NJA Consulting undertook one of our largest individual investigations for the Queensland
Department of Mines in relation to a high profile mine subsidence event that occurred in April 2008.
Part of the Ipswich suburb of Collingwood Park is underlain by two decommissioned underground
coal mines – Westfalen Number 3 and New Redbank Collieries. These mines used the “bord and
pillar” method of mining at depths from approximately 60m to 140m. Bord and pillar mining at
the collieries created numerous underground pillars ranging up to 11m in height in some areas of
Westfalen Number 3, and with various dimensions and shapes left behind to support the load from
the rock above the mine after coal was extracted.
A individual pillar may fail, triggering overload of neighbouring pillars, leading to roof failure and
caving of rock above pillars into the previously excavated roadways or mine voids, and ultimately
ground subsidence which may penetrate to the surface. In December 1988, a subsidence event
occurred near Lawrie Drive, Milgate Street and Rush Court in Collingwood Park. In April 2008, a
second subsidence event occurred, resulting in surface movement and damage to houses within
an area near the intersections of Duncan, McInnerney, McLaughlin and Moloney Streets. Both
subsidence events occurred as a result
of pillar failure within the Westfalen No. 3 Colliery.