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Courthouse conversion basement foundations completed

Construction work on the basement slab of a new hotel complex has got underway this week at the former Old Street Magistrates Court in London following six months of foundation work.

Miller Piling has handed over the site to main contractor McAleer Rushe after constructing piled foundations for a new three level basement and bearing piles for the 128 bedroom hotel.

The development is being built behind the façade of the Grade II listed Old Street Magistrates Court, which was built in 1903 but has stood empty since 1999.

Construction work on the £18M five star hotel is expected to be completed at the end of this year and will have a swimming pool, gym, cinema, bowling alley and car parking in the basement topped by a five storey bedroom complex.

The site is tightly constrained and called for 46 party wall agreements before Miller could start work on the secant piled basement boundary wall. According to Miller technical manager James Hayward, the capping beam built on the secant piles is less than half a metre from some of the surrounding buildings.

In total Miller constructed 310 750mm diameter secant piles walls to depths of 21m below ground level for the 8m deep basement and 170 bearing piles that were formed from ground level before the company carried out the bulk dig. The 600mm diameter rotary piles were sleeved through the basement and extend to 30m to found in the Lambeth Beds to support loads of up to 2,500kN.

“We carried out trials of the bearing piles during the early stages of the contract to prove the design, as they were more cost effective than using shorter, fatter piles,” said Hayward.

As well as dealing with the logistics of a busy London location, the other challenge on the scheme was carrying out the work without damaging the listed prison cells that projected out behind the main courthouse. The cells were structurally supported on a steel frame that featured plunge columns.

Miller also designed the bespoke propping for the 15,000m3 basement excavations.

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