Hume Pipe Culvert BOQ — Worked Example for an 8 m × 900 mm NP3 Rural Culvert

Hume pipe culverts are the single largest category of cross-drainage structure built in rural India — PMGSY road specifications mandate at least one culvert every 500-1000 m of road. The CPWD-standard configuration is a single-line NP3 or NP4 class RCC pipe (per IS 458) laid on PCC bedding with brick masonry headwalls and earth backfill. This article walks through a complete BOQ for the most common rural-road configuration — 8 m length × 900 mm internal diameter NP3 pipe with brick headwalls, wing walls and downstream apron.

Project Scenario

You're estimating a culvert under a PMGSY rural road crossing a small seasonal nallah. Carriageway is 5.5 m wide; with 1.25 m extensions on each side for the headwalls, the culvert length is 8 m total. The drainage catchment requires a 900 mm pipe (verified via Rational method against the design 25-year storm). Standard NP3 pipe is adequate — this is a rural panchayat road, not an NH/SH.

Design specification at a glance

• Length: 8 m (carriageway width + headwall extensions)
• Pipe diameter: 900 mm internal
• Pipe class: NP3 (medium duty, PMGSY rural roads, ≤ IRC Class B loading)
• Pipe-invert depth: 1.2 m below NGL
• Headwalls: Both ends, 1.2 m above NGL, 230 mm (full-brick) F.P.S. masonry
• Wing walls: 4 nos, 1.5 m each, 45° splay
• Downstream apron: 2 m × 1.5 m wide stone pitching / CC slab

The Complete BOQ — 9 Items in CPWD DSR 2023

The live BOQ Builder evaluates these formulas in real time — change pipe diameter (450 / 600 / 900 / 1000 / 1200 mm), pipe class (NP3 / NP4), headwall height, wing wall length, or apron length, and the quantities update instantly.

How Each Quantity Was Computed

1. Excavation — Item 2.8.1

Trench width = pipe diameter + 600 mm working space (300 mm each side for bedding + jointing access):

Trench width = 0.9 + 0.6 = 1.5 m
Trench depth = depth below NGL + PCC bedding
= 1.2 + 0.15 = 1.35 m
Excavation = 8 × 1.5 × 1.35 = 16.2 m³

2. PCC bedding + cradle — Item 4.1.8

Two parts: (a) 150 mm flat PCC bed under the full trench width; (b) cradle / haunch fill — 25 % of pipe diameter for NP3, taken on 70 % of the trench width to account for the pipe occupying the centre:

Flat bed = 8 × 1.5 × 0.15 = 1.80 m³
Cradle haunch = 8 × 1.5 × (0.9 × 0.25) × 0.7 = 1.89 m³
Total PCC = 3.69 m³

For NP4 heavy-duty pipes (NH / SH carriageway), the cradle is 50 % of pipe diameter per IRC SP 13 Cl. 5.3 — substantially more PCC for the same pipe.

3. RCC pipe — Item 19.35.3

Single line of 900 mm NP3 pipe, 8 m total — DSR rate is per running metre and covers supply + laying + jointing with collar / spigot-and-socket. Use DSR code 19.35.3 for 900 mm NP3; the equivalent NP4 code is 19.36.3 (≈ 18 % more expensive).

4 + 5. Brick headwalls

Both ends, 1-brick (230 mm) full-thickness, F.P.S. class-7.5 brick. The Builder allows for headwall thickness of 0.345 m to account for a strengthening bullnose / capping detail.

Headwall length = trench width + 1.5 m extension = 1.5 + 1.5 = 3.0 m each
Headwall foundation height = 1.2 (NGL depth) + 0.15 (PCC) + 0.15 (plinth band) = 1.5 m
Headwall above-ground = 1.2 (above NGL) + 0.9 (pipe dia) + 0.30 (cap) = 2.4 m

Foundation masonry (both ends) = 2 × 3.0 × 0.345 × 1.5 = 3.11 m³
Above-ground masonry (both ends) = 2 × 3.0 × 0.345 × 2.4 = 4.97 m³

6. Backfill — Item 2.25

Excavated earth re-fills the trench above the pipe. The pipe + cradle occupy ~25 % of the trench volume; the rest needs back-fill:

Backfill = trench above pipe − pipe cross-sectional area × length
= 8 × 1.5 × 1.2 − 8 × π × 0.45²
= 14.4 − 5.09 = 9.31 m³

Backfill must be done in 200 mm layers, watered and tamped — IS 1200 Part 1 Cl. 5.4. Otherwise settlement opens the road over the pipe.

