Attachment 12 - Geotechnical Investigation Report

                              PROPOSED RETIREMENT DEVELOPMENT
                              MYALL STREET, COOROY

6.2.2 Footing Design
The proposed bridge along the northern boundary is noted in more recent information to be a two lane
structure. There was insufficient information gained during the investigation to provide footing
recommendations for this, and it is noted that near creek bank subsurface profiles can vary significantly due
to the interfingered nature of alluvial deposition. The bridge structure is therefore excluded from the scope of
this report, and further investigation is recommended to provide site-specific information at each of the
proposed abutment locations.

6.2.2.1        Residential Allotments
It is anticipated that the proposed residential allotments would feature small, one storey structures, built on a
slab on ground. Walls could be of masonry construction, or clad in lightweight materials; with roofing
comprising lightweight sheetmetal materials.

Where residential structures are to be sited in cut areas, normally dimensioned, conventional high level
footings should be taken to found a minimum of 0.5 m in to the natural residual soils. These are likely to be
very stiff in consistency, based on the results of the existing boreholes, and where such material is
encountered at the base of footing excavations, could be designed with an allowable bearing capacity of
200 kPa. Where rock is exposed in the excavation subgrade, footings should penetrate at least 0.3 m below
the exposed surface, and could be designed with an allowable bearing capacity of 400 kPa. Footing design
should also account for a site classification of Class H1.

In filled areas, provided the fill has been placed, tested and certified to Level 1 standards (notwithstanding
our general recommendations above in Section 6.1.4), it is recommended that footings found a minimum of
0.75 m below the finished fill surface (not including any landscaping fill or mulch). Footings so founded could
be designed with an allowable bearing capacity of 100 kPa, and should account for a site classification of
Class H2.
Residences on allotments close to the transition from cut to fill should seek to have all footings extend to the
same natural clay material, to prevent adverse differential movements (settlement and ys).

6.2.2.2        Club House
Final footing design recommendations would be dependent on the bulk earthworks plan, position of the
clubhouse and proposed construction.

Information supplied with the project brief indicates that the clubhouse would be a two-storey masonry
structure; and that a pool would be present to the north-east side. Based on the existing preliminary
earthworks information, and the limited subsurface information from the investigation, the following
preliminary recommendations are provided.

Generally speaking, normally dimensioned, conventional high level footings would be appropriate for the
structure. These could be taken to found either 0.5 m in to the very stiff (or stiffer) natural clay soils, using an
allowable bearing capacity of 200 kPa, or 400 kPa in very low strength rock. Greater bearing capacity may
be available in rock, subject to confirmation by further site investigation, and inspection of footing subgrades
during construction by a suitably qualified RPEQ geotechnical engineer.

6.2.2.3        General
A suitably qualified and experienced geotechnical engineer should inspect all footing excavations during
construction to confirm the foundation materials and allowable bearing capacity.
If any soil conditions encountered during construction are found to differ from those noted in the
geotechnical investigation, Tectonic should be notified immediately and an inspection carried out to
determine if changes to footing design are required.




17 May 2019
Report No. 19071-001-Rev0                                11