Table 2.7 Summary of Construction Methods and Alternative Consideration

Major Works	Locations	Major Activities	Reasons & Consideration of alternative method
River Training	River widening and deepening ü Luk Tei Tong River River widening ü Luk Tei Tong By-pass Channel ü Sections of Pak Ngan Heung River	Earthworks include excavation by mechanical plant; disposal of excavated soil by dump trucks; and compacting by mechanical plant.	It is a common construction method. The impact to the environment is local and temporary. It can be mitigated by appropriate measures. It is recommended to maintain the existing river on one side and to carry out the widening works on the other side. This can ensure the river is maintained at any time to minimise the impact. The construction works will be carried out at dry condition to minimize the adverse effect on the rivers. Working in wet condition inside the rivers or temporary culverting the rivers are not recommended.
Retaining Walls, Box Culvert and Floodwall	Retaining walls Bottlenecks, inlet, outlet of rivers, as well as back side of gabion channel Box Culverts ü Pak Ngan Heung Diversion Box Culvert ü Crossings at Luk Tei Tong By-pass Channel	Earthworks include excavation by mechanical plant; disposal of excavated soil by dump trucks; and compaction by mechanical plant.	It is a common construction method. The impact to the environment can be mitigated by appropriate measures.
		Concreting works include formwork erection, reinforcement fixing and in-situ concreting. Piling works include installation of steel casings, reinforcement fixing and concreting.	The walls will be cast in-situ and it is a common construction technique. Precast unit for the retaining walls and box culvert is not preferable. As the size of retaining wall and box culvert is large, it requires a large plant to handle and install the precast units. Due to limited space, it is not feasible to transport the precast units to site for installation. Bored piles are used for the construction of retaining wall where space is limited. Percussion and driven piles are not recommended due to noise generation during construction.