沉管隧道介绍英文.pptx

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1、第1页/共44页Immersed tunnels are,more advantegous as a subaquous solution in soft soilsincreasingly used alternative to traditionally used shield tunnelling,without having the risks associated with pressure chambers and inrush of water.also suitable in water deeper than it is possible with the shield me

2、thod,which essentially is restricted to less than 30 m of water(concerning the maximum air pressure at which workers can safely work).Advantegous as there is less loss in height than with tunnelling deeply under the riverbed,and the tunnel may therefore be shorter overall.第2页/共44页The worlds longest

3、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.The fir

4、st tunnel of the concrete type was constructed in 1940 in Rotterdam under the Maas estuary.第3页/共44页The most profound effect of an immersed tunnel on the environment concerns the element it is meant to bypasswater.The influence of the tunnel on the groundwater and the surface water in the area plays

5、a predominant role in the tunnel design and construction methods.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 eq

6、uipped to receive them are environmental problems requiring novel techniques and quality control procedures.The more traditional environmental aspects are those encountered on any construction job:noise,dirt,and traffic hindrance.第4页/共44页The top of the tunnel should be protected by adequate protecti

7、ve 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.Tides and current effects of the waterway must be evaluated to determine conditions during

8、 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.Governmental agencies having jurisdiction over environmental protection,natural resources or lo

9、cal conditions must be consulted and approval of authorities should be obtained in the preliminary design stage.第5页/共44页FoundationThe 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 dynam

10、ic loadings,and earthquake loadings in particular.Pile foundations are an option but this solution has been used for a few tunnels only.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 detrime

11、ntal 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 e

12、lements.Construction of a durable foundation for the tunnel.第6页/共44页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:A trench is dredged in the bed of the water channel.第7页/共44页Tunnel Tr

13、ench DredgingThe dredging works required for the construction of an immersed tunnel will normally comprise some,or all,of the following items: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 navigatio

14、n channel in order to provide temporary navigation channels outside the marine working area.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.D

15、redging of the tunnel trench for the immersed tunnel section.Dredging of an access channel between the casting/launching basin and the tunnel trench.Maintenance dredging.第8页/共44页The dredging volume is generally in the order of l million m3 per km for a typical four-lane motorway tunnel.The excavatio

16、n 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.Because the top of the backfill has to be kept below the existing or future navigation channel profile,a trench bottom lev

17、el at between 25 and 30 m below Low Water level is quite common.Immersed tunnels in deep or open sea may require specially built dredgers.第9页/共44页Except for cases where very soft subsoil,deemed unsuitable for support of the tunnel,has to be removed and replaced by suitable materials,the general requ

18、irements for the dredging of the trench bottom are:A clean,even surface,as close as possible to the upper acceptable limit in order to avoid the economic consequences of having to fill overdredged areas;A minimum disturbance of the remaining exposed upper soil layers in the trench bottom,in order to

19、 limit the changes in the geotechnical characteristics of the subsoil.The possible physical disturbance and softening of the exposed soil layers in the trench bottom,particularly in cohesive subsoils,can have a considerable influence on the geotechnical behaviour of these soil layers later-and,hence

20、,on the quality of the tunnel support as a whole.This in turn influences the design of the structural tunnel body and,thus,eventually the overall economy.These technical requirements are met by:Using the proper type of dredger(s).Careful controlling the position of the cutting tool,bearing in mind t

21、hat the dredging normally has to be done in tidal waters and sometimes in waters subject to swell and waves.Careful planning the dredging operation in order to avoid undesirable failures of the slopes.Timing of the dredging operation,in order to limit the time that the trench bottom is exposed and,a

22、t the same time,to limit the sedimentation caused by subsequent dredging nearby.第10页/共44页第11页/共44页Construction of Tunnel Elements The tunnel elements are made fully or partially buoyant by means of temporary bulkheads installed at the element ends.In addition to providing proper structural strength

23、and controlling the weight of the element,the main design and construction task of the reinforced concrete tunnel is to provide a watertight structure.For many years,the answer was to wrap the tunnel element in a watertight membrane composed of steel on the bottom,outer walls and even on the roof.Al

24、ternatively,bituminous membrane has been used on the outer walls and roof.In recent years,reinforced concrete tunnels without a membrane at all are being used.Above all,this will require sophisticated control of concrete temperature during hardening to avoid cracking.In order to reduce the developme

25、nt of cracks during hardening,primarily in the walls when they are cast after the bottom slab,cooling of the lower part of the walls has been the practice for many years.Insulation of the formwork and careful sequencing of stripping of the forms are also used to control the concrete temperature.Impr

26、oved field concrete technology aimed at minimising the development of cracks during hardening,combined with moderate prestressing,seems to be the course to follow.第12页/共44页Tunnel elements are constructed in the dry,for example in a casting basin,a fabrication yard,on a ship-lift platform or in a fac

27、tory unit.第13页/共44页Casting Basins The tunnel elements can be prefabricated in a casting basin or in a dry dock.For shorter roadway and railroad tunnels,the elements are normally cast in one batch in a casting basin.A programme for control of concrete density and concrete dimensions is required in or

28、der to control the weight and displacement of the tunnel elements.The typical casting sequence is bottom/walls/roof,but sometimes all at once,in 15-20 m segments.The tunnel elements can be monolithic,or they can be provided with flexible joints between tunnel segments within the elements.The latter

29、arrangement minimises longitudinal bending moments caused by compression of the subsoil in the permanent stage,but is unsuitable for railway tunnels in soft ground and in seismic regions.Normally the tunnel elements will be buoyant and need to be ballasted prior to flooding of the casting basin in o

