ASTM F3079-14(2020)

Standard Practice for Use of Distributed Optical Fiber Sensing Systems for Monitoring the Impact of Ground Movements During Tunnel and Utility Construction on Existing Underground Utilities

SIGNIFICANCE AND USE
5.1 This practice is intended to assist engineers, contractors and owner/operators of underground utilities and tunnels with the successful implementation of distributed optical fiber sensing for monitoring ground movements prior to construction for site planning and during utility and tunnel construction and operation and the impact of such ground movements on existing utilities.  
5.2 Before the installation of distributed optical fiber sensing begins, the contractor shall secure written explicit authorization from the owner/operator of the new tunnel/utility and the existing utilities allowing an evaluation to be conducted for the feasibility of distributed optical fiber sensing for monitoring ground movements for the intended purpose and to have access to certain locations of the structure and the surrounding ground. It may also be necessary for the installer to have written explicit authorization from applicable jurisdictional agencies such as the Department of Transportation, the Army Corps of Engineers, the Department of Environmental Protection and other.  
5.3 Engineers, contractors, and owners/operators shall also be cognizant of how the use of distributed optical fiber sensing for monitoring ground movements around utilities and tunnels might interfere with the use of certain equipment or tools near the installed optical fiber sensing cable in some special situations. For example, repair activities may have to temporarily remove, relocate, or avoid the optical fiber cable.  
5.4 Engineers, contractors, and owners/operators should be cognizant of how installation techniques and optical fiber (OF) cable location and protection can affect the performance of DOFSS.
SCOPE
1.1 This practice specifically addresses the means and methods for the use of distributed optical fiber sensors for monitoring ground movements during tunnel and utility construction and its impact on existing utilities.  
1.2 This practice applies to the process of selecting suitable materials, design, installation, data collection, data processing and reporting of results.  
1.3 This practice applies to all utilities that transport water, sewage, oil, gas, chemicals, electric power, communications and mass media content.  
1.4 This practice applies to all tunnels that transport and/or store water or sewage.  
1.5 This practice also applies to tunnels that carry the utilities in (1.3), water for hydropower, traffic, rail, freight, capsule transport, and those used for storage.  
1.6 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.  
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.8 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Mar-2020
• ICS: 93.060 - Tunnel construction
• Technical Committee: F36 - Technology and Underground Utilities
• Drafting Committee: F36.10 - Optical Fiber Systems within Existing Infrastructure

Relations

• Replaces: ASTM F3079-14 - Standard Practice for Use of Distributed Optical Fiber Sensing Systems for Monitoring the Impact of Ground Movements During Tunnel and Utility Construction on Existing Underground Utilities
• Effective Date: 01-Apr-2020
• Refers: ASTM E2586-19e1 - Standard Practice for Calculating and Using Basic Statistics
• Effective Date: 01-Apr-2019
• Refers: ASTM E2586-14 - Standard Practice for Calculating and Using Basic Statistics
• Effective Date: 01-Jun-2014
• Refers: ASTM E177-14 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2014
• Refers: ASTM E2586-13 - Standard Practice for Calculating and Using Basic Statistics
• Effective Date: 01-Oct-2013
• Refers: ASTM E177-13 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2013
• Refers: ASTM E2586-12b - Standard Practice for Calculating and Using Basic Statistics
• Effective Date: 01-Oct-2012
• Refers: ASTM E2586-12a - Standard Practice for Calculating and Using Basic Statistics
• Effective Date: 15-Feb-2012
• Refers: ASTM E2586-12 - Standard Practice for Calculating and Using Basic Statistics
• Effective Date: 01-Jan-2012
• Refers: ASTM E177-10 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-Oct-2010
• Refers: ASTM E2586-10a - Standard Practice for Calculating and Using Basic Statistics
• Effective Date: 01-Sep-2010
• Refers: ASTM E2586-10 - Standard Practice for Calculating and Using Basic Statistics
• Effective Date: 15-May-2010
• Refers: ASTM E177-08 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-Oct-2008
• Refers: ASTM E2586-07 - Standard Practice for Calculating and Using Basic Statistics
• Effective Date: 01-Oct-2007
• Refers: ASTM E177-06b - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 15-Nov-2006

Overview

ASTM F3079-14(2020): Standard Practice for Use of Distributed Optical Fiber Sensing Systems for Monitoring the Impact of Ground Movements During Tunnel and Utility Construction on Existing Underground Utilities provides vital guidance for the implementation of distributed optical fiber sensing systems (DOFSS). This internationally recognized practice assists engineers, contractors, and owners/operators with monitoring ground movements before, during, and after tunnel and utility construction, helping to safeguard existing underground utilities.

