1、 International Telecommunication Union ITU-T L.73TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (04/2008) SERIES L: CONSTRUCTION, INSTALLATION AND PROTECTION OF CABLES AND OTHER ELEMENTS OF OUTSIDE PLANT Methods for inspecting and repairing underground plastic ducts Recommendation ITU-T L.73 Rec. I
2、TU-T L.73 (04/2008) i Recommendation ITU-T L.73 Methods for inspecting and repairing underground plastic ducts Summary After a conduit is installed in a trench and has been backfilled, but before any surface construction begins, it is common practice to check duct quality because certain plastic con
3、duits can become oval-shaped, pierced or broken. Recommendation ITU-T L.73 describes inspection methods such as the use of test mandrels and closed-circuit television (CCTV) systems to check duct quality, and also describes various methods that are utilized to repair underground conduits. Repairing
4、methods without digging, called “trenchless techniques“ are introduced, and traditional repairing methods (dig and replace) is also presented. Additionally, guidelines for selecting appropriate repairing methods are proposed. It is expected that this Recommendation will provide alternative solutions
5、 for inspection and repair work. Source Recommendation ITU-T L.73 was approved on 6 April 2008 by ITU-T Study Group 6 (2005-2008) under Recommendation ITU-T A.8 procedure. Keywords CCTV, inspection, mandrel, repair, trenchless techniques, underground duct. ii Rec. ITU-T L.73 (04/2008) FOREWORD The I
6、nternational Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical
7、, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in t
8、urn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 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. NO
9、TE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure
10、e.g. interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. 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
11、suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the
12、evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, whi
13、ch may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2009 All rights reserved. No part of this publication m
14、ay be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T L.73 (04/2008) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Definitions 2 4 Abbreviations and acronyms 2 5 Conventions 2 6 Methods for inspecting and repairing underground plastic ducts. 2 6.1 Inspect
15、ion methods for underground ducts 2 6.2 Repairing methods for underground ducts . 4 Appendix I Korean experience . 9 I.1 Inspection methods. 9 I.2 Repairing methods 12 Bibliography. 13 iv Rec. ITU-T L.73 (04/2008) Introduction Placing cables in conduits is preferred because it has a principle advant
16、age that the cable placement operation is separated in time from the actual conduit construction phase. The protection of the cable with the passage of time and the possibility of repeated access, cable removal and delayed cable installation make the method of placing cables in ducts more attractive
17、. The method, however, has a disadvantage in that the initial cost of conduit construction is expensive. It is noted that underground ducts are prone to being deformed by the burden of earth pressure, which makes it necessary to check the ducts before cable installation, and to repair defective duct
18、s before placing cables in conduits. Rec. ITU-T L.73 (04/2008) 1 Recommendation ITU-T L.73 Methods for inspecting and repairing underground plastic ducts 1 Scope This Recommendation: makes a classification of different methods for inspecting and repairing underground ducts; describes both trenchless
19、 methods and conventional methods; is limited to the methods for underground ducts in which no cables are installed; focuses on methods for underground ducts that have single-way duct unit systems and are made of plastic materials such as polyvinyl chloride (PVC) and polyethylene (PE); deals with pi
20、pes having diameters ranging from 90 to 110 mm. 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, the editions indicated were valid. All Recommendat
21、ions 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 currently valid ITU-T Recommendations is regularly publi
22、shed. 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 Recommendation ITU-T L.1 (1988), Construction, installation and protection of telecommunication cables in public networks. ITU-T L.11 Recommendation ITU
23、-T L.11 (1988), Joint use of tunnels by pipelines and telecommunication cables, and the standardization of underground duct plans. ITU-T L.35 Recommendation ITU-T L.35 (1998), Installation of optical fibre cables in the access network. ITU-T L.38 Recommendation ITU-T L.38 (1999), Use of trenchless t
24、echniques for the construction of underground infrastructures for telecommunication cable installation. ITU-T L.39 Recommendation ITU-T L.39 (2000), Investigation of the soil before using trenchless techniques. ITU-T L.40 Recommendation ITU-T L.40 (2000), Optical fibre outside plant maintenance supp
25、ort, monitoring and testing system. ITU-T L.46 Recommendation ITU-T L.46 (2000), Protection of telecommunication cables and plant from biological attack. ITU-T L.48 Recommendation ITU-T L.48 (2003), Mini-trench installation technique. ITU-T L.63 Recommendation ITU-T L.63 (2004), Safety procedures fo
26、r outdoor installations. 2 Rec. ITU-T L.73 (04/2008) 3 Definitions This Recommendation defines the following term: 3.1 trenchless technology: Technology of installing, repairing or renewing underground ducts using methods that minimize or eliminate the need for excavation. The use of such techniques
27、 can reduce environmental impact, social costs and at the same time provide economic alternatives to traditional open-cut methods of installation, renewal or repair. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: CCTV Closed Circuit Television LVDT Li
28、near Variable Differential Transformer PE Polyethylene PVC Polyvinyl Chloride 5 Conventions None. 6 Methods for inspecting and repairing underground plastic ducts 6.1 Inspection methods for underground ducts 6.1.1 Classification of defects Some defects that may occur in plastic ducts are given in Ta
29、ble 1. Table 1 Classification of defects Defects Causes Crack or fracture Excessive pressure. Insufficient duct strength. Duct failure Ground settlement. Excessive loads. Pointed deformation Sharp shaped crushed stone. Oval shaped deformation Excessive pressure. Insufficient duct strength. Dynamic c
