PTG_00259 - 0001 - Rev0 - Geotechnical Investigation Report (1)

                                                                                                           PTG Consulting
                                                                                                      ABN: 89 668 880 448
                                                                                                www.ptgconsulting.com.au



 10. SITE CLASSIFICATION AND SITE MOVEMENTS
 For information purposes, the empirical method described in ‘AS2870-2011 Residential slabs and footings’ was
 used to calculate the characteristic surface movement (ys) (ie. site reactivity) due to variation in normal seasonal
 moisture conditions and climatic effects, and subsequent site classification.
 In strict accordance with AS2870, the site is classified at the location of BH1 as Class ‘P’ due to:
      • The presence of uncontrolled fill; and
      • Abnormal moisture conditions as per section 2.1.3(e) caused by:
            o       Removal of an existing building or structure likely to have significantly modified the soil
                    moisture conditions under the footprint of the footing system of the building per section
                    1.3.3(a)
            o       Presence of trees on the building site or adjacent site as per section 1.3.3(c);
            o       The bearing strength is less than 50 kPa as per section 2.4.5

 Due to the site Class ‘P’ the footing and slab system will need to be engineer designed.

 Based on the laboratory test results and the empirical methods described in Section 2.3 of AS2870, the
 calculated surface movement (ys) at the borehole locations in response to normal seasonal soil suction and
 additional movement due to trees (yt) is expected to be between 0 mm and 20 mm which is consistent with a
 Class S classification.
 The indicated surface movement is based on a zero-crack depth factor, soil suction (∆u) of 1.2 pF and depth of
 suction (Hs) of 1.5 m as the site is in a ‘Alpine/Wet Coastal’ climate. It should be noted that the design for the
 footing system for tree-induced differential, centre heave, mound height (ym), is equal to 0.7ys + yt.


 11. FOUNDATIONS
 Bored/screwed foundations are considered suitable for the proposed development, though bored piles might
 have constructability issues with collapse and water ingress.

 All footing excavations should be inspected by Protest to confirm that bearing pressures have been achieved,
 and footings are clean and free from loose and/or water softened materials.

1.2.1 PILES
 Bored piles can be designed using the ultimate skin friction and base bearing capacities given in Table 4 below.
 Piles should be founded a minimum of two pile diameters into the nominated strata and have a minimum pile
 length of four times the pile diameter. The upper 1 m of pile length should be ignored due to pile load
 development and shrink swell effects. Settlement of properly designed and constructed footings should be less
 than 1% to 2% of the pile diameter. Piles should be designed using ‘AS 2159-2009: Piling - Design and
 installation’ and including the recommendations contained in Appendix G of AS 2870 – 2011.

 Table 4: Ultimate Pile Capacities for Bored and Driven Piles
                                                               Ultimate Skin Friction
                        Soil Type                                                       Ultimate Base Bearing (kPa)
                                                                       (kPa)
            Medium Dense natural SAND                                   NA                          600
                  Dense natural SAND                                      NA                        900
 Notes: *Assuming pile is founded to a minimum depth of 1.5 m, NA – Not applicable


 Screw piers could be designed for an ultimate end bearing of 550 kPa founding into the medium dense sand.
 Specialist piling contractors should be consulted when selecting and installing piles.

 To calculate the design geotechnical strength (Rd,g), the ultimate geotechnical strength should be multiplied by
 a suitable geotechnical strength reduction factor (фg) as per Section 4 of AS 2159–2009. Typically, for residential
 development with limited site investigation and design using empirical values, the assessed risk rating would be




 PTG/00259 – 25 Wyuna Drive, Noosaville                     Page 11 of 15                                  28 June 2024