1、 International Telecommunication Union ITU-T L.74TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (04/2008) SERIES L: CONSTRUCTION, INSTALLATION AND PROTECTION OF CABLES AND OTHER ELEMENTS OF OUTSIDE PLANT Maintenance of cable tunnels ITU-T Recommendation L.74 ITU-T Rec. L.74 (04/2008) i ITU-T Recomm
2、endation L.74 Maintenance of cable tunnels Summary Concrete structures such as buildings, bridges, roads, dams and tunnels are deteriorating. Cable tunnels are also deteriorating. For example, cracks and water leakages occur and these phenomena degrade the safety and serviceability of a cable tunnel
3、. If the deterioration is neglected, large-scale repair and reinforcement measures will probably be required, which will further increase the cost in the future. Therefore, it is highly recommended that periodic inspection and timely maintenance be performed. Safety plans related to the maintenance
4、of cable tunnels are discussed briefly in ITU-T Recommendation L.11. A model of a safety plan in the operational phase is presented in Tables A.1 and A.2 of ITU-T Recommendation L.11, with an indication of possible preventive measures. These tables, however, do not describe defects that may occur fr
5、equently in reinforced concrete structures such as cable tunnels, and the inspection procedures for maintenance. Therefore, recommendations concerning the maintenance of cable tunnels are needed. Source ITU-T Recommendation L.74 was approved on 6 April 2008 by ITU-T Study Group 6 (2005-2008) under t
6、he ITU-T Recommendation A.8 procedure. Keywords Crack, deterioration, inspection, non-destructive testing, water leakage. ii ITU-T Rec. L.74 (04/2008) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and
7、 communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide bas
8、is. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resol
9、ution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration
10、and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g. interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are m
11、et. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possi
12、bility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the R
13、ecommendation development process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest informa
14、tion and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2008 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. L.74 (04/2008) iii CONTENTS Page 1 S
15、cope 1 2 References. 1 3 Definitions 1 4 Abbreviations and acronyms 2 5 Conventions 2 6 Maintenance of cable tunnels . 2 6.1 Inspection . 3 6.2 Inspection technologies 3 6.3 Countermeasures 6 Appendix I Korean experience with maintenance of cable tunnels 7 I.1 Typical deteriorations. 7 I.2 Frequency
16、 of inspection . 7 I.3 Typical inspection items. 8 I.4 Tunnel inspection by GPR 10 Bibliography. 12 ITU-T Rec. L.74 (04/2008) 1 ITU-T Recommendation L.74 Maintenance of cable tunnels 1 Scope This Recommendation: describes the inspection and its frequency; describes the typical types of deterioration
17、 according to the cable tunnel type; describes the typical inspection methods and countermeasures. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication,
18、 the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the curre
19、ntly valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T L.1 ITU-T Recommendation L.1 (1988), Construction, installation and protection of telecommunication cable
20、s in public networks. ITU-T L.11 ITU-T Recommendation L.11 (1988), Joint use of tunnels by pipelines and telecommunication cables, and the standardization of underground duct plans. ITU-T L.38 ITU-T Recommendation L.38 (1999), Use of trenchless techniques for the construction of underground infrastr
21、uctures for telecommunication cable installation. ITU-T L.39 ITU-T Recommendation L.39 (2000), Investigation of the soil before using trenchless techniques. ITU-T L.40 ITU-T Recommendation L.40 (2000), Optical fibre outside plant maintenance support, monitoring and testing system. ITU-T L.46 ITU-T R
22、ecommendation L.46 (2000), Protection of telecommunication cables and plant from biological attack. ITU-T L.48 ITU-T Recommendation L.48 (2003), Mini-trench installation technique. ITU-T L.63 ITU-T Recommendation L.63 (2004), Safety procedures for outdoor installations. 3 Definitions This Recommenda
23、tion defines the following terms: 3.1 deterioration: Deterioration is any adverse change of normal mechanical, physical and chemical properties either on the surface or in the whole body of concrete, generally through separation of its components. Carbonation: Carbonation of concrete by attack from
24、atmospheric carbon dioxide will result in a reduction in alkalinity of the concrete, and increase the risk of reinforcement corrosion. Corrosion: Disintegration or deterioration of concrete or reinforcement by electrolysis or by chemical attack. 2 ITU-T Rec. L.74 (04/2008) Crack: An incomplete separ
25、ation into one or more parts with or without space in-between. Cracks will be classified by direction, width and depth. The following adjectives can be used: longitudinal, transverse, vertical, diagonal and random. Disintegration: Deterioration into small fragments or particles due to any cause. Dis
26、tortion: Any abnormal deformation of concrete from its original shape. Efflorescence: A deposit of salts, usually white, formed on a surface, the substance having emerged from below the surface. Erosion: Deterioration brought about by the abrasive action of fluids or solids in motion. Honeycomb: Voi
27、ds left in concrete due to failure of the mortar to effectively fill the spaces among coarse aggregate particles. Peeling: A process in which thin flakes of mortar are broken away from a concrete surface; such as by deterioration or by adherence of surface mortar to forms as they are removed. Pittin
28、g: Development of relatively small cavities in a surface, due to phenomena such as corrosion or cavitation, or in concrete, localized disintegration. Popout: The breaking away of small portions of a concrete surface due to internal pressure which leaves a shallow, typically conical, depression. Scal
29、ing: Local flaking or peeling away of the near surface portion of concrete or mortar. Spall: A fragment, usually in the shape of a flake, detached from a larger mass by a blow, by the action of weather, by pressure, or by expansion within the large mass. 3.2 inspection: Inspection means an examinati
