SLOPE PROTECTION OF THE DAM
- For the success of the earth dam, its U/S and D/S slopes have to be properly maintained.
- U/S slopes have to be protected against wave action, and sudden draw down conditions whereas D/S slopes against heavy down pours, and action of burrowing animals.
Following are some of the measures used for slope protection.
- Down stream slopes of the dams can be protected against erosion by developing turf.
- This measure is quite effective for slope protection.
2. Counter Berms.
- Down stream protection of the dam can be achieved to some extent by providing counter-beams.
- This measure is usually adopted for very high dams.
- Counter beams break the rhythm of the velocity of rain water, flowing down the berm.
3. Rip rap.
- This is the only measure of protecting the U/S slope against the action of wave erosion and sudden draw down.
- This measure can equally be used for protection of D/S slopes also.
- Rip rap is a layer of systematically dumped blocks on the slope.
- A gravel filter layer 40 to 50 cm thick is applied before blocks are laid over it.
- A survey conducted by US Corps of Engineers revealed that dumped rip-rap failed in 5% cases, hand packed rip-rap in 30% cases, and concrete pavement in 36% cases.
- It can very easily be inferred from this that dumped rip-rap is the most successful measure of slope protection.
- Thickness of rip-rap excluding the thickness of gravel filter is about 1 m.
- The performance of rip-rap depends upon the weight and size of blocks, quality of rick of which blocks are made, thickness of rip-rap, and slope of the embankment on which rip-rap is laid.
- The rip-rap thickness is adopted from following criteria.
- Rip-rap, revetment and pitching all mean the same thing.
The entire U/S face should be pitched