movements of the ground due to excavation of a 5m diameter tunnel in chalk were one of the geotechnical aspects studied during the tunnelling trials at chinnor, oxfordshire. surface and sub-surface movements were measured at a cross-section of a tunnel over a period of 5 months. the measurement techniques which were used are described and assessed, and the results are presented as graphs of ground movements in relation to the advance of the tunnel. ground movements began when the tunnel was 10m from the measurement section and continued until the tunnel had advanced to 40m beyond. the maximum observed subsidence of 22.3mm occurred 1m above the crown of the tunnel with a corresponding surface subsidence of 8mm. the maximum observed horizontal movement of 9mm towards the tunnel occurred at a point located 1m above axis level and 3m horizontally from the centreline. (a)

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