Prof. B.S. Thandaveswara. The various types of linings can be grouped into two categories: (i) Exposed and Hard

Transcription

1 Types of Linings The various types of s can be grouped into two categories: (i) Exposed and Hard Surface Linings, and (ii) Buried Membrane Linings. The advantages and disadvantages of various types of s which need to be kept in view while deciding on the type of to be adopted are indicated below. Exposed and Hard Surface Linings Exposed s include all s exposed to wear, erosion and deterioration effect of the flowing water, operation and maintenance equipment and other hazards. Such s are constructed across of cement concrete and mortars, asphaltic materials, bricks, stones and exposed membranes. Although the initial cost of all these s is generally high, the reinforced cement concrete s are costliest and are usually recommended for use only where structural safety is the primary consideration. Cement Concrete The in situ concrete is one of the most conventional type of which has successfully been used in India and other parts of the world. Cement concrete is more preferable than any other where channel is to carry high velocity water because of its greater resistance to erosion. Velocities up to 2.5 m/sec are generally considered permissible with adequate water depth although higher velocities up to 5.0 m/sec in case of Kosi Feeder in U.P. have been provided. Cement concrete eliminates weed growth and thereby improves flow characteristics. Provision of concrete reduces maintenance charges to a minimum. Frequent cracks due to contraction taking place from temperature change, drying and shrinkage and settlement of sub-grade. It is also likely to be damaged from alkaline water. Cement concrete without reinforcement may be damaged due to excessive external water pressure. The reinforced concrete can withstand the external water pressure but at a very high cost. When unexpected water pressures are encountered, un-reinforced will crack more easily than the reinforced and will relieve the pressure thereby reducing the area of damage.

2 Shot crete Spacing In this type of cement mortar is applied by pneumatic pressure. The may be considered with or without reinforcement (in the form of mesh or expanded metal), although reinforcement (in the form of mesh or expanded metal), although reinforcement increases its useful life, especially, when laid over earth sub-grade. Since the thickness of is limited to 5.0 cm mostly such s are applied on smaller channels or where operational requirements are not severe. Soil Cement This type of is made up of a mixture of cement and natural sandy soil. This type of may sometimes result in considerable saving as compared to cement concrete. It is not weather-resistant. Asphaltic Concrete Asphaltic concrete has greater ability to withstand changes in the subgrade. Asphaltic concrete can be used for repairing cement concrete by placing a resurfacing layer of asphaltic concrete. Velocities for this are limited to 1.5 m/s. Weed growth results in puncturing of ; sliding during hot season. Brick This type of has been extensively used in India and elsewhere. This type of is economical where aggregates for concrete are not available. Exposed Membrane Linings The various types of exposed membrane s are: sprayed in-place asphalt cements, prefabricated sheets of asphaltic materials and films of plastic and synthetic rubber. Exposed membranes have low resistance to puncturing and disintegrate rapidly, thicker sheets with greater resistance are expensive. Earth Linings Thick compacted earth is durable and can withstand considerable external hydrostatic pressure. Bentonite has shown considerable promise for use as a good material. Bentonite containing large percentage of montmorillonite, is characterised by high water absorption accompanied by swelling and imperviousness. It

3 can be used as 5.0 cm thick membrane covered by protective blanket or as a mixed inplace layer of soil bentonite and well compacted. Buried Membrane Linings Hot-applied asphaltic, prefabricated asphalt materials, plastic film and a layer of bentonite or other types of clays protected by earth or gravel cover are cheap s. These s can be provided immediately after completion of excavation or even later. Membrane s are susceptible to damage by weed root and permissible water velocity is limited to avoid erosion. The life of the is uncertain. Consideration for Selection Type of sub-grade, position of water table, climatic conditions, availability of materials, size of canal, service requirements and experience are the major factors affecting the economy and selection of suitable material REINFORCED PORTLAND CEMENT CONCRETE ASPHALTIC CONCRETE UNREINFORCED PORTLAND CEMENT CONCRETE 50 Shot crete steps of 6 mm CANAL CAPACITY (m 3 /s) Determination of thickness of hard-surface based on canal capacity (after U.S.B.R. - Linings for Irrigation Canals), 1963 Specifications of Linings The method of preparation of sub grade in different soil reaches of a canal based on IS: Thickness The minimum thickness of concrete based on canal capacity should be as given below:

4 Capacity m 3 /s Thickness of M 15 Concrete, mm Thickness of M 10 Concrete, mm Controlled Ordinary Controlled Ordinary 0 < Q < < Q < < Q < < Q < Q > Assessment of Seepage Losses from Canals Introduction The possible benefits from canal are saving in water, elimination of water logging, and reduction in maintenance cost. The reduction in seepage losses and prevention of water logging is becoming more and more important because of limited supply and increased demand of water for Irrigation and crops. Observations on Ganga Canal in U.P. and canals in Punjab have shown the only percent of the head discharge reaches the fields. The seepage losses from unlined canals in India have been found to vary from 0.3 to 7.0 m3/sec/106 m2 for different soil and drainage conditions. The following table gives the details of seepage losses measured in the field. Sl.No Canal Method Seepage loss in m 3 / sec / 10 6 m 2 1 Ganga Canal at km 37.6 Tracer Hardoi Branch between Inflow-outflow km and km Bokarheri Distributary between km 0.06 and km Inflow-outflow and seepage meter Tasipur Distributary Seepage meter (Saharanpur) and ponding Tubewell water courses: (i) Dehradun Group Ponding 6.60 (ii) Saharanpur Ponding 5.30 (iii) Roorkee Ponding 4.06

