MCU14/0106 Appendix E - Engineering Report

August 2004 -4- 04682104(AB)

 

5.0 INVESTIGATION FINDINGS
5.1 Preliminary Assessment

Available geological information’ indicates that the site is underlain by the late Triassic to
Jurassic age Tiaro Coal Measures comprising sandstone, siltstone, shale and coal. Quaternary
age flood plain alluvium comprising “clay, silt, sand and gravel” is indicated to overlie this
formation along the drainage lines and across the low-lying land in the southern part of the site.

Published ASS information’ classifies the majority of the site as “/and > 5 m AHD with a low or
negligible probability of ASS occurrence”, whilst the southern part is described as “land < 5 m
AHD with a low probability of ASS occurrence” (all based upon a “limited field assessment’).

5.2 Subsurface Conditions

The subsurface conditions across the elevated ridge area typically comprise up to about 0.5 m
depth of mostly non-plastic sand, or low plasticity material, underlain by low to medium
plasticity, very stiff sandy clay. The depth of non-plastic sand increases up to about 1 m in the
southern part of the site.

Medium to high plasticity clays were intersected below the low to medium plasticity clays at all
of the test locations, except test pit GA7. It is anticipated that these medium to high plasticity
clays may be exposed at the proposed cut subgrade level at test locations GA9, GA10, GA12,
GA14, GA15 and GA20 (ie. mostly in the east and partly across the ridge).

The results indicate that between about 0.5 m and 1.5 m of medium to high plasticity clay is
likely to be intersected in proposed excavations at test locations GAS, GA6, GA12, GA13 and
GA19-21 (ie. mostly across the ridge).

Extremely weathered, extremely low strength sandstone was intersected below depths of about
1.5 m to 2.5 m at test locations GA2, GA4, GA6 and GA7 (ie. south-western part of site) and at
test locations GA19 and GA21 below 1.5 m to 4.5 m depth (ie. across the ridge). The sandstone
will probably be encountered in the proposed excavations in the vicinity of test locations GA6
and GA21, where excavator bucket refusal was noted at 1.7 m and 3 m depth respectively.

Low rates of ground water seepage were noted in test pits GA2-4 (ie. western part of site) at
depths of between 2.2 m and 2.7 m. Ground water was not observed at the other test locations.
Moist to wet soil conditions were noted from close to ground level down to depths of 1 m to
1.5 m in test pits GA2 and GA3. It should be noted that the fieldwork was carried out following
a prolonged period of relatively dry weather.

 

> 1:100,000 Geological Map, GYMPIE SPECIAL, Sheet 9445 & Part 9545, DME, 1999
* 1:100,000 Redcliffe to Teewah ASS Map 2, DNR, 1999

Golder Associates