Through the appropriate use of DOFSS, this standard supports enhanced site planning, design decision-making, and ongoing operational safety. By leveraging the capabilities of optical fiber technology for continuous, real-time monitoring, stakeholders can reduce risks, respond promptly to ground movement, and protect critical infrastructure such as pipelines, cables, and tunnels.

Key Topics

• Scope and Applicability

  • Addresses the use of distributed optical fiber sensors for monitoring ground movement and assessing its impact on underground utilities and tunnels.
  • Applies to all types of utilities (water, sewage, oil, gas, chemicals, electric power, communications, mass media) and various tunnel applications (transport, storage, hydropower, rail, and utility conveyance).

• Pre-Installation Authorization and Compliance

  • Requires contractors to secure explicit written authorization from owners/operators of both new and existing utilities before installing DOFSS.
  • May also require permits from regulatory agencies such as Department of Transportation or environmental authorities.

• System Design and Selection

  • Covers choosing suitable materials, proper system design, installation techniques, as well as data collection, processing, and reporting.
  • Emphasizes the importance of installation methods, fiber cable selection/protection, and consideration of environmental or operational constraints.

• Performance and Interference Considerations

  • Warns of potential interference between DOFSS installations and repair activities or equipment use.
  • Recommends careful planning to avoid disruptions to sensing cables during maintenance.

• Technical Terms and Concepts

  • Defines core terms such as accuracy, attenuation, spatial resolution, strain, temperature measurement, and sensing cable construction.
  • Focuses on Brillouin-based sensing technologies for long-term ground movement monitoring.

Applications

Organizations engaged in underground construction and infrastructure management use ASTM F3079-14(2020) to:

• Monitor Ground Movements

  • Detect shifts or settlement in soil surrounding tunnels and utilities, protecting infrastructure integrity.
  • Support enhanced risk assessment and early warning for ground instability or subsidence.

• Support Site Planning and Construction

  • Collect real-time data for informed design adaptations and construction sequencing.
  • Optimize excavation or boring processes by monitoring the impact on adjacent assets.

• Ensure Operational Safety

  • Continuously protect water, sewage, gas, oil, electric, and telecommunications networks during and after construction.
  • Reduce emergency repair costs by identifying issues before they escalate.

• Enable Regulatory Compliance

  • Fulfill requirements for monitoring and reporting as dictated by local or national authorities.
  • Aid in documentation for project handover and future reference.

Related Standards

For comprehensive implementation and complementary technology guidance, consider referencing:

• ASTM E177: Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• ASTM E2586: Practice for Calculating and Using Basic Statistics
• IEC 61753-1: Fibre Optic Interconnecting Devices and Passive Components Performance Standard – Part 1: General and Guidance for Performance Standards
• IEC 61757-1: Fibre Optic Sensors – Part 1: Generic Specification
• ITU-T G.652: Characteristics of a Single-mode Optical Fibre and Cable

Other related standards may cover specific sensing technologies (such as Rayleigh-based methods) or address focused applications like pipeline monitoring.

