It is important to take precautions against trench collapse:
- Do not open trenches too far in advance of pipe laying;
- Support the sides of trenches that are deeper than 1.2 metres;
- Keep trench widths as narrow as practicable but not less than 300mm wider than the pipe diameter, i.e. 150mm clear each side of the pipe to allow proper compaction of the sidefill.
Bedding and backfill must be of the correct specification. Excavated ‘as-dug’ material may be suitable (see BS 5955: Part 6: 1980 for ‘as-dug’ suitability tests), otherwise a non-cohesive material is required (see Table 1).
|Nominal pipe bore (mm)||Nominal maximum particle size (mm)||Material specification (see note*)|
|100||10||10mm nominal single size|
|Over 100 to 150||15||10mm or 14mm nominal single size, or 14mm to 5mm graded|
Table 1: Processed Granular Bedding and Sidefill Materials for Flexible Pipes
*Note: Aggregates conforming to BS 882, air cooled blast fumace slag conforming to BS 1047, or lightweight aggregates conforming to BS 3797 are suitable as processed bedding and sidefill materials.
When the bedding formation is prepared, pipes should be laid upon it true to line and level. Each pipe should be checked and any necessary adjustments to level made by raising or lowering the bedding formation.
Just Drain pipes laid on 50mm minimum processed granular bed
Where the trench bottom can be hand trimmed by shovel and is not puddled when walked upon, a 50mm depth of bedding material may be used. In this case the material must be nominal 10mm single sized aggregate (see Table 1).
- Place suitable sidefill material evenly on each side of the pipe in 100mm layers. Hand tamp well at each layer up to the pipe crown.
- If ‘as-dug’ material is free from stones exceeding 40mm, imported processed granular material is not needed above the pipe crown (see Figure 1). Cover the pipe crown with a minimum of 300mm of compacted ‘as-dug’ material. If ‘as-dug’ material contains stones larger than 40mm, or the pipe is deeper than 2 metres in poor ground, extend the processed granular material for at least 100mm above the pipe crown.
- In both cases, hand tamp the material fully at the sides of the pipe while tamping lightly over the crown. Continue hand tamping until a finished layer of 300mm has been placed over the pipe.
Preparing pipe ends
Pipes cut on site must be clean cut at right angles to their horizontal axis. Deburr the cut end with a scraper.
Depth of entry mark
Some plain ended fittings have a depth of entry mark moulded on the spigot. This depth of entry allows the pipe to expand into the fitting socket by a minimum of 12mm. Insert the spigot into the socket until the depth of entry mark is just visible. All pipes (whether site cut or otherwise) and other plain ended fittings must be inserted to the full depth of the socket, marked at the socket face, and then withdrawn at least 12mm (see Figure 2).
Ring Seal Joints
Pipe couplers and most fittings in 110mm and 160mm sizes are supplied with either a single or double socketed end. These sockets are fitted with a loose ring seal, which acts as both a sealing and expansion joint.
The correct sequence for ring seal jointing is as follows:
- Check that the pipe is correctly prepared (see Figure 3 and 4) and that the ring seal is properly seated in its housing.
- Make sure that both the pipe and fitting spigot and ring seal socket are dry, clean and free from grit or dust.
- Lubricate evenly around the spigot (NOT the socket) with a suitable lubricant.
- Make sure that the components to be joined are correctly aligned.
- Push the spigot fully into the socket, mark the spigot at the socket face and then withdraw the spigot by a minimum of 12mm. If the spigot is already marked with the depth of entry, push it into the socket until the depth of entry mark is just visible.
Installation of Shallow Inspection Chamber – 0.6 metres
No additional trench excavation is needed.
- Lay suitable bedding material (as used for the drain line).
- Make pipe connections in the same way as for 110mm pipe/fittings. When using the components as a 90° change of direction, the main through channel should always be used. This can be achieved by inserting a 45° Short Radius Bend into the main inlet and outlet.
- Sit the chamber on a minimum 100mm bed of suitable granular material and surround it with similar material 150mm wide.
- Depending on the depth of invert required, push-fit either one or two shaft sections onto the base unit ensuring that the inside of the shaft section has been pre-lubricated. Intermediate depths may easily be obtained by cutting the shaft section to the required depth.
- Push-fit the Cover and Adjustable Frame, directly into the top of the shaft section, again ensuring that the inside of the shaft section has been pre-lubricated.
Installation of Intermediate Inspection Chamber – 1.2 metres
No additional trench excavation is needed.
- Sit the Chamber Base on a minimum 100mm bed of granular material. The main through channel must always be used.
- Make connections in the same way as for 110/160mm pipe/fittings. Push Blank-off Plugs externally into any unused inlets. When using the component as a 90° change of direction the main through channel must always be used. To achieve a 90° change in direction insert a 45° Short Radius Bend into the main inlet/outlet.
- Assemble Chamber to required invert depth by placing one, two or three shaft sections onto the base unit.
- Assembly of the chamber is very easy. A simple, sealant filled interference joint ensures a watertight installation (lubricant not supplied).
- Surround the chamber with 150mm of similar material to that used as bedding.
- Continue the sidefill to the level required for the installation of the cover and frame as appropriate.