RCC Box Culvert BOQ — Worked Example for a 2 × 2 m PMGSY-Spec Box
RCC box culverts are the workhorse cross-drainage structure on Indian roads above 600 mm pipe equivalent — the PMGSY / state-PWD / NH / SH standard for any drainage span between 1 m and 3 m. Above 3 m span, slab culverts take over; below 1 m, Hume pipes are economical. The IRC SP 13 + IRC 6 + IRC 21 + IS 456 standard: single-cell M20 RCC box with monolithic raft + walls + deck slab, brick wing walls splayed 45°. This article walks through a complete BOQ for the PMGSY default — 2 × 2 m clear opening × 8 m long.
Project Scenario
You're estimating a box culvert under a PMGSY road crossing a small seasonal nallah with moderate catchment. Hydraulic sizing dictates 2 × 2 m clear opening. Carriageway 5.5 m + headwall extensions = 8 m total culvert length. Walls and slab 300 mm thick, raft 300 mm, founded 1.5 m below NGL.
Design specification at a glance
- Length (along road): 8 m
- Internal span (clear width): 2.0 m
- Internal height (clear): 2.0 m
- Wall thickness: 300 mm RCC M20
- Deck slab thickness: 300 mm RCC M20
- Raft thickness: 300 mm RCC M20
- Wing walls: 4 nos × 2.0 m × 45° splay
- Apron + curtain walls: 2 m × full width at each end
The Complete BOQ — 14 Items in CPWD DSR 2023
| # | DSR Code | Item Description | Unit | Quantity |
|---|---|---|---|---|
| 1 | 2.8.1 | Earthwork in foundation pit, all-kinds-of-soil | m³ | 48.64 |
| 2 | 4.1.8 | PCC 1:4:8 bed below raft, 100 mm thick | m³ | 2.32 |
| 3 | 5.1.2 | RCC M20 in raft slab, 300 mm thick | m³ | 6.24 |
| 4 | 5.2.2 | RCC M20 in vertical side walls (2 nos) | m³ | 9.60 |
| 5 | 5.3 | RCC M20 in deck slab, 300 mm thick | m³ | 6.24 |
| 6 | 5.9.1 | Centering & shuttering for raft | m² | 20.80 |
| 7 | 5.9.2 | Centering & shuttering for walls (4 faces total) | m² | 64.00 |
| 8 | 5.9.3 | Centering & shuttering for deck slab | m² | 20.80 |
| 9 | 5.22.6 | TMT Fe-500D reinforcement (cut, bent, placed) | kg | 2,649.60 |
| 10 | 6.4.2 | F.P.S. brick masonry in CM 1:6 — 4 wing walls (45° splay) | m³ | 3.20 |
| 11 | 4.10 | 40 mm DPC course on wing walls | m² | 1.84 |
| 12 | 7.1.1 | Stone pitching apron at U/S + D/S ends (2 m × 300 mm) | m³ | 3.12 |
| 13 | 7.1.1 | Curtain (cut-off) walls at U/S + D/S ends | m³ | 0.94 |
| 14 | 2.25 | Backfill above culvert with excavated earth, watered + compacted | m³ | 0 (deep set — none needed) |
Total RCC volume = 22.08 m³. At 120 kg/m³ that's ~2.65 tonnes of steel — higher per-m³ ratio than a wall or drain because IRC 21 demands extra reinforcement for impact + fatigue. The live BOQ Builder evaluates these formulas in real time — change span (1-3 m), height, slab/wall/raft thickness, depth below NGL.
How Each Quantity Was Computed
1. Excavation — Item 2.8.1
External width = internal span + 2 × wall_thk = 2.0 + 0.6 = 2.6 m
External height = internal_h + slab_thk + raft_thk = 2.0 + 0.3 + 0.3 = 2.6 m
Trench width = 2.6 + 0.6 = 3.2 m (300 mm working space each side)
Excav depth = depth below NGL + raft + PCC = 1.5 + 0.3 + 0.10 = 1.90 m
Excavation = 8 × 3.2 × 1.90 = 48.64 m³
2. PCC bed — Item 4.1.8
PCC width = external_w + 0.30 = 2.9 m
PCC volume = 8 × 2.9 × 0.10 = 2.32 m³
3-5. RCC raft + walls + deck slab
Raft volume = 8 × 2.6 × 0.30 = 6.24 m³
Wall volume (2 walls × full internal height) = 2 × 8 × 0.30 × 2.0 = 9.60 m³
Deck slab volume = 8 × 2.6 × 0.30 = 6.24 m³
Note: walls run from raft top to slab underside, so wall height = internal clear height = 2.0 m.
6-8. Centering & shuttering
- Raft: under-side only (raft cast on PCC bed) = 8 × 2.6 = 20.80 m²
- Walls: 4 faces total (2 walls × 2 faces each) = 4 × 8 × 2.0 = 64 m²
- Deck slab: under-side only = 8 × 2.6 = 20.80 m²
9. Reinforcement — Item 5.22.6
Total RCC = 6.24 + 9.60 + 6.24 = 22.08 m³
Steel = 22.08 × 120 = 2,649.60 kg (~2.65 tonnes)
120 kg/m³ is typical for box culverts under IRC Class A loading. Heavy IRC Class AA / 70R tracked-vehicle loading pushes this to 150-180 kg/m³.
