Geotech Report · OPW26/0094

Project No. PG-10899                                                                                                      Page | 7
November 2023
Ref: PG-10899, 2023-10-16, GR VER 1
DD Sunnyside CD Sunnyside Pty Ltd – Geotechnical Investigation - Proposed Residence, 30 Mossman Court, Noosa Heads




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.

10.0 PERMANENT RETAINING WALLS

Basement walls should be designed using a pressure coefficient for the at rest case
of K0 = 0.5.

Unit wall force P is given by:-

                       P           =          0.5 K0  H12 (kN/m run of wall)

Passive resistance at the base of the wall can be calculated from:-

                       P           =          0.5 Kp  Hw2

           where Kp                =          3.25 (ignores wall friction effects) for medium dense sands

                       Hw          =          front face of wall contributing to passive resistance (m)

For the sliding resistance calculation, the angle of friction for sand () compacted to
not less than 75% density index can be taken as 32° for walls with a key. For walls
                                                                                                                     2
without a key, the angle of friction for sliding resistance should be taken as 3  or 21°.