Appendix B - Geotechnical Assessment · OPW23/0179

 Project No. PG-10375                                                                                                      Page | 7
 June 2023
 Ref: PG-10375, 2023-06-09, LTR VER 1
 Michael Cullen – Geotechnical Investigation - Proposed Residence, 128 Gympie Terrace, Noosaville




9.0 BATTERS – SHORT TERM EXCAVATION PROFILE

It is understood that cut batters to 3.0m in height will be required as part of the
basement construction.

Considering the proposed maximum height of cut, the following recommendations
are made for the bulk excavation of the site.

Batters < 2.0m in height

     •     1V:1.5H batter with crest of batter >2m from buildings or structures.
Batters > 2.0m in height

     •     1V:1.5H batter with the crest of the batter at least 2.0m inside the site boundary.
     •     2.0m minimum distance from any building or structure.
If batters are to be left exposed for an extended period of time, a battler angle of
1V:2H is recommended and berm widths are to be strictly maintained. The above
batter slopes assume no seepage is present in the batters and the batters are above
the water table.

10.0 TEMPORARY BATTER SUPPORT

Where the excavations cannot be battered to a stable angle, they will need to be
supported to prevent instability. Support systems could include:

     •     Sheet Piles – It is expected that cantilevered sheet piles will be an acceptable
           retention system. Anchoring or cross-bracing of the excavation may be
           required. Due consideration should be given to the potential for anchor
           installation and vibration to adversely affect adjacent areas.
     •     Contiguous Piles – whilst no vibration is associated with their installation, it is likely
           a more expensive solution.
Where sheet piles are to installed through medium dense or ‘denser’ sands, pre-drilling
may be required to ensure installation.

Where sands are retained, shoring pressures should be based on the lateral earth
pressure coefficients given in Table 3, in conjunction with a triangular pressure
distribution where the pressure can be calculated from P=0.5ka  H2, provided the
excavation is not surcharged by adjacent buildings/services and some tolerance or
movement exists.

TABLE 3                LATERAL EARTH PRESSURE COEFFICIENTS

                                                                                              Lateral Earth Pressure Coefficients
                                                                     Unit Weight
     Material                         Strength                                                                (K)
                                                                       (t/m3)
                                                                                                  Flexible           Propped
                            Very loose to loose                             1.8                     0.40               0.60
         Sands               Medium dense                                   2.0                     0.30               0.50
                           Dense to very dense                              2.1                     0.25               0.45