This report describes the instrumentation and monitoring of a section of a reinforced concrete box section tunnel at Chestfield, Kent. The monitoring was undertaken during construction and for the period up to the end of November 1999. The backfill compacted against the tunnel walls and over the top of the roof comprised London Clay. The plasticity indices place the clay well outside the range of materials normally acceptable for backfill to structures. The study therefore has provided a unique opportunity to measure the compaction pressures, wall deformations and bending moments developed during construction and, in the long term any swelling pressures that may be generated due to an increase in moisture content of the London Clay. (A)

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