Slope Analysis 18 Hay St

                                                                                                             ABN 51 640 311 842
                                                                                                             arcosgroup.com.au
                                                                                            Sunshine Coast | Brisbane | Gold Coast




8.1       RETAINING STRUCTURES
Retaining walls must be designed by a suitably qualified and experienced engineer and preferably in accordance
with AS 4678. The geotechnical parameters for use in design of either flexible or rigid wall systems are presented in
Table 2.
Passive forces should be ignored in areas where disturbance may occur (i.e. future trenching or earthworks
processes).
Compaction for retaining wall backfill should be undertaken with due care. Layers should be placed thinner than for
normal earthworks processes (say a maximum layer thickness of 100 mm) and compacted using light weight
equipment such as hand controlled compactive equipment to minimise the stresses on the wall. If hand controlled
equipment is not practical, temporary wall propping will be required.
Walls will need to incorporate full height drainage in accordance with good design practice to minimise hydrostatic
pressure. The below parameters do not include surcharge loadings.


TABLE 2: RECOMMENDED GEOTECHNICAL PARAMETERS FOR RETAINING WALL ANALYSIS

                              Material                                  Ɣ (kN/m3)              Ø (°)              C’ (kPa)
                   New FILL* and Very Stiff CLAY                             19                  26                   2
                      Loose SAND / GRAVEL                                    18                  30                   0
                             Soft CLAY                                       17                  22                   1
 Notes: Ɣ = Unit Weight (moist); Ø = Drained friction angle; C’ = apparent cohesion; * = Placed under Level 1 inspection and
 testing and behaves as clayey material.



8.2       FOOTINGS
In accordance with industry standards, a geotechnical engineer from Arcos should undertake the testing within the
footings to confirm that the encountered material is in alignment with the adopted parameters and assumptions
provided within this report. Where this does not occur, Arcos cannot be held liable for any of the information presented
within this report.
All footings will need to be designed to accommodate potential ground surface movement, settlement values and
any additional settlement values associated with the placement of new fill.
Settlement for suitably sized and designed high level footings should be in the order of 1-2% of the width of the
footing.
If footings are located adjacent to an underground service or other obstruction that is not homogenous with the
founding strata, the footing should be extended a minimum 0.3 m below an imaginary line projected at a 45 degree
angle from the lowest point of the service/obstruction. This is depicted graphically for reference:




Sunshine Coast | Brisbane | Gold Coast