Bourne to Succeed

Very often, we get asked to deliver awkward projects that our competitors either can’t get their heads around, or aren’t in a position to deliver.Here at HB Tunnelling, we’re proud to say that one of our strengths is our ability to think outside of the box, and deliver results that meet or exceed all the clients’ requirements. 

 McCarthy & Stone is the UK’s leading retirement house builder of privately owned property and recently they engaged the expertise of HB Tunnelling to undertake works supply & install 6M diameter Shaft, which will house the pumps for the new pump station. When completed, provide high quality accommodation for those over 60 and is the only new retirement development in the town.

 The site is located next to the River Thames in Bourne End, Buckinghamshire to which local author Enid Blyton whose home was located in Bourne End for many years.

Now having undertaken similar works in the area many years ago, this was yet another challenge as the ground conditions are some of the worst I have ever encountered throughout the UK.

The site posed many constraints such as water table at 2mtr depth & with the River Thames only 200mtrs away, discharging any water from site was restricted to 3ltrs per second.

Firstly HBT install a deep well on the perimeter of the proposed collar, to assist with the construction & installation of the guide collar.

Once the guide collar was installed the 6mtr diameter shaft would be excavated underwater as this would aid with keeping an equal balance & not discharging unnecessary water offsite into the Thames Water combined sewer network.

The would be build from the top & then once the centre of the shaft had been excavated using a telescopic grab the 4 number hydraulic rams would push the precast caisson ring down into the ground equally keeping nice & straight.

HBT could not pump any water out of the shaft during construction as this would unstable the ground at the bottom of the caisson shaft to which could cause the caisson shaft to move out alignment & end up like the leaning tower of Pisa.

Once the shaft was down to depth, the Caisson was then pinned to the guide collar to which was designed to aid the anti-flotation.

Divers was then mobilised to site to aid with the installation of the mass concrete plug to which would be poured underwater by tremie concrete method.

Once the concrete plug was poured & cured the shaft could then be pumped down ready to install the RC base slab to the finished levels.

For more information please contact Hugh or Andy on -  0845 388 3325