Code of practice on surface water drainage

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9.11
Grating over Closed Drain/Culvert
9.11.1 All gratings provided over closed drains/culverts shall be hinged to fixed frames securely embedded into the drain structures. Mild steel heavy duty gratings shall be used for closed drains subjected to vehicular loadings, whereas light duty gratings shall only be used for pedestrian loadings. The gratings, frames and chequered plates shall be galvanized. The details of the gratings and chequered plates shall be designed in accordance with the Land Transport Authority’s latest Standard Details of Road Elements.
9.11.2 For drains with internal width greater than m, access opening (m x m) shall be provided as shown in Drawing No. 2.
9.11.3 Where a culvert runs across the road, no sump/grating shall be sited on the road carriageway. Where necessary, sumps with galvanised mild steel gratings shall be provided at the two side-tables of the road. In the case of a dual carriageway, a sump with galvanised heavy duty mild steel grating shall be provided at the centre divider.
9.11.4 The size and spacing of gratings required shall be based on the internal width of the closed drain, as follows

Internal Width
Grating
(W)
Size
Spacing
W > 4 m
850 mm x 1000 mm
50 m (staggered) in addition 4 m x 2 m opening)
500 mm < W  4 m
850 mm x 1000 mm
50 m (staggered) in addition 1.5 m x 1.5 m (opening)
500 m
750 mm < W  2 m
850 mm x 1000 mm
6 m (for drain  1 m deep) or
18 m (for drain > 1 m deep) W  750 mm
700 mm x 850 mm
6 m Note (i) Rungs shall be embedded at the drain wall at every opening/grating for closed drains with internal depth equal to or greater than min accordance with Clause 9.10. ii) For drain or drainage reserve within the development site, maintenance opening shall comply with the requirements specified in Clause c.
* Subject to approval of the Board, if the minimum size of closed drain as specific in Clause 4.3.1 cannot be met, the details of the Grating maybe designed in accordance with the drawing as shown in Drawing No. A or B
9.11.5 Where a closed drain exceeds 3 m deep, access shaft (2 m by 1.5 m) maybe required by the Board. If the access shaft is deeper than 4 m, intermediate platform shall be provided as shown in Drawing No. 3.

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