Riddolls, B.W. 1978 Engineering properties of two low-strength Tertiary materials. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 312 12 p.
Abstract: Index and mechanical properties of New Zealands Tertiary sediments, the so-called soft rocks, have until recently not been investigated in any detail. Two current major construction projects have provided a good opportunity to sample extensively the materials involved, for a variety of tests. The Poro-o-tarao (NZMS1 N92/824543), on the North Island Main Trunk Railway between Te Kuiti and Taumarunui, a new tunnel is being constructed to replace the existing one (Parton, 1974). The tunnel is being driven through moderately soft (Brown and Martin, 1977) thinly bedded mudstones (Folk et al., 1970), with dark grey/grey green colour banding, and minor sandstones, part of the Mahoenui Group, of the Lower Miocene age (Nelson and Hume, 1977) The samples tested were collected from the tunnel face, 700 m from the north portal. In north Taranaki, the Maui Gas Pipeline is being constructed in steep Tertiary terrain, from which samples of very soft light grey Urenui Siltstone, of Upper Miocene age (Nelson and Hume, 1977), have been obtained for testing (NZMS1 N99/076127). To determine angles of shearing resistance and apparent cohesion cores were obtained mostly by drilling large blocks in the laboratory. The remainder of the blocks were then used for the determinations of moisture content, dry density, void index (Jaeger, 1972), NCB cone indenter number (Szlavin, 1974), slake durability (Franklin and Chandra, 1972) and Atterberg limits of slake durability residues. In doing these tests, a complimentary objective has been to evaluate and develop improved sampling procedures and test-methods for soft rocks in general, which are commonly more difficult to test than either soils or hard rocks. (auth)