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Summary The choice of the public for a route for the Dalton By-pass lay through an extensive area of well-worked and abandoned haematite mine workings. The geology of the area and the method of mining are described, and the reasons are given for the selection of the preferred route. The problems associated with the route are discussed, together with the detailed planning necessary to organize an extensive complex site investigation, involving almost 700 boreholes in a roadway length of 4½ km. A typical cutting is examined in some detail to illustrate the contractual and technical problems connected with the required excavation of a cutting slope directly over a major iron ore sop; these problems include the removal and treatment of the water-filled collapse cone over the rubble-filled cavern left by the ore extraction. The relative costing of an elevated structure and an embankment founded on collapsed workings are discussed. Some engineering conclusions are drawn from the site investigation regarding the suitablty of embankment fill, the rate of settlement of embankments on alluvium, and the stability of a rock slope.

The unusual problems connected with the re-furbishment of a distressed marine causeway in the Middle East are described, together with the design solution, comprising a double-layer permeable membrane/webbing filter system. A comparison is made between this design and the design requirement for a new causeway to be built in the same locality. P . R . RANKILOR FIG. 2. Filter webbing material showing minimal damage after rock test-drop from 10 m height. To the underneath side of the webbing (and not visible in these photographs) is welded a conventional geotextile lilter fabric. The webbing provides high tensile strength, protection from damage and protection from u.v. exposure.