A406 North Circular Road
Hale End to Chingford Underpass
Description of Work
As part of a general upgrading of the A406 North Circular Road by the Highways Agency (formerly the
Department of Transport) an underpass was to be constructed between the Chingford Road and the Hale
End Road in Walthamstow, North London. The scheme consisted of 2.5km of roadworks, the majority of
which was below existing ground level. Investigations showed a superficial layer of made ground, up to 2m
thick, overlying London Clay. In the original scheme, where formation was more than 5m below ground
level, support for the sides of the underpass was provided by base propped diaphragm walls in the form of
rectangular T shaped panels. At deeper sections temporary propping some 6m below ground level was
allowed for in the design. The permanent propping comprised an inclined V-shaped reinforced concrete
base slab, 0.65m thick, which dipped towards the centre of the underpass.
GCG was initially asked to assist with the design and checking of the original scheme but subsequently
GCG was retained by the contractor to provide advice on a revised design. An alternative scheme was
developed allowing significant cost savings to be made (approximately £10m). GCG played a major role in
the formulation and design of this scheme, providing sufficient detail to satisfy the promoter, the Highways
Agency. One aspect of GCG’s role was to undertake a series of soil-structure interaction analyses in order
to predict the behaviour of the underpass and the ground around it. Measurements taken during
construction showed very good agreement with these predictions. In addition GCG was involved in the
development of construction sequences using soil-structure interaction analyses for the assessment of
temporary works details.
Clients: Kvaerner Cementation Foundations
Kvaerner Construction
Bullen & Ptnrs
G. Maunsell & Ptnrs
Dates: 1988 - 1992
Estimated project cost: £60 million
Base propped retaining wall
Publications:
HIGGINS, K.G., FERNIE, R., POTTS, D.M., HOUSTON, C., MAIR, R.J. and ST JOHN, H.D., (1998). ‘The benefits of
using advanced numerical methods throughout the design and construction of a road scheme’, Proc. AGS Seminar
‘The Value of Geotechnics in Construction’, The Institution of Civil Engineers, November 1998, CRC, 101-113.
HIGGINS, K.G., FERNIE, R., POTTS, D.M. and HOUSTON, C., (1999). ‘The use of numerical methods for the
design of base propped retaining walls’, Proc. Int. Symp. on Geotechnical Aspects of Underground Construction in
Soft Ground, IS-Tokyo >99, Balkema, 511-516.
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