How to prepare for drainage construction October 19th 2018, by Ian Lishman

Drainage is one part of the groundworks  carried out on site prior to starting the above-ground construction. Whether a single building plot or a substantial housing development, once foul and storm drainage runs have been laid they are soon built over – leaving any potential issues to be discovered when it is least convenient to rectify them.

Putting together a drainage plan

Before a trench is excavated, site surveys and drainage design works will combine to create an overall plan of sustainable drainage features that are part of gaining planning permission.

Establishing facts such as soil type and water table level not only help in the design of the drainage plan, they also help the groundworks or drainage contractor to plan the practical aspects of the works.

Drainage construction – design vs reality

As with many areas of construction above ground, being careful to ensure the agreed specification for below ground works like drainage is followed is an important part of making sure design intent is achieved in reality.

A contractor may think they can save money, perhaps by omitting a rodding point or manhole, and thinking it won’t be an issue, but falling into that trap can cause real problems later if there is no adequate maintenance access. On large developments particularly, drainage systems are carefully engineered and even an apparently small problem could impact on many properties at once.

Similarly, preparing trenches to receive the correct pipe sizes, and achieve the correct levels to provide the right falls and connect into the existing drainage system, is an important part of site preparation. Understanding what needs to be achieved before starting work, and how best to achieve it once work has started, is key to a smooth-running project.

Drainage flows are also affected by the pipe material – installing a corrugated plastic pipe rather than a specified smooth-sided pipe can dramatically impact on the drainage flows achieved and on the success of the system. Having an appreciation of what has been specified in order to be able to achieve it on site is an important aspect of preparation.

Eliminating potential problems

Part of preparing for the drainage works can include planning and scheduling testing and survey activities for when the works are complete, before construction of the superstructure begins.

While the temptation is to get on with developing the site above ground as quickly as possible, taking the time to test the system and record it ‘as-built’ before covering it over could save time and money later on, should a problem be discovered.

Ultimately, the potential for many problems to occur can be reduced or removed entirely by working with an experienced, trusted drainage contractor. If they also provide the groundworks as part of a complete package, there is greater flexibility in scheduling across the site and more ‘joined-up thinking’ towards implementing the drainage plan as a whole.

Where the services are provided separately, a groundworks contractor might unintentionally damage drainage works already installed, then leave that work to be redone by the drainage contractor. A single contractor hopefully knows where they have already carried out drainage work – but can take responsibility and rectify things quickly if an unfortunate mistake occurs.

About FACE

For nearly two decades, FACE have delivered high quality civil engineering works on projects of all sizes. Our new turnkey service allows housing developers, whether small or large, to work with us and build a project-specific package of services that FACE then delivers.

The package can include highway works carried out under a section 278 agreement, drainage construction and groundworks. Acting as a single point of contact for multiple aspects of the infrastructure means we can offer improved coordination of works and minimise potential delays.

Find out more and enquire about our turnkey packages here.