Appendix D - Geotechnical Report

Table 4: Retaining Wall Design Parameters

                            Unit            Friction        Lateral earth pressure coefficients
 Retained material          weight          angle           Ka                  Ko                    Kp
                            (kN/m3)         (Degrees)       (Cantilever wall)   (Non-yielding wall)
 Very Stiff to Hard
 Residual Soils/XW               19              27                0.38                0.55                2.66
 Material
 Very Low Strength
 (or stronger)                   19              36                0.26                0.41                3.85
 Weathered Phyllite
 Future Fill                      *               *                 *                    *                  *
Note:   * depends on fill material type and level of compaction.

At a minimum, retaining structures must be founded as per the recommendations in Section 7.3 above
with the footings also designed to account for lateral loads imposed by the retaining wall. Detailed
design must include an assessment of internal and global stability, together with required bearing
capacity and founding depth, by the retaining wall design engineer.


7.5            Drainage
Adequate site drainage shall be installed to ensure that stormwater is directed away from proposed
building sites, including retaining walls and batters. This may be achieved using measures such as
surface swales, diversion bunds or grated channels.
All collected stormwater (including overflow from rainwater tanks) must be directed by lined channels or
pipes to discharge a minimum of 5 m downslope from any structure or earthworks, preferably towards
the existing drainage lines. Surface dissipation, such as a rock weir or similar, must be installed at the
stormwater outlet(s) to prevent soil erosion.
Subsurface drainage must be installed behind any retaining walls (e.g. slotted ‘aggi’ pipe wrapped in
filter ‘sock’ placed in gravel backfill). Depending on matters such as the extent of drainage installed and
site-specific groundwater conditions, the designer must assess hydrostatic pressure to be accounted for
in the design of the retaining structure. This should be collected and discharged as discussed above.
Subsurface disposal of stormwater must not be undertaken (including infiltration pits).


7.6            Geotechnical Certification of Operational Works
Should Tectonic be required to certify the Operational Works, inspections must be completed by
Tectonic at various stages during construction (e.g. following site stripping, post completion etc.) to
ensure the recommendations provided within this report have been adhered too. Tectonic should be
contacted prior to commencement of Operational Works to confirm specific inspection requirements.




Geotechnical Investigation
10 June 2026 | 26073-001-Rev0                                                                                     20