• 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.

1. Turfing.

  • 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.

Fig. 12.15. Details of rip-rap on U/S slope of the dam.

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.

Details of slope of the dam.

The entire U/S face should be pitched