Underground Utility Survey using PCL in Hong Kong
- Slides: 66
Underground Utility Survey using PCL in Hong Kong Speaker: Dr. Rebecca Tse Department of Land Surveying and Geo-Informatics Date: 26 February 2011 One Day Utility Seminar 1
Introduction • • • Introduction to Underground Utility Survey Advantages of Performing UUS Statutory Requirement What is PCL Operating a PCL Tracing Techniques Error in Depth Measurement Intelligent Marking System Work Procedures for US by PCL 26 February 2011 One Day Utility Seminar 2
What is Underground Utility Survey? 26 February 2011 One Day Utility Seminar 3
Advantages of Performing UUS • Prevent injury or death of life • Fulfill Legal Requirement • Prevent utility damage which cause sequence effect – affect daily live (no electricity, gas, water or flood of sewer) • Get information for Planning and design (Prevent unexpected traffic diversion) 26 February 2011 One Day Utility Seminar 4
Potential harzards – Flashover (electricity cables) – Explosion (electricity cable, gas pipe) – Fire (electricity cable, gas pipe) – Road collapse (water pipe, drain and sewer) – Interrupt communication (telecom, CATV) – Spread of disease (drain and sewer) 26 February 2011 One Day Utility Seminar 5
Utility accidents in the World • Direct Loss • Indirect Loss – – – 26 February 2011 Loss of time Legal problems Additional cost Insurance raised Loss of reputation One Day Utility Seminar 6
Utility accidents in Hong Kong 30 Dec, 03 Ming Pao 26 February 2011 14 Nov, 06 Apple Daily One Day Utility Seminar 7
Statutory Requirements • CAP 406 H Electricity Supply Lines (Protection) Regulation, April 2001 • CAP 51 B Gas Safety (Gas Supply) Regulations, Section 23 A Dec, 1996 26 February 2011 One Day Utility Seminar 8
Is it enough? • Regulations govern only electricity cables and gas pipes, how about the others? – Telecom cables (Interrupt communication and information transaction, especially affect the economic loss) – Water pipes (Road collapse, interrupt traffic or even delay in fire fighting) – Sewers (Flooding, may spread of disease) 26 February 2011 One Day Utility Seminar 9
What is PCL? • Detect electro-magnetic field • Locate any kind of metallic pipes or some kinds of non-metallic pipes 26 February 2011 One Day Utility Seminar 10
Basic theory of electromagnetic detection • A current flowing along a conductor creates a magnetic field. • The field forms a cylindrical shape around the conductor and is called “alteration current (a. c) or signal”. • The locators detect the magnetic field around the conductor (pipe line). 26 February 2011 One Day Utility Seminar 11
Two types of signals from buried conductors • Passive signal – Signals naturally present in conductors – 50 Hz and radio frequency (from broadcast systems) – Less definite detection – Unreliable depth measurement • Active signal 26 February 2011 One Day Utility Seminar 12
Characteristics of Using Passive Signal • • Fast & convenient No transmitter Unobvious Unable to identify the conductors unless tracing to the source (e. g. hydrant, lamp pole, manhole) to obtain clues • Reference only, not accurate measurement 26 February 2011 One Day Utility Seminar 13
Two types of signals from buried conductors • Passive signal • Active signal – – – Signal generator Trace and pinpoint target line By induction or signal clamp More precise work for depth measurement Direct connection, Signal Clamping, and Induction Grounding maximise the currect 26 February 2011 One Day Utility Seminar 14
Active Signal (1) Direct Connection • Direct contact to the target cable is necessary • Not suitable to detect electric cable • Suitable to use in locating metallic pipe 26 February 2011 One Day Utility Seminar 15
Active Signal (2) Signal • Clamping Very effective • Apply to exposed cable (trail pit) • Limited size of the able • The jaws of the clamp must be closed completely 26 February 2011 One Day Utility Seminar 16
Active Signal (3) Induction • Apply signal without access to the line • Not accurate • Signal can induce onto nearby lines as well as the target • Poor efficiency on deep targets 26 February 2011 One Day Utility Seminar 17
Active Signal (4) Grounding • Good grounding can maximise the applied current which improve the tracing range • Ideally, the target line needs to be grounded at each end using the signal clamp 26 February 2011 One Day Utility Seminar 18
