1、 International Telecommunication Union ITU-T L.83TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (07/2010) SERIES L: CONSTRUCTION, INSTALLATION AND PROTECTION OF CABLES AND OTHER ELEMENTS OF OUTSIDE PLANT Low impact trenching technique for FTTx networks Recommendation ITU-T L.83 Rec. ITU-T L.83 (07/
2、2010) i Recommendation ITU-T L.83 Low impact trenching technique for FTTx networks Summary With the miniaturization of the telecommunication infrastructure, i.e., with mini-ducts and mini-cables, it has been possible to use a low impact trenching technique to carry out all the steps of the network c
3、onstruction in one single day, in a less invasive way in terms of time and space, and with a smaller construction site than for the previous trenching technologies. Recommendation ITU-T L.83 describes this trenching technique, which allows the easy installation, in narrow trenches, of underground op
4、tical cables and mini-cables in ducts or mini-ducts or directly buried. This type of narrow trench allows the use of reduced dimension machinery in small sized roads, typically those in cities, producing a lower quantity of waste material and so should be used in urban areas. This technology is main
5、ly characterized by the simultaneous work of a suction machine and a trench saw, which allows for the possibility of opening and closing the work site the same day. History Edition Recommendation Approval Study Group 1.0 ITU-T L.83 2010-07-29 15 Keywords Environmental low-impact, FTTx network, reduc
6、tion, urban trenching technique. ii Rec. ITU-T L.83 (07/2010) FOREWORD The International 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
7、-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 basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four y
8、ears, 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 Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the ne
9、cessary 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 and a recognized operating agency. Compliance with this Recommendation is voluntary. Howe
10、ver, 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 met. The words “shall“ or some other obligatory language such as “must“ and the negative
11、 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 possibility that the practice or implementation of this Recommendation may involve the use o
12、f 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 Recommendation development process. As of the date of approval of this Recommendation, I
13、TU 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 information and are therefore strongly urged to consult the TSB patent database at http:/www.i
14、tu.int/ITU-T/ipr/. ITU 2010 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T L.83 (07/2010) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Definitions 1 3.1 Terms defined in this Recommendation . 1 4 A
15、bbreviations and acronyms 1 5 Conventions 1 6 The urban trenching cable-laying technique . 2 6.1 Preparatory step 2 6.2 Excavation requirements 3 6.3 Working phases for laying the infrastructure or cables 3 6.4 Identification . 4 6.5 Resurfacing . 4 6.6 Maintenance . 4 7 Daily urban trenching method
16、s and procedures . 5 8 Daily urban trenching application criteria 5 8.1 Entry to existing manholes or chambers 5 8.2 Road crossings 5 Appendix I Italian experience regarding “one day“ reduced mini trench . 6 Bibliography. 9 Rec. ITU-T L.83 (07/2010) 1 Recommendation ITU-T L.83 Low impact trenching t
17、echnique for FTTx networks 1 Scope This Recommendation: gives advice on general requirements of the main phases in which the work can be divided; gives advice on the methods and procedures for performing the work; gives some application criteria; describes situations where a low impact urban trenchi
18、ng technique is recommended. 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 Recommendations and other refe
19、rences 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 published. The reference
20、 to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T L.39 Recommendation ITU-T L.39 (2000), Investigation of the soil before using trenchless techniques. ITU-T L.48 Recommendation ITU-T L.48 (2003), Mini-trench installation tech
21、nique. ITU-T L.84 Recommendation ITU-T L.84 (2010), Fast mapping of underground networks. 3 Definitions 3.1 Terms defined in this Recommendation This Recommendation defines the following term: 3.1.1 urban trenching technique: It is characterized by a width of maximum 5 cm and typically a depth of ma
22、ximum 30 cm. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: FTTx Fiber To The x, where x stands for the final location on the end-user side GPR3D Ground Penetration Radar 3 Dimensions NGN Next Generation Network 5 Conventions None. 2 Rec. ITU-T L.83 (
23、07/2010) 6 The urban trenching cable-laying technique The urban trenching technique should be applied especially in urban areas, where car traffic and shop presence is very high and on routes that generally involve asphalted surfaces such as roads and sidewalks with a base of compact material (aspha
24、lt or concrete). It is not recommended that the technique be used on routes where the soil subgrade is sandy, gravelly or contains medium-sized cobbles (i.e., measuring 10 to 20 cm in diameter). The main advantages of this technique over traditional cable-laying technologies are the very small obstr
25、uction of the road and the low impact on traffic condition due to the road yard cleaning, the immediate removal of debris and the quickness of opening and closing of the road yard. The urban trenching technique is normally carried out by simultaneously cutting through the paving and digging a trench
26、 whose depth and cross-section vary in accordance with the number of ducts to be laid: depth is 30 cm, while cross-section can be 5 cm. In order to guarantee a protection against impact resulting from road-repairing, the depth of the laid infrastructure should be maintained constant at a known level
27、 that should be 5 cm deeper than the foreseen asphalt cutting depth normally specified for road surface repair works. Figure 1 shows some possible duct and mini-duct installation configurations that can be used. Figure 1 Examples of urban-trenching duct installation configuration Any crossings throu
28、gh unpaved sections (which should in any case have a compact subgrade) should be carried out using the same technique. 6.1 Preparatory step Generally, a detailed survey of the route should be carried out, the purpose of which is to identify the work required to be done before starting cable installa
