lining (courtesy R.W. Hill)

Transcription

1 Lecture 19 Canal Linings I. Reasons for Canal Lining Installing plastic canal 1. To save water (reduce seepage) lining (courtesy R.W. Hill) 2. To stabilize channel bed and banks (reduce erosion) 3. To avoid piping through and under channel banks 4. To decrease hydraulic roughness (flow resistance) 5. To promote movement, rather than deposition, of sediments 6. To avoid waterlogging of adjacent land 7. To control weed growth 8. To decrease maintenance costs and facilitate cleaning 9. To reduce excavation costs (when extant material is unsuitable) 10. To reduce movement of contaminated groundwater plumes The most common and (usually) most important reason is to reduce seepage losses (and this may be for a variety of reasons) The assumption that lining will solve seepage problems is often unfounded, simply because poor maintenance practices (especially with concrete linings) will allow cracking and panel failures, and tears and punctures in flexible membranes Seepage losses from canals can be beneficial in that it helps recharge aquifers and makes water accessible to possibly larger areas through groundwater pumping. The extent of aquifers is more continuous than that of canals and canal turnouts. But, pumping ($energy$) is usually necessary with groundwater, unless perhaps you are downhill and there is an artesian condition (this is the case in some places). Administrative losses and over-deliveries can add up to a greater volume of water than seepage in many cases (that means that canal lining is not always the most promising approach to saving water in the distribution system) Sometimes, only the bottom of a canal is lined when most of the seepage has been found to be in the vertical direction It may be advisable to perform soil compaction testing under concrete linings to determine if steps need to be taken to avoid subsequent settlement of the canal Lining to decrease maintenance costs can backfire (costs may actually increase) Concrete pipe is an alternative to lined canals, but for large capacities the pipes tend to cost more Many billions of dollars have been spent world-wide during the past several decades to line thousands of miles of canals BIE 5300/6300 Lectures 221 Gary P. Merkley

2 II. Some Types of Lining and Costs Type Typical Costs 1. Soil Lime Bentonite clay High-swell Bentonite & coarse clay or other bridging material Geosynthetic clay liner ( Bentomat ) Soil mixed with portland cement Thin compacted earth (6-12 inches) Thick compacted earth (12-36 inches) 2. Fly Ash... $3.00/yd 2 3. Masonry (stone, rock, brick) 4. Concrete (portland cement) 5. Plastic Nonreinforced concrete... $5.00/yd 2 Reinforced concrete (with steel) Gunite, a.k.a. shotcrete, a.k.a. cement mortar (hand or pneumatically applied; w/o steel reinforcement)... $12.00/yd 2 Gunite, a.k.a. shotcrete, a.k.a. cement mortar (hand or pneumatically applied; w/ steel reinforcement)... $15.00/yd 2 Polyvinyl Chloride (PVC)... $5.00/yd 2 Oil Resistant PVC Chlorinated Polyethylene (PE) Low Density Polyethylene... $4.00/yd 2 High Density Polyethylene... $10.00/yd 2 Polyurethane foam with or without coatings 6. Asphalt (bituminous) Sprayed ( blown ) asphalt Asphaltic Concrete... $4.00/yd 2 7. Synthetic Rubber Butyl Rubber... $8.00/yd 2 Neoprene Rubber Shotcrete over geosynthetic... $37.00/yd 2 Concrete over geosynthetic... $26.00/yd 2 Gary P. Merkley 222 BIE 5300/6300 Lectures

