Precast options for bad ground conditions

When Peter Harding Construction began work on a project at St Wilfred’s Academy, Blackburn they were presented with bad ground conditions, which needed a drainage solution that would enable them complete the works with maximum efficiency whilst ensuring the health and safety of every member of their team.

Having appraised the drainage drawings, the drainage design consultants designed orifice chambers and Hydro-Brake chambers within the surface water network using traditional systems.

However following several meetings and discussions in relation to an off-site option and also reviewing the initial cost implications and their options, Craig Evans, Trading Manager from the CPM Group presented a full package of sealed 1200mm and 1500mm Perfect Manholes and offsite options for orifice and Hydro-Brake chambers.

The discussions enabled minor changes to the cover levels that overcame an original concern with the overflow on the Hydro-Brake chamber, when reviewing the original design versus offsite proposal. The designed looked at using the Perfect Manhole system where possible but due to the unusual “S” style channel configuration in a constricted area it was not always ideal. An alternative proposal to use a 1500mm sealed Catchpit using an offset inlet and outlet with an in-situ cast was deemed the best option.

As well as evaluating the options for the manhole requirements a full appraisal of the pipe diameter and type were assessed and presented to the client which benefited from construction durability as well as the cost savings that are made by using the pipe bedding alternative. Where there had previously been an option for using a plastic pipe which would require a full granular surround (Class S Bedding) a precast concrete pipe option was given enabling the use of a different bedding requirement (Class N Bedding) which meant savings on the environmental factor of the project as well as cost savings.

450mm and 525mm precast concrete pipes were agreed as part of the drainage network due to design criteria and ground conditions along with the potential cost reductions.

Following the approval of CPM’s Perfect Manhole System and Offsite Solutions proposal, Ray Harding of Peter Harding Construction stated that: “The overall solution not only accelerates the installation of the drainage requirements, it also allows for the installation of the drainage in poor ground conditions, faster easier and more economically than traditional build”.

For further details on the CPM Perfect Manhole please click here and for Hydro-brakes click here.