Slope Stability Assessment

Jane & Cameron Blake                                                                                  22178-001-Rev0
                                                                                                         26 May 2022

4.3       Footings
All footings for the proposed structures (including retaining walls) must penetrate through any fill and
unsuitable natural soils to found as follows:
          On slopes of 10° (18%), or less – at least 0.3 m into stiff/medium dense (or stronger) natural
           materials.
          On slopes exceeding 10° - at least 0.3 m into extremely weathered (XW) materials/very low strength
           (or stronger) weathered rock.

High-level footings on slopes greater than 10° would be possible in areas of cut where the target foundation
stratum (i.e. XW materials/very low strength rock) is exposed at the subgrade level.

High level footings may be designed using allowable bearing pressures of:
          100 kPa in the stiff/medium dense or stronger natural soils.
          400 kPa in the XW materials or very low strength (or stronger) weathered rock.

Piled foundations may be designed using allowable end bearing pressures of:

          150 kPa in the stiff/medium dense (or stronger) natural soils.
          600 kPa in XW materials or very low strength (or stronger) weathered rock.

Note: A suitable soil test must be reviewed by Tectonic to assess the subsurface conditions across the
proposed development areas and to confirm the geotechnical recommendations prior to construction.
Inspections must be undertaken by a suitably qualified and experienced geotechnical/structural RPEQ during
construction to confirm the foundation stratum and bearing capacity.

Footing design should also account for potential soil reactivity, to be advised by others. It should be noted
that the placement of highly reactive clays, such as the onsite materials may result in a more adverse site
classification.

All footings should found such that they are not adversely affected by or affect any adjacent excavations,
trenches, footings or retaining walls that are not designed to support building loads. Footings should found
at least below a plane extending 1 m horizontally from the base of trenches/excavations/retaining walls (i.e.
the boulder wall downslope of the proposed pool), then rising up at 1V:1H, as illustrated in Text Figure 9.




                   Text Figure 9: Zone of influence diagrams – footings to be founded below these lines

Footing bases must be cleaned following mechanical excavation to expose undisturbed materials over the
full base area. It is essential that the piling contractor have a ‘mud bucket’ or similar to enable clean out of
the pile bases.




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