Method Statement for Subbase Preparation — UK
A free, Specification for Highway Works-aligned method statement for UK subbase preparation — covering Type 1 placement, compaction sequence, proof-rolling, plate-bearing test and the engineer's hold-point the highways inspector actually asks for.
UK (RAMS) example document — Two-Storey Rear Extension — 14 Birchwood Lane, Reading. Client: Mr & Mrs A. Whitfield (Private Client). Site: 14 Birchwood Lane, Reading, RG1 5JT. Scope: Construction of a two-storey rear extension (6.4m × 4.2m) to an existing semi-detached dwelling. Works comprise breaking out of existing rear elevation, trench-fill foundations to 1.0m, traditional cavity blockwork to first floor, pre-stressed concrete lintels, timber roof structure with natural slate finish, plus alterations to existing rear wall to form structural opening with rolled steel joist (RSJ 203×102 UB23). Works programmed over 9 weeks with a peak site team of 6 operatives. Hazards assessed: Manual handling — blocks, lintels, plasterboard, Working at height — independent scaffold & roof structure, Buried services strike during excavation, Collapse of excavation / trench wall, Hand-arm vibration (HAVS) — breaking out, drilling, Silica dust — cutting blocks, brick, concrete, Vehicle/pedestrian segregation — narrow domestic street.
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- Site-specific draft
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Built around recognised UK method statement structure — hazards, controls, sequence, PPE and sign-off. Ready for competent-person review.
Subbase preparation is the silent killer of pavement programmes — get the Type 1 specification, layer thickness or compaction wrong and the surfacing above will rut, crack or fail within two winters, with rectification costs typically 8–12 times the original subbase value. The HSE prosecution of a Midlands groundworks contractor in 2022 (£42,000 fine after a worker lost a leg to an overturning roller during late-evening compaction) is the most cited recent fatality-class incident, and the recurring theme in pavement-failure litigation is the same: no compaction test record, no plate-bearing certificate, no engineer's hold-point. This page sets out what a defensible UK subbase preparation method statement should cover — Type 1 supply, layer placement, compaction, testing — with a free editable template.
When is it required?
Subbase preparation on any UK adopted highway, commercial yard, industrial slab or sports surface needs a written method statement before the first load tips. National Highways' Specification for Highway Works (Manual of Contract Documents Volume 1, Series 800) clause 803 governs Type 1 unbound mixture, and any work for a Highways Authority adoption (S38 or S278) requires the MS, the compaction trial record and the plate-bearing test certificate as part of the technical approval pack. Under CDM 2015 the principal contractor must include it in the construction phase plan, and BS EN 13242 is the materials reference for the aggregate itself.
What a good one looks like
A strong subbase MS runs to 6–12 pages and names every specific. It identifies the aggregate (e.g. 'Tarmac Type 1 SHW 803, 0/63mm, recycled limestone, certificate ref TC-2026-04-122'), the layer thickness (typically 150–225mm laid in two lifts), the compactor (e.g. 'BOMAG BW213DH-5 13-tonne single-drum roller, 6 passes with vibration on, 2 final passes static'), the moisture target (±2% of OMC from Proctor test), the proof-roll criterion (no visible deflection under a 18-tonne tipper), and the acceptance test (plate-bearing test to BS 1377-9 with K150 ≥120 MN/m³). It links to the trial-compaction record and the materials test certificates by date.
Subbase Preparation hazards & controls
The site-specific hazards a subbase preparation MS must address, with the controls that take residual risk to an acceptable level.
| Hazard | Persons at risk | Controls | Residual |
|---|---|---|---|
| Plant strike — roller, tipper, dumper, excavator | All on site | Segregated pedestrian and plant routes barriered with Heras; banksman on every reverse; reversing alarms (white-noise preferred); plant operators CPCS-certified; 100% high-vis class 2 to BS EN 471; no pedestrian within roller working radius (typically 25m) | Medium |
| Roller overturn on edges or slopes | Roller op | Slope angles assessed pre-shift; never work parallel to edges <1m clearance; ROPS cab fitted and seat-belt worn; geo-fenced exclusion in proximity-detection where available; no late-evening work in poor light without floodlights ≥200 lux | Medium |
| Respirable crystalline silica from dust during dry placement | Crew, public | Water bowser on site for dust suppression; FFP3 RPE for any work upwind of dry stockpile; no dry-cutting on edges (wet-cut only); air monitoring if work continues >5 days dry; central low-emission zone NRMM declaration where applicable | Low |
| Hand-arm vibration from plate compactors at edges | Operator | Vibration register per tool; exposure points logged daily; rotation when 400 EAV points reached; anti-vibration gloves NOT a control; plate compactor specifications shown in appendix C | Medium |
| Noise (rollers and plates 95–105 dB) | Operator and nearby | SNR 30+ ear defenders mandatory; hearing health surveillance for >85 dB(A) daily; Section 61 prior consent where night/weekend work in residential area | Low |
| Manual handling — kerb units, edge restraints | Crew | Two-person lift for kerbs >25 kg; mechanical kerb grab (Probst MKZ) for granite or PCC kerbs >50 kg; carry distances <10m; daily rotation; no single-handed kerb setting | Medium |
| Buried services strike during sub-formation excavation | Excavator crew, all | CAT4+ scan before any dig; service drawings on site; trial holes by hand for any unknown; permit-to-dig signed before mechanical dig; gas/water/electric isolation booked where adjacent works | Medium |
| Slips, trips on loose Type 1 stockpile | Crew | Stockpiles maintained at 1:1.5 max angle; daily walk-through; safety boots with ankle support; no climbing on stockpile for any reason | Low |
Step-by-step sequence
- 1
1. Pre-start brief & subgrade hold-point
Subgrade signed off by engineer (CBR ≥5% typical for highway, ≥3% for car park). Trial compaction record reviewed. Material test certs in appendix A. Crew briefed, sign-on register.
