COMPANY CONFIDENTIAL
GLOBAL INFRASTRUCTURE X PROCESS EQUIPMENT X DIAGNOSTIC TOOLS
Locating buried pipes and cables
April 19, 2023 1
COMPANY CONFIDENTIAL
Radiodetection
ABC to XYZ of locating buried pipes and cables - For the beginner to the specialist
Radiodetection Corp.154 Portland RdBridgtonME, 04009877 247 3797
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Cable locators do not find cables.....
?
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...they find magnetic fields
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Because fields do things that pipes and cables don’t do
Why does it matter?
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Buried conductors don’t move, but the fields we’re tracing are subject to…
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Affected by:
1. Method of signal application2. Grounding3. Peak or Null4. Congestion5. Frequency applied
...Distortion
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What is a Magnetic Field ?
A magnetic field is radiated by a current carrying conductor
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…Which can be detected by a receiving coil which is excited by the expansion and contraction of the field.
Aerial
Volts
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What is Electromagnetic Induction?
If a bar magnet is inserted into a coil of wire, a voltmeter will show a deflection but only while the magnet is moving. When the magnet stops, the meter reads Zero. When the movement of the magnet is reversed, the meter deflection is reversed.
S
N
+ volts0
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one a.c. cycle
Alternating current creates a moving and reversing magnetic field
What is an Alternating Magnetic Field?
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What is Electromagnetic Induction ?
Direct current does not produce an electro - magnetic field detectable with a locator. DC Current builds to its voltage and produces a constant level of magnetism. There is no change in this voltage to excite an adjacent receiving coil.
Bulb will not light
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Passive
Active
There are two methods of signal detection
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Passive signals are a by-product of the 20th century. The proliferation of power and radio technology in this century has caused almost every underground metallic pipe or cable to emit detectable magnetic fields.
Passive
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Detectable Radio signals come from high power, low frequency international communication and navigation systems.
Such signals are present nearly everywhere on earth.
Passive
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FastEasyDoes not identify
Passive
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However tracking lines to their source can also aid identification
Passive
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Passive
Ensure a full grid search is done to detect conductors laid in different directions.
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Passive
Active
There are two methods of signal detection
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Increases Locator VersatilityDepth MeasurementPositive Identification
Active
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Affected by:
1. Method of signal application
…Distortion
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There are three main methods of Active Signal Application
Induction "Spill"
Connection "Clip"
Signal Clamp "Clamp"
Applying a signal
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Connection
A successful connection to the metallic pipe or cable will be indicated by a change in the transmitter audio or visual indicator. Always make the best possible connection for reliable signal.
mA
mA
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Requires three components:
1. A transmitter or signal source
2. A metallic conductor
3. A return path. Ideally, the earth.
Direct Connection Locating
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Affected by:
1. Method of signal application
2. Grounding
…Distortion
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Connection
The ground return point is the "back door" that the outgoing signal returns to. What you ground to and where you place the ground can significantly affect your results.
Remember: Every milliamp of signal that is going out the metal to metal connection on the red lead has to come back in through a metal to dirt connection on the ground lead.
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Ground stake too close to target conductor: Less range, some signal transfer.
Connection
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Badly positioned remote ground causes more signal transfer
Where possible, place ground rod away from known adjacent utilities which may act as return paths.
Connection
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Remote ground = better range, less signal transfer.
As a general rule, try to position the ground point at right angles to and 5-10' from the connection point and direction of conductor.
Connection
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Grounding to a structure which is also grounded can produce multiple signals.
The signal returns on every conductor that shares the same ground
Connection
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Connection
Positioning the ground stake in the direction you wish to locate will often encourage the signal to flow in that direction
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Connection
When locating Tees, position ground stake in the direction you wish to locate.
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Connection
For greater signal travel, an extension cable can be used to place the ground stake further away.
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The Cable Reel
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A double-ended connection does not use ground as part of the circuit and is more dependable. This is particularly true when trying to locate metallic pipes buried close together.
Connection
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Metal fences may seem a convenient ground point, but might produce interfering signals.
Always use an independent ground such as a ground stake, large screwdriver or other isolated metallic object buried in the ground.
Connection
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After making a connection, sweep a complete circle around a signal source; measure and mark all occurrences of signal. Repeat to assure accuracy.
Connection
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At older buildings where the services are all metallic and may share a common ground, connecting close to multiple service bondings may produce multiple signals.
Connection
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Energizing in the street and tracing toward the bonding point can be more reliable
Connection
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The Signal clamp is a current transformer which induces or spills a locate signal onto a target line
Clamp
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A clamp safely applies a signal to a live cable without interrupting the supply
Transmitter Clamps
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The Signal Clamp is a means of applying a transmitter signal to an insulated pipe or cable, without physical connection. It's most useful for live electric cables.
