1、 INTERNATIONAL TELECOMMUNICATION UNION L.39TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (05/2000) SERIES L: CONSTRUCTION, INSTALLATION AND PROTECTION OF CABLES AND OTHER ELEMENTS OF OUTSIDE PLANT Investigation of the soil before using trenchless techniques ITU-T Recommendation L.39 (Formerly CCIT
2、T Recommendation) ITU-T L.39 (05/2000) i ITU-T Recommendation L.39 Investigation of the soil before using trenchless techniques Summary This Recommendation describes the main techniques that allow an investigation of the soil in order to get information about the position of buried objects and the n
3、ature of the ground. This data is necessary to plan the execution of work using trenchless techniques and to optimize the drilling path thus avoiding the risk of damage to both the existing infrastructures and the drilling equipment; hence preventing drilling failures due to obstacles or ground char
4、acteristics. This Recommendation gives advice on general requirements of the three different phases in which the investigation work can be divided: preliminary operations, an on-site survey and the output of utility maps. Source ITU-T Recommendation L.39 was prepared by ITU-T Study Group 6 (1997-200
5、0) and approved under the WTSC Resolution 1 procedure on 12 May 2000. ii ITU-T L.39 (05/2000) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent
6、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 Conference (WTSC), which meets every four years, establishes
7、 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 WTSC Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards
8、 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 PROPERTY RIGHTS ITU draws attention to the possibility tha
9、t 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 Recommendat
10、ion 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, implementors are cautioned that this may not represent the latest information and a
11、re therefore strongly urged to consult the TSB patent database. Ge3 ITU 2001 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from ITU. ITU-T L.39
12、(05/2000) iii CONTENTS Page 1 Scope. 1 2 Preliminary operations 1 3 On-site survey . 1 3.1 Buried object detection . 2 3.2 Soil investigation 3 4 Output of utility maps . 7 Appendix I Available investigation methods 8 I.1 Boring methods. 8 I.2 Soundings and probings 9 I.3 Excavation methods for expl
13、oration. 10 I.4 Geophysical explorations 10 ITU-T L.39 (05/2000) 1 ITU-T Recommendation L. 39 Investigation of the soil before using trenchless techniques 1 Scope This Recommendation: describes the preliminary operations that are required before performing a direct on-site investigation; describes t
14、he main techniques and methods that can be used to make soil investigation and gives advice on some operational procedures; gives advice on how to produce the final map of the investigated area. 2 Preliminary operations Right from the first design phase, it is essential to acquire all the available
15、information about the existing utilities and the nature of the ground on site. This information is of the following kind: statutory/administrative; technological (e.g. presence of utilities or obstacles); geolithological, hydrogeological and geotechnical. The following action is recommended: to cons
16、ult the available existing documentation of any work carried out in the area (e.g.: laying of utilities); to collect all the administrative details regarding permits, monitoring, testing of existing utilities; to contact the technical offices of Local Authorities in order to obtain geological and ge
17、otechnical reports on work carried out in the area; to collect from local arts councils or museums archaeological and historical information relevant to the working site; to contact the contracting Companies which had previously worked on site in order to get more precise information, especially in
18、the case of potentially dangerous utilities (e.g. gas mains) or those of public importance (e.g. hospital power and telephone lines). 3 On-site survey In order to minimize the risk of mistakes due to the use of out-of-date maps or to the possible differences between “planning“ and “executive“ drawin
19、gs, a direct on-site investigation has to be performed. The available techniques to perform buried object detection and soil investigation are described. 2 ITU-T L.39 (05/2000) 3.1 Buried object detection 3.1.1 Ground Penetrating Radar (GPR) In addition to its normal use for locating objects in air,
20、 radar can also detect discontinuities below ground. A planar antenna transmits an electromagnetic wave into the ground and the back-scattered radiation is received by another antenna and then processed, to extract the information relevant to buried objects. Usually any discontinuity of the electrom
21、agnetic properties of the soil (dielectric constant and conductivity) is detected. Objects can be classified according to their geometry: planar surfaces, long and thin objects (cables and pipes), local objects. Wideband time-domain impulse radar systems are available commercially and are usually of
22、fered with a range of antennas to suit the desired probing range. The extent of ground penetration is limited by the attenuation of the signal: the penetration increases at longer wavelengths, but resolution is higher at shorter wavelengths, so the choice of frequency is usually a compromise between
23、 the two. The investigation depth is also strictly related to the nature of the ground: GPR works best in dry granular soils and may not be able to see far through waterlogged or dense clay. For average environmental conditions, medium frequency antennas (400-600 MHz) to reach an investigation depth
24、 up to 2 metres and low frequency antennas (100-200 MHz) to reach investigation depths up to 3 metres will be used. Most antenna have relatively small footprints which means that rapid and wide-area surveying can only be achieved with multichannel radar systems. These systems use more than one anten
25、na, mounted on a fixed scheme, which allows the acquisition of a large amount of data in a relatively short time, and so makes easier the final interpretation of the probing results. Particularly in urban areas, it is recommended to use a multichannel radar system, mounting an array of antennas, to
26、improve the probability of detection of underground utilities and reduce the overall investigation time. In order to achieve a correct interpretation of the radar data a calibration procedure should be performed. As manual on-site calibration may cause information distorsion, it is recommended to co
27、llect non calibrated data on-site and process it later using the automatic calibration algorithms. In this way on-site calibration error is avoided, and the subsequent automatic calibration procedure can be repeated in the case of unsatisfactory results. The acquisition system of modern GPR equipmen
