IS 4127:2017 (Code of Practice for Laying and Construction of Sewers) requires a written method statement for every drainage structure built on site — and manholes are the most-built drainage component on any project (every urban site needs 5-50 manholes; large layouts run into hundreds). A signed method statement before work begins ensures the contractor's crew knows exactly what depth, what materials, what bedding, what testing applies to this specific manhole location.

The method statement is also the PMC's preview of contractor's proposed approach. PMC reviewers catch problems here — wrong concrete grade, missed precast vs in-situ specification, inadequate excavation plan, no working-platform detail — before the trench is open and money has been spent. A rejected method statement is cheap; a rejected manhole after construction is expensive.

Sequence: 1. Survey the manhole location → mark invert level, chamber dimensions, cover finish level 2. Issue method statement to crew before excavation starts; PMC approval mandatory before work 3. Excavate per spec — depth, side slopes, dewatering plan if water table high 4. Bedding course — well-compacted granular bedding 100-150 mm; verify with plate-load test if specified 5. Construct base slab — RCC M25 typical; check reinforcement + concrete cover per Section 16 of IS 456 6. Build chamber walls — brickwork in CM 1:4 OR precast RCC OR cast-in-situ RCC; cover slab + opening + frame to suit traffic class 7. Backfill + compact — granular below the pipe invert level; mass concrete or compacted soil above 8. Test — air pressure test (low-pressure sewers per IS 4127) or water-fill test (gravity sewers) 9. Sign-off — PMC + contractor + client representative; method statement closed out

Who uses: Contractor's drainage engineer prepares; site supervisor executes; PMC engineer reviews + signs off; project manager owns the document.

1. Wrong concrete grade for chamber walls — clay-area projects sometimes use M15 for cost; IS 4127 specifies M25 minimum for any traffic-loaded manhole. Method statement catches this at design review.

2. Inadequate bedding — pipes resting on unbedded soil settle differentially; joints separate; leakage develops. Method statement mandates granular bedding + verification.

3. No air-test specification — for low-pressure sewers, IS 4127 requires air pressure test per Annex F. Sites that skip this discover infiltration / exfiltration months later. Method statement should explicitly cite the test pressure + duration.

4. Wrong invert level — manhole invert must match upstream + downstream pipe inverts; getting it wrong creates back-pitch + flow problems. Survey + method statement catch this before construction.

5. Inadequate concrete cover — for buried RCC manhole walls, IS 456 Table 16 cover for severe exposure = 45 mm. Sites that use 25 mm cover have rebar corrosion within 5-10 years.

6. Missing dewatering provisions — high-water-table sites need active dewatering during excavation + curing. Method statement should specify dewatering pump capacity + duration.

Companion QA/QC: - Drainage Register (QC-DRN-REG-001) — track each manhole through construction - Smoke Test (QC-DRN-TST-002) — leak-detection post-construction - Sewer Method Statement (QC-DRN-FRM-001) — companion for sewer-pipe construction

Codes referenced: - IS 4127:2017 — Code of Practice for Laying and Construction of Sewers (the primary) - IS 458:2003 — Precast concrete pipes (when precast pipes connect to manhole) - IS 456:2000 — Plain and Reinforced Concrete (manhole RCC construction) - IS 12592:2002 — Precast RCC manhole frames and covers (the cover + frame) - CPHEEO Manual on Sewerage 2013 — National sewerage manual (referenced for major projects)