Canal Lining Systems

The transport of water from the source to the point of use has been a problem to man since the beginning of time. Canal systems have been used widely for this purpose since the times of the Romans and before. Engineers have tried almost everything to line their water conveyance canals including clay, bricks, concrete spray on chemicals and geomembranes.

The use of geomembranes to line new canal systems and as part of a retrofitting operation is well documented. Many standards are being developed for the use of geomembranes specifically for canal lining systems. GDT has extensive experience with lining systems in general and has worked with a wide range of lining materials including Elvaloy (Modified PVCs), Polypropylene laminates, heavy PVC laminates, HDPE and polyurethane. GDT is also able to arrange installation & testing of membranes.

BASIC CONSIDERATIONS FOR GEOMEMBRANE LINING SYSTEMS

Liner Cross Section. The liner is placed directly in contact with the subgrade or on top of a previously placed geotextile. Frequently an overlying or uniform or tapered thickness soil cover layer is provided. Where a cover layer of soil is provided the possibility of scour must be addressed. The maximum permissible channel velocity is dependent upon the type of cover soil. Typical values range from 27-110 m/min. An important consideration in the design of the canal cross section is the tractive force developed by the moving water. An assessment can be made of the distribution of tractive forces over a standard trapezoidal canal section.

Thickness. Care with subgrade preparation, low normal stress, low hydraulic heads etc allow the use of minimum thickness liners for canal applications. The US Bureau of Reclamation recommends a minimum thickness for liners of 0.5mm.

Cover Soils. Cover soils have been used with liners although correct practice is to leave the liner exposed. Cover soils were used:

• To provide the membrane with erosion resistance.
• To hold the liner in place and to dissipate the tractive forces.
• To protect the liner from exposure to UV, light, ozone and wind.
• To protect the liner from damage caused by water action, plant growth, animals, vandalism and canal maintenance equipment.

It may be that cover soil with adequate resistance to erosion can not be found in particular areas and a covering layer can not be provided. The best cover materials are well graded sandy gravels.

Seam-Joint Overlap. Seams should be such that the overlap is in the downstream direction. The overlap should generally be longer than normal.

Remediation Work. Since many canals have in the past been lined with reinforced or plain concrete, remediation projects are plentiful. They occur from a number of situations such as settlement induced cracking, thermal cycle fatigue cracking, deteriorated expansion joints, opened construction joints, deterioration due to chemical attack etc. When a crack does occur in a concrete lining the amount of leakage that does occur is alarming. Geomembrane have been used widely as remediation liners. In order for there use to be successful the contact surface must be thoroughly cleaned and patched. No loose sections of concrete can remain in place. It may be required to fit a layer of geotextile over the concrete surface. In this situation edge fixing details are very important.

Concrete Covers. New construction often justifies placing the liner under a layer of concrete. Often a needle punched geotextile is placed between the liner and the concrete to assist in the removal of leakage water.

Geosynthetic Liners are ideally suited and a cost effective solution to the waterproofing of canal systems. A body of knowledge has been built up over the years and an assessment can be made of such aspects as required thickness for various subgrade conditions, bottom anchorage, drag forces and chemical and ultrviolet resistance.

Should you require professional assistance with your project please contact us.