more space. If the soil has a 17% swell factor, the loose volume becomes 18 × 1.17 = 21.1 m³. This is the volume you need to transport away — always use loose volume when ordering trucks.
Bank volume is the soil in its natural, undisturbed state in the ground. Loose volume is the same soil once excavated — it breaks up and swells by 5–40% depending on soil type. Compacted volume is soil that has been placed as fill and compacted with rollers or tampers — it shrinks below bank volume by 5–25%.
| Soil Type | Swell | Shrinkage | Density (kg/m³) |
|---|---|---|---|
| Rock | 25–40% | 20–30% | 1800–2200 |
| Hard Clay | 20–30% | 16–23% | 1700–1900 |
| Medium Clay | 15–20% | 13–17% | 1600–1800 |
| Sandy Clay | 10–15% | 9–13% | 1650–1750 |
| Sand | 5–10% | 5–9% | 1500–1700 |
| Topsoil | 15–25% | 13–20% | 1200–1500 |
Truck loads = Loose volume ÷ Truck capacity. Standard tipper trucks in Pakistan carry 4–8 m³ of loose material. Always round UP — you cannot order a partial truck load. For 45 m³ of loose soil with 6 m³ trucks: ceil(45/6) = 8 loads. Account for loading time of 15–30 minutes per truck when planning your excavation schedule.
When excavating without shoring, you must cut side slopes to prevent collapse. The required slope depends on soil type. The prismatoid formula accurately calculates volume for sloped pits: V = h/6 × (A_bottom + A_top + 4×A_mid). Firm rock can be cut vertically. Hard clay uses 1:4 to 1:2 slopes. Medium clay needs 1:1 slopes. Sandy and loose soils require 1.5:1 to 2:1 slopes — meaning the excavation widens significantly at the top.
On sloping ground, the goal is to balance cut and fill to minimise importing or exporting soil. Survey the site, establish a datum level, and calculate average cut and fill depths across the area. If cut volume exceeds fill, you export the surplus. If fill exceeds cut, you import material. A topographic survey with level readings on a grid gives the best accuracy for large sites.
In Pakistan, excavations deeper than 1.2m in firm soil generally require shoring or stepping. Never allow workers in an unsupported trench deeper than 1.5m. Sandy or waterlogged soils can collapse without warning at any depth. Always conduct soil tests before deep excavations. Check the water table level — dewatering may be needed for basement excavations below the water table, which adds significant cost.