29、tion operations. Such work could include, for instance, the preparation at bridges, or at road or rail crossings. Further, it is necessary to determine closure locations and section ends. The location of all underground utilities should be determined in order to establish the correct route for the t
30、rench. This is normally accomplished by means of cartographic documentation provided by the administrations that own the road or by the utility company, and/or through instrumented field surveys. The detailed utilities investigation should be made with the GPR3D fast solution technique ITU-T L.84. T
31、he designed route should be free from sharp changes in direction. Where such changes are unavoidable, they should be made by means of cuts angled so as to comply with the minimum bend radii specified for the ducts and cables. Where necessary, the contractor can take core samples along the planned ro
32、ute to determine the type of subsoil or as a further method of checking for obstacles. A GPR3D fast solution should be used in order to detect ground characteristics ITU-T L.84. Rec. ITU-T L.83 (07/2010) 3 6.2 Excavation requirements The following requirements should be observed in cutting while app
33、lying the urban trenching technique: comply with all provisions and regulations established by the administrations involved as regards excavation permits, schedules, etc; place the barriers and road signs required by current legislation, regulations and the administrations involved, in clearly visib
34、le locations around the excavation site. Generally, the site is opened and closed during the same day, so the excavation should not remain open during the night. 6.3 Working phases for laying the infrastructure or cables All the construction activities should be split in separate operational steps i
35、nvolving subsequent phases (Figure 2). This synergism should allow: flexible use of smaller machines; reductions of time and space occupancy. L.83(10)_F02Backfilling Pipes laying Suction TrenchingFigure 2 Daily reduced trenching technique logical scheme 6.3.1 Simultaneous trenching dig phase and cle
36、aning phase It is recommended that the urban trenching technique be characterized by the simultaneous work of the trench saw and the suction machine. This combined action should allow the waste material to be collected while produced by the saw, leaving the site clean immediately after the end of th
37、e trenching phase and completely removing dust problems. 6.3.1.1 Trenching dig phase The urban trench should be made using a small size saw disk, mounted on small dimension operating machines. The trenching cut should not damage the urban road pavement near the dig section. The saw should be inside
38、a protective carter connected via a flexible tube to a vacuum pump installed on the suction machine. 6.3.1.2 Spoil suction phase The debris suction and the digging phase should be performed simultaneously in order to accelerate the trench cleaning action. Spoil should be transported to authorized di
39、sposal sites in accordance with current local laws. The trench cleaning shall be made with automated methods in order to avoid or limit troubles to people and environmental pollution. At the end of this phase, the trench cross-section should be completely free of stones and the bottom of the trench
40、should be clean. The trench and the near zones should be completely clean of debris that could reduce the backfilling material features. 4 Rec. ITU-T L.83 (07/2010) 6.3.2 Ducts or cable laying The reel can be mounted aboard a machine subsequent to the saw, so that the duct(s) or cable can be automat
41、ically fed into the trench, via a suitably shaped guide integrated into the ploughshare, as the excavation proceeds. The equipment and procedures used for this purpose should guarantee that: initial duct or cable configuration and position in the urban trenching technique are maintained along the en
42、tire route unless special circumstances dictate otherwise; if obstacles or situations are encountered which make it impossible to proceed with the urban trenching technique, the reel (and thus the ducts or the cable) can be removed from the machine without having to cut the ducts, thus ensuring that
43、 cable deployment can be continued using conventional methods without performing splices that are unnecessary from the technical standpoint. 6.3.3 Backfilling phase After the ducts, mini-ducts or cables are installed, the trench should be backfilled with a highly resistant and fast-hardening materia
44、l. The trench backfilling shall be made with rapid cement mortar casting. The mortar should be quick setting, with fluid consistency, containing cement with high strength, selected aggregate and special additives. Bitumen material shall be avoided. The backfilling material should have particular fea
45、tures in order to assure vehicle traffic restoration within two to four hours and it shall present high compatibility with mechanical and visual characteristics of existing pavement surface. 6.3.3.1 Mortar features The cement mortar should have the following features: high compressive strength ( 50
46、N/mm2), better than jet concrete (30 N/mm2) and similar to precast concrete, in order to protect the infrastructure below; slip resistance similar to that of asphalt (60) EN 1340; it should undergo controlled shrinkage in order to adhere to trench walls in a good way (“silos“ effect); intrinsic flui
47、dity of the material in order to fill completely the trench; high resistance to thermal variation, above all to frost and thaw cycles; easily removable, in case of pavement resurfacing, without causing damage to the infrastructure. 6.4 Identification The urban trenching technique should not need any
48、 kind of identification, because the backfilling material laying is just an identification element for the new infrastructure. 6.5 Resurfacing The urban trenching technique should not need pavement resurfacing. That should be achieved with backfilling material, both on the road and on the sidewalk.
49、At the end of the activity there should not be cracks, steps or smear. The new pavement colour should be similar to the current one. 6.6 Maintenance The maintenance of buried cables and ducts should be performed with the same techniques and tools as for normally buried infrastructures because the backfilling concrete mortar should be easily removable. Rec. ITU-T L.83 (07/2010) 5 7 Daily urban trenching methods and procedures The debris suction phase and the cutting phase should be executed at the same time. All phases descri
