Test: Plate load test

Plate load test is a field test to determine the ultimate bearing capacity of the soil, and the probable settlement under a given loading.

Where,
q_up, q_up = Ultimate load of plate and footing respectively,
B_f, B_p = Width of footing and plate respectively.
Given:
q_up = 200 kN/m², B_f = 1.5 m B_p = 0.3 m

Additional Information:
For cohesive soil, q_up = q_up
Bearing Capacity is independent of footing size or plate width

The bearing plate is either circular or square, made of mild steel of not less than 25 mm in thickness.

The loading to the test plate may be applied with the help of a hydraulic jack. The reaction of the hydraulic jack may be borne by either any of gravity loading methodor reaction truss method.

The settlement of the plate is measured with the help of sensitive dial gauges. For square plate, two dial gauges are used. The dial gauges are mounted on independently supported datum bar.

A minimum seating pressure of 70 g/cm² (0.7 t/m²), shall be applied and removed before starting the load test.

In order to determine the safe bearing capacity, it would be normally sufficient to use a factor of safety of 2 or 2.5 on the ultimate bearing capacity.

In 1929, Housel suggested the following expression for a c-φ soil:
Q = A .q + P .s
Where, Q = total load on bearing area;
P = perimeter of footing;
S = perimeter shear;
A = contact area of footing or plate.

The plate load test essentially consists in loading a rigid plate at the foundation level, and determining the corresponding to each load increment.

The bearing plate used varies in size from 300 to 750 mm with a chequered or grooved bottom.