[精选]沉管隧道介绍(英文)--资料

FoundatBiblioteka on• The foundation method to be used must be chosen with due consideration, first of all, for the subsoil conditions and the degree to which the tunnel will be subject to dynamic loadings, and earthquake loadings in particular. Pile foundations are an option but this solution has been used for a few tunnels only.
• Tides and current effects of the waterway must be evaluated to determine conditions during dredging and tube sinking operations.
• Importantly, dredging and backfilling operations should be executed in such a manner as to limit disturbance in the natural ecological balance at the construction site.
• Compensation grouting to make up for the reduction of the waterway cross section caused by the permanent tunnel works, and thereby avoiding changes in hydrographical and biological conditions in the waterway.
• Governmental agencies having jurisdiction over environmental protection, natural resources or local conditions must be consulted and approval of authorities should be obtained in the preliminary design stage.
• The first tunnel of the concrete type was constructed in 1940 in Rotterdam under the Maas estuary.
• The most profound effect of an immersed tunnel on the environment concerns the element it is meant to bypass—water.
• Advantegous as there is less loss in height than with tunnelling deeply under the riverbed, and the tunnel may therefore be shorter overall.
• The world's longest and deepest application to date is the twin-tube subway crossing of San Francisco Bay, constructed between 1966 and 1971 with a length of 3.6 miles (5,8 km) in a maximum water depth of 41 m. The 100 m long, 15 m wide sections were constructed of steel plate and launched by shipbuilding procedures.
– joined, connected and protected by backfilling the excavation. – The sections may be fabricated in shipyards, in dry docks, or in
temporary construction basin serving as dry docks.
• A trench is dredged in the bed of the water channel.
Tunnel Trench Dredging
The dredging works required for the construction of an immersed tunnel will normally comprise some, or all, of the following items:
For both steel and concrete types of tunnels, the main tasks are: • Excavation of a tunnel trench to specifications and to keep it free
of siltation that may be detrimental to the permanent foundation until this foundation has been constructed and the tunnel has been brought to rest on it. • Construction of watertight and durable tunnel elements. • Installation of the tunnel elements in the tunnel trench. • Construction of watertight and durable joints between the tunnel elements. • Construction of a durable foundation for the tunnel.
Immersed Tunnels
Typically, an immersed tunnel is made by • sinking precast concrete boxes into a dredged channel
and joining them up under water.
– Tunnel sections in convenient lengths, usually 90 to 150 meters, are placed into a pre-dredged trench,
• Dredging of the tunnel trench for the immersed tunnel section.
• Dredging of an access channel between the casting/launching basin and the tunnel trench.
• Once completed, an immersed tunnel is no different operationally from any other tunnel. However, it is built in a completely different way.
The Construction technique:
• The influence of the tunnel on the groundwater and the surface water in the area plays a predominant role in the tunnel design and construction methods.
Immersed tunnels are,
• more advantegous as a subaquous solution in soft soils
• increasingly used alternative to traditionally used shield tunnelling, without having the risks associated with pressure chambers and inrush of water.
• An aspect of more recent concern affecting construction is the possible presence of contaminated soils that must be removed for the tunnel trench. Ways of removing these soils and transporting them to depositories that are especially equipped to receive them are environmental problems requiring novel techniques and quality control procedures.
• Maintenance dredging.
The dredging volume is generally in the order of l million m3 per km for a typical four-lane motorway tunnel.
The excavation must provide space for the prefabricated tunnel body; the sand or gravel foundation under the body as wells as the protective backfill on the sides and on the top of the tunnel.
• The more traditional environmental aspects are those encountered on any construction job: noise, dirt, and traffic hindrance.
• The top of the tunnel should be protected by adequate protective backfill, extending about 30 m on each side of the structure and confined within dykes or bunds. The fill must be protected against erosion by currents with a rock blanket, protective rock dykes or other means.
• also suitable in water deeper than it is possible with the shield method, which essentially is restricted to less than 30 m of water (concerning the maximum air pressure at which workers can safely work).
• Dredging of a casting or launching basin.
• Dredging of test pits in the waterway for evaluation of siltation of tunnel trench.
• Widening of the existing navigation channel in order to provide temporary navigation channels outside the marine working area.