Geotechnical Investigation Report

6.1.2 FILLING

All structural fill should be placed and compacted under Level 1 inspection and testing in accordance with site specific
design drawings and specifications. Minimum earthwork requirements should be in accordance with ‘AS3798-2007
Guidelines on Earthworks for Commercial and Residential Developments’. In summary, AS3798 guidelines
recommend the following:
Strip vegetation and uncontrolled fill (if any);
Test rolling using the following plant and load conditions. It is noted that sand/silty sand exposed at subgrade
level can be prone to displacement during the test roll however when confined (i.e. beneath pavements) performs
adequately:
© astatic smooth steel wheeled roller with a mass not less than 12 tonne and a load intensity under a wheel load
not less than 6 tonnes;
© a pneumatic tyred plant with a mass not less than 20 tonnes and a ground pressure not less than 450 kPa per
tyre; or
o ahighway truck with rear axle loaded not less than 8 tonnes with tyres inflated to 550 kPa;
Subject to site specific conditions, any soft areas identified might need to be removed and replaced with select
material; and
Structural fill should be in near horizontal layers, commonly termed ‘lifts’, and generally not to exceed 300 mm
thick (uncompacted) and compacted to a 98% minimum dry density ratio (DDR) for general fill and 100%
minimum DDR in the upper 0.5 m depth beneath slabs and pavements with a moisture variation not exceeding
+2% of the optimum moisture content (OMC). The maximum particle size should be limited to two-thirds of the
compacted layer thickness. Where structural fill abuts slopes generally steeper than 8H:1V (if any), benches equal
to the height of the fill layer should be cut into the slope before filling.

Other earthwork considerations include:
The most suitable plant for compaction is a smooth drum roller for granular (i.e. clean sand soils); and

PTG can provide Level 1 supervision and testing following site specific design drawings and specifications and AS
3798-2007 if required.

6.1.3 EXCAVATION CONDITIONS

Excavation of the encountered fill and natural sand soils could be achieved using excavators of any size. Based on the
development plans and site conditions, a 14t excavator is suggested as most suitable.

6.1.4 SUITABILITY OF SITE WON MATERIAL

Topsoil encountered across the site is not considered suitable for reuse as engineered fill. Topsoil material (excluding
rootlets) can be stockpiled and reused as topsoil post earthworks.

Provided that there are no limitations on fill (ie shrink-swell, CBR, WPI), clean dune sands encountered onsite could
be considered suitable for reuse as engineered fill.

6.2 SITE CLASSIFICATION AND SITE MOVEMENTS

In accordance with AS2870, the site is classified as ‘P’ due to:
The bearing strength is less than that specified in Clause 2.4.5 as per Section 2.1.3(a);
The site contains uncontrolled or controlled fill as identified in Clause 2.5.3;
o Removal of an existing building or structure likely to have significantly modified the soil moisture conditions
under the footprint of the footing system of the building as per section 1.3.3 (a);
o Removal of trees prior to construction as per section 1.3.3(b);
o. Presence of trees on the building site or adjacent site as per section 1.3.3(c);