The correct answer is: B. between 300 mm and 750 mm.
The size of the square bearing plate in a plate loading test is typically between 300 mm and 750 mm. This is because the test results are more accurate when the plate size is comparable to the size of the foundation that will be built on the soil. If the plate size is too small, the test results will not be representative of the bearing capacity of the soil under the foundation. If the plate size is too large, the test results will be affected by the weight of the plate itself.
The plate loading test is a method of determining the bearing capacity of soil. The test involves applying a load to a square or circular plate that is placed on the surface of the soil. The load is then increased in increments until the soil fails. The bearing capacity of the soil is then calculated based on the load that caused the soil to fail.
The plate loading test is a valuable tool for engineers who are designing foundations for buildings and other structures. The test results can be used to determine the size and depth of the foundation that is required to support the structure.