Active Signal. Grounding Locations (5) • Ground rod should place far away from the alignment • Place the ground rod in the direction where detection is carried out • Place the ground rod near the branch to be detected 26 February 2011 One Day Utility Seminar 19
Operating a PCL Factors affect signal transmission • • Material of the utilities Size (diameter) of the utilities Wet or dry soil conditions, and Signal frequency. 26 February 2011 Ref: HKIUS-GEN-009 One Day Utility Seminar Last update: 19 Oct 09 Version: 1 20
Signal response Peak and Null responses Horizontal aerial – Peak Response 26 February 2011 Vertical aerial – Null Response One Day Utility Seminar 21
Peak mode Signal strength Receiver 2 1 3 Soil Target line 26 February 2011 One Day Utility Seminar 22
Null mode Signal strength Receiver 2 1 3 Soil Target line 26 February 2011 One Day Utility Seminar 23
Peak Mode or Null Mode? Advantages Disadvantages Peak Mode Higher accuracy in utility congested area Broader response Null Mode Sharper response Interfered by nearby utilities easily, low accuracy in utility congested area • Therefore, apply peak mode to trace the alignment, then verify the result by applying null mode. • Both mode yield the same results if no lines nearby. 26 February 2011 One Day Utility Seminar 24 24
Peak mode in utility congested area Higher peak Lower peak Soil Target line 26 February 2011 Nearby line One Day Utility Seminar 25 25
Null mode in utility congested area Null 1 2 Target line 3 Nearby line Ghost line 26 February 2011 One Day Utility Seminar 26 26
PCL Tracing Technique • Sweep and search – Passive sweep – Search by induction • Trace alignment • Pinpoint 26 February 2011 One Day Utility Seminar 27
Passive sweep • Detects signals naturally present on lines Cable Traverse the area in grid search Stop when the receiver indicate the presence of a line Pinpoint the line and mark its position 26 February 2011 Search traverse One Day Utility Seminar 28 28
Search by induction • 2 operators, a transmitter and receiver are employed • The distance of the transmitter and receiver shall be at least 20 paces. • The receiver shall be perpendicular to the probable direction of the buried lines. http: //www. ridgid. com/Tools/Induction-Using/index. htm 26 February 2011 One Day Utility Seminar 29 29
Trace alignment Apply peak mode to identify theto Apply null mode confirmlocation the result (If the result is same as peak mode, the location is correct. If the results are different, the signal (Apply peakbeen mode may have again) Turn the twisted. ) receiver to detect Orientation the strongestof signal. receiver shall be the same as the line, turn 90° to see Walksignal along the if the falls alignment, move the significantly 26 February 2011 receiver left and right to see if the response is reducing while moving to One Day Utility Seminar either sides 30 30
Pinpoint • Move the receiver from side to side across the line, locate the point of maximum response • Turn the receiver around without moving it, locate the point of maximum response • Adjust sensitivity to get the best result • Mark the position and direction of the line 26 February 2011 One Day Utility Seminar 31 31
An example of - PCL survey 26 February 2011 Ref: HKIUS-GEN-009 One Day Utility Seminar Last update: 19 Oct 09 Version: 1 32
Error in Depth Measurement • Receiver calculates depth based on the assumption of the magnetic field presents on a conductor is circular • Errors in depth calculation always due to the interference of the nearby lines 26 February 2011 One Day Utility Seminar 33 33
Common reason • Congested utilities • When the lines are mutually bonded, signal of the target line may couple to nearby lines or take other lines as return path • Transmitter energize all the cables in the area • Soil is conductive because the return current through soil also carries magnetic field 26 February 2011 One Day Utility Seminar 34 34
Twisted signal • Two lines are too close, the magnetic field will be interfered by each other • The magnetic field will be twisted instead of circularshaped • Twisted signal seems comes from another point 26 February 2011 One Day Utility Seminar Combined magnetic field 35 35
Differences between peak and null mode • The results of using peak mode and null mode are different • That means the magnetic field is twisted • The depth measurement is inaccurate 26 February 2011 One Day Utility Seminar Peak Null Depth 36 36
