Taylor Square, Tavistock

 

Client: Saxton Drilling Ltd
Main Contractor: ROK Construction Ltd
Engineer: Queste Structural Consulting Ltd

Piled Retaining Wall, Tavistock

An anchored contiguous bored piled wall was designed by AGE to allow excavation and development of a confined site adjacent a disused railway viaduct. Ground conditions were mainly made ground overlying cohesive alluvial deposits with weak rock beneath typically identified as weathered slate and shales with interbedded volcanic rocks all of Carboniferous Age. The wall utilised 220 mm diameter drilled micropiles and was designed for both temporary and permanent load cases although, in the latter, the majority of the wall was propped by the permanent structure. Permanent loading to the upper part of the wall was required to support a car parking area.

Maximum retained heights in excess of 4.5 metres were allowed for, together with surcharge loadings from the adjacent property. The wall was tied back with temporary rock anchors with design working loads of up to 275 kN, installed through every alternate pile gap with purpose-designed walings to act as load spreaders along the pile line.

The piles were designed as 220 mm diameter piles with 3 mm wall temporary casing used through the unstable ground and 190 mm diameter rock socket diameter in the underlying rock. Centralised 140 x 8 mm wall CHS tubes were used as the main pile reinforcement. The rock anchors, consisting 32 mm hollow core bars, were designed so as to not encroach outside the adjacent road.