Get the low down from HB Tunnelling

Article: Mind The Gap

HB Tunnelling was contacted to assist with new installation of a 225mm diameter foul line at Penshurst Rd, London.

Upon undertaking a site visit it appeared that the main foul sewer had been penetrated by local builders using piling equipment & filled sewer with concrete.

Thames Water & Framework contractor was looking at alternative possibilities of re-diverting the main sewer, and the only suitable place would be through back gardens & then along the footpath entrance to the rear of properties in Penshurt Rd. However the road level was 2mtrs higher than the front garden as the properties had basements within.

Open cut trenching was obviously out of the question as a 4mtr deep trench would and could damage the adjacent properties & unsure of the footing on both properties.

Ground was a good London Blue Clay, however there was a possibility that rubble could be encountered as the area was under increasing bombings during the war.

HBT was able to provide a number of techniques but it would depend on risk with client, HBT carefully explained risk with all the techniques being offered. The client then chose Guided Augerboring to install the new 225mm pipe.

We strongly advised that a heave & settlement calculation be undertaken prior to any works taking place, this would allow us to see what predictions of movement there will be& if any damaged would be caused to the properties.

HBT set off to undertake the heave & settlement calculations, due to the ground staying as clay then the predictions was low, with expected settlement below 1mm.

With this added confidence the client raised the order for the works to precede. An emergency road closure was installed ready for the launch shaft excavation.



Works then commence of installing the launch shaft within Penshurst Road & HBT mobilised to site with their BM400 guided augerboring rig.




HBT specialist operatives then set up the BM400 augerboring rig to the given line & levels and commenced piloting operations.



At 12mtrs into the pilot operations HBT encountered obstruction, upon undertaking investigation works it appeared that the pilot rod is just catching the footing on one of the properties, the client then instructed HBT to remove and re-align moving away from the footing.

HBT then pulled the pilot rods out & filled the void with bentonite & recommenced with realigning the BM400 rig.

At the second attempt the pilot went through to the rear garden & then augerboring commenced & 225mm clayware installed in under 1 week.

The works was completed in a total of 5 days, this included the mobilisation & demobilisation.



For more information please contact 0845 388 3325 to speak to the HBT team.

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