The Great Man-Made River
( Page 2 of 4 )
Where the concentration of chlorides and sulphates is high, and in the potential presence of groundwater, additional protection in the form of a barrier coating applied to the outside of the pipe is necessary to prevent the deterioration of the cement in the concrete from sulphate attack and the corrosion of the high tensile wire wrapping the pipe core from the effects of chloride attack. Cathodic protection may also be provided, if it is shown to be necessary, after the first few years of pipeline operation.
Steel bell and spigot joint rings are welded to the ends of the steel cylinder and embedded in the concrete core to provide a joint with adjacent pipe sections. The joint between pipes is made by forcing the spigot end of a pipe, with a rubber gasket held within a groove, into the bell end of a previously laid pipe, to form a watertight seal with a degree of flexibility.
Purpose-built plants were constructed at Sarir and Brega to manufacture the pipe sections, each of which is seven and a half metres long, and 18 bar pressure rating and weighs up to 86 tonnes. Both pipe plants are self-sufficient, generating their own electricity and provided with other utility services. Cement for the concrete is obtained from the Libyan Cement Plant at Benghazi; aggregate from quarries near the pipe plants. The water required for mixing the concrete, and for other uses at Brega, was drawn from local wells drilled for this purpose in the Jalu area and pumped to the pipe plant, while the water required for the pipe plant at Sarir was drawn from the existing wells near the plant.
For easy reference the quantities of material used for construction of the first phase only are listed below :-
Total number of pipe sections : 250,000 approximately.
Number of inspection chambers : 3,000
Air vacuum valves : 1,500
Cement : 2.5 million tonnes.
Aggregate : 13 million tonnes.
Pre-stressed wire : 2 million kilometres.
Steel cylinders : 25 million square metres.
Excavation : 85 million cubic metres.
Rubber gaskets : 6 million linear metres.
To deal with these huge quantities, the largest concentration of handling and earth-moving equipment in the history of civil engineering has been gathered together including :-
Heavy crawler cranes 64
Bulldozers and tractors 238
Excavators 110
Heavy trucks 367
Truck trailers 226
Tank trucks 50
Buses 40
Forklifts 40
Light trucks 524
Ambulances 19
Light generators 91
Central generators 35
Compactors 115
Heavy backfill equipment 19
Concrete pouring trucks 40
In addition to the civil engineering work described above, many other associated works were required. An example was the permanent communication and control system ( PCCS ). The PCCS is allowing staff in the Benghazi Headquarters control centre to direct the operation of the entire project. Instructions will be issued from Benghazi to personnel at the other control centres to adjust water flow and storage throughout the system and they, in turn, are able to remotely control the wellfields, reservoirs, and turnout stations from control panels. A computer system is allowing operating personnel at Benghazi Headquarters to calculate water flow parameters and process information associated with water use. Computer terminals at the other control rooms are monitoring water flow and levels at the wellfields and reservoirs. The same computer system is also monitoring control equipment, maintenance efforts and spare parts inventory, and other ancillary activities. The design of the PCCS provides a sufficient number of communication channels to maintain continuous operation even if some components become inoperative.
Electrical power is essential for the operation and control of the project. The total power demand for Phase One, of around 65 megawatts, is provided mainly from a power generating plant constructed at Sarir as part of the project. Power from this plant is being transmitted directly to Sarir wellfield via a 66 kV transmission line, and indirectly to the Tazerbo wellfield via the existing national power supply system, at 220 kV. The power is transformed down to 66 kV at Tazerbo substation and transmitted to the distribution stations at Tazerbo wellfield via a 66 kV line constructed for this purpose. Sarir power generating plant consists of six gas turbine generating sets which can operate on diesel fuel if the need arises.Because of the great distances involved, five operation, support and maintenance centres are required for the efficient operation and maintenance of the project; the five facilities are to be located at Benghazi, Sirt, Ajdabiya, Sarir and Tazerbo respectively. Each centre will include the administrative offices and industrial maintenance buildings required to secure project self-sufficiency, as well as permanent housing and amenities. At each of these five locations, control panels will graphically illustrate the layout of the facility and indicate the operational status of all relevant equipment.
At an average flow rate of. 0.95 metres/second, it will take the water over nine days to cover the pipeline distance of 800 kilometres from Sarir to Sirt or the 783 kilometres from Tazerbo to Benghazi. To maintain the flow over these distances, a sufficient number of air relief valves will be installed at high points along the pipeline route to discharge air accumulated inside the pipeline which would otherwise reduce the flow rate. The system is provided with sufficient outlets along the route to discharge water from the pipeline when needed, principally for maintenance which cannot be undertaken without emptying the pipeline. Access points are also provided at reasonable distances, to allow insertion of mobile maintenance equipment as required.The design of this conveyance system allows it to convey an additional flow of about 1.68 million cubic metres a day from Kufra wellfield. The necessary connections have been provided to allow for the installation of future pumping stations, the locations of which have already been determined. Isolating valves have been installed in the first phase of construction to avoid any suspension of operation when such pumping stations are constructed, to ensure an uninterrupted supply of water to farms, industries and municipal users.
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