30、ompacting loads during construction. Soil intrusion Disconnection of ducts. Offset Faulty construction. Ground settlement. Rec. ITU-T L.73 (04/2008) 3 6.1.2 Inspection methods 6.1.2.1 Conventional method After the trench has been backfilled, but before any surface construction begins, certain plasti
31、c conduits can become oval-shaped, pierced or broken. Accordingly, it is necessary to check for duct deflection before any cable installation. Each duct should allow the passage of a test mandrel consisting of a rod carrying a solid disc. The test mandrel is sized to be smaller than the inside diame
32、ter of the duct so that some deflection of the ducts is allowable. The test mandrel can be attached to a pneumatic duct cleaner as shown in Figure 1a. It is possible to perform this operation by simply blowing it inside the duct; it will reach the other end of the duct if no restrictions or obstruct
33、ions are present. Ducts may also be examined by test mandrels as shown in Figure 1b. A test mandrel is pulled through the duct by means of a rope or cable. If the mandrel can be pulled through the tested section, then the section is considered acceptable. If deformations are present and the mandrel
34、gets stuck, the blocked area of conduit can be repaired. The mandrel, however, would have difficulties in checking multiple defective parts if it became stuck as a result of the first defect and could not continue its passage through the duct. In this case, the mandrel is pulled out, and the test is
35、 repeated using a smaller one. If the mandrel cannot be pulled through the entire length of the duct, there are several possible reasons. Firstly, the duct may have deflected beyond what the mandrel will tolerate. Secondly, the mandrel may have become caught in the sleeve due to a tight radius. Thir
36、dly, debris may be blocking the path of the mandrel. It is recommended that the cause of the mandrel blockage be ascertained using a closed circuit television (CCTV) system. Figure 1 Test mandrels with duct cleaner 6.1.2.2 CCTV method As an alternative, a more precise inspection can be performed usi
37、ng a CCTV system with a semi-rigid cable which allows the camera to be pushed through the duct from an access point. The quality of the duct can be assessed by viewing the image continuously. It should be noted that duct inspection using only CCTV cameras is inherently subjective by nature and there
38、fore of limited value. To accurately measure features within a duct and to provide an objective assessment, an innovative technology has been developed recently. Laser profiling technology can provide precise 4 Rec. ITU-T L.73 (04/2008) measurements of duct parameters such as “ovality“, unobstructed
39、 cross-sectional area, and duct deformations. 6.1.2.3 Other methods CCTV systems, however, may not always provide a clear image, for example when the duct contains dirty water. When it is not possible to measure the internal condition accurately and to detect defects reliably with a standard CCTV ca
40、mera, other methods may be required to measure the inside diameter and profile of the duct. 6.2 Repairing methods for underground ducts 6.2.1 Selection of repairing methods Until now, many methods used to repair and/or rehabilitate essential services such as telecommunication, electricity, water mai
41、ns, sewer and gas lines have been developed worldwide. A classification of repair methods is given in Table 2 and brief descriptions of each technique follow. Table 2 Duct repair methods Test Duct rod (Note 1) Mandrel Inspection by CCTV (Note 2) Potential repairing methods The whole length of duct i
42、s clean and does not have any defects. No need to repair Can pass the whole length without any difficulties Debris or sludge that may block test mandrel is observed inside a duct. High pressure water jetting Can pass the whole length without any difficulties Cannot pass the whole length without any
43、difficulties If defective parts such as cracks, duct failure, oval-shaped deformation, and offset are observed, it is considered that the defective parts are not severe and are limited to a small extent. Conventional methods (dig and replace). Methods for removing irregularities or enlarging a duct:
44、 re-rounder method; robotic repair system. Cannot pass the whole length without any difficulties If the CCTV camera cannot pass because of blockage or obstruction, it is considered that the defects are severe and affect a large section of the duct. Conventional method (dig and replace method). Pipe
45、bursting and/or splitting method. NOTE 1 A duct rod is a tool that is used to manually insert pulling lines through the duct. NOTE 2 Inspection by CCTV is applied only when the mandrel cannot pass due to defects in the duct. Rec. ITU-T L.73 (04/2008) 5 6.2.2 Conventional method The conventional repa
46、ir methods are “open-cut“ or “dig-and-replace“. These methods involve direct replacement of the defective section with a new duct in the open-cut trenches as shown in Figure 2. Repair procedures that are usually used are as follows: Remove a sufficient amount of backfill material to completely expos
47、e the damaged duct, and also provide adequate working space in the trench. Cut out the damaged portions of the ducts (step 1). Cut the replacement section from a piece of duct with the same outside diameter and wall thickness. Thoroughly clean the exposed ends of the fixed duct and both ends of the
48、replacement section. Slide the repair (or sleeve-type) couplings over the ends of the fixed duct (step 2). Mark lines around the ends of the replacement section, one half the length of the repair coupling away from the ends, in order to centre the repair couplings. Apply adhesive on both ends of the
49、 replacement section and on the exposed ends of the fixed duct (step 3). Place the repair section into the duct line and centre the repair couplings over the joints to the lines marked on the replacement section. Rotate the couplings approximately one-quarter turn to distribute the adhesive (step 4). Cut ends squareDamaged sectionRepair couplingsa) Step 1 b) Step 2Replacement sectionApply adhesivec) Step 3 d) Step 4Figure 2 Conventional duct repairing method Although conventional methods are simple and reliable, they involve social
