About the Trench Excavation BOQ
Trench excavation quantity calculation estimates the volume of soil to be excavated for cable trenches in a solar plant — used for civil contractor cost estimation and for planning spoil disposal or backfill requirements.
Formula
Trench volume (m³) = Length × Width × Depth
- Length (m)
- Total trench route length
- Width (m)
- Trench width — typically 300–600 mm for cable routes; wider for duct banks
- Depth (m)
- Minimum 600 mm below finished grade for LT cables; 750 mm for HT cables (per IE Rules)
How to calculate it
- 1Map the cable route on the plant layout to determine total trench length.
- 2Determine trench width: for 1–3 cables in a trench, 300 mm wide is sufficient; for duct banks (4+ circuits), 600–900 mm is typical.
- 3Trench depth: LT cables — minimum 600 mm cover from finished grade (IE Rules); HT cables — 750–1,000 mm cover.
- 4Soil classification: loose soil (easy digging) vs hard soil vs rock — each has different excavation rates and costs.
- 5Backfill: after laying cables, backfill with fine sand (150 mm above cable), brick marker tiles, then compacted soil. Surplus spoil to be disposed of.
Worked example
A 500 kWp ground-mount plant with 400 m total cable route. DC trench: 300 mm wide × 700 mm deep × 200 m = 42 m³. AC HT cable trench: 400 mm wide × 900 mm deep × 200 m = 72 m³. Total excavation: 114 m³. Backfill sand (150 mm layer): 0.3 × 0.15 × 400 = 18 m³ of sand needed.
What you can calculate
- Volume m³
- Bulking factor
- Truck loads
- IS 1255 depth
Frequently asked questions
What is the minimum burial depth for solar DC cables in India?
IE Rules require a minimum 600 mm of cover (soil above the cable) for LT cables (up to 1,000 V). Solar DC cables at 600–1,500 V DC are classified as HT by some inspectors — confirm with your local Chief Electrical Inspector (CEIG) office. In any case, 750 mm cover is a safe standard that satisfies both LT and HT interpretations and protects against accidental damage during routine digging.
Can solar DC cables be run in cable trays instead of trenches?
Yes — cable trays (above ground) are commonly used for runs inside the plant's internal roads and between equipment. Trays must be UV-resistant (GI or FRP/GRP for outdoor use) and elevated > 300 mm above grade to prevent waterlogging. Underground trenching is preferred for long cross-site runs (> 50 m) and anywhere vehicle movement is expected — overhead cable trays require clearance management and are more vulnerable to physical damage.
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