---

By adhering to ASTM F3079-14(2020), stakeholders can confidently implement distributed optical fiber sensing systems for critical monitoring tasks, ensuring the protection and longevity of underground utilities and infrastructures during tunnel and utility construction.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: F3079 − 14 (Reapproved 2020)
Standard Practice for
Use of Distributed Optical Fiber Sensing Systems for
Monitoring the Impact of Ground Movements During Tunnel
and Utility Construction on Existing Underground Utilities
This standard is issued under the fixed designation F3079; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
1.1 This practice specifically addresses the means and 2.1 ASTM Standards:
methods for the use of distributed optical fiber sensors for E177 Practice for Use of the Terms Precision and Bias in
monitoring ground movements during tunnel and utility con- ASTM Test Methods
struction and its impact on existing utilities. E2586 Practice for Calculating and Using Basic Statistics
2.2 Other Standards:
1.2 This practice applies to the process of selecting suitable
IEC 61753-1 Fibre Optic Interconnecting Devices and Pas-
materials, design, installation, data collection, data processing
sive Components Performance Standard—Part 1: General
and reporting of results.
and Guidance for Performance Standards
1.3 This practice applies to all utilities that transport water,
IEC 61757-1 Fibre Optic Sensors—Part 1: Generic Specifi-
sewage, oil, gas, chemicals, electric power, communications
cation
and mass media content.
COST Action 299 “FIDES” Optical Fibres for New Chal-
1.4 This practice applies to all tunnels that transport and/or lenges Facing the Information Society
ITU-T G.652 Characteristics of a Single-mode Optical Fibre
store water or sewage.
and Cable
1.5 This practice also applies to tunnels that carry the
utilities in (1.3), water for hydropower, traffic, rail, freight,
3. Terminology
capsule transport, and those used for storage.
3.1 Definitions of Terms Specific to This Standard:
1.6 The values stated in inch-pound units are to be regarded
3.1.1 accuracy—the closeness of the measured value to the
as standard. The values given in parentheses are mathematical
true or the ideal value of the parameter being measured.
conversions to SI units that are provided for information only
Accuracy represents the difference between the measured
and are not considered standard.
result and the true value and is affected by both bias and
1.7 This standard does not purport to address all of the
precision.
safety concerns, if any, associated with its use. It is the
3.1.2 attenuation—thedecreaseinpowerofasignal,orlight
responsibility of the user of this standard to establish appro-
wave, from interaction with the propagation medium. The
priate safety, health, and environmental practices and deter-
decrease usually occurs as a result of absorption, reflection,
mine the applicability of regulatory limitations prior to use.
diffusion, scattering, deflection, dispersion or resistance.
1.8 This international standard was developed in accor-
3.1.3 attenuationbudget(alsocalledopticalpowerdynamic
dance with internationally recognized principles on standard-
range and link budget)—the maximum cumulative one-way or
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
1 3
This practice is under the jurisdiction ofASTM Committee F36 on Technology Available from International Electrotechnical Commission (IEC), 3, rue de
and Underground Utilities and is the direct responsibility of Subcommittee F36.10 Varembé, 1st floor, P.O. Box 131, CH-1211, Geneva 20, Switzerland, https://
on Optical Fiber Systems within Existing Infrastructure. www.iec.ch.
Current edition approved April 1, 2020. Published April 2020. Originally For additional information, visit http://www.cost.eu.
approved in 2014. Last previous edition approved in 2014 as F3079–14. DOI: Available from International Telecommunication Union (ITU), Place des
10.1520/F3079–14R20. Nations, 1211 Geneva 20, Switzerland, http://www.itu.int.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F3079 − 14 (2020)
two-way power loss between the interrogator and the measure- 3.1.20 failure criteria of the sensor—the measurement un-
ment point that allows a measurement with a specified perfor- certainty due to overstressing, overheating and other factors
mance. leading to results or data that are unreliable.
3.1.4 bias—the difference between the measured result after 3.1.21 gauge length (GL)—the length of the fiber that
averaging and the ‘true’value. The true value can be obtained contributes to the measured output value of a single channel.
either by measuring a reference standard maintained by the
3.1.22 life expectancy—a period of time during which the
national standard organizations or by using a traceable mea-
measuring system or its components are expected to operate
suring instrument.
according to its specifications for defined conditions.
3.1.5 bofda—Brillouin optical frequency domain analysis.
3.1.23 limiting conditions—the extreme conditions that a
3.1.6 bofdr—Brillouin optical frequency domain reflectom- measuring instrument is required to withstand without damage,
etry. needingtoswitchoffordegradationofspecifiedcharacteristics
when it is subsequently operated under its rated operating
3.1.7 botda—Brillouin optical time domain analysis.
conditions.
3.1.8 botdr—Brillouin optical time domain reflectometry.
3.1.24 linearity—the tolerance to which the transfer re-
3.1.9 characteristic frequency and/or wavelength at refer-
sponse characteristics of a measurement system (scale factor)
ence temperature (Brillouin technologies)—the wavelength
approximates a straight line over the sensor range of the
that characterizes the sensor response at reference temperature
system. For Brillouin sensors, it means that the range of
as monitored by the interrogator.As Brillouin frequency varies
