Inflatable Dams Analysed Using Numerical Methods
This is an old technical paper which was written some thirty years ago for my first degree. The contents might be obsolete to present days' technologies but theoretical inference could stay stand.
The development of high strength flexible synthetic rubberized membrane has created reliable yet economic alternatives to conventional concrete and steel structures in the storage, conveying or treatment of the majority of materials used in the engineering field today.
An inflatable dam is one of the products which makes use of a sealed tube capable of being pressurized with either water or air, or a combination of both, and adaptable for installation on any stream, river, or waterway for varied purposes such as flood control, water conservation, tidal control, lock systems, recreational facilities etc.
The construction of an inflatable dam is simple and it takes little time to install. It is usually constructed from a flat sheet of rubberized fabric, folded into a tabular shape and sealed in place during installation. Generally, it is fastened in placed to a reinforced concrete slab or foundation with structural steel members and anchor bolts.
The installation of an inflatable dam on its foundation can be made either using double or single anchor lines. Perspective sketches of inflatable dams installed with the two anchorage methods are shown in figures (1a) and (1b). For the double anchored dam, the base length of the inflatable dam is well defined, i.e. the distance between the anchor lines, provided the membrane of the downstream face of the dam does not lie flat on the foundation face. The base length of an inflatable dam fixed with single anchor line is defined as the transverse length of the membrane which lies flat on the foundation surface or the dam base. The base length of a single anchored dam varies under varied loading conditions.
The two free ends of an inflatable dam are sealed either in circular shape or by connecting membrane to membrane at each end in simple straight ties. The ends are usually bolted to concrete walls or abutments. An inflatable dam tubing may be specified to extend above riverbanks where other ways of end fixing can be devised.
The inlet and outlet of the internal pressure of an inflatable dam are made either through the dam base or through the ends of the dam.
In general there are several variations of fabric constructions and several methods of installation, depending on the application, location, flows, stresses etc. Fig. (2) shows engineering drawings for installation of an inflatable dam (7).
Firestone Tyre and Rubber Company, in its General Report(7) , has listed a few of the possible applications of inflatable structures. These include:-
- Diversion structures
- Check structures for flow control
- Flash board replacement
- Lock system
- Sluice gate
- Tidal barriers
- Salinity barriers
- Raising the height of existing spillways
- Raising the height of water reservoirs
- Control gates for sewage plants
- Control gates for water treatment plants
- Replacement of steel gates on concrete structures
- Replacement of low concrete dam to 10m in height
- Barriers for beach erosion
Inflatable dams have been applied for various purposes in various places. In Australia in 1965, an inflatable dam was installed on top of Koombooloomba Dam(6) to raise the height of water level in the reservoir. The inflatable dam was 60.96 meters long and could be inflated to a height of 2.32 meters. The membrane used was neoprene rubber-nylon reinforced with butyl rubber skin coating. The weight and thickness of the membrane were 4.5 Kg/m2 and 3.43 mm respectively. The result of the installation was an increase of the water storage capacity and this in turn allowed the generation of more electric power to the area.
An inflatable dam of 21.34 meters long and 1.22 meters high has been laid across the River Avon to help to maintain water supplies to Bournemouth residents(8). The dam acts as a weir to hold up the local river level at the Bournemouth and District Water Company's pumping station, and thus solves pump suction difficulties at the station.
Advantages and Disadvantages
The use of an inflatable dam as an alternative to a conventional concrete or steel structure, has both advantages and disadvantages. Conner(5) listed them as:-
- Comparatively low initial cost
- Little maintenance
- Ease of installation
- Easy water level control
- The structure can be deflated, giving greater free flow of flood water
- Life of the dam is expected to be about 20 years
- The fabric is vulnerable to vandalism
- The dam is not suitable for high flow
- Uncertainty of fabric behaviour with age and under a continuation of dynamic loads
To compare and discuss theoretical and experimental profile shapes of the dam.
Foundation of The Inflatable Dam
Inflatable dam has to be installed or bolted down onto specific rigid base, normally of reinforced concrete. Below is a vid of window desktop application written in old VB6 which automate details of reinforced concrete beams and columns onto autodesk acad drawing, source code is available on https://github.com/sohmod