Attachment 4 - Geotech Report · MCU23/0030

                                   50 NOOSA PARADE, NOOSA HEADS
                                   PROPOSED RESIDENCE

5.0         INVESTIGATION FINDINGS

5.1          Regional Geology
Published geological information 1 indicates that the site is underlain by anthropogenic deposits comprising
“man-made deposits of gravel, sand and silt being generally associated with land-fill or mining” (Ref. Text
Figure 7). This is generally due to the area having been previously developed for residential use.
Natural soils below are indicated to be Quaternary (Holocene) age, and a mixture of recent channel alluvium
including sand, silt and clay; and slightly older “esturine channels and banks” comprising “sandy mud, muddy
sand [and] minor gravel.” Ultimately the site is likely underlain at depth by residual soils and bedded
sedimentary rock materials associated with the late Triassic to Jurassic age Tiaro Coal Measures.




              Subject Site




Text Figure 7: Extract of 1:100,000 Laguna Bay Surface Geology Map


5.2          Subsurface Conditions
Subsurface conditions encountered in the boreholes were generally consistent with the published geology
and are summarised below.
          Topsoil and Historic Fill – comprising mostly loose to medium dense sand and silty sand to depths
           of between 1.0 and 2.1 m BGL, being typically deeper on the northern side of the site (BH2); then
           Alluvial Soil – generally comprising loose to dense alluvial sand/silty sand extending to at least BH2
            termination depth (3.5 m BGL), and to about 6.6 m BGL in BH1. Very dense, indurated sand/silty
            sand (‘coffee rock’) was then encountered in BH1 to a depth of 9.4 m BGL, followed by interbedded
            layers of medium dense to dense silty sand and firm to stiff silty clay to about 15.6 m BGL; overlying
          Residual Soil – comprising stiff to hard silty and sandy clay to 20.7 m BGL in borehole BH1,
           underlain by hard, extremely weathered sandy clay to 21.4 m BGL; then
          Weathered Rock – comprising low strength sandstone, becoming low to medium strength at 21.7 m
           BGL to borehole termination at 22.06 m BGL.

Proposed basement and pool excavations are expected to disturb historic fill and alluvial soils to a depth of
about 3 m BGL, typically comprising loose to medium dense sand and silty sand.




1
    Department of Natural Resources, Mines and Energy, 1:100,000 Laguna Bay Surface Geology Map, Sheet 9545, 2018


2 February 2023
Report No. 22500-001-Rev0                                       5