Sunshine Butterflies - Attachment D - 010816-2

                                   OUR BACKYARD
                                   468 MCKINNON DRIVE, COOROIBAH

Footing bases must be cleaned following mechanical excavation to expose undisturbed materials over the
full base area. It is recommended that footings be inspected by an experienced engineer prior to placement
of steel reinforcement to confirm allowable bearing pressures and cleanliness of excavations.
If any soil conditions encountered during construction are found to differ from those noted in the geotechnical
investigation, Tectonic should be notified immediately and an inspection carried out to determine if changes
to footing design are required.

6.3            Retaining Structures
Design for temporary or permanent retaining structures could be carried out using a triangular pressure
distribution applicable to the wall type and based on the parameters listed in Table 2. The values in Table 2
assume that the walls are fully drained and no allowance is included for hydrostatic pressures, construction
loading, up-slope footing loadings, the effects of sloping ground and backfill compaction stresses.
Table 2: Retaining Structure Design Parameters
                                                                      Lateral earth pressure coefficients
                             Unit       Friction
 Retained material          weight       angle                Ka                         Ko
                            (t/m 3)    (Degrees)                                                            Kp
                                                       (Cantilever wall)         (Non-yielding wall)


 Natural Sand/Clay           1.8           30                    0.3                     0.5                3.0


 Future Fill                   *            *                     *                       *                  *

Note:    * depends on fill material type and level of compaction.


6.4            Pavement Design
Laboratory testing indicates CBR values ranging from 3% to 25% for the natural high plasticity clays and silty
sands, respectively. Typically, the maximum CBR value adopted for silty sand materials in the subtropics is
10%. Considering the current lack of information regarding the extent of earthworks, it is our
recommendation that the design of pavements be based upon a CBR value of 3%. Up to a maximum CBR
value of 10% may be adopted following visual assessment and testing of exposed subgrades by an
experienced engineer following earthworks.

Pavement subgrades must be ‘proof rolled’ and visually assessed by an experienced engineer to ensure no
heaving or unacceptable subgrade deflection occurs prior to the placement of any ‘topping’ base course
layers. Should heaving or deflection occur, excavation of ‘soft spots’ may be required, followed by
reinstatement with compacted select granular fill.
The recommended design CBR value is applicable to properly drained subgrades only, and must be
confirmed by subgrade inspection and testing by an experienced engineer following earthworks. ‘Properly
drained subgrades’ require open graded drains, site grades that shed water and prevent ponding, and
subsurface drains adjacent to pavements.

6.5            Permanent Drainage
Adequate site drainage must be installed to ensure that surface water runoff is directed away from building
walls, pavements and footings. This could be achieved by installing swales around the site together with
grated channel drains along pathways and pavements. Surface water should be directed to a discharge
point well away from any effluent disposal areas and structures.
Subsurface drainage must be installed behind retaining walls in order to prevent the development of
hydrostatic pressure.




4 May 2016
Report No. 16081-001-Rev0                                    8