temperature or strain should be within the Brillouin frequency
with wavelength of the light source, this also changes the
which is linearly proportional to the strain or temperature. For
temperature and strain coefficients for various sensing fibers.
Optical Frequency-Domain Reflectometry (OFDR) systems it
Therefore, the characteristic frequency and the wavelength at a
means that the wavelength or frequency shift is linearly
specified reference temperature and at zero strain are usually
proportional to temperature or strain over certain length.
provided by the producers.
3.1.25 linkbudget(alsocalledopticalpowerdynamicrange
3.1.10 cladding—optical transparent material over the core
or attenuation budget)—the maximum cumulative one-way or
of the fiber optic cable, with a refractive index lower than that
two-way power loss between the interrogator and the measure-
of the core, to provide total internal reflectance.
ment point that allows a measurement with a specified perfor-
mance.
3.1.11 connector—coupling device that permits a signal to
pass from one optical fiber to another.
3.1.26 location accuracy—the estimated location of a mea-
surement or other system output, such as a detection report,
3.1.12 connector insertion loss—the power loss due to the
insertion of a connector between two elements. minus the true location of the stimulus that generated the
measurement or output.
3.1.13 contractor—usually, the entity in charge of construc-
tion of the new tunnel or other infrastructure that may impact 3.1.27 measurement range—a set of values of measured
parameters for which the error of a measuring instrument is
the utility.
intended to fall within specified limits.
3.1.14 core—the primary light-conducting region of an
optical fiber. The refractive index of the core is higher than its 3.1.28 measuring spatial resolution—the minimum distance
over which the DOFSS is able to detect the value of the
cladding, the condition necessary for total internal reflection.
measured parameter, such as strain or temperature, averaged
3.1.15 cross-sensitivity—the unwanted change of measured
over this minimum distance, within the specified uncertainty.
result due to the influence of physical factors other than the
measured parameters. 3.1.29 measuring time—therequiredtimeintervalneededto
obtain a measurement within the specified uncertainty, the
3.1.16 distributed optical fiber sensor system (DOFSS)—a
spatial resolution, and the system range, including any time
system using optical fiber cable as a sensor, without discrete
required for data post-processing.
elements such as wound mandrels or fiber Bragg gratings, that
is sensitive over its entire length to deliver spatially continuous 3.1.30 noise—the random variation in the measurement
result unrelated to the measured parameter. It primarily affects
and resolvable data on the desired measured parameters.
the precision of measurement.
3.1.17 drift—a slow change in time of the monitoring
characteristics of the measurement system. 3.1.31 operating temperature range of the measurement
unit—the range of temperatures over which, the measurement
3.1.18 durability—a quality of a manufactured component
unit can collect data on the parameters of interest, without
of a measurement system or of the entire measurement system
losing its capacity for performance and reliability.
measured by how well it withstands a sustained period of
specified operation. 3.1.32 operator—the firm hired by the owner to perform
operation and maintenance of the tunnel or utility.
3.1.19 engineer—the licensed professional engineer desig-
nated by the owner/operator of the utility or the tunnel to 3.1.33 optical fiber sensing cable—cable formed using one
represent the owner’s/operator’s interests during the ground or more strands of optical fiber to sense physical parameters
movement monitoring process. and/or transmit data.
F3079 − 14 (2020)
3.1.34 optical fiber sensor—composed of one or more fiber, cf, using dx5dt*cf⁄2. The spatial sampling interval shall
optical fiber sensing cables and the associated light signal be at least one-half of the spatial resolution.
processing equipment as pertinent to DOFSS defined in 3.1.16.
3.1.49 system distance range—the length of fiber over
3.1.35 optical power dynamic range (also called link budget which the measurement can be performed within the stated
and attenuation budget)—the maximum cumulative one-way precision, or the system can achieve its stated performance (for
example, probability of detection, location accuracy.).
or two-way power loss between the interrogator and the
measurement point that allows measurement with a specified
3.1.50 tester—the person or the entity responsible for car-
performance.
rying out the evaluation of the impact of tunneling or utility
3.1.36 owner—the person(s) or a governing body charged construction.
with construction, operation and maintenance of the under-
3.1.51 total internal reflection—reflection that occurs in a
ground utility or tunnel system.
medium when the incidence angle of a light ray striking a
3.1.37 precision—describes how repeatable a measurement boundary of the medium is greater than the critical angle and
the entire energy of the ray is reflected back into the medium.
result is. Precision is measured by the estimated standard
deviation of a specified series of measurements.
3.1.52 true value—the result of a measurement that would
beobtainedbyaperfectmeasurementwithnoprecisionorbias
3.1.38 Rayleigh cotdr—Rayleigh coherent optical time do-
main reflectometry. error.
3.1.53 updating time—the time interval between updates of
3.1.39 repeatability—the closeness of the agreement be-
the measured value of all channels of the DOFSS. This is the
tween the results of successive measurements of the same
same as the temporal sampling interval for systems other than
measured parameter carried out under the same conditions of
multi-channel or those that provide data incrementally.
