14169-001-Rev0 17 Webb Rd -Revised Draft · 132002.220527.1

                              17 WEBB ROAD, SUNSHINE BEACH
                              PROPOSED RESIDENCE

7.0      ENGINEERING ASSESSMENT
7.1      Earthworks
It is assumed that cut and fill up to about 1.5 m BGL may be required to form the ground level building pad.

7.1.1        Site Preparation and Trafficability
Following removal of sections of the existing building, and clearing of vegetation and any unrequired below
ground elements (e.g. services), tree stumps and large roots must be ‘grubbed out’ and any organic rich
topsoil stripped from the construction area. Topsoil materials must not be used in structural fill, however may
be placed across landscaping areas.

The subgrade materials exposed after site stripping and excavation to design levels (up to 1.5 m BGL) are
expected to medium dense sands and silty sands. The soils would be subject to strength loss from repetitive
vehicle loading (particularly from rubber tyred plant). Due to the potential for poor trafficability, placement of
a minimum 150 mm thick granular working platform may be required to create a ‘confining’ layer to prevent
loosening of the sand, particularly across access and laydown areas.

The site should be graded to shed surface water runoff away from construction areas. Swale drains should
be constructed along the toes of any cuts, and above cuts where possible, with the drains graded to
discharge collected waters to a control point before release off-site.

7.1.2        Excavations
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Excavations to depths of up to 1.5 m BGL in the mostly loose to medium dense sands should be achievable
using conventional earthmoving plant (e.g. small to medium excavators) with toothed bucket attachments.
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Temporary cuts in loose to medium dense sand and batters in controlled fill may be formed no steeper than
1V:1H. Any permanent batter slopes in such materials should be formed at 1V:2H, or flatter if possible
(1V:3H). Flatter batters may be required if groundwater seepage is encountered, or if earthworks are
undertaken during a period of heavy rainfall.

Any excavations required adjacent to existing structures, including those on adjoining properties, will need to
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be specifically designed to ensure that the structures are not adversely affected (e.g. 'undermined').

The above recommendations do not supersede any existing safety regulations or legislation applicable to
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excavations (e.g. limits on personnel entry into trenches).

7.1.3        Filling
Should any importation of fill be required, the use of low reactivity materials (plasticity index less than 15%) is
recommended for any fill under the building.

All structural fill should be compacted at moisture contents within the range of ±2% of optimum moisture
content for Standard Compaction. Fill should be placed in 250 mm thick (loose thickness) layers and be
compacted by repeated rolling to achieve a dry density ratio of at least 95% of the maximum Dry Density
Ratio (DDR), based upon the Standard Compaction method, or 70% Dry Density Index.

To compact sand fill it is normally necessary to place the loose fill layer, flood the area with water and
compact with a vibratory smooth drum roller. Care will need to be taken with the addition of water if the
sands are particularly silty.

Confirmatory compaction testing must be carried out at regular intervals. A minimum of two tests per vertical
lift is recommended where structural fill heights are to exceed 300 mm. Further details for control and testing
of fill are given in Australian Standard AS 3798-2007 Guidelines on Earthworks for Commercial and
Residential Developments.

Fill must be ‘benched’ into the natural slope, over-filled by 0.5 m (horizontally) and then trimmed back to the
well compacted material.

Due to the close proximity of houses on adjoining properties, care will need to be taken within any activities
which may cause excessive ground vibrations (e.g. fill compaction). It would be prudent to conduct a


26 February 2015
Report No. 14169-001-Rev0                               11