HWY/Specialist/TBT-HWY-012

Highway Drainage Installation

Highways & Road Works › Specialist › Highway Drainage Installation

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Highway drainage installation includes gullies, pipe runs, manholes, and attenuation systems beneath roads.
Work takes place within or adjacent to live carriageways, requiring traffic management throughout.
Trench excavation in highways encounters dense buried services including gas, water, electric, and telecoms.
Manhole construction involves working in progressively deeper excavations with confined space potential.
Heavy precast manhole rings and cover slabs require crane or excavator lifts with proper rigging.
Connection to existing live drainage systems may involve working in flowing water and sewage.
Backfill and reinstatement must meet the specification to prevent road surface settlement.
Gully installation involves cutting into the road surface with disc cutters generating silica dust and noise.
NRSWA permits and highway authority approvals are required before any work in adopted highways.
Phased working and temporary drainage diversions maintain road drainage function during construction.

Traffic hazard	Workers in highway drainage trenches are within metres of live traffic, requiring continuous TM protection.
Buried services	Highway verges and carriageways have the highest density of buried services on any construction site.
Trench collapse	Deep drainage trenches in highways are destabilised by traffic vibration and surcharge from passing vehicles.

Don't

Install Chapter 8 traffic management before excavating in or adjacent to the highway
Locate all buried services using CAT, Genny, service plans, and trial holes
Support trench sides to resist soil pressure plus traffic vibration and surcharge
Obtain NRSWA permits before starting any excavation in adopted highway land
Use RPE and hearing protection when cutting road surfaces with disc cutters
Rig precast manhole rings and covers using rated slings and a detailed lift plan
Assess deep manholes for confined space hazards before workers enter
Reinstate backfill and road surface to the specification to prevent settlement
Maintain temporary drainage function during phased construction works
Brief the team on traffic management layout, escape routes, and buried service locations

DON'T excavate in a highway without NRSWA permits and traffic management in place
DON'T enter unsupported drainage trenches adjacent to live traffic lanes
DON'T lift precast manhole components without rated slings and a lift plan
DON'T connect to live drainage without assessing confined space and biological hazards
DON'T cut road surfaces without silica dust controls, RPE, and hearing protection
DON'T backfill drainage trenches with material that does not meet the reinstatement spec
DON'T leave open trenches or manholes unguarded in the highway during darkness
DON'T ignore traffic vibration effects on trench stability — increase support accordingly
DON'T allow surface water to flood during construction by blocking existing drainage
DON'T skip the permit to dig process because you believe services have been cleared

See also: Highway Works Safety Awareness | Below Ground Drainage Installation

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