20220109 - Geotech · OPW23/0182

                              PROPOSED RESIDENCE
                              21 MAHER TERRACE, SUNSHINE BEACH

Specific design would need to be carried out to determine working platform requirements for any heavy plant
(e.g. mobile cranes), and a thicker rock fill platform may be required than recommended above, particularly if
established at ground level on adjoining land.

6.3.2       Excavations
Provided plans indicate that excavations in the order of about 4 m deep will be required for the proposed
basement. Excavations to this depth are anticipated to encounter mostly stiff to very stiff clays, loose to
medium dense sands and XW materials at depth. Excavations in such materials should be achievable
using conventional earthmoving plant (e.g. medium to large tracked excavators) with a toothed bucket,
possibly with the assistance of ripper attachments at depth or in confined areas.
Although not expected to the proposed excavations depths, should very low strength (or stronger) sandstone
be encountered during basement excavations, the use of larger earthmoving plant with ripper and/or
hydraulic rock breaking attachments may be required, particularly for any confined excavations (e.g. lift pit
overruns). Should any medium strength (or stronger) rock be encountered, the use of hydraulic rock
breaking or more specialised excavation techniques (e.g. pre-splitting using expansive grout) may be
required. Apart from rock strength, excavatability of the weathered rock will be dependent upon the
frequency and continuity of joints within the rock mass.

Any excavation required adjacent to existing structures/infrastructure will need to be specifically designed to
ensure that the structures are not adversely affected (e.g. ‘undermined’). Prior to bulk earthworks, it is
recommended that footing exposures or confirmation of foundations via certified building plans be
undertaken to assess the possibility of undermining. If undermining is a potential issue the existing
structures may need to be underpinned or excavations may require temporary shoring. The advice of a
suitably qualified and experienced RPEQ structural engineer must be sought regarding any potential
undermining, along with the design and construction of any underpins or shoring (if required).

Care would need to be taken during installation of the selected retention system and excavation to the
design levels to manage potential vibration impacts on nearby structures. It would be prudent to conduct a
dilapidation survey of adjacent structures (including internal walls) prior to commencement of the site works,
then ground vibration monitoring during construction.
Where battering is achievable during construction, temporary batter slopes of 1V:1H would be acceptable for
the materials encountered in the boreholes, provided groundwater is not encountered, and no surcharging of
batters is affected. This would be applicable over a maximum excavation depth of 4 m. Deeper cuts, if
required, should be specifically assessed by Tectonic.

If filling or permanent cuts exceed 1 m, then these must be retained. Permanent cut and fill batters up to
1 m high shall not exceed 1V:2.5H. Any permanent soil and fill batters will require erosion protection (e.g.
revegetation or surface protection).

It is likely that above temporary batter slopes will not be able to be achieved, due to spatial restraints, and so
temporary shoring will be required (e.g. sheet piles) as per the recommendations in Section 6.5 below.
The above recommendations do not supersede any existing safety regulations or legislation applicable to
excavations (e.g. limits on personnel entry into trenches).




16 July 2021
Report No. 21236-001-Rev0                               12