Page 14 - Contractors World - UK & Ireland Edition Vol 2 No 7

Massive
support
props for
massive
basement excavation
Groundforce has recently supplied 10 large hydraulic props incorporating their wireless load monitoring system, -
including six of their largest 500 tonne capacity MP500 Super Struts - to support a basement excavation for 3 Merchant
Square, part of a multi-million mixed-use development just off the Edgware Road at Paddington in West London.
The 9 m deep basement excavation is located just a few metres away from Paddington Basin on the Grand Union
Canal and is lined with a combination of steel sheet piles and a secant piled wall.
Poor ground conditions and the close proximity of the canal mean that significant and variable lateral forces are
imposed on the piled retaining wall. To ensure stability, groundworks contractor PJ Carey cast a heavy capping beam over
the piles and specified Groundforce struts for structural support.
Four knee-braces comprising 150 tonne working load capacity MP150 struts are used to support one end of the
excavation; at the other, support is unnecessary as an existing concrete retaining wall provides stability.
Most of the lateral support is required across the width of the huge excavation which is more than 100 m long and 49
m wide for most of this length.
Support here is supplied by the five MP500 Super Struts located at the point of highest calculated load.
The loadings are not consistent or evenly distributed so at this point we have had to use our largest strut to ensure
stability,” says Mark Whitmore, technical sales manager with Groundforce.
All 10 of the struts are braced against the capping beam, which has specially designed steel corbels cast into it, to
accept the connectors at the ends of the MP150 and MP500 struts.
The equipment was chosen primarily to maximise the amount for working space inside the excavation so that the
contractor could cast the basement slab and begin construction of the central core without undue interference due to
supporting steelwork.
Biggest struts reduce number
required
The MP500 struts employ our 1220 mm diameter
Super Tube extensions which give them the
strength and rigidity to span the 49 m width
without intermediate support,” said Mr Whitmore.
Using our biggest struts also allowed us to
minimise the number of supports required.”
The strut was first developed in 2008 for use
on the Tyne Tunnel project for French contractor
Bouygues. Essentially a bespoke product designed
for a specific purpose, it has now been updated,
Page 14
Contractors World - UK & Ireland Vol 2 No 7