1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T L.48TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (03/2003) SERIES L: CONSTRUCTION, INSTALLATION AND PROTECTION OF CABLES AND OTHER ELEMENTS OF UTSIDE PLANT Mini-trench installation technique ITU-T Recommendation L.48 ITU-T Rec. L.48 (03/2003) i ITU-T R
2、ecommendation L.48 Mini-trench installation technique Summary This Recommendation describes the so-called mini-trenching technique, that allows the installation in small trenches of underground optical cables in ducts or directly buried copper cables. The advantages of this technique over convention
3、al cable laying technologies lie essentially in its speed of execution, lower cost, significantly lower environmental impact and limited disruption to road traffic and, as a consequence of the previous items, easiness in obtaining permits for the taking over of public area. Source ITU-T Recommendati
4、on L.48 was prepared by ITU-T Study Group 6 (2001-2004) and approved under the WTSA Resolution 1 procedure on 29 March 2003. ii ITU-T Rec. L.48 (03/2003) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Tele
5、communication 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 basis. The World Telecommunication Standardization
6、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 Resolution 1. In some areas of information technology
7、 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 and a recognized operating agency. INTELLECTUAL
8、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 evidence, validity or applicability of claimed Intellectual Property Rights, whether as
9、serted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned th
10、at this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. ITU 2003 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.48 (03/2003) iii CONTE
11、NTS Page 1 Scope 1 2 The mini-trenching cable-laying technique 1 2.1 Preparatory steps 2 2.2 Excavation requirements 3 2.3 Mini-trench cleaning 3 2.4 Laying of the infrastructure or cables. 3 2.5 Pull cord and plugs . 4 2.6 Backfilling 4 2.7 Mechanical protection 5 2.8 Identification. 5 2.9 Resurfac
12、ing. 5 2.10 Maintenance of cable or duct after laying 6 3 Mini-trenching methods and procedures 6 3.1 Manual procedure. 6 3.2 Partially automated procedures 6 3.3 Fully automated procedures . 7 4 Mini-trenching application criteria. 7 4.1 Entry to existing manholes or chambers 7 4.2 Road crossings 7
13、 ITU-T Rec. L.48 (03/2003) 1 ITU-T Recommendation L.48 Mini-trench installation technique 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 works; gives some application
14、 criteria. 2 The mini-trenching cable-laying technique The mini-trenching technique can be applied on routes that generally involve asphalted surfaces such as roads and sidewalks with a subgrade of compact material. It is not recommended that the technique be used on routes where the soil subgrade i
15、s sandy, gravelly or contains medium-sized cobbles (i.e., measuring 10 to 20 cm in diameter). If other underground utilities crossing a planned route already exists at a depth interfering with the depth of the mini-trench, this technology is not appropriate. The advantages of this technique over con
16、ventional cable laying technologies lie essentially in its speed of execution, lower cost, significantly lower environmental impact and limited disruption to road traffic and, as a consequence of the previous items, the easiness in obtaining permits for the occupation of public area. Mini-trenching
17、is normally carried out by simultaneously cutting through the paving and digging a trench whose depth and cross-section vary in accordance with the number of ducts to be laid: depth is normally between 30 and 40 cm, while cross-section can vary between 7 and 15 cm. In order to guarantee a protection
18、 against impact resulting from road-repairing, the depth of the laid infrastructure shall be maintained constant at a known level that must be 5 cm deeper than the foreseen asphalt cutting depth normally specified for road surface repair works. Figure 1 shows one of the possible installation configu
19、rations that can be used. Which configuration is selected will depend on the type of machinery employed and the number of ducts or cables envisaged in the project. L.48_ f0110 cm30 cmducts/cablescompact soil subgradehot mix asphaltwearing courseFigure 1/L.48 Example of mini-trenching installation co
20、nfiguration 2 ITU-T Rec. L.48 (03/2003) In cases where the mini-trench is dug along a road with no curb or sidewalk, the excavation shall normally be located at distance of around one metre from the edge of the road (or if possible just on the external side of the lateral line). In special circumsta
21、nces where this is not possible, the mini-trench may be dug in the shoulder at the edge of the asphalt. Any crossings through unpaved sections (which must in any case have a compact subgrade) should be carried out using the same technique. 2.1 Preparatory steps The mini-trench is excavated using app
22、ropriate disc-type cutting machines as shown in Figures 2 and 3. Figure 2/L.48 Example of standard cutting machine Figure 3/L.48 Example of fully automated trenching machine The designed route shall be free from sharp changes in direction. Where such changes are unavoidable, they shall be made by me
23、ans of cuts angled so as to comply with the minimum bend radii specified for the ducts and cables. ITU-T Rec. L.48 (03/2003) 3 The location of all underground utilities must be determined in order to establish the correct route for the trench. This is normally accomplished by means of cartographic d
24、ocumentation provided by the administrations that own the road or by the utility company, and/or through instrumented field surveys. Where other means of determining the location of underground utilities are not available, ground penetrating radar shall be used at detection depths between 0 and 100
25、cm. Where necessary, the contractor can take core samples along the planned route to determine the type of subsoil or as a further method of checking for obstacles. 2.2 Excavation requirements The following requirements shall be observed in cutting the mini-trench: Comply with all provisions and reg
26、ulations 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 visible locations around the excavation site. If the excavation must remain o
27、pen or the road will be otherwise obstructed during the night or under low-visibility conditions, road signs shall be complemented by lighting devices of the color, shape and size envisaged by applicable regulations. 2.3 Mini-trench cleaning The following operations shall be carried out after excava
