24-01-2020 - Appeal No. 245 of 2019 - Final Order of Judge Rackemann · 51987.2951.01

McInnes Wilson Lawyers



Shear-wave velocity values and patterns typically associated with weathered sedimentary rock were
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encountered from depths ranging between about 12 m to 20 m BGL (refer Figure 2). Available information
indicates that the rock is inferred to be Late Triassic to Jurassic age Myrtle Creek Sandstone The testing
indicates that the rock dips towards the ocean and that its strength generally increases with depth.


    Coffee rock on the Sunshine Coast: what, where and why?
    Coffee rock is the colloquial term for cemented (indurated) sand, that often has the physical characteristics of
    weathered rock.
    It comprises ancient alluvial sands of the Pleistocene age (2 million to 10,000 years ago). Coffee rock is typically
    dark brown in colour, and when disturbed breaks up into dark brown silty sand (hence the colloquial name ‘coffee
    rock’).

    Cementation in these sands is thought to have occurred as a result of the interaction of organic matter and mineral-
    rich sand, e.g. flocculation at the interface of a fluctuating groundwater level.
    Coffee rock can be weakly or strongly cemented, and is often discontinuous and of variable strength and thickness.
    It is generally of low permeability, and often associated with high ‘perched’ groundwater.

    On the Sunshine Coast, coffee rock is common at many locations along the coastline, generally buried under
    younger alluvial soils (e.g. dune or beach sand). Coffee rock is often exposed and re-buried in the intertidal zone by
    cycles of natural sand movement. Coffee rock is generally significantly more resistant to erosion than typical beach
    or dune sands, thereby providing a ‘barrier’ to erosion during storm events.
    Previous investigations have found coffee rock to be underlain by dense, non-cemented sand in most areas, or soft
    alluvial clay in some instances.
    Coffee rock presents geotechnical constraints and opportunities to infrastructure development and maintenance, e.g.
    excavatability, groundwater management, and foundations. It is considered a key element in the stability of the
    region’s coastline, likely providing protection from erosion and storm events.




1
    Wilmott and Stevens, 1988



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