3 III. Comments on Different Lining Materials The USBR has had a long-standing research program on canal lining materials and installation techniques (began in 1946, but essentially discontinued in recent years) Pneumatic application of shotcrete There are many publications with laboratory and field data, design guidelines and standards, and other relevant information (but you have to dig it all up because it doesn t come in one book) Many technical articles can be found in the journals on canal lining materials, construction methods, and experience with different types of linings Earthen Linings Earthen linings usually require significant over-excavation, and transport of suitable material (in large volumes) from another site Many earthen linings are 2-3 ft thick; thin linings are 6-12 inches thick Clay linings can crack after only a few cycles of wetting and drying, causing increased seepage loss. Bentonite clay swells considerably when wet, but cracks may not completely seal after the canal has been dried, then filled with water again. Bentonite is a special kind of clay, usually made of up decomposed volcanic ash, and containing a high percentage of colloidal particles (less than cm in diameter) High-swell Bentonite may swell 8 to 12 times in volume when wetted; other types may swell less than 8 times in volume Bentonite disperses well when mixed with soft water, but may flocculate (clump up) when mixed with hard water. Flocculation can be avoided by adding one or more dispersing agents (e.g. tetrasodium pyrophosphate, sodium tripolyphosphate, sodium hexametaphosphate). Low-swell Bentonite tends to flocculate easier. Repeated drying-wetting cycles can cause loss of lining density, loss of stability, and progressive deterioration of the lining Other than Bentonite, clay linings may be of montmorillonite, or montmorillonite - chlorite Some clay linings have been treated with lime to stabilize the material. The addition of lime to expansive soils (e.g. Bentonite) improves workability and increases structural strength BIE 5300/6300 Lectures 223 Gary P. Merkley

4 Portland Concrete Small concrete-lined canals are usually non-reinforced Rubber strip at panel joint Steel reinforcement (rebar or steel mesh) is also not commonly used on large canals anymore unless there are compelling structural reasons The elimination of steel reinforcement from concrete canal linings saves about 10 to 15% of the total cost (USBR 1963) During the past several years it has become popular to install concrete linings in small canals at the same time as final excavation and finishing, often using a laser to control the alignment and longitudinal slope Some underwater concrete lining operations have been performed in recent years on full canals (so as not to disrupt delivery operations) Careful shaping, or finishing, of the native soil is an important step in the preparation for concrete lining simply because it can greatly reduce the required volume of concrete (significantly lowering the cost) Manual concrete lining of a canal reach (every other panel is poured first to facilitate formwork) Gary P. Merkley 224 BIE 5300/6300 Lectures

5 Reinforced concrete can contain rebar and or wire mesh. Reinforcement is usually for structural reasons, but also to control cracking of the lining Concrete panel joints may have rubber strips to prevent seepage Weep holes or flap valves are often installed in cut sections of a concrete-lined canal to relieve back pressures which can cause failure of the lining Flap valves may be installed both in side slopes and in the canal bed Some concrete-lined canals have (measured) high seepage loss rates, particularly in fill sections of canal, and in soils with high permeability (usually sandy soils) -- but, seepage rates are rarely measured; they are assumed based on tables in books British researchers report that their investigations show that if 0.01% of the area of a concrete canal lining is cracked (0.01% are cracks), the average seepage rate may be the same as that of an unlined canal Soil mixed with Portland cement, especially sandy soil, can be an acceptable cost-saving approach to canal lining IV. Concrete Lining Thickness Lining thickness is often chosen in a somewhat arbitrary manner, but based on experience and judgment, and based on the performance of existing linings on other canals Thinner linings may crack, but this does not have to be a problem if the cracks are sealed during routine maintenance (not all concrete-lined canals enjoy routine maintenance) Concrete lined channels often have high seepage loss rates due to cracks and unsealed panel joints Grooves are often specified to control the location and extent of cracking, which can be expected even under the best conditions The selection of lining thickness is an economic balance between cost and durability (canals perceived to be very important will have more conservative designs -- municipal supplies, for example) The USBR has suggested the following guidelines: Lining Type Thickness (inch) Discharge (cfs) Unreinforced concrete , ,500-3, > 3,500 Asphaltic concrete , > 1,500 Reinforced concrete , > 2,000 BIE 5300/6300 Lectures 225 Gary P. Merkley

