How to Construct Drainage?

1. Survey and setting-out

The proposed drain line shall be set-out by qualified surveyor. The original/existing ground levels shall also be checked.

2. Excavation or digging work

Before commencement of any excavation or digging work, underground services within the working area shall be carried out or request a set of detection report from the client immediately. All underground service cables shall be marked with color spray. If soil condition is soft or unstable, install temporary timber support or sheet pile is required.

3. Installation of piles

Once the excavation works has reached the required level, proceed to install timber piles or RC piles according to design.

4. Compaction and lean concrete

Once the piling works is complete, proceed to lean concrete for the base. Before placing of concrete, ensure the surface is dry. If the surface is soft, cut the loose material and lay a layer of compacted hardcore or lean concrete. After leaning the concrete base, proceed to trim the pile head to the required cut-off level.

5. Securing steel reinforcement and formwork for drain base

Fixing in position and tie the reinforcement or wire mesh for drain base (part of drain wall) according to the construction details. Check that there is sufficient lapping length and cover in accordance to requirement. Once all the reinforcement is in position, put up the formwork for the side of the drain base.

6. Concreting of drain base

Before concreting, check that the reinforcement is in position and the area to be casted is clean. If construction joints are required, ensure that loose aggregate is removed before placing the new concrete. After completing the drain base, lay the precast channel and carry out the benching for base as well as the kickers for the drain walls.

7. Positing steel reinforcement and formwork for drain walls

Position and tie the reinforcement or wire mesh for drain wall according to the construction details. Before closing the formwork for the drain wall, install the PVC pipe for weep holes. If there is loose aggregate on the wire mesh, clean the reinforcement before closing the formwork for the drain wall.

8. Concreting of drain wall

Once the formwork is in position, proceed with the concreting work for the drain wall.

9. Concreting of drain top slab

For box culvert drain, after completion of concreting of drain wall, proceed to fix the top slab reinforcement or wire mesh according to the drawing details. Once the reinforcement or wire mesh is in position, proceed to erect the formwork for the soffit of the drain top slab. After the formwork is in position, provide propping to support the soffit of the slab. Ensure that the propping support is in position before proceeding with the concreting of the top slab.

10. Laying of hardcore and geotextile

After completion of all the concreting works, lay the geotextile to the weep holes. Once the weep holes are covered with the geotextile, backfill with hardcore according to the required thickness.