Buried and Protected type Membrane Lining

  • These linings are such lining in which a waterproof thin membrane is place on the prepare subgrade.
  • Thereafter it is covered by a protective layer of earth or gravel.
  • The protective layer provides protection to the lining against damage due to outside effects.
  • Membrane itself provides imperviousness.
  • The commonly used buried membranes may be:

1. Sprayed asphaltic lining.

  • In this hot asphalt is sprayed on the subgrade which acts as water proofing barrier.
  • 2. Prefabricated asphaltic membrane lining.
  • In this, asphalt lined papers, clothes, mats etc. are used to put a barrier against seepage.
  • All these fabrications are available in marked in form of rolls.
  • The membrane is laid on smooth well prepared subgrade and covered with a fine soil or earth.

3. Plastic or rubber membrane lining.

  • In this case, plastic or synthetic rubber membrane is used as water proofing membrane.
  • Out of numerous such membranes polyethylene film has shown encouraging results.
  • This lining is liable to be easily ruptured by sharp stones or weed growth and as such.
  • The subgrade should be prepared smooth and treated with herbicide so as to prevent weed growth. .

4. Bentonite and clay membrane lining.

  • It has not been used on irrigation canals as yet.
  • The main characteristic of Bentonite is swelling due to absorption of water.
  • On swelling the membrane becomes perfectly water-tight and controls seepage from canals.
  • The bentonite layer is formed by laying 2.5 to 3 cm thick layer of bentonite over a prepared subgrade.
  • The layer is lastly covered with 15.30 cm protective blanket of suitable earth or gravel.

Earth Lining

Under this category of lining following linings come.

(i) Soil cement lining.

  • In this lining, 2 to 5% cement is mixed dry with fine soil of which 35% passes through 200 sieve.
  • This mixture is prepared in dry state of the soil.
  • The water is sprinkled on this mixture and compacted on the prepared subgrade.
  • The lining is kept wet for about a week before water is allowed to flow in the canal.

(ii) Clay puddle lining.

  • The clay puddle is prepared by first excavating the clay and then exposing it to weathering.
  • After a week or 10 days of exposure, water is added and clay is pugged throughly.
  • The pugged clay is known as clay puddle.
  • The pugged clay is put along the perimeter of the canal to act as lining.
  • The lining of clay puddle may be about 30 cm.
  • It is generally protected by earth layer so that it is not exposed and cracked when canal is closed for few days.

(iii) Sodium carbonate lining.

  • A mixture is prepared with local soil by mixing about 10% clay and 6% sodium carbonate.
  • This mixture is added with water and laid in a layer of 10 cm thickness.
  • It may be used on water courses or other small channels.
  • It is not suitable for larger canals as it is not durable.

Porous Type Lining

  • In head reaches, the groundwater table is generally much higher than the bed level of the main canal.
  • The porous lining is advisable in such circumstances.
  • The porous lining allows water pressure to be released and thus occurrence of back pressure is eliminated.
  • 15 cm inverted filter is spread evenly on the prepared sub-grade and stone pitching is done by hand packing.
  • If stones are not available near the site, brick pitching may be done.
  • This lining does not provide any imperviousness but is used for the drainage of the banks.

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