6 Lining Type Thickness (inch) Discharge (cfs) Gunite (shotcrete) > 400 Plastic and Rubber Plastic linings are also referred to as geomembranes or flexible membrane linings Plastic canal linings have been in use for approximately 40 years Plastic and rubber linings are covered with soil, soil and rock, bricks, concrete, or other material for 1. protection ozone attack and UV radiation puncture due to maintenance machinery and animal feet, etc. vandalism 2. anchoring flotation of the lining (high water table) resist gravity force along side slope wind loading Plastic linings are typically 10 to 20 mil (0.010 to inches, or 0.25 to 0.5 mm) -- thicker membranes are usually recommendable because of increased durability, and because the overall installation costs only increase by about 15% for a doubling in thickness The USBR previously used 10 mil plastic linings, but later changed most specifications to 20 mil linings Plastic linings of as low as 8 mil (PE), and up to 100 mil have been used in canals and retention ponds Low density polyethylene (LDPE) is made of nearly the same material as common trash bags (such as Hefty and Glad brands), but these trash bags have a thickness of only mils Plastic canal linings are manufactured in rolls, 5 to 7 ft in width, then seamed together in a factory or shop to create sheets or panels of up to 100 ft (or more) in width Rubber membrane linings can have a thickness ranging from 20 to 60 mil Flexible plastic and synthetic rubber linings are susceptible to damage (punctures, tears) both during and after installation Flatter than normal side slopes (say 3:1) are sometimes preferred with plastic linings to help prevent the possible migration of the lining down the slope, and to help prevent uncovering of the lining by downward movement of soil Gary P. Merkley 226 BIE 5300/6300 Lectures

7 Correctly installed plastic and synthetic rubber linings are completely impervious, provided they have not been damaged, and provided that the flow level in the channel does not exceed the height of the lining Plastic liners will age and lose plasticizer, causing a loss of flexibility and greater potential for damage. Increased plasticizer during fabrication has been shown to be effective in this regard plas-ti-ciz-er (plas'tuh sie zuhr) n. a group of substances that are used in plastics to impart viscosity, flexibility, softness, or other properties to the finished product Some canals in central Utah have had plastic linings for more than 30 years, and most of it is still in good condition (measured seepage is essentially zero in the lined sections, but some evidence of puncture/tearing has been found) Plastic lining material is sometimes used to retrofit existing concrete-lined canals after the concrete lining canal fails and or continued maintenance is considered infeasible Preparing a canal section for buried membrane lining (courtesy R.W. Hill) In the former Soviet Union, thin PE lining has been placed under precast slabs of concrete lining in some canals In India, some canals have been lined with plastic (PE) on the bottom, and bricks or tiles on the side slopes Polyethylene (PE) is the lowest cost geomembrane material, PVC is next lowest. Some newer materials such as polyolefin are more expensive Exposed and Buried Membranes Exposed membrane linings have been tried, but tend to deteriorate quickly for various reasons Exposed membrane linings have recently been installed in some full (operating) canals BIE 5300/6300 Lectures 227 Gary P. Merkley

8 Buried membrane lining should have a cover layer of soil of approximately 1/12 th of the water depth, plus 10 inches Some vegetation can penetrate these types of linings (asphaltic too), so sometimes soil sterilant is applied to the soil on the banks and bed before lining Fly Ash Fly ash is a fine dust particulate material (roughly the size of silt) produced by coal-burning power plants, usually in the form of glassy spheres Fly ash contains mostly SiO 2 (silicon dioxide), Al 2 O 3 (aluminum oxide), and Fe 2 O 3 (iron oxide) Fly ash is often mixed with soil to form canal linings, the mixture being more dense and less permeable than soil alone Fly ash is sometimes mixed with both soil and portland cement V. References & Bibliography ASAE Standards. Amer. Soc. Agric. Engr., St. Joseph, MI. Davis, C.V. and K.E. Sorensen (eds.) Handbook of applied hydraulics. McGraw-Hill Book Company, New York, N.Y. Frobel, R.K EPDM rubber lining system chosen to save valuable irrigation water. Proc. of the USCID conference, October 13-15, Salt Lake City, UT. USBR Buried asphalt membrane canal lining. USBR research report No. 12, Denver Federal Center, Denver, CO. USBR Linings for irrigation canals. USBR technical report, Denver, CO. USBR Performance of plastic canal linings. USBR technical report REC-ERC-84-1, Denver Federal Center, Denver, CO. USBR Synthetic rubber canal lining. USBR technical report REC-ERC-71-22, Denver Federal Center, Denver, CO. USBR Tests for soil-fly ash mixtures for soil stabilization and canal lining. USBR technical report REC-ERC-86-9, Denver Federal Center, Denver, CO. USBR Water operation and maintenance. USBR technical bulletin No. 170, Denver Federal Center, Denver, CO. Gary P. Merkley 228 BIE 5300/6300 Lectures