Plate Load Tests

Reliable soil stiffness and shallow foundation settlement Parameters from the plate load test.

The plate load test is a simple and robust means of obtaining reliable information relating to near surface soil stiffness and likely load/settlement characteristics for shallow footings.  The value of the test data obtained is that foundation design can be optimised to suit actual site conditions and the project requirements thereby producing a more efficient and cost effective solution.

CMW regularly undertakes plate load testing where direct measurement of the soil reaction to vertical load are obtained. The test is conducted on site and involves applying load to a steel plate, placed on the ground surface at the anticipated foundation level, with a hydraulic jack.  Reaction is usually provided by jacking against the underside of an excavator or an alternative suitable item of plant.  Independent reference beams and dial gauges are used to measure plate settlements corresponding  to the, incrementally applied, increasing load.

Where projects adopt shallow footings over relatively soft or loose ground strata the test data obtained enables addessment of an efficient foundation scheme as measured load/settlement performance can be matched with building geometry and loads and checked for compliance with the specified settlement tolerances. 

The CMW team interprets the load settlement curves obtained from the test and, following detailed analysis, can provide reliable ultimate capacity and stiffness parameters for shallow foundation design. Where relevant on sites with marginal foundation ground strata, this testing process can facilitate detailed design and selection of cost effective ground improvement techniques that are applied to reduce footing sizes and project costs.

The plate load test is particularly valuable when dealing with sites, in areas such as the Pilbara in WA, where collapsible soils may be present.  The standard plate load test is changed to incorporate a “wetting up” of the soil below the test plate under sustained load that corresponds to the anticipated footing bearing pressure.  This enables the actual collapse potential to be assessed and the likely severity calculated.  In this way unnecessary additional costs can be avoided where the collapse potential can be shown to be negligible and alternatively, where required, foundation designs can be optimised to suit a measured collapse potential.  

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