Q. Explain the design of graded filter?

Use of graded filter has been traditionally used below the revetment and protection works. The material used in the granular / graded filters is normally durable. The graded filter material has good surface contact with both the sub-soil and the top protection works. Under gradually changing conditions, sometimes, the graded filter can show "self healing" results. However, the graded filter requires strict quality control in design and execution. Procurement of suitable material, and maintaining the desired uniformity of filter material can be a problem. Therefore, the quality of the final product is not certain. Graded filters of more thickness show spreading effect causing damage to the protection works on the top.