This report presents the results of finite element analyses of construction and long term performance of the Haycroft Relief Sewer tunnel in soft clay at Grimsby. TRRL has undertaken an 11 year case history study of the tunnel, with particular emphasis on the long term settlements above it. Relevant details of the tunnel construction and settlement measurements are summarized in this report, together with results of piezometer measurements, permeability tests and laboratory tests on samples of the soft clay. The objective of the finite element analyses was to compare predictions of the long term settlements with the field measurements. Various assumptions concerning tunnel lining permeability are explored. Good agreement is obtained between predicted and observed settlements for the case when the tunnel lining is assumed to have a low permeability, equal to one tenth of that of the clay. The analyses show that, as was observed in the field, the long-term component of the surface settlement profile is significantly wider than the short-term profile associated with tunnel excavation. Together with the field observations, the analyses provide a valuable insight into the long term behaviour of a tunnel constructed in soft clay.

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