1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 , TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU#/.3425#4)/. G0G0).34!,!4)/.G0G0!.$02/4%#4)/.G0G0/(b) that the rules governing this type of ducting vary significantly from country to country;(c) that the importance of the joint use of tunnels increases wit
2、h increasing density of population and shrinkingopen spaces, i.e. in large towns;recommendsthat Administrations, who in the future will be interested in this type of installation, follow the rules describedin this Recommendation.1 General considerationsDuct tunnels and trenches are constructions con
3、taining one or generally more ducts belonging to differentnetworks. Tunnels which can be inspected (inspectable tunnels) include one or more gangways for initial assemblywork and for subsequent control, maintenance and repair operations. A tunnel without standing room, but designed forcrawling shoul
4、d have a clear internal height of at least 0.8 m. Duct gangways may not be entered.The above principles apply to inspectable tunnels, and apply by analogy to tunnels with crawling room only.Tunnels may contain ducts belonging to the following types of networks: collective antennas; telecommunication
5、s; electricity; gas; water; district heating; ducted transport (e.g. pneumatic tubes); drainage water.2 Establishment of a routing plan2.1 StructureTunnel routing must take into account the structure of networks and their levels of priority.The transport ducts of different networks do not generally
6、follow the same itinerary, since neither theproduction units (e.g., power plants, pumping stations or telephone exchanges) nor the transit points from transport toprimary distribution coincide. On the other hand, in densely populated areas, primary and secondary distribution ductsoften do follow the
7、 same itineraries, so that it is advisable to run tunnels under arteries containing primary andsecondary distribution ducts.2.2 Decision criteriaThe following factors should be taken into account when opting between trenches and tunnels:2 Volume IX - Rec. L.112.2.1 Distribution securityA high level
8、of distribution security will depend on the following factors: durability of material and joints; rapid location of damage when if occurs, easy access and minimum repair times; low exposure to outside effects (e.g. damage caused by third parties or by earthquakes).Ducts laid in tunnels generally off
9、er high durability and a low risk of deterioration. They may be repairedrapidly.2.2.2 Third party risk, disturbances due to installation and repair workAccount should be taken of disturbances caused by installation and repair work (rerouting of traffic, noise) andof the possible consequences of dama
10、ges ducts (water and fire damage).2.2.3 Economic considerationsEconomic considerations should include not only the cost of constructing and maintaining tunnels, but also thesavings which will arise in the future from avoiding the secondary effects of buried ducts. By secondary effects aremeant the e
11、ffects produced on local inhabitants, local activities, vehicle traffic and the environment in general by theinstallation, malfunction, repair and maintenance of ducts.2.2.4 Technical considerationsBefore either of the laying methods is chosen, the following factors should be considered: ducts, netw
12、ork, dimension (cross-section), power (capacity), material, protection against corrosion,number, distribution priority, duct routing, compatibility with other ducts, state of ducts, repairs, overhaul,replacement, reserves, extensions, emergency ducts, provisional installations connections to buildin
13、gs; roadway, road width, pavement width, greenery strip, traffic density, surface water drainage,superstructure; subsoil, type of ground, groundwater level, existing ducts, existing underground constructions; schedules, beginning of works, duration of works (stages), start-up.When a tunnel is planne
14、d, special attention should be paid to branch connections with buildings, which may bederived directly from the tunnel if the necessary openings have been provided. An alternative method is to burysecondary distribution ducts alongside the tunnel.3 Recommendations applicable to tunnels3.1 PhasesThe
15、following sequence of phases should be considered: construction phase; operational phase.3.2 General recommendationsIn both the construction and the operational phases, the following requirements should be observed: Introduction of duct components in the tunnelIt should be possible to introduce any
16、components either through normal access points or through specialopenings. Cable pullingCables in tunnels should be placed in appropriate technical containers, in order to facilitate theirinstallation, repositioning or removal. Construction aidsFor construction work, especially in the case of heavy
17、tubing, securing devices should be provided atappropriate locations. Movement of duct components in tunnelThe necessary facilities should be provided for the transport of duct components inside a tunnel.Volume IX - Rec. L.11 3 Reserve facility for network extensionSince networks are likely to be ext
18、ended on the future, appropriate reserve space should be set aside in thetunnel cross-section plan. Clear space around ductsEnough clear space should be allowed between a tunnel wall and ducts, as well as between ducts inproportion to their diameter (to facilite maintenance, repair and branching). A
19、mbient temperatureHigh temperatures may occur in tunnels containing heat-emitting ducts. Care should be taken to maintainphysiologically acceptable environmental conditions in order to avoid any impairment to health duringwork or inspections. For telecommunication cables, see 3.3.2. Corrosion of duc
20、ts, fixtures and equipment accessoriesThe working life of fixtures and equipment accessories should be as long as that of the ducts. High levelsof humidity may produce condensation and cause non-rustproof metals to corrode. The appearance ofcorrosion should be considered in the light of Recommendati
21、on L.1. Metal components (pillars, racks orsupports) should preferably be made of hot galvanized steel. In some cases, cathodic protection may beapplied. VibrationsSome ducts may be sensitive to vibrations. In some cases, vehicle traffic may produce vibrations which arepropagated inside the tunnels.