measurement. This means that for every one hundred repeated
strain or temperature measurements, repeatability is the mea-
3.1.54 warm-up time—the duration from the time power is
sure of the highest probability associated with either the strain
turned on until the system performs in accordance with all
or the temperature.
specifications.
3.1.40 report—the official written work product or project
3.1.55 wavelength—the length of a wave measured from
deliverable that contains a description of the scope of work
any point on a wave to the corresponding point on the next
done, data collected and presented in various forms, interpre-
cycle of the wave.
tation of the data, findings and recommendations for further
3.1.56 wavelength of operation—the range of wavelengths
action.
ofopticalradiationthesensorusestoprovidetherequireddata.
3.1.41 reproducibility—the closeness of the agreement be-
NOTE 1—Every effort has been made in the above definitions to be
tween the results of measurements of the same measured
consistent with those defined in Cost Action 299 and IEC 61757-1.
parameter carried out under changed conditions of measure-
ment.
4. Summary of Practice
3.1.42 resolution—the smallest change in the measured
4.1 Distributed optical fiber sensing technology has many
parameter that can be indicated by the measurement system.
advantagesovercurrentmethodsusingdiscrete“point”sensors
Not to be confused with precision. This is often called the
for monitoring ground movements around underground utili-
“quantization interval” of the measurement system.
ties and tunnels.The advantages include, but are not limited to:
3.1.43 responsivity—the change in the response (output
4.1.1 Their distributed nature means that there are no
signal) of a complete measurement system to the correspond-
monitoring gaps, as compared to conventional point sensors,
ing change in the stimulus (input signal).
provided the distributed optical fiber sensing cable is installed
over the whole length, area or volume of interest;
3.1.44 scale factor—the inverse of the ratio of a change in
the stimulus to corresponding measured change.
4.1.2 Asingle optical fiber sensing cable can provide tens of
thousands of continuously distributed measurement points;
3.1.45 scale factor at reference conditions—the ratio of the
4.1.3 No electricity used within the optical fiber sensing
measured input parameter’s engineering units to the output
cable; thus, it is immune to electromagnetic interference and
parameter’s units.
does not cause electromagnetic interference (EMI), other than
3.1.46 sensor range—the range between the smallest and
that generated by the electro-optical equipment—which can be
the largest allowable value of the measured parameter.
shielded and controlled;
3.1.47 spatial resolution—the minimum distance between
4.1.4 They are generally safe in explosive environments;
two step transitions of the measured parameter in time domain
4.1.5 They can be made robust to chemical exposure
that can be independently observed with a specified perfor-
throughproperdesignandmaterialsselectionfortheprotective
mance.
outermost sheath of the cable;
3.1.48 spatial sampling interval (dx)—The spatial distance 4.1.6 Cost-effective due to the ability to collect data over
along the fiber between two adjacent outputs of the DOFSS. long distances from a single electro-optical interrogator unit;
This is usually controlled by the high-rate temporal sampling cable lengths for a single system of 60 miles (100 km) are
interval of the optical detector, dt, and the speed of light in the achievable.
F3079 − 14 (2020)
4.2 Successful broader adoption of this technology depends ground. It may also be necessary for the installer to have
on the proper selection of most appropriate materials, design, written explicit authorization from applicable jurisdictional
installation, data collection, interpretation and reporting user agencies such as the Department of Transportation, the Army
interface design. Corps of Engineers, the Department of Environmental Protec-
tion and other.
4.3 This practice offers the minimum standards on the
essential aspects of this technology. 5.3 Engineers, contractors, and owners/operators shall also
be cognizant of how the use of distributed optical fiber sensing
4.4 There are many different technologies that fall within
for monitoring ground movements around utilities and tunnels
the classification of DOFSS that can be used for measuring
might interfere with the use of certain equipment or tools near
ground movement during tunneling or utility construction and
the installed optical fiber sensing cable in some special
its impact on existing utilities. The focus in this practice,
situations. For example, repair activities may have to tempo-
however, is solely on the most widely used Brillouin scattering
rarily remove, relocate, or avoid the optical fiber cable.
technologies (BOTDR / BOTDA).
5.4 Engineers, contractors, and owners/operators should be
4.5 The user of this practice needs to be cognizant that a
cognizant of how installation techniques and optical fiber (OF)
companion standard covers the standard practice for leak
cable location and protection can affect the performance of
detection in pipelines using Rayleigh Coherent Optical Time
DOFSS.
Domain Reflectometry (COTDR). That standard describes the
complementary technology to Brillouin DOFSS in far more
6. Instrumentation Objective, Design and Layout
detail. Rayleigh COTDR can also be used for very precise
6.1 Brief Overview—The effect of Brillouin scattering is the
detection of short-term ground movements. It is most
most widely used form of DOFSS technology which provides
applicable, however, to short-term strain events because Ray-
a monitoring technique to measure strain and temperature
leigh methods cannot measure very low frequency strain in the
alongtheintendedopticalfiberrouteasshownintheschematic
