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Surface Water Drainage

Installation design – radii, crossings, junctions and bends

Radii

Highway/Mini Highway:

• To form external radii of 25 metres or less (minimum 6 m), special radius units should be used (see table below). As these do not cover all individual radius dimensions, some slight gaps are required between units as indicated in Highway radii gap widths table.
• For external radii greater than 25 metres, lay straight units with open joints.
• To form internal radii (minimum 6 metres), use 7/6 internal radius units.

Clearway/Safeticurb:

• Where necessary, standard (straight) units may be laid to form radii or bends.
• Safeticurb units: alignment ring within bore acts as a former for infill mortars to seal joint.

Crossings

Highway/Mini Highway:

• Use crossing base units to carry drainage runs under side roads / vehicular crossing points Grid units available.
• Safeticurb (DBK unit only):
• To continue linear drainage at road junctions, kerb crossing points (pedestrian/vehicular), use transition units to reduce kerb height to road level. These connect with standard grid or slot units as necessary.

Junctions/sharp bends

Clearway/Safeticurb:

• Use silt box top at outlets or with suitable uPVC pipe fittings (cut to fit) to form junctions or sharp bends.

Highway radii gap widths

Installation design – units

General principles

All units are unreinforced: protect from stresses caused by thermal expansion of cementitious paving materials. Leave 1mm gap between each unit to prevent damage from thermal expansion of the units themselves.

Expansion joints MUST be installed on each side of drainage runs in concrete pavements or those incorporating a cement bound/lean mix concrete roadbase.

DO NOT place these joints directly adjacent to any trafficked unit as this would allow units to rock under trafficking and may allow water ingress into the base or sub-grade.

Recommended position of joints (minimum distances):

• 600 mm from Clearway/Safeticurb units.
• 125 mm from Highway units.

Note: As Highway units are not regularly trafficked, expansion joints could be placed directly against them. However, 125 mm distance is recommended to avoid ingress of water between the unit and carriageway construction.