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Concrete spotlight: Out of a hole

FP McCann has recently tested its recently launched precast concrete manhole base unit with integrated water-tight propylene liner on a housing estate in Northumberland

Pegswood housing estate in Northumberland was among the first projects to benefit from a recently launched concrete manhole base unit.

FP McCann launched the prefabricated system, called Easi-Base, after securing approval from water and environmental consultant WRc earlier this year.

Speaking about the project, Northumberland County Council highways development control engineer David Dent says: “The Easi-Base system is an innovative development in manhole construction.

“The ability to get the manhole base quickly installed without the need for concrete benching and the required protection from the weather is a real benefit. We are confident that Easi-Base will give us long-term performance and efficiency in the management of waste water from this site.”

The precast system incorporates a fully integrated, watertight polypropylene liner in an attempt to replace the outdated labour-intensive method of in situ manhole base construction.

The unit dresses the processes associated with traditional methods of manhole construction, such as relying on:

  • ready mixed concrete to form the base and rough benching  
  • a clay, concrete or uPVC channel to connect the inlet, outlet and branches together 
  • trowelled mortar to provide a smooth surface on top of the rough benching

This operation often occurs in a deep waterlogged pit, requiring trench supports to protect up to two or three people during the laborious construction process. Poor site practices, combined with inclement weather conditions, often lead to short and longer term integrity failures, including in the concrete base formation and also in connections between the channel and the concrete.

The pre-formed base and channels significantly reduce the number of visits and time spent in the manhole during construction.

The consequences of the resultant leaks are twofold: groundwater is contaminated with polluting raw sewerage and clean groundwater infiltrates the already overloaded raw sewerage system of pipelines and treatment plants.

With Easi-Base, the preformed base and channels significantly reduce the number of visits and time spent in the manhole during construction.

The unit is placed on a formation comprising compacted granular material. A 1% preformed fall in the channel exits towards the outlet, as clearly indicated.

Pipe connection is made simple because benching is pre-fabricated and connection bells are cast into the base for the specific pipe in use, which allows the ground worker to simply push the pipe into the base via the sealed connector. A watertight seal is instantly achieved. Conventional methods of constructing the manhole above the base are then followed, with precast concrete rings placed on top.

Easi-Base has been used on other contracts for Anglian Water as well as for contractors Buckingham Group and GKL Group.

Concrete spotlight: Out of a hole

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