Geo-environmental Investigation · MCU25/0020

basement walls and floor will therefore need to include allowance for hydrostatic pressures. This would
need to include allowance for the highest astronomical tide and potential flood/storm surge levels,
together with predicted rises due to climate change. It may be possible to incorporate a permanent
pressure relief system for the basement; however, due to ongoing requirements for treatment of
extracted groundwater, such a system is not likely to be feasible.
Design for temporary and permanent retaining structures could be carried out using the pressure
distribution applicable to the wall type and based on the parameters listed in Table 4. These values do
not include allowance for hydrostatic pressures nor transient (e.g. construction) or adjacent footing
loadings.

Table 4: Retaining Structure Design Parameters

                                                              Lateral earth pressure coefficients
                                Unit         Friction
    Retained material          weight         angle         Ka               Ko
                              (kN/m3)       (Degrees)   (Cantilever     (Non-yielding               Kp
                                                           wall)            wall)

        Firm Clay                17             23         0.44              0.61               2.28


        Loose Sand               17             30         0.33               0.5               3.0


 Medium Dense Sands              18             34         0.28              0.44               3.54

  Dense to Very Dense
                                 19             38         0.24              0.38               4.20
         Sands

The advice of a specialist contractor must be sought regarding feasibility, design and installation of the
preferred retention and dewatering system for this site. It will be necessary to conduct numerical
analysis to optimise the retention system. Temporary and permanent retention design must be designed
and certified by a suitably qualified and experienced RPEQ engineer.


6.4          Building Foundations
6.4.1        Settlement Analysis
For the proposed two storey building with single level basement, SCG has indicated that contact
pressures beneath a possible raft slab would be in the order of about 30 kPa to 40 kPa. To assess the
geotechnical feasibility of supporting the building on a stiffened raft footing system at basement floor
level, settlement analysis has been carried out using Settle 3D. The analysis considered a flexible footing
founded on medium dense sand and assumed that over-excavation and replacement of any loose/firm
materials would be undertaken near the basement level, as outlined in Section 6.1.1. Our analysis
indicates that elastic and consolidation settlements would be in the order of the values provided in Table
5 overleaf.




Geo-environmental Investigation Proposed Residence
11 March 2025 | 25040-001-Rev0                                                                            14