30、rder to make sure that they remain parked until they are to be brought to the immersion location.This ballasting is normally done with water contained in purpose-built ballast tanks inside the tunnel element.Pumps and associated pipelines allow charging and removal of the ballast.A number of lifting

31、 eyes and bollards must be provided on the element roof.Watertight,temporary bulkheads are installed at the ends of the element,and rubber gaskets are mounted around the periphery of the one end of the tunnel element,while a plane steel plate is provided at the opposite end.Later,when the tunnel ele

32、ment is joined to the previously placed tunnel element,this gasket provides a watertight seal between the two tunnel elements.As the casting basin is flooded or as the tunnel is launched from the dock,the tunnel element is checked for watertightness,the attention being directed principally towards t

33、he temporary bulkheads and pipe let-ins.Recently a system of constructing concrete tubes on floating pontoons is developed.By removing the need for casting basins on the river or canal costs are reduced,and the process is more environmentally friendly.第14页/共44页Cooling of concrete in outer tunnel wal

34、ls 第15页/共44页The ends of the element are then temporarily sealed with bulkheads.Each tunnel element is transported to the tunnel site-usually floating,occasionally on a barge,or assisted by cranes.第16页/共44页Installation of tunnel elements in the trenchFor transportation of the element from the flooded

35、 casting basin or dock to the tunnel trench,conventional towage is normally used.The warping,which ends with the tunnel element being moored for immersion,is normally carried out by the contractors organisation responsible for the subsequent sinking and joining,whereas towing normally is done by exp

36、erienced towage companies.The immersion of the tunnel element is carried out after the tunnel element bas been moored and the element has been ballasted as necessary to provide adequate loads in the immersion tackles.第17页/共44页The tunnel element is lowered to its final place on the bottom of the dred

37、ged trench.第18页/共44页The new element is placed against the previous element under water.Water is then pumped out of the space between the bulkheads.Water pressure on the free end of the new element compresses the rubber seal between the two elements,closing the joint.第19页/共44页Once placed,the elements

38、 are joined;first by bringing rubber gasket at the joint into contact with the steel face of the previously placed tunnel element,and then draining the joint chamber,thereby mobilising the full hydrostatic water pressure on the tunnel cross section remote end.第20页/共44页Backfillmaterial is placed besi

39、de and over the tunnel to fill the trench and permanently bury the tunnel,as illustrated in the figures.第21页/共44页Approach structures can be built on the banks before,after or concurrently with the immersed tunnel,to suit local circumstances.第22页/共44页Immersed tunnels have been in widespread use for a

40、bout 100 years.Over 150 have been constructed all over the world,about 100 of them for road or rail schemes.Others include water supply and electricity cable tunnels.The examples given indicate the diversity of projects that have been realized.第23页/共44页第24页/共44页第25页/共44页第26页/共44页Immersed tunnels do

41、not suit every situation.However,if there is water to cross,they usually present a feasible alternative to bored tunnels at a comparable price,and they offer a number of advantages,such as:Immersed tunnels do not have to be circular in cross section.Almost any cross section can be accommodated,makin

42、g immersed tunnels particularly attractive for wide highways and combined road/rail tunnels.Some examples of realised cross sections are shown below.第27页/共44页Immersed tunnels can be placed immediately beneath a waterway.In contrast,a bored tunnel is usually only stable if its roof is at least its ow

43、n diameter beneath the water.This allows immersed tunnel approaches to be shorter and/or approach gradients to be flatter-an advantage for all tunnels,but especially so for railways.第28页/共44页expensive,such as the soft alluvial deposits characteristic of large river estuaries.They can also be designe

44、d to deal with the forces and movements in earthquake conditions,as in the example illustrated above,to be placed in very soft ground in an area prone to significant earthquake activity.第29页/共44页Bored tunnelling is a continuous process in which any problem in the boring operation threatens delay to

45、the whole project.Immersed tunnelling creates three operations-dredging,tunnel element construction and tunnel installation,which can take place concurrently,thus moderating programme risk considerably.Partly for this reason,an immersed tunnel is generally faster to build than a corresponding bored

46、tunnel.第30页/共44页ARE THERE ANY SPECIAL PROBLEMS?Immersed tunnels are sometimes perceived by newcomers to the technology as difficult due to the presence of marine operations.In reality though,the technique is often less risky than bored tunnelling and construction can be better controlled.The marine

47、operations,though unfamiliar to many,pose no particular difficulties.第31页/共44页The perceived problems include:DREDGINGDredging technology has improved considerably in recent years,and it is now possible to remove a wide variety of material underwater without adverse effects on the environment of the

48、waterway.第32页/共44页INTERFERENCE WITH NAVIGATIONInterference with navigation:On busy waterways,it is sometimes assumed that construction of an immersed tunnel would be impractical as it would interfere with shipping.In fact,such tunnels have been successfully built in some exceptionally busy waterways

49、 without undue problems.第33页/共44页WATERTIGHTNESSIt is often assumed that the process of building a tunnel in water,rather than boring through the ground beneath it will increase the likelihood of leakage.In fact,immersed tunnels are nearly always much drier than bored tunnels,due to the above-ground

50、construction of the elements.Underwater joints depend on robust rubber seals which have proved effective in dozens of tunnels to date.第34页/共44页A NEW DEVELOPMENT:THE SUBMERGED FLOATING TUNNEL Traditional immersed tunnelling results in a tunnel buried beneath the waterway which it traverses.A new deve