presence of the background thermal variation in most environ-
view in Fig. 1. The optical cable itself plays the role of
ments. This practice’s focus is primarily on the most widely
hundreds of thousands of sensors of multiple parameters of
usedBrillouintechnologyformeasuringlong-termstrains.The
interest for long distances. Usual telecommunication optical
users of this practice may refer to companion standards for
fiber cables are designed to protect the optical fibers from the
specific guidance on the use of other forms of optical fiber
surrounding environment. In a strain sensing cable, however,
sensing technologies to meet the needs of similar or other
the environment causing stimuli must be efficiently transferred
applications.
to the optical fiber core that transmits light or the medium in
4.6 The DOFSS technologies discussed in Section 6 of this
which we can measure the effects of Brillouin scattering.
practice measure the longitudinal strains along the optical fiber
Typical optical fiber sensing cable designs are shown in Figs.
sensing cables to assess the impact of new tunnelling and
2-4. When light travels through a transparent media such as
utility works on existing tunnels or utilities. The conversion of
glass, most of it goes through the core of the fiber, while a
the strain measurements to displacement measurements require
small fraction is back scattered due to the perturbation follow-
processing of the strain data with appropriate assumptions for
ing the principle of total internal reflection illustrated in Fig. 5.
the boundary conditions. Therefore the resulting indirect dis-
Different components of the back scattered light can be
placement measurements are expected to yield an estimate of
identified, including the Brillouin scattering components, such
the in-situ displacements. As a result, the measured ground
as the peaks shown in Fig. 6; these are carefully analyzed and
movements referred to in the text of this practice shall be used
used to measure temperature or strain along the fiber. In this
bearing this in mind. Better accuracy may be achieved,
technology, two laser beams are injected into an optical fiber
however, when procedures discussed in 9.3 and 9.5 of the
core from both its ends, as shown for BOTDA in Fig. 7. One
practice are used.
is called the pump signal, being a pulse-modulated (for
BOTDA systems) or a sinusoidally modulated (for BOFDA
5. Significance and Use
systems) laser beam of a unique wave profile; the other one is
5.1 This practice is intended to assist engineers, contractors
the continuous (CW) probe laser, sometimes referred to as the
and owner/operators of underground utilities and tunnels with
Stokes laser.The interaction of these two laser beams produces
the successful implementation of distributed optical fiber
an acoustic wave through the phenomenon called “electrostric-
sensing for monitoring ground movements prior to construc-
tion.” The pump signal is backscattered by the phonons, and
tion for site planning and during utility and tunnel construction
the energy is transferred between the pump signal and the CW
and operation and the impact of such ground movements on
probe light. The Brillouin Loss Spectrum (BLS) or Brillouin
existing utilities.
Gain Spectrum (BGS), as the function of frequency difference
5.2 Before the installation of distributed optical fiber sens- between the two laser beams, is measured by scanning the
ing begins, the contractor shall secure written explicit autho- frequency of the CW probe light. The value of the strain or the
rization from the owner/operator of the new tunnel/utility and temperature can be estimated using the shift of the peak
the existing utilities allowing an evaluation to be conducted for frequency of BLS/BGS (Brillouin frequency), whilst its posi-
the feasibility of distributed optical fiber sensing for monitor- tion calculated from the light round-trip time as shown on the
ing ground movements for the intended purpose and to have right one-half of Fig. 7. Similar set up for the BOTDR
access to certain locations of the structure and the surrounding technology is shown in Fig. 8. Therefore, an appropriate
F3079 − 14 (2020)
FIG. 1 Typical Layout of a DOFSS
FIG. 2 Components of Various Optical Fiber Sensing Cables
FIG. 3 Components of an Optical Fiber Strain Sensing Cable
interrogator, like the one shown in Fig. 9, with a graphic user thousands of locations along the route of the optical fiber,
interface shown in Fig. 10, and the software, for example essentially in real time. Typical results from such BOTDAand
shown in Fig. 11, can acquire and keep track of the position BOFDA are shown for strains in Fig. 12 and Fig. 13,
and the magnitude of the strain or temperature at hundreds of respectively.
F3079 − 14 (2020)
FIG. 4 Components of an Optical Fiber Strain and Temperature Sensing Cable
FIG. 5 Principle of Total Internal Reflection
FIG. 6 Brillouin Peaks as Functions of Wavelength
6.2 Effect of Brillouin Scatter Facilitating Temperature and to temperature and strain, and measurements can be made on
Strain Measurements—Brillouin scatter is extremely sensitive the effects of such environmental stimuli on the serviceability
toanychangesintemperatureandthedeformationorthestrain of a buried pipeline or the ground responding to the impact of
experienced by the optical fiber. In this regard, most environ- tunneling or new utility construction. The frequency shift, ν ,
B
mental stimuli the optical fiber is exposed to can be correlated can be calculated using:
F3079 − 14 (2020)
FIG. 7 Principal Components of the BOTDA System
FIG. 8 Details on a BOTDR System
FIG. 9 Typical BOTDA
ν 5 2nVa ⁄ λo (1)
$ % where:
B
K = the bulk modulus, and
where:
ρ = the density of the optical fiber.
n = the effective refractive index of the propagating mode,
The density of the optical fiber is dependent on temperature;
Va = the acoustic wave velocity in the optical fiber, and
