Geological and geotechnical considerations, associated with some sections of the M25 construction

Abstract

Introduction A joint meeting of the Engineering Group and the Institution of Highway Engineers was held at Burlington House on Tuesday, 10 January 1984. The topic of the meeting inspired practising engineers, academics and researchers alike, and this was reflected in an extremely well attended meeting. The audience listened to a number of speakers who have been actively involved with construction of particular sections of the M25 and who related their experiences in dealing with various ground engineering problems. There is currently no project so prestigious nor so intently observed in the UK as the M25, and this fact together with the fascination of ground engineering meant that the meeting was destined to be of great interest. The Chairman of the Engineering Group of the Geological Society, Dr A. B. Hawkins, introduced the meeting and related some facts about the M25. The 120 miles of 3–4 lane dual carriageway will constitute the largest orbital road in the world. The most heavily trafficked sections, for instance between the A30 and M4 in the southwest sector, are expected to accommodate between 70 000 and 80 000 vehicles during a 16-h day in 1987. The M25 will provide a much needed fast and problem-free route to cross London and its connections to 18 major radial link roads will greatly improve communications to and from central London. It is anticipated that it will generate traffic and that its excellent communications will encourage development of a new network of industry. Figure 1 shows the present

Foundations in Gault Clay

“…On sections of the M25 on Gault in Kent the empirical correlation by Stroud (1975) of SPT Nvalues with undrained shear strengths is noted by Newman (1985) to give a better correlation with depth than conventional laboratory testing of undisturbed Kay & Parry (1982) Samuels (1975 The authors Garrett & Barnes (1984) The authors…”

“…Newman (1985) observed that prior to the construction of the M25 and M26 Motorways in Kent the Gault Clay exposure was mainly pastureland and woodland probably reflecting the historical appreciation of its high shrinkage and swelling properties. There has been a high incidence of house damage insurance claims in recent years related to shrinkage problems.…”