INVERTED FILTER

it helps to protect coastal area from erosion due to coastal waves. it also helps to maintain the stability of earthen dams.

1. Created by: NAWAL KISHOR SINGH PROTECTIVE FILTERS

2. CONTENTS DEFINITION INTRODUCTION WORKING PRINCIPLE DESIGN CRITERIA APPLICATIONS CONCLUSION

3. DEFINITION Protective filters consists of one or more layers of coarse-grained , free-draining material placed over a less pervious soil called base. It is also called inverted filter .

4. INTRODUCTION Protective filters concept was invented by Karl Terzaghi . It was first used to prevent dams from falling by water piping through foundation .

5. There are generally two approaches to prevent the possibility of erosion and piping: 1. To control of seepage and seepage force. 2. Use of protective filters .

6. WORKING PRINCIPLE A protective filter prevent the migration of finer particles without affecting the flow of seepage water. It is achieved by using specific size grains inside the filter and proper desining .

7. DESIGN CRITERIA Size of voids in filters: 1.It should not be much larger than finest grain of base. 2.It should not be too small. Terzaghi laid down certain criteria in year 1922. Based on grain size distribution. 1. D 15 (filter) / D 85 (protected material) < 5 2. 4 < D 15 (filter) / D 15 (protected material)< 20 3. D 50 (filter) / D 50 (protected material)< 25

8. Layer thickness is insufficient. Multi-layered filter called inverted filter.

9. APPLICATIONS Used as a bedding layers on which a coastal structure rest.

10. Used in rubble mound structure.

11. Used in dams. 1. Seepage through earth dam.

12. 2. Seepage through concrete dam.

13. CONCLUSION ADVANTAGES 1. Helps to provide stable foundation. 2. Filter material have high durability and widely available, so inexpensive .

14. LIMITATIONS 1. Difficulty in assuring uniform construction under water. 2. Filter failure

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