slope stability

Integra Partnerships                                                                                     22340-001-Rev0
                                                                                                      14 September 2022

Steel reinforced concrete bored piles founded as noted above may be designed using an allowable end
bearing pressure of 300 kPa. Parameters for screw pile design are given in Table 1 below. Settlements
under such pressures should be no more than about 25 mm.

Table 1: Screw Pile Design Parameters


                                                                                           Ultimate           Allowable
                                                                        Bearing
                                Unit weight       Friction angle,                          Bearing             Bearing
    Founding Material                                                   Capacity
                                 (kN/m3)                Ø (°)                            Capacity fbult      Capacity fball
                                                                       Factor, Nq
                                                                                            (kPa)               (kPa)

 Medium dense natural
                                     18                 32                  25                1200             400 (Note 1)
 sand
 Dense to very dense (or
                                     19                 36                  35                1800                600
 denser) natural sand
 Notes:
     1)   Allowable pressure based on a working stress factor of safety value of 3 on the ultimate pressure. If a limit state
          design methodology is adopted the ultimate bearing capacity may be used and must be multiplied by a
          geotechnical reduction factor Øg determined in accordance with AS2159-2009 to obtain the Design
          Geotechnical Strength (Rd,g).


The advice of a specialist piling contractor must be sought regarding feasibility, design and installation of the
piling system for this site, including an assessment of potential vibration effects on nearby structures, and
monitoring requirements.

If steel screw piles are adopted, it will be important to ensure close supervision of installation, as piling may
not encounter sufficient drilling resistance (from torque measurement) in sands at the suggested founding
depth, and piles could extend to much greater depth than necessary.

It is therefore recommended that site specific static load testing be conducted from screw piles, if adopted, at
a minimum. Where tension or compression capacity developed in the footings is critical for the future
structure (e.g. resistance to uplift forces from high winds), then cyclic load tests (including measurement of
deflections under tension and compression cycles) should also be undertaken prior to construction.
Kentledge for static testing, or simulated cyclic loads, should prove the piles to a minimum of two times the
expected working load within tolerable deflections.

All footings should be founded such that they are not adversely affected by or affect any adjacent
excavations, trenches, retaining walls, or in ground structures that are not designed to support building
loads. Footings should be founded at least below a plane extending 1 m horizontally from the base of
trenches/excavations/retaining walls/swimming pool, then rising up at 1V:1H, as illustrated in Text Figure 9
overleaf.




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