Close-up of Piled Retaining Wall at Azure Project site

The Azure Project, Plymouth

April 2006

Client: Saxton Drilling Ltd
Main Contractor: Ardmore Construction Ltd
Engineer: Stones Underhill Associates

Rock bolt revetment and slope stabilisation together with a propped contiguous bored piled wall was designed by AGE to allow excavation and development of a site adjacent a six story hotel. Ground conditions were variable depths of made ground overlying strata of the Plymouth Limestone Formation. Karst effects including disaggregated 'rubbly' limestone and open rock fissures were encountered both near surface and at depth. In the particular area of the hotel a large clay pocket and poor quality karst limestones were present.

Site at The Azure Project Plymouth, showing Pile Retaining Wall

Temporary stabilisation of open cut faces in both made ground and through the underlying rock were designed following a site mapping exercise. The piled wall was located immediately adjacent to the hotel and utilised drilled micropiles of 220 and 273 mm diameters with 190 and 240 mm diameter rock sockets. They were installed at 400 to 500 mm centres. Centralised reinforcement adopted in the design was of a variety of 140 mm CHS with 8 mm wall thickness and 168 mm CHS of 8 to 12 mm wall thicknesses.

Retained heights of between 3.5 to 7.0 metres were designed for, together with significantly high surcharge loadings from the adjacent hotel. The wall was propped by a temporary walling and raking prop scheme, also designed by AGE.