22、3.3 Comments on distribution networks3.3.1 Collective antennasExtra space has to be provided in places to house amplifying equipment. Apart from that, collective antennacables have no special requirements.3.3.2 Telecommunication cablesThe following requirements should be taken into account: Distance
23、s from power linesMinimum distances from main ducts should be applied (see 5). Protection against thermal loadSince telecommunications cables are vulnerable to thermal load, thermal conditions in tunnels must betaken into account. This applies especially for optical cables. Protection against corros
24、ion and lightningTelecommunication cables should generally be protected by metal sheaths or shields. This protection maybe applied, but the use of joint earth electrodes is either not required or not permissible. Protection against electrical interferenceNormally no special measures need be taken, a
25、lthough cable constructions with a high screening factor orovervoltage relays may be used in some cases. Protection against mechanical forcesMetal shields may be used to protect cables against mechanical effects such as vibrations or impacts. In thecase of lead sheaths, vibration-resistent alloys sh
26、ould be used. Protection against outside effectsPlastic-covered cables may be protected against rodents with fibreglass or aramid-fibre shielding.Contractable cable joints may provide protection against earthquakes. BendsSince cable curvature is limited, layout plans must take account of permitted c
27、urvature radii. Specialized workSince work has to be done relatively frequently on telecommunication installations, particularly on sleeves,sufficient working space should be provided (e.g. alcoves or chambers).4 Volume IX - Rec. L.113.3.3 Power cablesThe following requirements should be taken into
28、account: BendsThe same rules apply, by analogy, as for telecommunication cables. Ambient temperatureThe load capacity of electrical cables depends, among other parameters, on ambient temperature, whichshould be determined in each case to achieve the ideal balance between tunnel cooling and cable loa
29、dcapacity.3.3.4 GasTunnels containing gas ducts should be ventilated (naturally or artificially). Dilation sleeves should beleakproof and located in separate chambers.3.3.5 WaterThe choice of tunnel layout or cross-section should take account of the dimensions of special water ductcomponents. Water
30、ducts may require special precautions against climatic effects to avoid overheating or freezing.Ducts with a nominal diameter of 150 mm may give rise to special problems, in which case the following factorsshould be taken into account: Temperature riseA rise of temperature in a tunnel will have only
31、 a negligible effect on the quality of drinking water. Freezing in ductsThe temperature in inspectable tunnels rarely falls below freezing. Should there be a risk of freezing,appropriate measures should be taken to protect the duct. Bleeding and drainingBleeding and draining facilities should genera
32、lly be located outside tunnels.3.3.6 District heatingThe following requirements should be taken into account: Position of ductsFor assembly purposes, the distance between district heating ducts (not including insulation) and the tunnelwall should not be less than 0.3 m. HeatproofingContinuous therma
33、l insulation will diminish heat losses and help prevent the occurrence of thermal shockin the event of a burst water duct. Junctions and intersectionsPermitted radii of curvature for ducts should be observed at junctions and intersections. Dilation devicesPlans should allow sufficient space for dila
34、tion devices.3.3.7 Water drainageThe following aspects should be considered: GeneralIn most cases pipes will be naturally drained. The means that their level and slope can be adapted to tunnellayouts only within certain limits. Link between drain and tunnelIn view of the risk of backflow, there shou
35、ld be no open link between the drain and the tunnel.Volume IX - Rec. L.11 54 Safety plan4.1 Safety objectivesVarious aspects of safety should be considered: safety of persons working in the tunnel; safety of persons and property outside the tunnel; security of distribution.For the first two items, s
