Plate Bearing Test for Modulus of Sub-grade Reaction

The modulus of sub-grade reaction is an important parameter in the design of flexible pavements. It is defined as the force required to produce unit deformation in the sub-grade soil. The modulus of sub-grade reaction is evaluated from the plate bearing test.

Plate Bearing Test

The plate bearing test is a field test used to determine the bearing capacity and settlement characteristics of soils. The test involves loading a circular plate of known diameter and weight onto the soil surface and measuring the settlement of the plate under a known load. The test is repeated at different loads and the settlement measurements are used to determine the modulus of sub-grade reaction.

Steps in Plate Bearing Test

The following are the steps involved in the plate bearing test for the evaluation of the modulus of sub-grade reaction:

1. Preparation of Test Site: A test site is prepared by excavating the soil to a depth of at least 1.5 times the diameter of the plate.

2. Placing of Plate: The plate is placed on the soil surface and leveled.

3. Loading of Plate: The plate is loaded with a known load and the settlement of the plate is measured using a dial gauge or a surveying instrument.

4. Repeat Loading: The loading is repeated at different loads and the settlement measurements are recorded.

5. Calculation of Modulus of Sub-grade Reaction: The modulus of sub-grade reaction is calculated using the following formula:

K = (q/p) x (D/∆)

Where,
K = Modulus of sub-grade reaction
q = Incremental load applied to the plate
p = Settlement of the plate under the load
D = Diameter of the plate
∆ = Depth of the plate in the soil

Conclusion

Thus, the plate bearing test is a simple and reliable method for the evaluation of the modulus of sub-grade reaction. It is an essential parameter in the design of flexible pavements, as it helps to determine the thickness of the pavement layers and the required strength of the sub-grade soil.