In general, the following types of linings are generally used:- 1. Concrete Lining 2. Shotcrete Lining 3. Boulder Lining 4. Earth Linings.
Type # 1. Concrete Lining:
Cement concrete lining made from selected aggregate gives very satisfactory service. Despite the fact that they are frequently high in their initial cost, their long life and minimum maintenance make them economical. Cement concrete lining are best suited for main canals which carry large quantities of water at high velocities.
However, a firm foundation is essential for avoiding any possibility of cracking due to foundation settlement. Expansive clay soils should be avoided and proper moisture and density control of the sub grade soil should be maintained while lining.
In areas where the ground water table is likely to rise above the invert level of the lining and cause undue uplift pressure, drains are laid below the lining to release the water and relieve the pressure, generally, a thickness of about 5 to 12 cm is generally adopted for M 15 concrete and 7.5 cm to 15 cm for M 10 concrete for larger canals and stable side slopes are considered to be between 1.5 H : 1 V to 1.25 H : IV. Reinforcement to the extent of 0.1 to 0.4 percent of the area in longitudinal direction and 0.1 to 0.2 percent of the area in the transverse direction reduces width of the shrinkage cracks, thereby reducing seepage.
Type # 2. Shotcrete Lining:
Shotcrete, that is, cement mortar in the ratio of 1 cement to 4 sand proportions is through a pump-pipe-nozzle system on the surface of the channel. Wire mesh reinforcement is generally, though not necessarily, is clamped to the channel surface (as for a rocky excavation) before applying shotcrete. Equipment units used for shotcrete construction are relatively small and easily moved. They are convenient for lining small sections, for repair of old linings, and for placing linings around curves or structures.
Shotcrete linings are generally laid in a thickness of about 2.5 cm to 6.5 cm as per requirement. Brick or Burnt Clay Tile Lining precast Concrete Tile Lining. This type of lining is popular because of certain advantages like non-requirement of skilled mason or rigid quality control.
Since it is more labour intensive, it generates employment potential. Brick tiles can be plastered to increase the carrying capacity of canal with same section and help in increasing the life span of the lining. The top layer is generally laid in 1 : 3 cement mortar over 15 mm thick layer of plaster in 1: 3 cement plaster.
The size of tiles is generally restricted to 30 mm × 150 mm × 53 m. This type of lining is stable even if there is settlement of foundation, since the mortar joint between bricks or tiles provides for numerous cracks so fine that seepage is insignificant. This type lining has been used in Punjab on Bhakra and Haveli canals.
Type # 3. Boulder Lining:
Also called dry stone lining or stone pitching, is used for lining the earthen canal cross section, by proper placement and packing of stones, either after laying a filter layer over the soil surface or without any such filter, depending upon the site requirement. To reduce the resistance to flow, a 20 to 25 mm thick cement plaster is provided as a finishing surface. Stones are generally placed on leveled sub-grade, and hand packed.
This type of lining is of course suitable where stones of required specification are available in abundance locally. One advantage of this type of lining is allowing free flow of water from the submerged or saturated sub-grade into the canal. Hence, this type of lining does not need any drainage arrangement or pressure relief values, etc. which may be required for concrete or brick lining.
Type # 4. Earth Linings:
The different types of earth linings that are used in canals include the following:
i. Stabilized Earth Linings:
Here, the sub-grade is stabilized using either clay for granular subgrade or by adding chemicals that compact the soil.
ii. Loose Earth Blankets:
Fine grained soil is laid on the subgrade and evenly spread. However, this type of lining is prone to erosion, and requires a flatter side slopes of canal.
iii. Compacted Earth Linings:
Elere the graded soil containing about 15 percent clay is spread over the sub-grade and compacted.