10-11. Wing walls + DPC
Wing wall avg height = (external_h + 0.30) × 0.6 = 2.9 × 0.6 = 1.74 m
Wing wall brick (4 walls × 2 m × 0.23 m × 1.74 m) = 3.20 m³
Wing wall DPC = 4 × 2 × 0.23 = 1.84 m²
12-13. Apron + curtain walls
Apron (2 ends × 2.0 m × 2.6 m × 0.30 m) = 3.12 m³
Curtain wall (2 ends × 2.6 × 0.30 × 0.60) = 0.94 m³
When to Use Box Culvert vs Hume Pipe vs Slab Culvert
| Span / discharge | Recommended structure | BOQ Builder |
|---|---|---|
| ≤ 0.6 m equivalent (small drain) | NP3 / NP4 Hume pipe | Hume Pipe Culvert |
| 0.9 - 1.2 m pipe equivalent | Single-line NP4 Hume pipe | Hume Pipe Culvert |
| 1.0 - 3.0 m span (medium catchment) | RCC box culvert | Current article ⤴ |
| 4 - 12 m span (high catchment, open stream) | Slab culvert / minor bridge | Slab Culvert |
| ≥ 12 m span (proper bridge) | T-beam / PSC girder bridge | Custom design (no template) |
What This BOQ Excludes
- Bearing pads / elastomeric bearings at slab-wall junction (only relevant for spans > 6 m + simply-supported design)
- Haunches at slab-wall corner — small triangular RCC fillets, +5 % RCC volume
- Parapet / railing on deck — for safe pedestrian use; mandatory on NH/SH
- Expansion joints — every 30 m linear in long culverts
- Waterproofing of deck top — only for culverts with < 600 mm earth cover
- Approach slab on either side — 3.5 m × 0.30 m RCC prevents settlement transition; ~₹40-60k
- Road overlay on top — separate bituminous or CC road BOQ
Common Estimation Mistakes
- Using 100 kg/m³ steel "RCC standard" — box culverts under wheel loads need 120-150 kg/m³ for fatigue + impact. Under-steeling cracks the deck within first monsoon.
- Forgetting wing walls — without them, soil from approach embankments slides into the culvert mouth, blocking flow within 2 monsoons.
- Specifying RCC wing walls when brick suffices — for PMGSY rural roads, brick wing walls (DSR 6.4.2) are 30-40 % cheaper than RCC (5.2.2) and entirely adequate. RCC wing walls are needed only for NH/SH where wheel-impact loads are likely.
- Skipping apron + curtain wall — at the discharge end, water exiting the culvert at high velocity scours the bed. Without apron + curtain wall, the headwall foundation is undermined within 2-3 monsoons.
- Treating raft + walls + slab as one RCC item — they have different DSR rates (5.1.2 raft < 5.2.2 walls < 5.3 slab). Lumping under one rate misses ~₹50-80k per culvert.
- Over-designing for "future-proofing" — bumping from 2 m span to 3 m "to be safe" adds ~₹3-5 lakh to a single culvert. PMGSY hydraulic sizing already includes 25-year storm + safety factor.
What Changes for a Different Box
- 1 × 1 m (small drainage) — half the RCC volume, 250 mm walls/slab sufficient. ~₹3-4 lakh total.
- 3 × 3 m (heavy duty NH) — 350 mm walls/slab/raft, M25 grade per IRC 21, steel ratio 150 kg/m³. Often paired with RCC wing walls + parapet.
- Low earth cover (< 600 mm above slab) — add waterproofing membrane on deck top; bump slab thickness for direct-wheel-load consideration.
- Two-cell box (high catchment, low road grade) — duplicate the slab + raft cost per cell; share the central wall.
- Soft soil (SBC < 100 kN/m²) — bump raft to 400 mm + add pile foundation. Easily doubles foundation cost.
- NH / SH carriageway — M25 design mix (DSR 4.20.1.4), 150 kg/m³ steel, RCC wing walls, M30 deck slab for IRC Class AA loading.
Get Your Box Culvert Cost in 30 Seconds
Change span, height, wall / slab / raft thickness, length, wing wall length, depth — the Builder regenerates the BOQ + downloads Excel with formulas embedded. Customize for Your Project →
References & Companion Reading
- IRC SP 13:2004 — Guidelines for Design of Small Bridges and Culverts
- IRC 6:2017 — Standard Specifications for Loads & Stresses on Bridges
- IRC 21:2000 — Standard Specifications for Cement Concrete Road Bridges
- IS 456:2000 — Plain and Reinforced Concrete
- IS 1786:2008 — TMT Fe-500D reinforcement
- IS 1200 Part 5:1982 — Concrete measurement
- Sister article: Hume Pipe Culvert BOQ
- Sister article: Slab Culvert BOQ
- CPWD DSR 2023