Civils and Drainage FAQs
Civils and Drainage FAQs
Concrete Drainage Pipe FAQs
Are there any precautions to take for concrete pipes laid to steep gradients? keyboard_arrow_down
It is recommended that anchor blocks be cast into the ground every 3 or 4 pipe joints behind the socket (also consider installing packers on the face of sockets to prevent concrete to concrete contact).
Do you supply certificates of conformity for your standard products? keyboard_arrow_down
No – they are not required as our standard products are certified under the BS ‘Kitemark’ system – certification can be viewed here.
How frequent should I be testing the pipeline during installation? keyboard_arrow_down
It is highly recommended to test the pipeline every 3 or 4 pipes laid as an absolute minimum (do not wait until whole line is installed before carrying out such test).
What are the appropriate roughness values for concrete pipes? keyboard_arrow_down
Roughness values are:
- Foul sewers: 1.5mm
- Surface water sewers: 0.6mm
What concrete pipes are generally reinforced? keyboard_arrow_down
Marshalls CPM concrete pipes are generally reinforced in sizes DN675 and above (it is possible to reinforce some of the smaller sizes and also to provide un-reinforced pipes in some of the larger sizes – usually made to order).
What is the maximum permissible velocity in concrete pipes? keyboard_arrow_down
Limits are not normally placed on maximum velocities but certain criteria such as the potential for erosion should be considered for steep gradients.
What is the maximum working pressure that concrete pipes can withstand? keyboard_arrow_down
Concrete pipes are designed to operate at low heads of water. The BS performance requirement is set at a minimum of 0.5 bar.
What is the most likely cause of air test failure for a concrete pipeline on site? keyboard_arrow_down
Common causes of air tests failures include:
- Displaced seals (usually due to use of wrong pipe lubrication during installation)
- Poor laying technique
- Faulty testing equipment
- Poor seal between testing equipment and face of concrete pipe
What is the recommended maximum jetting pressure acceptable for concrete products? keyboard_arrow_down
5000 psi is the generally accepted maximum, although higher pressure can be accommodated by concrete drainage products.
What materials can be used as backfill for a concrete pipeline? keyboard_arrow_down
In many situations the ‘as-dug’ trench material is suitable for backfill (should be readily compactable and free from large boulders etc).
What sizes of concrete pipes are subject to testing when installed? keyboard_arrow_down
It is common practise to carry out air or water testing of pipes normally up to DN750 and a visual inspection above this size.
What strength of concrete pipes is available? keyboard_arrow_down
Circular concrete pipes are all manufactured to strength class 120 (minimum crushing load for a particular size of pipe is equal to 120 multiplied by DN of pipe divided by 1000).
What typical joint gaps should be achieved when jointing concrete pipelines? keyboard_arrow_down
Joint gaps between pipes should be measured on the internal surface and should ideally be between 5-25mm.
Where can I get additional assistance on the use of concrete drainage products? keyboard_arrow_down
Additional assistance can be sought through the British Precast Drainage Association
Do you recommend surrounding pre-cast concrete manholes with in-situ concrete? keyboard_arrow_down
Concrete surrounds to manholes are not always necessary in the majority of situations. However if the sewer is to be adopted, this may be a requirement.
What are the recommended minimum depths of cover for concrete pipes? keyboard_arrow_down
Minimum depth of cover to top of pipes is 0.6m with bedding class S (360o granular bedding). For cover depths less than 0.6m, then the pipeline should be protected with either a full concrete surround, or a reinforced concrete slab should be placed over it (spanning sufficient distance onto trench walls).
What are the recommended self-cleansing velocities for foul and surface water concrete sewers? keyboard_arrow_down
Minimum self cleansing velocities are:
- Foul sewers: 0.75m/sec at one third design flow
- Surface water sewers: 1.0m/s at full pipe flow
What is the standard position of the access opening in cover slabs? keyboard_arrow_down
The standard access position is 150mm in from the chamber wall below (measured from centre of nearest access edge to inside of chamber wall below). Other positions/access sizes/multiple access slabs can be made to order.