therefore, the Brillouin peak shifts when plotted as a function
λo = the vacuum wavelength of the incident light.
of the difference in the frequency between the laser pump and
It is clear that the Brillouin frequency shift is affected by the
the signal varying with temperature as shown in Fig. 14.
acoustic wave velocity, which can be expressed using the
Similarly, any deformation or strain in the optical fiber affects
theory of elasticity, for homogenous, isotropic, linearly elastic
thedensityoftheopticalfiberasshowninFig.15.Insummary,
solids as:
the temperature and the strain induced in the optical fiber can
0.5
Va 5 K⁄ ρ (2) be measured using the effects of Brillouin scattering.
$ %
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FIG. 10 Typical Graphic User Interface
FIG. 11 Typical Screen Shot of Software of BOFDA
6.3 Instrumentation Objective—The instrumentation objec- resolution, the sampling interval, the accuracy and the
tive has to be clearly stated by the involved parties in terms of repeatability, the system range, the strain range of the instru-
what problem is going to be solved (for example, detection of ment and the optical fiber sensing cable, and the temperature
ground movements, quantification of axial elongation or range of the instrument and the optical fiber sensing cable. In
shortening, bending, shear, stresses, strains in the utility pipes). addition, the system components and especially the cable need
Theobjectiveshallalsoincludethedefinitionofthetimeframe to be of adequate durability to survive the harsh soil
of the monitoring-during a limited time period such as when environment, ground water, rodents, and other environmental
there is nearby construction, a specific season or the lifetime of forces.
the structure. The objective shall also include a clear statement
6.5 Instrumentation Layout—The instrumentation layout
on how the resulting data will be used and who will be
specifies the details of the object to be instrumented and the
responsible for data management and analysis. If the system is
projectoverall.Itneedstobedefinedwhere,whenandhowthe
used to generate alerts, a clear response plan to all types of
optical fiber sensing cable are to be placed, attached and
possible alerts also shall be prepared.
protected, where the readout unit is to be placed and what
6.4 Instrumentation Design—The instrumentation has to be services are available at that location, what the overall time
designed in a way so that the objective can be achieved by the frame is and whether for all construction stages, and the
system components’ specifications, such as the spatial locations of the necessary connections and the interfaces.
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FIG. 12 Typical Results on Strain Measurements from BOTDA
7. System Components one-half as short as the spatial resolution. Sometimes it is
defined as spatial accuracy or distance resolution.
7.1 Specifications for the Sensing Instruments:
7.1.3 Measured Accuracy—This represents the smallest
7.1.1 SpatialResolution—ThisspecifiesforaDOFSSbythe
change in the measured parameter, meaningfully detectable by
minimum resolvable distance between two step transitions of
the measurement system.
the measured parameter of amplitude greater or equal to 20
7.1.4 Repeatability—This is defined as the closeness of the
times of the system resolution. The spatial resolution has its
agreement between the results of successive measurements of
physical origin in the optical pulse width in time domain
the same parameter carried out under the same conditions of
systems, or the equivalent pulse length in frequency domain
measurement.
and correlation domain systems.
7.1.2 Spatial Sampling Interval—This specifies the spatial 7.1.5 Frequency Range—This term only applies to
Brillouin-based systems. This is the frequency range, in which
distance between two sequential data points along the cable in
the output of a distributed sensing system. The sampling a Brillouin frequency shift can be measured. The temperature
interval is dominated by the sampling rate of a time domain and the strain sensing ranges are derived from this with the
system and has no direct impact on the spatial resolution. It is knowledge of the characteristic fiber parameters. This property
necessary, however, to use a sampling interval which is at least changes from one fiber to another. When different sensing
F3079 − 14 (2020)
FIG. 13 Typical Results on Strain Measurements from BOFDA
FIG. 14 Peak from Brillouin Scattering Affected by the Temperature of the Optical Fiber
fibers are used, the Brillouin frequency for a known tempera- obtained, corresponding either to the dominant or to the
ture and strain and their temperature and strain coefficients maximum strain or temperature value. Peak fitting involves the
must be given for any measurement. Often it is for a standard use of a higher order polynomial function for the peak in a set
room temperature of 73 °F (23 °C) and the fiber in a loose of data points on Brillouin gain with, for example, Lorentz’
condition. algorithm to minimize the variance. Especially for abnormal
7.1.6 Frequency Step—This is the minimum frequency step strain or temperature locations, when the disturbance is shorter
with which the Brillouin gain profile is scanned. than the spatial resolution, it is important to pick up the
7.1.7 Data Processing-Peak Search—When a structure is maximum strain or the temperature rather than the maximum
subjected to varying strain or temperature within a spatial peak associated strain or temperature for the purpose of
resolution, often a few Brillouin peaks appear in the Brillouin structural health and hydraulic health monitoring of pipes.
spectrum; the peak fitting process must be imposed to consider Some Brillouin interrogators are able to provide multiple
the realistic strain or temperature condition in adjacent values for the same location, if several levels of strain or
