RFI -Attachment 6 - Geotechnical Investigation Report CORE.pdf

Walsh Consulting Engineers



To minimise the potential for any adverse interaction effects, footings should found at least below a plane
extending 1 m horizontally from the base of trenches/batter slopes/excavations/ retaining walls, then rising
up at 1V:1H. This requirement is illustrated in the following diagram.




      6.2.2   General Comments on Footings
If any soil conditions encountered during footing construction are found to differ from those noted in the
geotechnical investigation, Core should be notified immediately, and further assessment carried out to
determine if changes to footing design are required.
Inspection and testing of footing excavations to confirm design bearing pressures by Core is recommended.

6.3 Retaining Wall Design and Parameters
Retaining structures should be designed in accordance with AS 4678-2002 Earth retaining structures.
Allowance should be made for construction loading, up-slope footing loadings, the effects of sloping ground,
hydrostatic loads, and backfill compaction stresses. Positive permanent drainage must be installed behind all
walls unless they are designed for development of full hydrostatic pressures.
Retaining walls should be designed using the parameters in Table 3 and founded as described in
Section 6.2.

Table 3: Retaining structure design parameters.
                                       Unit          Friction                    Lateral Earth Pressure Coefficients
       Retained Material             Weight            Angle        Cantilever Wall          Non-yielding Wall
                                                                                                                       Kp
                                      (t/m3)        (Degrees)              (Ka)                    (Ko)
 Loose Sand                             1.7              28                0.36                    0.53                2.77
 Medium Dense Sand                      1.9              34                0.27                    0.43                3.61
 Dense Sand                             2.0              39                0.22                    0.36                4.5
 Compacted Fill                          *               *                   *                       *                  *
 *: Variable depending on the type of material used and the degree of compaction achieved.


6.4        Soil Dispersion & Erosion Protection
Any excavations or disturbance of materials should be carefully monitored and managed during the
construction phase to minimise potential for scour/erosion and sediment run off.
Emerson class number (ECN) laboratory testing measures the tendency of the soil’s clay fraction to go into
colloidal suspension in water. Dispersive soils are those which by nature of their mineralogy, and the
chemistry of the water in the soil, are susceptible to separation of the individual clay particles and
subsequent erosion of these particles through fine cracks or fissures in the soil under seepage flows.
ECN testing indicates that the samples tested are non-dispersive.



J001390-001-R-Rev0                                            8