| S.No. | Checkpoint | IS Requirement | Status |
|---|---|---|---|
| A. INSTALLATION PROCEDURE | |||
| A1 | Step 1: Trench excavated to design depth with sand cushion (100mm) placed Acceptance: Trench ready, sand layer in place | Cl. 5 — Preparation | |
| A2 | Step 2: Pipes laid on sand, joints made with mortar, benching in manholes Acceptance: Pipes installed, joints completed, invert level correct | Cl. 6 — Laying | |
| A3 | Step 3: Support layer (150mm sand) placed over pipes; backfill soil added in 200mm lifts Acceptance: Support and backfill completed, compacted | Cl. 7 — Backfilling | |
| A4 | Step 4: Water test (30 minutes hold) and smoke test performed; defects repaired Acceptance: Tests passed, zero leakage, ready for service | Cl. 10-11 — Testing | |
| B. SAFETY MEASURES | |||
| B1 | Work site secured, trench properly shored for depth >1.5m, PPE provided to workers Acceptance: All safety measures in place, no incidents | Cl. 12 — Safety | |
Sewer pipes are buried for decades; any installation defect causes leakage, infiltration, root ingress, or collapse — all expensive to repair (excavating + replacing 100 m of sewer can cost ₹5-15 lakh). IS 4127:2017 mandates a written method statement before sewer construction starts.
The method statement defines: excavation methodology, bedding preparation, pipe selection + jointing method, backfilling sequence, testing protocol, and reinstatement. Reviewed + approved by PMC + structural engineer before crew enters trench. This protects against trench collapse (worker safety), wrong pipe specification (network failure), and poor compaction (settlement).
1. Survey + setting out — verify alignment, depths, gradients per drawing 2. Excavation — trench depth as per design + 150 mm bedding allowance; sides battered or shored if deep (> 1.5 m mandatory shoring per BOCW Rules) 3. Dewatering if water table high 4. Bedding course — 100-150 mm well-compacted granular bedding per IS 783 5. Pipe laying — alignment + gradient check at every joint; gradient typically 1:80 to 1:200 for self-cleansing velocity 6. Joint sealing — rubber rings (IS 5382 / IS 13177) for concrete pipes; solvent cement for UPVC; electrofusion for HDPE 7. Air pressure test per IS 4127 Annex F (low-pressure sewers) or water-fill test (gravity) 8. Backfilling in lifts — granular below pipe top + 300 mm above; selected soil thereafter; compaction per IS 2720 Part 8 (modified Proctor) ≥ 95% 9. Reinstatement — pavement / road / landscape restored to original 10. Sign-off — contractor + PMC + client; method statement closed out
1. Inadequate bedding — pipes laid on uneven trench bottom; differential settlement; joints separate; infiltration → groundwater contamination + flow loss.
2. Wrong gradient — 1:200 (1.0 m/200 m) typical for 200 mm pipe; flatter → solids settle; steeper → erosion + scour. Method statement forces verification.
3. No air test — pipes commissioned without pressure test; leakage discovered during operation. Mandatory test per IS 4127 Annex F.
4. Wrong joint type — using cement-mortar for rubber-ring concrete pipes; joints fail at first ground movement. Method statement specifies.
5. Inadequate backfill compaction — uncompacted backfill settles; pavement collapses; pipe damage from above. Specify 95% MDD minimum.
6. No trench shoring — deep trench collapse → worker fatality. BOCW + IS 4081:1986 mandate shoring above 1.5 m depth.
7. No alignment check at every joint — pipes off-line; flow disrupted at curves; method statement mandates.
Companion QA/QC: - Drainage Register (QC-DRN-REG-001) — system-level installation tracking - Manhole Method Statement (QC-DRN-FRM-002) — chambers - Smoke Test (QC-DRN-TST-002) — leak detection
Codes: - IS 4127:2017 — Laying and construction of sewers (primary) - IS 458:2003 — Precast concrete pipes - IS 4985:2000 — UPVC pipes - IS 4984:1995 — HDPE pipes - IS 8329:2020 — Ductile iron pressure pipes - IS 5382:2018 — Rubber sealing rings - IS 783:1985 — Code of practice for laying of concrete pipes - IS 4081:1986 — Safety code for blasting and related drilling operations (trench safety) - CPHEEO Manual on Sewerage 2013 — national standard