In situ testing for ultimate bearing capacity

8.9.1 The plate loading test

In this test an excavation is made to the expected foundation level of the proposed structure and a steel plate, usually from 300 to 750 mm square, is placed in position and loaded by means of a kentledge. During loading the settlement of the plate is measured and a curve similar to that illustrated in Fig. 8.11 is obtained.

On dense sands and gravels and stiff clays there is a pronounced departure from the straight line relationship that applies in the initial stages of loading and the qu value is then determined by extrapolating backwards (as shown in the figure). With a soft clay or a loose sand the plate experiences a more or less constant rate of settlement under load and no definite failure point can be established.

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