This test is used to find the ultimate bearing capacity by the load-settlement curve. A test plate square or circular in the shape of size either 30cm,60cm,75cm but in no case less than 30cm and thickness 25cm. A large size plate is used for loose or soft soil and a smaller size plate is used for dense or stiff clay. The plate act as a model of a prototype foundation. Loads are applied on test plate in an increment of 20% of estimate safe load up to failure or at least a settlement of 25mm or total settlement exceed 10% the width of plate (whichever is earlier).
Plate load test, though useful in obtaining the necessary information about the soil with particular reference to the design of foundation has some limitations. The test results reflect only the character of the soil located within a depth of less than twice the width of the bearing plate. Since the foundations are generally larger than the test plates, the settlement and shear resistance will depend on the properties of a much thicker stratum. Moreover this method does not give the ultimate settlements particularly in case of cohesive soils. Thus the results of the test are likely to be misleading, if the character of the soil changes at shallow depths, which is not uncommon. A satisfactory load test should, therefore, include adequate soil exploration ( see IS: 1892-1979* ) with ~due attention being
paid to any weaker stratum below the level of the footing.
The plate load test is conducting to find out the Safe bearing capacity of Soil. Based on this bearing capacity structural engineer design the building( size of the foundation, pillar .. etc including the steel reinforcement required).Bearing capacity of Hard Strate of soil like Murum is from 15MT/ sqm to 25MT / sqm. Bearing capacity of rock is 35MT/ sqm to 80MT / sqm, depending on the type of rock like Sheet Rock, Rock boulder, soft rock & hard rock. The load test on a pile foundation is to verify the load-bearing capacity of the pile in par with the design load.