this report is one of a series of case studies which pay particular attention to the site investigation aspects of tunnelling projects. the general implications of the site investigation experience are examined in the light of the ground conditions encountered and the tunnelling methods used. the 3 km length of sewer construction examined is part of the south bank interceptor sewer of the tyneside sewerage scheme, and involved sewer construction through made ground, glacial deposits and variable coal measures rocks using hand and shield tunnelling, heading construction and open trench methods. the borehole investigation gave a good indication of the range of drift materials and rock present, and allowed the sewer to be designed and methods of construction to be planned for the variable conditions of the site. the variable nature of both drift and rock, with rockhead at a variable level and with variable depths of weathering, prevented detailed prediction of local tunnelling conditions and called for flexible methods of working. probing ahead from the face was employed when small-scale mine workings were met during construction.(a)

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