36、afety objectives concern the risk of personal injury.Security of distribution is independent of personal safety. The importance of distribution ducts should not beoverlooked, however, not only because of the convenience they provide to the public in general, but also because theymay constitute in ce
37、rtain circumstances a vital factor of survival.4.2 Safety plan4.2.1 Safety during the construction and installation phaseThe safety plan should comply with existing rules governing safety at work. Special attention should be paid torules concerning construction work in enclosed spaces. In all cases,
38、 the maximum permissible levels of harmfulsubstances or vapours, as defined by insurance companies, should not be exceeded.4.2.2 Safety during the operational phaseThe company owning an installation should be responsible for issuing instructions to be observed from the startof operations.In the even
39、t of maintenance or extension work, the safety measures laid down for the construction phase shouldbe observed.Fire risk and fire-fighting facilities should be established in consultation with the fire brigade.Tables A-1/L.11 and A-2/L.11 show a model of a safety plan in the operational phase, with
40、an indication ofpossible preventive measures.The rules applicable to the construction of a tunnel, as described in 5, should be established in the light of thesafety plan.4.3 Special problems to be consideredA special study of safety aspects should be made, where necessary, with regard to the follow
41、ing points: interference between telecommunication lines and high voltage or d.c. railway lines; tunnel design; ventilation; thermal protection; water drainage; electrical installations; gas or fire detection systems.5 Construction5.1 Transversal cross-section5.1.1 GeneralThe transversal cross-secti
42、on of a tunnel comprises the following elements: ducts and related facilities, including free spaces for repairs and maintenance; reserve spaces; duct intersections and junctions; service gangways.6 Volume IX - Rec. L.115.1.2 Positioning of ductsOver and above assembly requirements, the following ru
43、les should be applied: Telecommunications and antenna cablesThe following spaces should be observed in relation to power lines: low voltage, up to 1000 V: 0.3 m high voltage with low induction: 0.3 m high voltage with high induction: to be determined(rigid earthing systems) Power line ductsWhere cab
44、les are supported by brackets or racks, thermal and electromagnetic interaction should be takeninto account. Natural gas ductsThese should be placed as high as possible in the tunnel. This will protect them against mechanical damageand in the event of a leak, gas will accumulate under the ceiling. W
45、ater ductsThese should be placed as low as possible in the cross-section, for which facilitates installation andanchoring. A further factor is that ambient temperature tends to be lower on the tunnel floor.5.1.3 Service gangwayIn order to facilitate free and safe transit through the tunnel, no steps
46、 should be placed across the servicegangway.Gangway dimensions should be subject to the following rules: minimum width: 0.7 m minimum height: 1.9 m dimension of the largest element to be introduced in the gangway, plus at least 0.2 m. dimensions to be increased according to circumstances, particular
47、ly at bends, intersections and workingalcoves.5.1.4 Transversal slopeA transversal slope should be provided for water drainage.5.1.5 Examples of tunnel profilesFigures B-1/L.11 and B-2/L.11 represent circular and rectangular tunnel cross-sections respectively. They showhow the available space can be
48、 divided among the different networks.5.2 Openings, access and partitions5.2.1 Openings for equipmentOpenings large enough should be provided to introduce the largest pieces of equipment during assembly andmaintenance work in the tunnel. The openings should be located directly above the service gang
49、way. Further openingsmay be provided during construction, but these should be sealed off before operations begin. Access should beprovided for delivery vehicles.5.2.2 Access doors for staffStaff access points should be located in accordance with escapeways and alarms. Generally speaking, thedistance between two access points should not exceed 500 m. The possibility of introducing emergency exits betweenaccess doors should be considered.Access doors should be arranged so that they cannot be obstructed nor allow water