Do not measure depth at bend d 26 February 2011 d One Day Utility Seminar d 37 37
Do not measure depth at tee d d d 26 February 2011 One Day Utility Seminar 38 38
Do not measure depth near another line d d 26 February 2011 One Day Utility Seminar 39 39
Do not measure where depth change d 26 February 2011 d One Day Utility Seminar d 40 40
Do not measure depth near the transmitter or signal clamp d d 26 February 2011 One Day Utility Seminar 41 41
Intelligent Marking System (1) RECEIVER TRANSMITTER 26 February 2011 One Day Utility Seminar 42
Intelligent Marking System (2) Marker locating Path locating • For metallic services only • To locate the path of the service • Receiver detects the signal carried by the service from the transmitter • Require access point for signal injection 26 February 2011 • For both metallic and nonmetallic services • To locate a specific point • Marker absorbs signal transmitted by the detector and reflects back to detector • Marker has to be buried next to the service at installation One Day Utility Seminar 43
How does the system work 1. Detector transmits signal to the marker 2. The marker in return, absorbs and stores the signal energy. 3. After the trasmitting, the detector switches to receive mode and then the stored energy in the marker starts to discharge. 4. The marker acts as a transmitter to send signal back to the detector. 5. The detector receives the incoming signal and emits a continuous audible tone. The tone is strongest when the detector is exactly over the marker. 26 February 2011 One Day Utility Seminar Tone Outpu t Detector Soil Marker Signal Transmit Signal Ball Marker Buried Splice 44
i. D ball markers • Adopt same color code and response frequency as conventional markers • Both the conventional markers and the new i. D markers can be read by conventional detector and i. D marker locators • Each marker has a unique serial number • Information can be programmed into the marker on site to denote the function represented by the marker. Field names and contents can be chosen from given list or user defined 26 February 2011 One Day Utility Seminar 45
i. D ball marker locators • Can read both conventional and i. D markers • Can detect 2 kinds of markers simultaneously • Give audio and visual responses to the user • Measure the depth of the marker • Store recent read and write records which can be uploaded to PC for data management • Store frequently used data formats as templates 26 February 2011 One Day Utility Seminar 46
Standard Colour Codes for i. D Markers Colour Utilities Telecom Waste Water Supply Water Towngas CATV General Purpose Electricity 26 February 2011 One Day Utility Seminar 47
Current Practice of Underground Utility Survey Basic Survey Computation Microsoft Excel Macro Automapper LISCAD STC 25 WINCAN 26 February 2011 One Day Utility Seminar 48
Work Procedures Before the survey • Check Record Plans, Traffic Permit and other information • Boundary Definition and Visual Inspections for valves, chambers and pits of different utilities • Safety precautions – Permit To Work, Temporary Traffic Arrangement, Personal Protective Equipment 26 February 2011 One Day Utility Seminar 49
Steps to be noted • Record plans of the survey extent from the utility undertakers/ relevant Government Departments should be collected • Use different frequencies and techniques alternatively to get the best result • The result should reach the accuracy of (+/-) 165 mm or 0. 1 d (depth) which the levels should be related to the center for the metallic pipe or cables, crown of ducts and inverts of sewers and drains 26 February 2011 One Day Utility Seminar 50
Commencing the survey • Operation shall be carried out by OMHKIUS(at least 3 years experience) or AMHKIUS (at least 2 years experience). The whole operation shall be supervised by OMHKIUS • When there is a signal found, mark the point by spray paint or other means • Use total station to produce site records • Last minute check and complete daily report 26 February 2011 One Day Utility Seminar 51
Survey Report • • • Survey report – name and certificate number of competent person, mandatory information, survey result, recommendation Site photographs Information of equipments used Utility survey drawing – alignment, depth, diameter, direction (drainage services), type of the services, location of manholes and other related surface installations Report to be confirmed by Registered Professional Utility Specialist 26 February 2011 One Day Utility Seminar 52
