During a previous contract, precast arched segments were being used to create a tunnel section within an existing Railway Cutting, to create land space above, for the construction of a new Supermarket.
During the backfilling operation, some of the tunnel segments collapsed onto the railway, blocking and closing the track for several months.
The remedial action on a subsequent project, required the construction of a tied back bored pile wall 900mm in diameter, and 23m deep, along the length of the tunnel, to allow the subsequent removal of the existing backfill material, in order that the tunnel segments could then be used as a permanent shutter to form a new concrete arched structure.
Martello Piling used their restricted access MP4000 series rig to construct a 750mm diameter bored pile wall where the access space was restricted to a platform just a few metres wide, and in the other areas 2 MP5000 series rigs were used, installing 10.0m of temporary casing and constructing 900mm diameter piles to 23.0m. The contract was scheduled to last approximately 6 months, and successfully completed approximately 3 weeks early.
Stanmore Tube Station is located at the end of the Jubilee Line. A new platform was required at the station and the only available space could be created by cutting into a steep clay embankment. At the top of the embankment was commercial and residential property. The geotechnical investigations indicated clay sub-soil and a contiguous bored piled wall was considered the most suitable option to create the space for the new platform. The geotechnical investigation indicated that only relatively light weight piling rigs could be placed onto the embankment due to overall stability considerations. It was also necessary to have piling rigs with a low mast height due to the proximity of the existing tube lines.
The Martello rig, weighing just 13 tonnes with a working height restriction of 4.5 metres proved to be suitable. The site was very long and narrow and due to maximum weight considerations, all spoil had to be removed by dumpers and concrete either pumped or brought to the pile head by a dumper. The reinforcing steel was coupled together in order to comply with the maximum headroom constraint. Piles of 600mm diameter up to 14 metres deep were constructed.
Stanmore Tube Station
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