measurements of the surface settlement caused by driving a 3.4 m diameter tunnel through soft alluvial soil beneath a motorway embankment near avonmouth are described in this report. construction was carried out within a shield in compressed air at a depth of cover of about 4.5 m. settlement measurements were made on both motorway hard shoulders across the line of tunnel. maximum settlement was about 25 mm, and both settlement troughs were exceptionally wide possibly due to consolidation effects. the measured cross sectional area of the settlement trough was 0.36 m2 which is equivalent to 4 per cent of the excavated face area.(a)

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