Appendix 5. Geotechnical Engineering Report [As Published] · 132007.2399

October 2007                                  - 12 -                         077682076(AB)


5.6.2    Stockpiles and Handling

Wherever practical the earthworks handling should involve transport directly from cut to
treatment/fill area and stockpiling of untreated ASS should be avoided. The recommended
maximum time period for which soils can be temporarily stockpiled without treatment is 18
hours for sands and 2 to 3 days for other soils.

Where it is necessary to stockpile untreated ASS for moderate periods (up to 3 weeks) the
following additional management measures must be followed:

•   Stockpiles are to be contained by bunds with stormwater runoff directed to a collection
    sump. Bunds are to be constructed from low permeability materials that are not ASS or
    have been fully lime treated.

•   A guard layer of neutralising agent should be spread across the soil surface prior to
    placement of the stockpile. The rate of neutralising agent applied should be based on 0.3
    times the average total potential plus existing acidity for every 1m height of soil in the
    stockpile.

•   The surface area of the stockpile is to be minimised by shaping and possibly capping or
    covering to prevent moisture loss and rainfall entry.

•   Keep the surface of the stockpile moist using a spray of water or neutralising solution
    with care to avoid over-wetting.

5.6.3    Excavation for Services

Assessment can be made on an individual basis of the extent of excavations and where these
potentially disturb the ASS. However, in general the residential development area may
involve excavations extending into underlying soils, which may have potential acidity.
Trenching works would need to be carried out under a management plan which for linear
excavations that typically would include:

•   Lime treatment, thoroughly mixed into the soil at the appropriate rate for full
    neutralisation of potential plus actual acidity.

•   As a general practice in trenching operations, stockpiles of excavated material should not
    be left exposed for longer than the minimum practical time before being replaced beneath
    the groundwater table before oxidation can occur. The QASSIT Soil Management
    Guidelines recommend reburial below the water table within 18 hours for coarse textured
    soil.

•   Minimise the extent of groundwater drawdown adjacent to the excavation by staging the
    excavation in short sections that are kept open for a limited duration (eg. 18 hours).




                                     Golder Associates