Stent, part of Balfour Beatty Ground Engineering, has started work on the foundations for a brand new eight-storey office block at One Waterloo Street, in Glasgow's city centre for the main contractor Miller Construction.

THE project, which involved the demolition of a six-storey office building as part of a major regeneration programme in the city, got off to a traffic-stopping start earlier this month when the entire street had to be closed down one Sunday to accommodate the equipment needed.

One of the biggest challenges Stent faced was getting a piling rig onto the site from a busy main road. The difficulty stemmed from the fact that the site is one storey below street level on a busy Glasgow street with tall office buildings on either side. With limited room for manoeuvrability, Stent had to think of a way to get its rig onto the site as safely as possible and with minimum disruption to the local community.

Its solution was to use a 300-tonne mobile crane from Ainscough to lift the piling rig onto the site, ready to commence work on the foundations. The rig deployed was a Casagrande B125, chosen due to its relative lightness compared to the rest of the Stent fleet, which made it easier to manoeuvre into position. The crane was also used to lift a smaller 80-tonne Sennebogen crane into the basement ready for use throughout the duration of the project. This machine is particularly effective in confined spaces due to its fully hydraulic boom.

The project will now see Stent constructing 62 large diameter bored piles under vinyl polymer support fluid over six weeks. This type of pile was chosen due to the ground conditions - loose granular deposits overlying stiffer soils that are typical of central Glasgow.

Vinyl polymer is being used as a support fluid because it does not require significant ancillary plant like its bentonite alternative, making it a more economically viable option for smaller developments. Vinyl Polymer support fluids are also considered to be more environmentally friendly, mainly due to the ease with which they can be disposed of. Although heavily alkaline when in use, once exposed to a cleaning agent, vinyl polymer support fluids instantly turn PH neutral, allowing them to be disposed of quickly and safely down the nearest drain.