28、ting the mini-trench: Remove spoil from the sides of the excavation1. Remove adjacent paving materials which were damaged as a result of excavation. Clean the bottom of the trench. At the end of these activities, the trench cross-section shall be completely clear and the bottom free from stones. 2.4
29、 Laying of the infrastructure or cables The infrastructure or cables can be installed in two ways: 2.4.1 Simultaneous excavation and ducts or cables laying Reels can be mounted on board of the cutting machine (see Figure 3) so that the duct or cable can be automatically fed into the trench, via a su
30、itably shaped guide integrated into the ploughshare, as excavation proceeds. The equipment and procedures used for this purpose must guarantee that: the operations envisaged in 2.3 are carried out. initial duct or cable configuration and position in the mini-trench are maintained along the entire ro
31、ute unless special circumstances dictate otherwise. if obstacles or situations are encountered which make it impossible to proceed with the mini-trench, the reel (and thus the ducts or the cable) can be removed from the cutting machine without having to cut the ducts, thus ensuring that cable deploy
32、ment can be continued using conventional methods without performing splices that are unnecessary from the technical standpoint. _ 1Spoil must be transported to authorized disposal sites in accordance with current legal requirements. 4 ITU-T Rec. L.48 (03/2003) 2.4.2 Non-simultaneous excavation and d
33、ucts or cables laying After completing the excavation, ducts or cables are installed using the conventional method and in accordance with the requirements specified in the installation standard. Ducts and cables installed in trenches shall maintain their initial configuration and position in the exc
34、avation unless special circumstances dictate otherwise. 2.5 Pull cord and plugs To prevent extraneous materials such as dust and water from penetrating the ducts, the ends shall be sealed with suitable watertight plugs during all stages of work. To permit subsequent fiber optic cable installation in
35、 each duct in the infrastructure, a pull cord shall be inserted and attached to the end of the plugs. When performing this operation, care must be taken to ensure that the cord is installed with sufficient slack. 2.6 Backfilling After the ducts or cables are installed, the mini-trench is backfilled
36、by pouring concrete (e.g., 200 kg/m3cement) with suitable foaming additives to ensure that a large amount of air is entrained, thus making the resulting structure mechanically as similar as possible to the soil subgrade surrounding the trench. Backfill shall satisfy the following performance require
37、ments: Volumetric stability. Backfill shall adhere to the walls of the excavation and to the infrastructures. The entire excavation volume shall be filled. There shall be no differential settling. Setting times and developed strength shall be such that paving can be reinstated at least 24 hours afte
38、r backfilling. Compressive strength shall be such as to withstand the stresses produced by light and heavy traffic. Backfill shall be permeable to gases and liquids. Backfill shall be readily removable. Backfill shall be highly workable (concrete mix shall be stable, cohesive, and sufficiently fluid
39、 to permit the use of pumps). Backfill shall be strong enough for vehicle load. No breaking or jumping out of backfill-piece can be permitted from the point of view of safety in traffic. Special requirements for backfill expressed by the administrations which own the road must be evaluated on a case
40、-by-case basis. In addition to securing the infrastructure in position at the bottom of the mini-trench, backfilling materials provide ducts and cables with mechanical protection. In both installation methods indicated in 2.4, infrastructure or cable geometry shall be guaranteed, and suitable measur
41、es shall be taken to avoid undesired floating of the ducts or lightweight cables during backfilling operations. Where ducts are laid by hand, they may be secured to the bottom of the mini-trench by means of weights or retainers located at intervals along the excavation before proceeding with backfil
42、ling operations. In such cases, retainers shall be removed upon completion of backfilling. ITU-T Rec. L.48 (03/2003) 5 When backfilling the excavation, the contractor shall use suitable means to keep asphalt paving clean. While waiting for the road to be resurfaced upon completion of backfilling, th
43、e contractor shall take all necessary precautions (use of temporary barriers and warning signs, filling the excavation to street level in special cases such as crossings, etc.) in order to prevent hazardous situations and ensure that safety requirements are satisfied. 2.7 Mechanical protection 2.7.1
44、 Galvanized iron channel Where interference with other utilities can occur and it is not possible to comply with the spacing requirements envisaged by current regulations, ducts shall be provided with mechanical protection in accordance with applicable standards and regulatory requirements. Where th
45、e infrastructure is installed near trees whose roots could cause damage, it shall be protected by means of U-shaped galvanized steel raceways of suitable dimensions, equipped with covers and embedded in the same type of concrete backfill envisaged for the excavation. 2.8 Identification To ensure tha
46、t the infrastructure or cables location is clearly apparent in future excavation operations, and those carried out by other service providers in particular, the following identification shall be provided: Access and transport network Identification shall not be visible from the exterior, and shall b
47、e accomplished by adding suitable coloring agents (oxides) to the concrete backfill. Coloring shall be permanent. Transport network In addition to the identification described above, transport network infrastructures shall be provided with identification visible from the exterior, and accomplished u
48、sing appropriate signs, adhesive label, etc. 2.8.1 Installation criteria for identification Identification visible from the exterior of the infrastructure or cables shall be installed in accordance with the following criteria: Identification shall be provided at all points where route changes direct
49、ion, and shall be located as close as possible to the infrastructure. Along straight sections of route, identification shall be provided at intervals of not more than 300 m. Preference should be given to installations adjacent to road intersections. Where stakes are used to facilitate identification, they shall be installed perpendicular to the roadbed. 2.9 Resurfacing It shall be proceeded with resurfacing after at least 24 hours have passed from the time the mini-trench was backfilled. If not otherwise requ
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