How to conduct a safe and good survey? • Follow the code of practice and the regulations • Appoint suitable person for the job • Undertake the survey with reasonable steps • Investigate the result • Submit a written report 26 February 2011 One Day Utility Seminar 53
Electricity Supply Lines (Protection) Regulations (電纜保護規例) (ESLPR) 26 February 2011 One Day Utility Seminar 54
Specification of ESLPR (1) A person shall not carry out or cause or permit another to carry out in the vicinity of an underground or overhead electricity cable works of any kind unless before the works are begun all reasonable steps have been taken to ascertain the existence within the proposed works site and its vicinity of any such underground electricity cable and its alignment and depth or any such overhead electricity line and its alignment, distance from the ground and voltage 26 February 2011 One Day Utility Seminar 55
Specification of ESLPR (2) A person who carries out or causes or permits another to carry out in the vicinity of an underground or overhead electricity cable works of any kind shall ensure that all reasonable measures are taken to prevent the occurrence of an electrical accident or an interruption to the supply of electricity arising from those works. 26 February 2011 One Day Utility Seminar 56
What are reasonable steps? • Appoint a competent person to undertake an investigation to ascertain the existence within the proposed works site and its vicinity of any underground electricity cable and its alignment and depth • A written report of the survey findings is produced by the same competent person 26 February 2011 One Day Utility Seminar 57
The roles of a Competent Person (1) • The requirements set in the regulation(cap 406 H) for a Competent Person is described as follow: – A competent person who undertakes an investigation to ascertain the existence, alignment and depth of an underground electricity cable – Shall not delegate the function and duty of the investigation to another person – May carry out the investigation with the assistance of any other persons, but such persons shall be directly supervised by that competent person at the proposed works site in the course of the investigation 58
The roles of a Competent Person (2) in a manner that does not – shall carry out the investigation cause damage to, or impair the operation of, the underground electricity cable – shall provide the person requesting the investigation with a written report of his findings as to that matter. – Other than the above listed, in general terms, a competent person shall also: • • • Familiar with the requirements under the regulation Familiar with the Code of Practice Prepare for suitable material before work commence Work in safe manner and with PPE at all time Protect others by giving appropriate notices and providing precaution measures on the working site such as barriers, lighting and guarding and warning signs 59
• The roles of a Competent Person (3)by providing best possible result to Minimize the disruption to the public the client and to alert the client to use hand tools for trial pits • Provide clear and appropriate records and information to client for their future reference • Issue permit to dig certificate only when he is comfortable that the necessary information has been located in the site. Keep and maintain a copy of all the results acquired from survey and to be inspected by the relevant authorities when required • Others may be required under other related regulations Note: Under the regulation, the competent person is competent for locating underground cables only. You should seek for help from other types of competent person (eg. Registered Safety Officer & Licensed Electrician) for advice on different issues. 60
Guide to Utility Survey by Non-destructive Method (Using PCL in HK) • Preparation • Equipment • Procedures • Standards • Limitation of survey • Personnel Requirement • Sample Photos and forms 26 February 2011 One Day Utility Seminar 61
Pamphlet of PCL Survey 26 February 2011 One Day Utility Seminar 62
26 February 2011 One Day Utility Seminar 63
Guide to Utility Survey 26 February 2011 One Day Utility Seminar 64
26 February 2011 One Day Utility Seminar 65
Q&A 26 February 2011 One Day Utility Seminar 66
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