i) Plate load test is field test to determine the ultimate bearing capacity of soil and probable settlement under given loading.
ii)The test essentially consist in loading a rigid plate, called bearing plate at the foundation level and determining the settlement corresponding to each load increment.
iii) The ultimate bearing capacity is taken as the load at which plate starts sinking at a rapid rate.
iv) The test pit having width equal to 5 times the width of bearing plate is dug upto a depth of proposed foundation. Plate size may vary in width from 300mm to 750mm and 25mm thick.
v)The loading to the test plate may be applied with the help of hydraulic jack. The reaction of hydraulic jack may be borne by reaction truss method.
vi) The truss is held to the ground through soil anchors. These anchors are firmly driven in the soil with the help of hammers. The reaction truss is usually made up of mild steel sections. Guy ropes are used for the lateral stability of the truss.
vii) When the load is applied is applied to the plate, it sinks or settles. The settlement of plate is measured with the help of sensitive dial gauge and for square plate two dial gauge.
viii) The dial gauges are mounted on independently supported datum bar. As the plate settles, the ram of the dial gauge moves down and settlement is recorded.
The load is indicated on the load gauge of the hydraulic jack. The load is applied in increment of 1/10th of estimated failure load.
ix) Settlement readings are made at regular interval of 1, 2, 5,10,20,40 and 60 minutes, until the rate of settlement becomes the less than about 0.02 mm/hr.
x)The results of test are plotted between settlement and load intensity and ultimate bearing capacity (qu) of soil is found out.