Signal Clamp must be completely around line with jaws closed.
Clamp
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When using a clamp, the applied signal moves away from the nearest ground to a distant ground. For this reason, it's a useful way to put a locate signal on a specific line.
Clamp
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At higher frequencies - or with longer lines - capacitive leakage completes the circuit.
Clamp
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Direct connection does not give reliable identification on multiple bonded lines
As an exception, connection to the bonding ribbon in a manhole will send tone in one direction, allowing the conduit run to be located.
Connection
6 12 14 6
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Generally, clamping produces more reliable signal identification.
Excellent on headers. Especially with using current measurement and direction.
Clamp
6 22 10 6
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Place the clamp below the earth bond when locating cables. Do not place above the earth bond.
If there is no bonding strap, the clamp may not transmit a signal.
Clamp
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If using the clamp around a metallic pipe, any insulating flange must be bridged.
Clamp
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Induction
Induction allows the user to quickly and easily apply a locate signal, by placing the transmitter in the vicinity of a known conductor or conductors
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min. 10 paces
A minimum distance of 10 paces between receiver and transmitter is necessary to avoid the receiver detecting the signal directly from the transmitter. This is known as "Air coupling".
Induction
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Often induction will energize every metallic conductor close to the transmitter. This is useful for checking an area for buried conductors, but not useful for finding specific conductors in congested areas.
Induction
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The induced transmitter signal is usually strongest on the line directly below and in line with the transmitter
Induction
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Aerial
The orientation of the aerial is important as seen with an AM radio
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When the aerial is not in line with the magnetic field, no signal is detected. This is known as "Nulling".
Aerial
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When the transmitter is turned onto its side so the coil axis is vertical, the induction signal is spread over a wider area; but this results in zero signal directly below the transmitter. Which can be useful...
Induction
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Min. 10 paces
Using transmitter on its side to 'Null out''When the transmitter is over the target cable, minimum signal will be found by the receiver and the adjacent conductors will be energized strongly.
Induction
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100 20 5.8 2.7
Induction
Estimated induction signal ratios
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50 30 19 140
Estimated induction signal ratios
Induction
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Induction Search (two person).Maintain minimum Rx/Tx separation.
Sweep 3 times ! +/- 30-40 degrees
Induction
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Induction search, radial.
Maintain constant Rx/Tx separation
- Lazy Susan idea
Induction
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Affected by:
1. Method of signal application
2. Grounding
3. Peak or null
...Distortion
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Aerial Responses
Different aerial orientations can be used for different responses
1 2 3
Signalresponse
1 2 3
Signalresponse
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In Null, minimum signal is encountered exactly over the center of the buried conductor field
A maximum signal response will be detected on each side of the minimum. If both of the "shoulders" are symmetrical, the Null point is accurate.
Receiver Response
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Null antenna gives a sharp response which gives the impression of good accuracy, but can be less accurate than Peak.
100%
5%
Receiver Response
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Peak coil response is less sharp, but actually more accurate.
100%95%
Receiver Response
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This is a typical peak signal response over a buried conductor. Peak response provides position and direction.
Note that the maximum signal response occurs directly over the center of the underground conductor
Receiver Response
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Peak response is more reliable. It enables you to measure depth.
Peak response is more accurate in congested areas
Peak
Receiver Response
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Null is useful for deep lines and rapid line tracing , but...
Null
d
Receiver Response
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Null response in an area with congested plant is often useless and misleading
Null
Receiver Response
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Peak and Null coils produce opposite types of error when tracing bends
PeakNull
Receiver Response
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Affected by:
1. Method of signal application
2. Grounding
3. Peak or Null
4. Congestion
...Distortion
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Distortion
Current on one line may induce 'stray' signals onto nearby conductors
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When the conductors are close together, the magnetic fields can interfere with each other, causing a distorted field which is no longer cylindrical. This can lead to poor locate results and inaccurate measurements.
Distortion
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d
PeakNull
d
Distortion and Depth
When there is a discrepancy between the aerial responses the following must be observed.1. The Peak response will always be more accurate.2. Push button depth estimation should not be used until the two responses agree
Peak Null
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Peak
Null
13
This distortion varies depending upon the direction and magnitude of the current flow, causing a discrepancy between the peak and null aerial responses.
Distortion
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dd d
Because we know the field is likely distorted,it's not a good idea to rely on depth readings taken near a change of direction...
Depth
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dd
d
or near a tee
Depth
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dd
or near another line
Depth
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dd d
or near a depth change
Depth
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d dmin. 30 paces
or near an inducing transmitter
Depth
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100%70%
d
d
Depth Triangulation Peak Aerials
Depth estimation can be verified using a triangulation technique. Move the receiver from 100% to 70% signal strength, on each side of conductor and measure the distance. This distance will be approximately equal to the depth.
