The construction methodology is based on that of the feasibility study. Expected periods of construction and the nature and quantities of excavated material to be produced are provided in Table 3 -23 for each sub-component. Technical precautionary measures will be taken for all structures to meet seismic construction specifications. Construction phase is expected to be completed within three years.
The expected rock type to be encountered while drilling the tunnel is strong, permeable limestone. This rock type should be self-supporting after the tunneling works. The groundwater table lies well below the tunnel level and is not expected to cause any significant problem during construction. At valley crossings, such as the Nahr Damour crossing whereby alluvial deposits will be encountered the tunnel construction will be lined and impermeable.
The tunneling will be carried out mainly using a tunnel boring machine (TBM). New or improved access roads will be required for the equipment to reach the tunnel portals. The TBM will be deployed at the following sections:
From Ourdaniye WTW to Joun regulation structure
From Ourdaniye WTW to Nahr Damour; and
From Khalde to Nahr Damour
The “cut and cover” excavation method will be used at the Nahr Damour inverted siphon rather than the TBM. A substantial cofferdam is likely to be required to cross the river. Environmental implications of the cofferdam will have to be examined and addressed once the final design is completed.
The vertical shaft of the inverted siphon will be formed by “raise boring”. A hole will be drilled from the surface and raise boring machine assembled in the bottom of the low level tunnel. This will be gradually raised to the upper level tunnel. Spoil will be discharged at a low level, i.e. at the base of Nahr Damour Valley. The tunnels will be formed with in-situ reinforced concrete lining with an external impermeable membrane to reduce leakage and, in some cases, the addition of a steel liner. A schematic hydraulic profile and cross-sections along the tunnel are given in Figure 3 -3, Figure 3 -4 and Figure 3 -5, respectively.
The proposed site of the Ouardaniye WTW is characterized by moderate slopes and easy access. However, access roads will require some improvements before start of construction. The site will be excavated up to 12m deep in rock by means of drilling and blasting. A suitable site will be required for disposal of the excavated material from the WTW and the tunnels. Some could be crushed and used as backfill material on site of the Ouardaniye WTW.
The buildings and structures associated with the WTW will be designed in a manner which reflects the nature and exposure of the site and its location and takes into account local aesthetics and building practices. Since the process structures will all be in reinforced concrete, this material will also be used for the associated building to provide low maintenance, functional facilities.
The WTW site will be landscaped in a manner appropriate to the fairly harsh environment, with low maintenance planting. The perimeter of the WTW will be marked with a suitable security fence, with entry controlled at a gatehouse built into fencing. Site lighting will be provided by high pressure sodium floodlights over process units, working areas and roads. Perimeter and security lighting will be provided in accordance with the prevailing local practice of major WTW.
Chemical and storage fuel tanks will be bonded, and suitable precautions adopted for chemical (especially chlorine gas) storage.
An emergency overflow (600mm diameter) will carry overflow water from the treatment units along the upgraded access road, discharging into a local stream course below the new coastal highway, and then ultimately into the sea or into groundwater.
Storm water from the treatment works site will discharge through a 600mm diameter pipe to the north into Wade Baraz and likewise into the sea or into groundwater.
Excavation for the twin ductile iron pipelines from Khalde Tunnel Portal to the Khalde Flow Distribution chamber and then on to the Hadath and Hazmieh Reservoirs will be up to 10m wide and 2.5m – 3.0m deep. However, at road, river, and culvert crossings, deeper excavations may be required, especially at the Ghadir River crossing. Heavy rippers and rock breakers might be used in areas with strong limestone to reach formation level. Blasting will be required for excavation through the hill side below the Hadath reservoir.
Excavation in alluvial and raised beach deposits should not present any significant problems but the stability of the resulting excavation will depend on the precise groundwater level. Construction of the twin 1400mm diameter ductile iron pipelines from Khalde to Hadath Reservoir partly along Chouwaifat road will be through a heavily built up area with significant, but substantially unrecorded underground services. The same applies to the twin 1300mm diameter ductile iron pipes from Hadath to Hazmieh Reservoir.
Distribution Chamber and Reservoirs
The Joun Regulation Structure will be constructed in an area of strong limestone rock requiring drilling and blasting below the layer of alluvial deposits as well as the Wadi Abou Yabes washout.
At the Khalde Distribution Chamber the rock is not expected to be found close to the surface and the majority of the excavated material is likely to be sand fill with rock fragments. Some drilling and blasting may be needed at formation level. A 450mm diameter emergency washout pipeline will discharge from the chamber to an adjacent dry stream bed.
Blasting will be required at the sites of the proposed Hadath and Hazmieh Reservoirs.
Temporary contractors’ working areas will be required for each of the main project components. These will have workshops, concrete batching plants, spoil handling facilities, etc., where appropriate. These areas are expected to be within the expropriated land for construction of the component. However, some additional working areas may be required. The extent of these will have to be defined at a later stage after receiving the proposal of the Contractor.
New roads are required to be constructed and some existing road to be improved to allow suitable access for the construction traffic and in some cases operational vehicles, to a number of the project components. Table 3 -25 summarizes the required access roads.