Compiled Reference Document - MCU25/0020 (As Published)

6.           Engineering Assessment
6.1          Revetment Wall Global Stability
Design drawings indicate that the proposed residence and pool will be setback at least 2 m horizontally
from the existing revetment wall fronting the canal. The proposed development is expected to have a
‘non-worsening’ impact on the global stability of the existing revetment wall based on the following:
    No surcharge loads (including filling, etc.) are to be exerted on the existing revetment wall unless
     assessed and approved by a geotechnical RPEQ, who must also assess global stability of the wall.
     Where structures and/or filling are within the zone of influence of the revetment wall (Ref. Section
     6.4.5), load transfer below the zone by shallow piles or the like would be necessary.
    Excavations for the basement level are expected to range between about 7 m and 8 m deep.
     Therefore, all footings and associated building loads will be founded well below the zone of
     influence of the revetment wall.


6.2          Earthworks
Architectural drawings indicate that excavations for the basement level will generally range between
about 7 m and 8 m deep. It is understood that engineered shoring is proposed around the fill perimeter
of the basement. Filling must not be undertaken unless assessed and approved by a geotechnical RPEQ,
in order to check any impacts from such on settlement and global stability.

6.2.1        Site Preparation and Trafficability
After excavation to the design basement level, the subgrade is expected to comprise medium dense to
very dense sand/indurated sand. Following bulk excavation, the exposed subgrade must be assessed by
a suitably qualified and experienced geotechnical RPEQ to determine the depth of any over-excavation
required to achieve a stable working platform and foundation for the building. This may be based upon
visual appraisal via a static proof roll, say using a minimum 4 tonne roller, and/or testing such as by the
dynamic cone penetration method.
Select removal of unsuitable materials and replacement with rock fill (R&R) may be required to achieve a
stable building foundation subgrade, and a working platform for general construction works. This would
be particularly important if a raft footing system is adopted (Ref. Section 6.4). The temporary retention
system should be designed to tolerate deeper excavations to account for possible R&R.
Replacement materials must comprise good quality granular fill (e.g. ‘150 minus’ rock fill) compacted as
outlined in Section 6.2.4.
Depending on prevailing weather and tidal conditions at the time of construction, groundwater may be
present at shallow depth and could lead to subgrade heaving and strength loss under trafficking by
construction equipment. Lighter, tracked plant should therefore be used for earthworks where possible,
and heavy vehicles (particularly wheeled plant) should avoid trafficking directly on the subgrade.
Care must be taken with the use of vibratory equipment to ensure that there are no adverse impacts on
surrounding structures, and that vibration does not cause groundwater to ‘pump’ into and weaken the
subgrade. The impacts from ground vibration must be closely monitored and managed during
construction. It would be prudent to conduct a dilapidation survey of nearby structures before
commencement of construction.



Geo-environmental Investigation Proposed Residence
4 June 2025 | 25040-001-Rev1                                                                                10