GRW/Drainage/TBT-GRW-002

Below Ground Drainage Installation

Groundworks & Earthworks › Drainage › Below Ground Drainage Installation

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Below ground drainage installation involves laying pipes in trenches to create foul, surface water, and combined sewer systems.
Trench collapse is the primary fatal hazard — drainage trenches are often deep, narrow, and in variable ground conditions.
Pipes and fittings are heavy and awkward to handle — mechanical aids should be used for pipes larger than 150mm diameter.
Working in live sewer connections exposes workers to biological hazards including leptospirosis, hepatitis, and bacterial infections.
Buried services including gas, electricity, and water frequently cross drainage routes and must be located before excavation.
Correct bedding and surround material is essential for pipe integrity — poor installation causes structural failure and flooding.
Laser-guided pipe laying requires constant access to the trench, making safe entry and egress critical throughout the operation.
Testing including air testing, water testing, and CCTV survey must be carried out before drainage is accepted and backfilled.
Groundwater dewatering may be required to keep trenches dry during installation — this affects surrounding ground stability.
Manholes, chambers, and inspection points involve working in progressively deeper excavations with confined space characteristics.

Trench collapse	Drainage trenches are often deeper than 1.5 metres in variable ground — proper support prevents the burial deaths that occur in this work.
Biological hazards	Connecting to live sewers exposes workers to sewage-borne disease — hygiene measures and vaccination are essential protections.
Service strikes	Drainage routes cross existing buried services — failing to scan and hand dig near services causes electrocution and gas explosions.

Don't

Support or batter all drainage trenches according to the method statement and ground conditions.
Scan for buried services along the full drainage route before starting any excavation.
Use mechanical lifting for pipes larger than 150mm diameter — do not lift them manually.
Vaccinate against hepatitis and tetanus before carrying out live sewer connection work.
Wash hands with antibacterial soap before eating, drinking, or smoking after sewer work.
Provide safe ladder access into drainage trenches at regular intervals.
Install correct bedding and surround material as specified for the pipe type and loading.
Test completed drainage runs before backfilling — record results for handover documentation.
Monitor dewatering systems and groundwater levels throughout the drainage installation.
Follow confined space procedures when building deep manholes and inspection chambers.

DON'T enter unsupported drainage trenches deeper than 1.2 metres under any circumstances.
DON'T dig drainage routes without scanning for existing buried services first.
DON'T manually lift large-diameter pipes — use the excavator or a pipe handler.
DON'T work on live sewer connections without vaccination and proper hygiene measures.
DON'T eat or drink before washing hands after contact with sewer contents.
DON'T work in drainage trenches without safe means of escape within easy reach.
DON'T backfill with incorrect material — pipe failures from poor bedding cause flooding.
DON'T cover drainage before testing is complete and results are formally accepted.
DON'T ignore rising groundwater — it weakens trench walls and causes sudden collapse.
DON'T build deep chambers without treating them as confined space entries.

See also: Excavation Safety Awareness | Trench Collapse Prevention

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