Reference Document - MCU25 0101 (As Published)

 Project No. PG-13872                                                                                                      Page | 7
 August 2025
 Ref: PG-13872, 2025-08-14, GR VER 1
 Stephen & Jane Struss – Geotechnical Investigation - Proposed Residence, 28 Kingfisher Drive, Peregian Beach




9.0 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 – anchoring or cross-bracing of the excavation are likely to be
           required for sheet piles or possibly cantilevered, and 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 2, 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 2                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

Pressures for unsurcharged propped walls could be designed based on a uniform
pressure distribution with depth, where the pressure P = 0.65ka  H (kPa) where H is the
depth of the excavation. The shoring wall should also be checked for a triangular
distribution calculated using the lateral earth pressure coefficients present in Table 2
for a propped wall.

The temporary support system should also take into consideration the possible needs
to over-excavate the basement for ground improvement works.

It should be noted that lateral deflection of the retention system will occur, irrespective
of the retention system adopted. In additional to lateral movements, vertical
movement of the soils behind the retention system will result. The effects of the vertical
and horizontal movements may be seen at a distance equal to 2 or 3 times the height
of the excavation.

Subject to detailed design, movements as much as 1% to 2% of the depth of the
excavation could occur behind a cantilevered pile wall.