Reference Document - RAL25/0020 & OPW25/0194 (As Published)

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Table 6: Maximum Allowable Bearing Pressures for High Level Foundations
 Material                                                Maximum Allowable Bearing Pressure
                                                         (kPa)
 Engineered fill*, stiff clays                           100
 Very stiff clays                                        200
 Hard clays                                              450
Notes: * Depends on fill material type and level of compaction. Assumes clayey material compacted under ‘Level 1’
inspection and testing.


All footing excavations should be inspected and tested by an experienced geotechnical engineer
from Douglas to confirm bearing pressures prior to casting of concrete.

Experience indicates that properly designed and constructed high level footings sized using the
above allowable bearing pressures are likely to undergo settlements in the order of 1% of the
footing width. Further advice should be sought from Douglas regarding settlements once actual
footing configurations and design loads are known.

Where footings are located adjacent to underground services, the footings should extend to
below invert level for a distance of 1 m out from the trench. Beyond 1 m from the trench, the
footings should be taken to below an imaginary line drawn up at 45 degrees from the invert level.
These requirements do not override minimum structural footing base levels. Where necessary
footings may be made up with mass concrete poured to the underside of footing, or alternatively
constructed over excavated pedestals.

6.7    Retaining Walls

The design of flexible and rigid retaining walls could be undertaken using a triangular pressure
distribution and the earth pressure parameters given in Table 7. Flexible walls are those which
are free to rotate or tilt (such as gravity and cantilevered walls) and should be designed using an
active (Ka) earth pressure coefficient. Rigid walls are those which are laterally restrained against
rotation or tilt (ie. single anchored/propped walls) and should be designed using the at-rest earth
pressure coefficient (Ko).

Passive resistance (Kp) at the toe of the wall should be ignored in the zone where future
disturbance (eg. services trenches) could occur.

Table 7: Earth Pressure Coefficients (non-sloping crest backfill)
 Material                           Bulk Unit      Friction        Active          At-Rest        Passive
                                    Weight         Angle Ø’        Pressure        Pressure       Pressure
                                    (kN/m3)                        Ka              Ko             Kp
 Firm sandy silt                    18             22              0.45            063            2.2

 Controlled fill*, stiff clays      19             24              0.42            0.60           2.3

 Very stiff clays                   19             26              0.40            0.55           2.5
Notes: * Depends on fill material type and level of compaction. Assumes clayey material compacted under ‘Level 1’
inspection and testing.




Proposed Subdivision                                                                          237894.00.R.001.Rev0
12-14 Gympie Street, Tewantin                                                                        October 2025