28、t includes a PC connected with the antennas both of which are mounted on a trolley that allows easy manoeuvring. The operator has an immediate view of the acquired data in the field, which can be helpful for the final interpretation of the results. A focal point among the field operations is represe
29、nted by the establishment of a reference system in the local environment to which the radar data should accurately refer in order to produce precise maps of the buried utilities. ITU-T L.39 (05/2000) 3 It is therefore necessary to define in the survey area a reference line (zero line) preferably in
30、correspondence with an existing one (e.g. a wall, the edge of a pavement, etc.), which represents one of the two axes of the local coordinate system, and an origin of the axes (zero point). In this way by performing survey along lines at a known distance from the axes, all the GPR profiles with the
31、relevant position of each detected object can be automatically referred to the local co-ordinate system. In order to determine the position of the GPR profiles with respect to the local coordinate system, a survey wheel directly connected to the GPR trolley shall be used. 3.1.2 Cable and pipe locato
32、rs Most locators work by detecting the electromagnetic signals generated around “live“ cables and can operate at various frequencies to suit electricity and telecommunication lines. A metallic pipe locators can be used as a simple metal detector, but it is better to use it in conjunction with a tran
33、smitter which induces a signal in the pipe, that can be picked up by a receiver. Systems are available which can trace the path of cast iron and other metallic pipes at depths up to 10 m. The location of non-metallic pipes is more difficult and it can be performed only if it is possible to rod or to
34、 pull a small transmitter through the pipeline while following the signal with a receiver on the surface. To trace non-metallic live gas or water pipes, the locators shall be used in conjunction with a standard transmitter attached to a connector block on the tail of a semi-rigid coated wire inserte
35、d into the pipe. 3.2 Soil investigation A geological investigation, because of its extent and thus expense, should contain available bibliographical knowledge of the area and also information taken from an on-site investigation. The techniques used to perform the investigation can be divided into tw
36、o classes: direct and geophysical methods. Direct investigation techniques consist mainly in boring and excavation methods and mechanical soundings. All of these methods are based on direct observation of soil samples or on the result of mechanical tests, thus giving reliable responses about the nat
37、ure of the soil in the areas close to the investigated points. In geophysical explorations some physical parameters, such as electrical resistance, magnetism or wave propagation velocity can be measured by sensing devices to interpret the characteristics of the ground. They perform a non-disruptive
38、investigation and some of them also allow a continuous investigation of large areas. Such geophysical explorations supply information for bedrock profiling, define the limits of granular soil areas and large organic deposits. They yield a general definition of subsurface conditions including the dep
39、th of the ground water. However, there are limitations to the information obtained by these methods and they should not be expected to give reliable or useful results for all subsurface conditions. 4 ITU-T L.39 (05/2000) To reach a convenient compromise between the time and cost of investigation, th
40、e reliability of the results obtained and the impact on the working-site, as a general rule, the following items shall be taken into account: to perform mechanical soundings or to collect samples of the soil by boring at a limited number of points along the investigated line and to extrapolate the d
41、ata using the continuous acquisition results obtained by the use of an appropriate method; to ensure the optimum utilization of such investigational techniques, geologists or technicians experienced in both soils and geophysical theories should be consulted to determine the applicability of geophysi
42、cal procedures to the area under investigation. 3.2.1 Direct investigation methods Soundings generally have the advantage of speed and low cost when compared to borings. To obtain more information several soundings can be used as substitutions for a single boring. In addition, soundings can be used
43、to obtain additional information between borings at minimal cost once it has been ascertained that conditions vary in between the borings. Soundings are particularly useful when performed to obtain information on stratification that normally would not be available until additional borings were perfo
44、rmed in a later stage of exploration. Excavations that are large enough to permit the entrance of one or more persons represent one of the most valuable and dependable means of exploration, since they permit detailed examination of the subsurface materials in situ. The following action is recommende
45、d: to use soundings in the mapping of soil strata during the early stages of explorations when the number of borings that can be drilled is normally limited; to integrate the results obtained by soundings with other data in order to avoid misleading results caused by the presence of local obstacles
46、(gravel, boulders, roots, etc.); to limit the use of excavation methods to the digging of pits necessary for the use of trenchless techniques, in order to reduce obstruction to traffic and pedestrians on site. 3.2.2 Geophysical methods 3.2.2.1 Electrical resistivity method Two types of resistivity s
47、urveys are used for subsurface explorations, namely, horizontal electric sounding and vertical electric sounding. Horizontal electric sounding is performed by maintaining constant electrode spacing as the electrodes are moved across an area and a resistivity measurement is made for each new location
48、 of the electrodes. Data from a series of such traverses across an area may be presented in the form of a series of contours of equal resistivity. Horizontal electric sounding can be used to delineate an area of permeable soil deposits, to locate fault planes, and to locate steep contact surfaces be
49、tween different materials. Vertical electric soundings are made by maintaining the centre of the electrode spread at a given location and taking a series of resistivity readings as the electrode space is increased. As the spacing ITU-T L.39 (05/2000) 5 is increased, the depth of material that effects the resistivity increases, and changes in material are reflected in the resistivity values obtained. Vertical electric sounding is used to estimate the depth to bedrock, sand and gravel, or water-bearing strata and to estimate the thickness of strata. The following action is therefore recommen