- 2
2. First lift placement (typically 150mm)
Type 1 tipped and spread to design level using a paver or a grader. Surface trimmed to ±10mm of design. No segregation at edges. Loads kept clean — no top-soil contamination.
- 3
3. First-lift compaction
Compaction per trial — typically 6 passes with vibration on a 13-tonne single-drum roller. Plate compactor on edges and against kerbs. Moisture check with on-site nuclear gauge or Proctor mould samples.
- 4
4. Second lift placement & compaction
Second lift (typically 75–150mm) placed only after first lift signed off. Same compaction sequence. Final 2 passes static to close the surface.
- 5
5. Proof-rolling
Loaded 18-tonne tipper driven across the full surface. Any rutting or visible deflection >5mm marked for re-work. Signed off by site engineer before next stage.
- 6
6. Plate-bearing test (PBT) to BS 1377-9
PBT at minimum 1 test per 1000m² for highway, 1 per 500m² for industrial. K150 ≥120 MN/m³ typical highway acceptance, higher for HGV pavements. Cert filed to QA file before surfacing.
- 7
7. Hand-over to surfacing & records
Subbase surveyed for level and tolerance (±10mm typical). Photographs of every layer. MS, trial record, materials cert, PBT cert and as-built bundled to the works information pack. S38/S278 technical approval submitted within 28 days.
1,200m² industrial loading yard subbase, Tarmac Type 1 in two lifts (Tamworth)
This is a fictional composite showing the level of task detail a reviewer may expect. It is not a customer case study or an approval claim; the competent person, client and principal contractor must review the real project.
A Midlands civils contractor on a logistics yard scheme produced a 9-page MS for the subbase to a 1,200m² HGV loading yard. Key entries: Tarmac Type 1 SHW 803 0/63mm recycled limestone (cert TC-2026-04-122, plasticity index NP, LA value 28 — within SHW limit 35); subgrade CBR confirmed 7.2% on 4 in-situ CBR tests by Geotechnical Engineering Ltd; design thickness 225mm in two lifts (150mm + 75mm); BOMAG BW213DH-5 13-tonne single-drum roller (NRMM compliant Stage V), 6 passes vibration + 2 static per trial compaction record dated 02/05/2026; plate compactor (Wacker Neuson DPU 6555) on kerb-side 600mm strip; moisture check by nuclear density gauge (Troxler 3440) every 25 linear m, 8 readings logged, all within OMC ±1.6%; proof-roll with 18-tonne Volvo FMX tipper, 2 areas of 0.3m² re-worked, otherwise pass; plate-bearing test (BS 1377-9, 300mm plate, ELE PBT-300) at 4 positions per 1000m² rule, K150 results 138, 142, 135, 145 MN/m³ — all above the 120 MN/m³ target; subbase signed off by Tamworth highways officer 07/05/2026, surfacing started 09/05/2026, S278 technical approval submitted 22/05/2026. Zero call-backs to date. The MS, the trial record, the material cert and the PBT cert were the four documents the highways adoption auditor checked.
Or build a site-specific subbase preparation MS in 5 minutes
The free template is a blank Word document. The Riskora builder ships with the subbase preparation hazard library baked in — pick the preset, edit the site-specific bits, download a signed PDF.
Common mistakes that get a subbase preparation MS rejected
- ·Placing 300mm in a single lift instead of two — the bottom 100mm will be undercompacted and the pavement will rut over the wheel paths within a winter
- ·No trial compaction record — the specification needs evidence that THIS roller on THIS material achieves the density target, not a generic '6 passes' assumption
- ·Skipping the plate-bearing test on a 'small' job — adopting authorities (S38) routinely refuse handback without the cert
- ·Roller working parallel to an unprotected edge — the 2022 Midlands fatal sat exactly here
- ·Forgetting the NRMM declaration for the central Manchester, Birmingham or London CAZ — non-compliant rollers turned back at the gate
- ·Mixing recycled and virgin Type 1 across the same layer without an updated test cert — graders will mix them anyway, but the QA file needs the combined test
Frequently asked questions
Is Type 1 the same as MOT Type 1?
Yes — 'MOT' is the historic Ministry of Transport designation, now formally Specification for Highway Works clause 803 Type 1 unbound mixture, BS EN 13242. The material is the same; modern test certs reference SHW 803, not MOT.
What's the minimum CBR for the subgrade?
5% for adopted highway under SHW; 3% acceptable for car parks and light-trafficked yards. Below 3% you typically need capping under the subbase. The subgrade CBR must be evidenced by in-situ test before the subbase MS is signed off.
How thick should the subbase be?
Design-dependent — 150mm for car parks, 225mm typical for industrial yards, up to 450mm for HGV pavements. Layer thickness is capped at 150mm per lift for proper compaction. Single-lift placement of >150mm is the most common cause of pavement failure.
Do we always need a plate-bearing test?
Yes for adopted highway (S38/S278), industrial pavements and any HGV-trafficked surface. Domestic driveways and patios typically don't need PBT but the MS should still record the compactor and the number of passes.
What's the K150 acceptance value?
K150 (modulus of subgrade reaction from 300mm plate) is typically specified at ≥120 MN/m³ for adopted highway subbase. Higher values (180+ MN/m³) for HGV pavements. The acceptance value must be in the MS and on the PBT cert.
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