5 t = Thickness of the Permeability of K 1 Permeability of subsoil K H h 1 b 2 FREE SURFACE WITHOUT LINING FREE SURFACE WITH LINING Distance in km Effect of on seepage Manual on Canal Linings h project/ canal Type of (i) Bed width (m) (v) (i) Discharge (ii) Velocity (iii) Value of Manning's n Nangal Hydel (Punjab) Sundernagar Hydel, Beas Project (Punjab) Yamuna Power Gandak Canal & & : : 1 1.5: : 1 N.A / in 6666 NA NA NA NA (i) 49.9 km of concrete (ii) 14.4 km of tile Concrete and tile NA 13.6 km From km to km Cement concrete 10 cm thick in the bed and 12.7 cm in the bottom Concrete in bed, brick and concrete tile on sides. Brick tile

6 project/ canal Type of (i) Bed width (m) (v) (i) Discharge (ii) Velocity (iii) Value of Manning's n Lower Ganga Canal-Link Canal Kosi Feeder Rajasthan Feeder Main Canal Dantiwada Project (Gujarat) (Cement Concrete Lining) to to in upper reaches and 6.4 in lower reaches : 1 1 : 1 1.5:1 1.5: /9250 1/675 to NA NA 1/ NA NA NA km 10 km 64.3 km 0.48 Sandwiched Ist class brick. Cement concrete tile Single tile in bed and double tile in sides 1:3 cement concrete

7 project/ canal Type of (i) Bed width (m) (v) (i) Discharge (ii) Velocity (iii) Value of Manning's n Banaskantha Left Bank Main Canal Dantiwada Project (Gujarat) (Brick Lining) Mahi Right Bank Canal (Gujarat) Shetrunji Canal Project (Gujarat) (Masonry Lining) Shetrunji Canal Project (Gujarat) (Lime Concrete Lining) /2 : :1 2 : 1 1 : NA NA NA NA 1 in in NA NA NA km km 0.12 km 0.43 km cm thick sandwiched brick on bed and sides 13.3 cm thick sandwiched brick tile on bed and sides cm thick masonry Concrete on bed and sides

8 project/ canal Type of (i) Bed width (m) (v) (i) Discharge (ii) Velocity (iii) Value of Manning's n Tungabhadra Project (A.P) Krishnarajasagar Canal (Karnataka) Krishnarajasagar Right Bank Low Level Canal (Karnataka) (Soil Cement Lining) Krishnarajasagar Right Bank Low Level Canal (Karnataka) (Lime Surkhi Concrete Lining) NA : : : : NA NA NA NA NA NA 2.89 NA NA NA NA NA NA NA NA 0.64 km NA NA 180 m NA Cement concrete in bed and sides. In reaches of deep cutting rubble masonry 1 : 4 has been provided on sides. 1 : 5: 10 cement concrete, Top has been plastered with 1 :6 cement mortar, 12 mm thick. 100 mm thick soil - cement. Lime surkhi concrete 1 : 4 : 8, 89 mm thickness, slabs of different widths of 0.762, 1.524, 2.286, 3.048, 3.8, 4.5, m.

9 project/ canal Type of (i) Bed width (m) (v) (i) Discharge (ii) Velocity (iii) Value of Manning's n Manniaru Canal (Tamil Nadu) Pattanamkal Mail Canal (Tamil Nadu) Rathapuram (Tamil Nadu) PAMBA IRRIGATION PROJECT Left Bank Main Canal, Pamba Irrigation Project :1 1 : 1 1 : 1 1 : cm in in in in NA NA NA 10 km In situ cement concrete. 7.6 cm thick. 1:6:10, Cast insitu plastered with cement mortar 1:4, 12 mm thick on the bed. The side slope of the canal is lined with cement concrete 1:4:7 using 60 percent of 38 mm metal and 40 percent of 19 mm metal. The top finished with cement mortar plaster 1:4. The bed of the canal is lined with cement concrete 1:6:10 using 60 percent of 38 mm metal and 40 percent of 19 mm metal. The top of the bed is finished with 1:4 cement mortar plaster. The thickness of is 7.6 cm. Randon rubble masonry has been provided in places where the canal is taken through row cutting. The side slope of the canal is lined with cement concrete 1:4:7 using 60 percent of 38 mm metal and 40 percent of 19 mm metal. The top finished with cement mortar plaster 1:4. The bed of the canal is lined with cement concrete 1:6:10 using 60 percent of 38 mm metal and 40 percent of 19 mm metal. The top of the bed is finished with 1 :4 cement mortar plaster. The thickness of provided for the main canal is 7.0 cm Random Rubble. masonry has been provided in places where the canal is taken through rock cutting R.R. Masonry and C.C.

10 project/ canal Type of References: (i) Bed width (m) (v) (i) Discharge (ii) Velocity (iii) Value of Manning's n Kuttiady Irrigation Project Partially completed by 2/73 Peechi Irrigation Scheme Left Bank Canal 1953 March 1972 Kuthanur Branch March : 1 1 vertical to 0.5 horizontal average 1 : 1 1 : m m 0.3 average 0.24 / / / in 5280 app. average km m (Main canal) precast C.C. slabs Rubble masonry in cement mortar km m Precast slabs and blocks. Bitumen and cement Manual on Canal Linings Technical Report No. 14. Research Scheme Applied to River Valley Projects, Central Board of Irrigation and Power.