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This paper attempts to relate the lithology and fabric of four main groups of Newcastle Coal Measures rock types to their geotechnical properties and engineering behaviour. The four groups comprise: massive sandstone and conglomerate; claystones and tuffs; mudstone, shale and siltstone; and the coal itself. Although their geological relevance is primarily concerned with underground coal mining, these rocks are exposed at the surface across most of Newcastle and its suburbs, and are thus significant in terms of urban environmental geology. The key mining issues include longwall support design and panel layouts, caving and subsidence mechanisms, soft floors and stiff roofs, water inflows and pillar design. The urban geotechnical issues include landslides and rock falls, shallow abandoned mine workings, reactive and erodible soils, waste disposal and potential sources for geomaterials. [ABSTRACT FROM PUBLISHER]

Porcellanite is a siliceous duricrust which has developed within altered Cretaceous mudrocks in the Darwin city area and is well exposed in coastal cliffs to the north. Its distinctive geotechnical properties include low bulk density, variable strength that is highly dependent on moisture content, and relatively high (but inconsistent) durability. The porcellanite rock mass is inhomogeneous and anisotropic; it is unrippable at the surface, but becomes weaker with depth. It is also highly permeable in places, even karst-like, due to solution cavities. These characteristics are common to all duricrusts and result from processes of solution, replacement and redeposition by silica-laden groundwater. Such processes may have been intermittently active through most of the Cenozoic and there is evidence that they continue to the present. The upper 2–4 m of the porcellanite profile is made up of a brittle, high-strength rock with a silica content approaching that of silcrete. The underlying altered and porous siltstone is much weaker and deforms plastically under loading, due to a cellular microfabric composed largely of opaline silica replacing clay minerals. Porcellanite has long been used as the main building stone in Darwin and is now quarried for shoreline filling. Although some of it is of select fill or road sub-base quality, crushed porcellanite contains an excess of plastic fines making it unsuitable for basecourse. Porcellanite has been a failure as breakwater stone, despite producing blocks of adequate size. [ABSTRACT FROM AUTHOR]

The former Northern Coalfield, comprising much of the Newcastle–Maitland–Cessnock–Lake Macquarie region, has now been mined for two hundred years. Most of the twenty-odd seams in the Newcastle, Tomago and Greta Coal Measures have been worked, but the bulk of production has been drawn from just four coalbeds: the Borehole, Greta, Homeville and Great Northern Seams. Literally hundreds of mine names are on record for the coalfield, the great majority working these seams at depths of less than 30 m. This paper reviews regional subsidence problems in the context of mining history, past mining practices and coal measures geology. Subsidence over shallow bord-and-pillar workings may result in highly disturbed ground, open fissures, cratering, seam fires and ‘creeps’ (slow surface movements caused by gradual closure of mine cavities). This form of subsidence differs from that over modern longwall mines in being less predictable, affecting much smaller areas, and occurring sometimes decades after mine abandonment. The geological factors contributing to this subsidence hazard include the multiplicity of seams, the strong roof sandstones, stiff coal and relatively soft floors, and the presence of faults and dykes. The working of thick seams like the Borehole Coal in up to three phases, leaving high, slender pillars, also contributed to later ground instability. Contrary to expectation, the main problem areas are not over haphazardly laid-out convict-era pits, but rather above small hand-worked scavenger mines (‘ratholes’) which operated as late as the 1950s. Many of these short-lived collieries still contain large voids at shallow depth, sometimes only a few metres, which must eventually collapse or be backfilled. [ABSTRACT FROM AUTHOR]

An account is given of an investigation into the peel strength of wool fabrics bonded with different compositions of vinyl acetate-ethylene copolymer latices for which a 180° peel-testing method was used. The effects on the bond strength of changes in viscosity, thickness, contact time, contact pressure, and method of application of the adhesive are also examined. Modifications to the surface of the wool fibre were found to have a significant effect on the bond strength, as did the effective area of the superimposed fabrics. [ABSTRACT FROM AUTHOR]