RFI -Attachment 6 - Geotechnical Investigation Report CORE.pdf

Walsh Consulting Engineers




 ▪       Fill embankments should be ‘over built’ then trimmed back to the well compacted material.
 ▪       Fill in sloping areas should be ‘benched’ into the natural ground.
Further details for control and testing of fill are given in AS 3798-2007. It is recommended that earthworks
be undertaken in accordance with ‘Level 1’ standards.

     6.1.5    Batter Slopes
For short-term construction periods, excavated unsurcharged faces up to 3 m in vertical height could be
battered at the following maximum slopes:
     ▪    Medium dense (or denser) sand:            1V:2H
Flatter batters or temporary support systems (e.g. ‘shields’ or ‘shoring boxes’ for trenches) will be required if
significant groundwater seepage is encountered or if exposed faces are not protected from erosion by
rainfall. Shoring will be required to enable safe personnel entry into trenches (with vertical sides) deeper than
1 m.
Permanent excavation batters should be less than 3 m high and formed no steeper than:
     ▪    Medium dense (or denser) sand:            1V:3H
Permanent batters that are not retained should be protected from erosion with some form of surface
protection (e.g. revegetation or geotextile matting) and drainage.
Positive support by engineer designed retained structures will be required where space restrictions prevent
trimming of batters to safe slopes and where slopes are surcharged or near movement sensitive structures.
The above recommendations do not supersede any existing safety regulations or legislation applicable to
excavations (e.g. limits on personnel entry into trenches).

6.2 Foundation Design and Parameters
     6.2.1    Site Classification
Site classification derived in accordance with Australian Standard AS 2870-2011 Residential slabs and
footings (AS 2870-2011) can provide an indication of the likely magnitude of reactive (shrink and swell)
movements associated with normal seasonal moisture variations.
Due to the presence of uncontrolled fill, the site is classified ‘Class P’. Areas underlain by at least medium
dense sand can be re-classified ‘Class A’, with little or no movement due to soil moisture changes.
The predicted order of movement is based on the existing soil profile (i.e. no cutting or filling), and moisture
content changes within soils due to normal seasonal moisture variations only.
A specific site classification must be undertaken for each building following completion of any earthworks
greater than 0.3 m (cut or fill) and prior to building design and construction.

     6.2.1    High-level Footings
The proposed structures could be supported by a ‘high-level’ strip or pad footing system suitable for the
applicable site classification. High-level footings founded in medium dense (or denser) alluvial sand (or future
‘Level 1’ controlled fill) could be designed using an allowable bearing pressure of 100 kPa. Settlement
beneath such appropriately design footings is anticipated to be less than 20 mm. Footings in uncontrolled fill
or loose/medium dense sand are not recommended.
To achieve the design recommended pressures, footing excavations must be dry and cleaned of any loose,
disturbed or saturated materials prior to pouring concrete.
All existing and proposed footings should found such that they are not adversely affected by any adjacent
excavations, batter slopes, trenches, or retaining walls that are not designed to support building or fill loads.




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