30、on of the soundness of a tunnel based on a comparison of the investigation, observation and measurement results according to the judgement standards. The tunnel inspection is conducted in order to grasp whether or not deformation has an influence on structural safety and durability, and then to take
31、 appropriate countermeasures to secure the function of the tunnels based on the evaluation results. 3.3 non-destructive testing (NDT): Non-destructive testing is also called non-destructive evaluation (NDE) and non-destructive inspection (NDI). This method does not destroy the test object. To detect
32、 different defects such as cracking and corrosion, there are different methods of testing available, such as the ultrasonic pulse velocity method and stress wave propagation method. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations: GPR Ground Penetrating Radar NDE No
33、n-Destructive Evaluation NDI Non-Destructive Inspection NDT Non-Destructive Testing 5 Conventions None. 6 Maintenance of cable tunnels Like other public infrastructures such as bridges, roads and buildings, cable tunnels also have trouble caused by cracks or water leakage as a result of deterioratio
34、n of steel-reinforced concrete or reinforcing steel. It is found that typical deteriorations that may happen in cable tunnels are cracks, water leakage and the corrosion of reinforcing steel. If such deteriorations are left unrepaired, additional large-scale repair and reinforcement projects will pr
35、obably be required, which will ITU-T Rec. L.74 (04/2008) 3 further increase cost in the future. The purpose of maintenance is to detect the defects in cable tunnels at an early stage and to take appropriate actions in order to enhance its durability and serviceability. 6.1 Inspection Notwithstanding
36、 how well a cable tunnel is constructed, it will require preventive maintenance to preserve its integrity and to prolong its life. Maintenance will necessarily require inspection and testing to determine the condition of the structures and to establish appropriate repair and maintenance measures. Th
37、e inspection of cable tunnels is performed to detect damage or defects that are detrimental to the structural safety and durability. When crucial damage or defects are observed, they are evaluated by skilled experienced engineers, and then appropriate and prompt countermeasures, such as repair and r
38、einforcement work, are taken. Inspections can be divided into regular and detailed inspections as follows. 6.1.1 Regular inspections Regular inspections, also called routine inspections are usually performed visually to check the degradation status of the concrete surface such as cracks, water leaks
39、, or exposed reinforced steel. At this stage, deformation is detected, and is evaluated to judge whether or not detailed inspections and/or temporary countermeasures are needed. It is recommended that there are established procedures for the manager of the cable tunnel to schedule/undertake regular
40、inspections. These inspections are mainly done by observing the surface of the cable tunnel by visual inspection, and measuring crack width with a crack gauge. The inspection is carried out using comprehensive identification sheets on which observations and measurements can be conveniently recorded.
41、 6.1.2 Detailed inspections Detailed inspections are carried out when the defects and deformations are critical to the safety of the cable tunnel. These inspections are also carried out when there is degradation that cannot be identified by visual inspection or when the cause of degradation must be
42、clarified to judge whether countermeasures are needed and to select the optimum method. At this stage, a detailed investigation of the measurements and deformation detected in the regular inspection are conducted by a specialist. These inspections use destructive testing of a concrete sample and che
43、mical analysis of a core sample to determine the degree of degradation. In addition, non-destructive testing methods can be used to determine abnormalities, defects and voids. 6.1.3 Frequency of inspection It is recommended that the frequency of inspection be determined by the type and the current s
44、tate of cable tunnel concerned, and the changes in the operating environment. 6.2 Inspection technologies 6.2.1 Typical inspection items Items used for inspection differ depending upon the type of cable tunnel. Cable tunnels are generally divided into two types as follows: Rectangular cross-section
45、(box type); Circular cross-section. 4 ITU-T Rec. L.74 (04/2008) A rectangular cross-section cable tunnel is constructed by a cut and cover method, and is made of reinforced steel concrete. On the other hand, a circular cross-section cable tunnel is constructed by methods such as shield driving, bori
46、ng, drilling and blasting, and jacked tunnelling. The cross-sections of these two types of cable tunnels are shown in Figure 1. Reinforced concreteLining concretea) b) Figure 1 Typical types of cable tunnel: a) rectangular or box type; and b) circular type Since the designs and construction procedur
47、es of these cable tunnels are different from each other, the deteriorations occur differently. Typical inspection items are summarized in Table 1. Table 1 Typical inspection items Regular inspection Detailed inspection Rectangular cross-section cable tunnel Cracks; Water leakage; Exposed steel. Incl
48、ude regular inspection items; Compressive strength of concrete; Corrosion of reinforcing steel; Carbonation depth, etc. Circular cross-section cable tunnel Cracks in lining surface; Water leakage; Contamination of lining concrete; Spall of lining concrete. Include regular inspection items; Deformati
49、on of lining; Heaving of tunnel bottom; Settlement of tunnel bottom; Cavities inside lining concrete; Voids behind lining. 6.2.2 Inspection technologies Inspection methods mainly consist of visual inspection and non-destructive testing methods. When a defect is found during visual inspection, its cause is then established and its size and condition are investigated in detail. Since the crack is one of the most important inspection items, it is recommended to measure the crack width and depth using a crack gauge, and to check whet
