Plate Load Test

Hi there,

• Aim : To perform the Plate Load Test(PLT) on an in situ soil sample, and to find out the deformation modulus.

• Theory:

Plate Load Bearing test is an in-situ soil test used to find out the Modulus of subgrade reaction. This checks the bearing capacity of the soil, the load it can take without undergoing an appreciable deflection. This test can be used for the design of the foundations of the buildings and also the soil-subgrade of the highways.

• Apparatus:

 This requires a set of the rigid steel plates, either square or circular in shape of standard sizes of 75 cm, 60 cm, 45 cm and 30 cm.
Along with the plates is a loading arrangement comprising of a jack with a reaction frame.  Jack is attached with a proving ring to note down the loading. As a standard there are 4 dial gauges to be attached along the periphery of the plates to note down the vertical deflection of the plates.
To note down the deflection correctly, dial gauges are attached to a datum frame, which is kept at far distance from the loading area so as to be free from any disturbances to the reading.
In short here is the list of important apparatus to be used in this test:

1. Rigid Steel plates of standard sizes(75 cm, 60 cm, 45 cm and 30 cm.)
2. Jack with a reaction frame and a proving ring.
3. 4 Dial gauges to note down the deflection.

• Procedure:

1. The testing area is properly leveled and prepared for the testing. Plate of size 75 cm is kept at the lowest level and then for equal distribution of the load, subsequent plates are kept over it. 
2. First a seating load of 0.07 kg/cm^2 is applied and then released. 
3. Then loading is applied at a such a rate so as to cause a vertical deflection of 0.25 mm. 
4. Once the deflection is reached up to 0.25 mm, loading is again increased to cause another 0.25 mm deflection. 
5. The loads are noted down correctly and are increased at same rate until a total of 0.175 cm deflection is reached.

• Calculations: 

A graph showing the mean penetration and the corresponding loading is prepared and then load is noted for the deflection of the 0.125 cm. 

Modulus of subgrade reaction is given by   K = p (Kg/cm^2)/0.125(cm)  

                       here,   K = modulus of subgrade reaction
                                 p = Load/pressure in kg/cm^2 required for a deflection of 0.125 cm.
                                 0.125 cm  is the deflection at which the load is noted.

• Result: the modulus of subgrade reaction is = ...

Thanks for your kind visit!