engineering · 132001.210327.1

                                                                                                             ABN 51 640 311 842
                                                                                                                       CONTACT
                                                                                                               arcosgroup.com.au
                                                                                                                        OFFICES
                                                                                           Sunshine Coast | Brisbane | Gold Coast




5.2 BATTERED EXCAVATIONS
The sand will tend to collapse when cut to near vertical. It is suggested that an allowance for battering at
1H:1V of temporary shallow (<1.5 m depth) excavations be made in planning purposes.


5.3 SITE CLASSIFICATION
In strict accordance with AS 2870, due to the presence of trees and very loose sand with an assessed allowable
bearing capacity of less than 100 kPa, the site in its present state would be given a ‘Class P’ (problem site)
classification, requiring design by engineering principles.
It should be noted that the site is likely to be subject to Class S characteristic surface movements (ys) were it
not for the Class P.
The developed site should be maintained in accordance with the CSIRO publication "Foundation Maintenance
and Footing Performance: A Homeowners Guide", a copy of which is included in (see attachments). The guide
describes suggested site maintenance practices aimed at limiting foundation movements and at keeping
cracking within acceptable limits.


5.4 FOUNDATIONS
The use of steel screw piles (raked for lateral support) with a pile cap could be adopted for lightly loaded
structures requiring minimal lateral resistance. Screw piles could be designed using the ultimate values
indicated in Table 2 below.
TABLE 2: DEEP LEVEL FOUNDATION GEOTECHNICAL DESIGN PARAMETERS (ULTIMATE)

Material                                                      fb (kPa)                              fs (kPa)

Medium dense sand (below approx. 2 m)                           600                                    NR

Notes: fb = Ultimate base bearing pressure for compression pile; fS = Ultimate shaft adhesion pressure for compression
or tension pile; NR = Not recommended.

The pile parameters presented above are ultimate values. Arcos has not been provided with adequate
information to determine:
•   Each weighting factor (wi) of Table 4.3.2(A) of AS2159-2009
•   Each risk factor (IRR) of Table 4.3.2(B) of AS2159-2009
In the absence of more detailed information, the most conservative selection has been adopted. In accordance
with Table 4.3.2(C) of AS2159-2009, the geotechnical strength reduction factor (Øgb) would be:
•   0.40 for low redundancy piling system; or,
•   0.47 for high redundancy piling system.
A higher value of Øgb may be applied if further information is available to reassess the above items.
The ultimate geotechnical strength (Rd,ug) of steel and bored piles can be calculated using the ultimate shaft
adhesion and end bearing values given in Table 2. The values given in Table 2 will need to be reduced by
applying a suitable geotechnical strength reduction factor (Φg) for limit state.
To achieve the base pressure, it is recommended that piles are embedded at least one pile diameter into the
founding strata.
The nominated pressures assume that the piles are “long” and that the material underlying the base of the
piles equal to a depth of at least four times the footing diameter are as strong or stronger. Where a weaker
material is encountered, the pressure associated to this weaker material must be adopted.
Settlement values are subjected to a variety of factors; however, a properly designed and constructed pile
should have a total settlement value less than a value equal to approximately between 2% and 3% of its’


                                                                                                                         Page 7