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Affected by:
1. Method of signal application
2. Grounding
3. Peak or null
4. Congestion
5. Frequency applied
...Distortion
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Which frequency should I use ?
Very LowLess than 1 kHzVery Long RangeNo InductionLittle "Spillage"Better IDent
Low1-10 kHzLong RangePoor InductionLess "Spillage"
High10-50 kHz.Easy InductionShorter RangeMore "Spillage"
Very High50kHz+Short RangeExcellent InductionSevere "Spillage"
Characteristics of different frequencies.
All of these characteristics get better or worse linearly with frequency. There is no signal that is magically better for one than another.
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High frequency signal quickly escapes from target line and may return on an adjacent line Lines in close proximity will readily accept signal. This can lead to field distortion and poor locate information.
Which Frequency ?
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Higher frequency = shorter range (greater capacitive signal loss to ground) This frequency is better for induction onto small or short length conductors, such as telephone drops, CATV cables or street light cables.
Which Frequency ?
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Low frequency = long range (minimum capacitance signal loss to ground)
This frequency is better for connection and locating longer metal pipes or cables
Which Frequency?
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High frequency may locate service drops which are not grounded at the termination point but range on main line is reduced and may induce onto crossing services
Which Frequency?
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Low frequency tends to keep to main line, does not induce onto crossing lines and bypasses service drops which are not grounded.
Which Frequency ?
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High frequency can use a capacitive ground connection through a metal plate
This provides a ground in areas where direct earth ground cannot be achieved
Which Frequency ?
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General Locating
When pinpointing the signal, keep the bottom of the receiver blade close to and parallel to the ground.
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Always pivot receiver to ensure maximum signal is received
This is particularly true prior to taking a depth reading
General Locating
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General Locating
Searching for laterals
Use Peak and search 2 paces away from and parallel to the main line
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Problems
If multiple signals are received at uniform distances apart, you are probably trying to locate through reinforcing bars.
Raise the receiver up to chest height. This should allow the main signal to be detected.
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Problems
Lost signal must be either: End of line
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Problems
OR: a T lateral
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Problems
OR: a bend
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Problems
OR: a depth increase
The field has simply become weaker at the coils because of the change of depth
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Small Waterproof self contained transmitters enabling non metallic ducts, drains or sewers to be located and traced with a Receiver.
Transmitting Sondes
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Ghost Ghost
Receiver response to a Sonde signal. Small ghost signals may be detected either side of main signal
Note: Receiver is held in line with Sonde
Sondes
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Sondes
Location procedure for pinpointing Sondes
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Sondes
Location procedure for pinpointing Sondes
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Using a Sonde to find a collapsed sewer
Sondes
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Tracking an inspection camera with a Sonde
Sondes
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Tracking a boring tool with built-in Sonde
Sondes
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Sondes
A sonde in a vertical position gives a very precise "null" signal
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Sondes
This can be used for very accurate positioning through a wall prior to drilling etc
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Locating a leak in a non metallic water pipe using a Sonde inside a "Pig“
Need VLF for metal pipes
Sondes
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A B
d=0.7AB
d
Triangulation depth method for verifying "push button" depth or estimating depth which is beyond the receiver's depth range
Sondes
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Levels of Confirmation
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Automatic Gain Control - AGC
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m
%
mA
m
%
mA
Signal strength
Current reading
Depth
Signal strength
Current reading
Depth
Change of depth effects signal strength but not current reading
RD400 Digital Series
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mA mA mA
Current losses returning to signal source
RD7/8000 Digital Series
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mA mA
Current loss due to poor insulation
There is very specialized equipment for this
RD7/8000 Digital Series
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mA
mA
mA
Current loss due to a Tee connection
RD7/8000 Digital Series
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Expected current direction indications and return signal path
For locators equipped with current direction indication only
Target line always
identifiable by current direction
RD7/8000 Digital Series
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Possible current direction indication on conductors.
RD7/8000 CD Series
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100%
60%40%
Modern equipment has many “Levels of Confirmation”
RD7/8000 Digital Series
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Current flow through an earth fault
FaultFind
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Meter readings before, at and after the fault.
FaultFind
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Distant fault – no indication
Line fault
ahead
Line fault
behind
FaultFind
Meter readings along a faulted cable
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FaultFind
FaultPositionLocate
Faultline
Locate line
It is possible to detect a fault a reasonable distance away, and to the side of the cable
FaultFind
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Pinpointing a fault under a roadway with two or more bearings (triangulation)
Fault line 1
Fault line 2
Faultposition
FaultFind