7. Wing walls — Item 6.4.2

4 wing walls (2 at each end of culvert, 45° splay outward from pipe outlet / inlet). Each 1.5 m long, 230 mm thick:

Wing wall average height = 60 % of (headwall_above + headwall_found) ≈ 2.34 m
Wing wall masonry = 4 × 1.5 × 0.23 × 2.34 = 3.23 m³

8. Downstream apron — Item 7.1.1

Stone pitching or CC slab on the downstream bed prevents pipe-outlet scour:

Apron volume = 2 (length) × 1.5 (width) × 0.30 (thickness) = 0.9 m³

NP3 vs NP4 — Which to Use

NP3 medium-duty (DSR 19.35.x) is rated for occasional vehicular loading up to IRC Class B + 1.2 m earth cover above pipe crown. Use for PMGSY rural roads, village internal roads, panchayat roads, farm-access roads, residential colony storm drains.

NP4 heavy-duty (DSR 19.36.x) is rated for IRC Class A + AA wheel loads and full 70R tracked-vehicle loading. Mandatory for NH / SH carriageway crossings, district roads, urban arterials, industrial corridors, any culvert under cover < 1 m.

Cost difference: NP4 is roughly 12-20 % more expensive than NP3 for the same diameter. Specifying NP4 unnecessarily on rural roads is a common over-design that inflates the BOQ by ~10 %. Conversely, using NP3 on NH/SH under-spec the structure and risks pipe failure under 70R loading.

Pipe Diameter Selection (Hydraulic Sizing)

Rule-of-thumb: pipe diameter = function of (catchment area × design rainfall intensity ÷ Manning hydraulic capacity). PMGSY default values:

Always verify via hydrological assessment for actual design — never rely on this table alone for tender-grade work.

What This BOQ Excludes

• Pipe-collar / jointing material (cement mortar collar bands at each joint) — typically absorbed in DSR 19.35.3 rate, but verify with your local SOR
• Cushion concrete on inlet/outlet bed (IRC SP 13 Cl. 8.3) — separate stone-pitching / CC item
• Stone pitching on side slopes — DSR 7.X random rubble for embankment protection
• Guard stones at headwall ends — to prevent vehicle from striking corner masonry
• Reflective markers + signage — IRC 67 + IRC 67-2012 for culvert delineation
• Road overlay on top of backfill — separate bituminous or concrete road BOQ

Common Estimation Mistakes

• Forgetting wing walls — open-end pipes without wing walls suffer erosion at the pipe inlet/outlet from concentrated flow. 4 wing walls of 1.5 m each is a baseline; longer for high-flow drains.
• Specifying NP4 on a rural PMGSY road — wasted ~10 % on pipe cost. NP3 is rated for the actual loading.
• Skipping the downstream apron — over a 2-3 year cycle, scour erodes the pipe outlet bed and undermines the headwall. The 0.9 m³ apron prevents this for ~₹4-6k.
• Backfill in single lift — must be 200 mm layers, watered + tamped. Single-lift backfill causes road settlement over the pipe within 6-12 months, leaving a pothole.
• Under-sizing the trench width — at least 300 mm working space on each side of the pipe for cradle compaction and jointing access. Smaller trenches force the contractor to skip cradle compaction → pipe rocks → joints fail.
• Using RCC headwall when brick suffices — for PMGSY rural roads, F.P.S. brick masonry is adequate and 30-40 % cheaper than RCC. Reserve RCC headwalls for NH/SH culverts where wheel-impact loads are likely.

What Changes for a Different Culvert

• Larger catchment (1200 mm pipe) — switch pipe code to 19.35.5; trench width grows to 1.8 m; cradle volume scales up proportionally.
• NH / SH carriageway — pipe class to NP4 (19.36.x), headwalls to RCC (5.2.2), apron concrete to M20 (5.3 or 5.1.2), wing walls extended to 2.5-3 m each.
• Two-line or three-line culvert (high catchment, low cover) — duplicate the pipe + bedding cost per line, single shared headwall sized to span all lines.
• Cover < 600 mm above pipe crown — special slab cover (mini-slab culvert) required; switch to Slab Culvert Builder.
• State-PWD SOR — switch to your state's road-works SOR (typically more current for PMGSY work).

Get Your Culvert's Cost in 30 Seconds

References & Companion Reading

• IS 458:2003 — Precast Concrete Pipes (with and without Reinforcement) — Specification
• IRC SP 13:2004 — Guidelines for the Design of Small Bridges and Culverts
• IRC 5:2015 — Standard Specifications for Road and Bridge Works
• IS 1200 Part 1:1992 — Earthwork measurement (trench excavation rules)
• IS 1200 Part 3:1976 — Brickwork measurement
• Sister tool: Slab Culvert BOQ Builder — for low-cover sites
• Sister tool: Box Culvert BOQ Builder — for very high catchments or large spans
• CPWD DSR 2023 — full SOR with rates by item
• MoRTH SOR — for NH/SH culverts (uses dedicated NP4 + RCC headwall items)