The Perth Sand Penetrometer (PSP) provides a reliable method for testing the compaction of soil for residential foundations. PSP testing is carried out in accordance with the Australian Standard 12126.96.36.199.
The PSP consists of a 16 mm diameter flat ended rod and is driven using a 9 kg hammer dropping 600 mm (AS 1289, Test 6.3.3). This test was developed for testing the density of sands and is not effective on clay sites.
When considering compaction requirements for residential structures, retaining walls, swimming pools etc., it is critical to ensure that the natural sand and/or clean fill sand on the base of footings site is be compacted to achieve a minimum density index of 70% (96% of maximum dry density of modified compaction). Typically for sands, which are commonly found in Perth, a minimum of 7 PSP blows for the test depth interval 150 mm to 450 mm is required to achieve the minimum relative compaction of 96% of maximum dry density (modified compaction).
In many situations it is required to import clean sand fill, and the imported material must be well compacted in not more than 0.3 m thick layers by a vibrating plate or vibrating roller. An adequate compaction result for sand fill not containing gravel sized material is the achievement of a blow count of 7 or more per 0.3 m using the PSP.
Organic Matter, Tree Roots and Rubble
The effort in undertaking the site preparation will often maximise the effectiveness of compaction activities thus ensuring adequate long term performance of the foundation. The Australian Standard 3798 "Guidelines on Earthworks for Commercial and Residential Developments (section 6 – site preparation)" provides the minimum requirements in relation to earthworks and would involve the following:
Strip building area and perimeter apron of organic material and rubbish;
Removal of any trees and/or tree stumps and back fill with clean compacted sand free of any voids;
Removal of any deleterious material such as rock or clay from the building area or apron;
Cut and/or fill site to form up pad with clean compacted sand to the required level;
Refer to structural drawings for compaction requirements;
Construct footings and slab as per the structural footing details.
The presence of tree roots can contribute to subsidence and settlement in the foundations of new dwellings over time. If the foundation material is not free of rubble and deleterious material, it can likely result in localised areas that will not achieve the required compaction. Poorly compacted material will undergo further volume reduction, manifested as settlement at the surface and as localised differential settlement. These observations can be compounded by the presence of organic matter in the soil but only testing in accordance with AS 1289.4 would confirm the proportion of organic material.
Compaction Testing Certificate
The compaction requirements are stipulated by the design engineering which in most cases for residential projects is a structural engineer engineer. In most cased the applicable soil compaction requirements are stipulated in AS2870 Residential slabs and footings. A satisfactory test for sand fill not containing gravel sized material is the achievement
of a blow count of 7 or more per 0.3 m using the penetrometer test described in
Compaction testing can be undertaken by trained engineers and the compaction testing certificate must report the following results and general information, as appropriate:
Location of compaction testing.
The penetration resistance, (blows per 300 mm penetration).
Any variation to the normal testing procedure.
Moisture condition of soil, i.e. wet, dry or moisture content, if determined.
Date of test.
Reduced level of ground surface at test site.
Reference to Standard, i.e. AS 12188.8.131.52.
Compaction Testing in Perth and the South West
Our team is able to assist with compaction testing and certification throughout the Perth Metropolitan area and the South West.
If you have any questions about compaction testing, get in touch with us to discuss your requirements and to obtain a free quote.
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