Where each layer sits
- Subgrade: compacted natural soil or selected earth, tested for CBR.
- GSB, granular sub-base (MoRTH 401): spreads the load and drains water out of the pavement; typically 150–200 mm compacted.
- Base course: WMM (MoRTH 406), typically 250 mm laid in two layers, on highways; WBM (MoRTH 404) in 75 mm layers on village, PMGSY and estate roads.
- Bituminous layers: DBM, then BC on top.
GSB and WMM are stacked in one road; WBM is an alternative base, not a third layer. In a concrete road, GSB sits under the dry lean concrete and the concrete slab.
GSB, WMM and WBM side by side
| GSB | WMM | WBM | |
|---|---|---|---|
| MoRTH section | 401 | 406 | 404 |
| Position | Sub-base on the subgrade | Base on GSB (highways, bypasses) | Base (village, PMGSY, estate roads) |
| Top size | 53 mm (Gradings II–VI) or 75 mm (Grading I) | 53 mm | 63 mm (Grading 2) or 53 mm (Grading 3) |
| Material | Crusher-run blend with fines | Crusher-run blend, non-plastic fines | Single-size stone plus screenings |
| Laying | Spread, water, roll | Pugmill mix at optimum moisture, paver, vibratory roller | Spread stone, roll, brush in screenings with water, roll |
| Typical layer | 150–200 mm | 250 mm in two layers | 75 mm per layer |
| Key limits | Soaked CBR ≥ 30, LA abrasion ≤ 40%, plasticity index ≤ 6 | LA abrasion ≤ 40%, flakiness + elongation ≤ 35%, non-plastic fines | LA abrasion ≤ 40%, flakiness + elongation ≤ 35% |
| Our ex-works rate | ₹425 per MT | ₹450 per MT | ₹450 per MT |
From our team
Notes, photos and examples added by the M&B Chetty team, with the author and the date.
GSB Grading II and the WBM gradings
| IS sieve | GSB Grading II | WBM Grading 2 | WBM Grading 3 |
|---|---|---|---|
| 90 mm | — | 100 | — |
| 63 mm | — | 90–100 | 100 |
| 53 mm | 100 | 25–75 | 95–100 |
| 45 mm | — | 0–15 | 65–90 |
| 26.5 mm | 70–100 | — | — |
| 22.4 mm | — | 0–5 | 0–10 |
| 11.2 mm | — | — | 0–5 |
| 9.5 mm | 50–80 | — | — |
| 4.75 mm | 40–65 | — | — |
| 2.36 mm | 30–50 | — | — |
| 0.425 mm | 10–25 | — | — |
| 0.075 mm | 3–10 | — | — |
Older copies of MoRTH show 10–15% at 0.425 mm for GSB Gradings I and II; the current revision shows 10–25%. We blend to the revision named in your contract and print the target band on each lot's gradation certificate.
WBM screenings are Type A (13.2 mm nominal) or Type B (11.2 mm). Crusher dust can replace graded screenings where it meets the plasticity limits; confirm with the engineer on the package.
Tonnes and loads per kilometre
Road layers are designed in compacted cubic metres and bought in weighbridge tonnes. Multiply length × width × compacted thickness by about 2.2 t/m³ for GSB and 2.25 t/m³ for WMM.
| Carriageway width | GSB 200 mm | WMM 250 mm | 18 MT loads (GSB + WMM) |
|---|---|---|---|
| 3.75 m (single lane) | ≈ 1,650 MT | ≈ 2,110 MT | ≈ 209 |
| 5.5 m (intermediate lane) | ≈ 2,420 MT | ≈ 3,090 MT | ≈ 306 |
| 7.0 m (two lane) | ≈ 3,080 MT | ≈ 3,940 MT | ≈ 390 |
Carriageway only; add shoulders separately. Loose material is about 1.2–1.3 times the compacted volume.
| Item | Typical quantity | In loads / units |
|---|---|---|
| Results appear here (JavaScript is needed for the calculator). | ||
Typical estimate: length × width × compacted thickness × compacted density. The contract drawing and the MoRTH layer thicknesses govern.
A kilometre of GSB plus WMM on a two-lane road is close to 7,000 MT. For packages we plan supply as a weekly convoy against your chainage programme.
Price per tonne, per m³ and delivery
- GSB ex-works: ₹425 per MT
- WMM / WBM aggregate ex-works: ₹450 per MT
- Per compacted m³: multiply the per-MT rate by about 2.2 for GSB or 2.25 for WMM.
- Per unit or per brass (100 cft): multiply by about 4.8 for loose GSB.
| Area | GSB (Granular Sub-Base) delivered / MT | WMM / WBM Aggregate delivered / MT | Distance | Truck time | Quote |
|---|---|---|---|---|---|
| Tiruvallur | ~₹866 | ~₹893 | ~67 km | 2–2.5 h | |
| Gummidipoondi | ~₹866 | ~₹893 | ~82 km | 2.5–3 h | |
| Sriperumbudur | ~₹971 | ~₹998 | ~87 km | 3 h | |
| Ponneri | ~₹866 | ~₹893 | ~85 km | 3 h | |
| Chennai | ~₹1,045 | ~₹1,071 | ~90 km | 3–3.5 h |
Every load is a 10-wheeler tipper of 16–20 MT with a weighbridge slip, GST invoice (HSN 2517, 5%), AP e-transit pass and an e-way bill where needed. Royalty is itemised at actuals.
Rock from the same Perindesam deposit was source-approved by the supervision consultant for GSB, WMM and bituminous works on the Chennai Peripheral Ring Road in December 2025.