locations, so that a realistic strain or temperature can be temperature are observed within the spatial resolution. It is
F3079 − 14 (2020)
FIG. 15 Peak from Brillouin Scattering Affected by the Strain in the Optical Fiber
important to recognize that the events that affect only a section minimum requirements on the following components and their
much shorter than the spatial resolution or the smaller stress or attributes, when applicable:
temperature change than the Brillouin peak width might not be
7.2.1 Optical Fiber Sensing Cable—The optical fiber sens-
detected at all.
ing cable consisting of a bundle of optical fibers protected by
7.1.8 Dynamic Range—This specifies the ratio between the
one or more buffer tubes and protective layers over the fibers
strongest and the weakest optical scattering event to be
is a critical element in the performance of the DOFSS. The
detected by the distributed sensing system within the specified
optical fiber sensing cable may be composed of either one or
performance.Thisismostrelevantforscattering-basedsensing
several, for different purposes (strain and temperature) or for
systems.
redundancy. Therefore, often the optical fiber sensor is formed
7.1.9 Attenuation Budget—The maximum cumulative one-
of multiple optical fiber sensing cables and other materials.
way or two-way power loss between the interrogator and the
Buffering and protection coating are critical elements in the
measurement point that allows a measurement with a specified
performance of the DOFSS. The sensing cable has to be
performance. This is relevant for both BOTDR and BOTDA/
designed in a way that the fiber within is able to be affected in
BOFDA systems. With long sensing length, and double pas-
a predictable manner by the parameter to be measured, and
sage of the scattering and pump wave, the attenuation budget
provide the required sensitivity needed to protect the asset. If
can envelope the entire dynamic range, although Erbium-
the processing units cannot distinguish individual components
Doped Fiber Amplifier (EDFA) and Raman amplifiers can be
or decouple co-mingled contents forming the output from the
useful to mitigate any excessive use of the attenuation budget.
optical fiber sensing cable, cross-sensitivity of an optical fiber
7.1.10 Compatibility to the Type of Fiber—Thiswhenspeci-
sensing cable has to be avoided. An example of this is the
fied can include material (silica, polymer etc.), geometry
cross-sensitivity of strain and temperature in Brillouin-based
(single-mode, multi-mode, non-zero dispersion-shifted
systems-which are generally solved by using a cable design
(NZDSF), polarization maintaining (PM), few-mode fibers,
with a strain coupled and strain-decoupled fiber for tempera-
etc.), references to standards (such as ITU-T G.652.D) and
ture reference, or by combining Brillouin and Raman interro-
others. If a special parameter is crucial for the sensing
gators. Sensing cables are specially designed products—
performance, this is to be specified (such as the requirement on
optimized tight buffered and loose tube cable elements. In the
single Brillouin peaks).
former, the plastic buffer tubes are bonded to the glass fiber,
7.1.11 General Caution—Spatial resolution, accuracy, mea-
and the strain on the outside of the cable is very well coupled
suring time and attenuation budget (measurement range)
to the strain in the fiber—which is then measured by the
strongly depend on each other. It is very difficult to define a
interrogator. The disadvantage of tight buffered designs is that
representation that grasps all the cross-influences of these
they are prone to micro bends, increasing the attenuation of the
parameters in a way that is helpful to the user. The best spatial
fiber, or even breaking it. These sensing cables are typically
resolution is sometime not related to the best temperature or
avoided for long cable runs because of their handling sensitiv-
strain resolution, and associated sensing length. It is important
ity; however, they are used in strain measurement systems that
to verify with suppliers the required performance for specific
attempt to measure absolute strain down to very low
parameters will meet the expectation for the product in the
frequencies, including static strain. Loose tube designs were
specific combinations that will be used in the project.
specifically developed to protect the fiber from damage and
7.2 Distributed Optical Fiber Sensing Systems—The con- change in optical propagation characteristics due to handling
tractor shall consider the following guidance and include and environmental stresses. These do not communicate the
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static or very low frequency strain in the environment around 7.2.9.2 Mechanical Coupling Between Optical Fiber Sens-
the cable to the fiber itself, and are therefore unsuitable for ing Cable and the Outside Medium—The other components of
measuring strain. Because the fiber is isolated from mechanical the DOFSS and the optical fiber sensing cable construction
strain effects, however, the Brillouin frequency shift is only a were discussed above in the section on the comparison of tight
function of local temperature changes and these cables can be buffered and loose-tube cables, and the importance of gel fill in
used for temperature compensation when installed along the loose-tube cables. See also interfacing.
side of strain cables. The sensing cables to be used is to be
7.2.9.3 Load-Elongation Relationship—The Brillouin fre-
chosen consciously and specifically as a function of the
quency is linearly proportional to the load. The coefficient
application requirements, cost, environment characteristics,
depends on the material characteristics of the fiber jacket.
type of sensing technology, required mechanical performance,
7.3 Interfaces:
compatibility with installation procedures; in other words, the
7.3.1 Interface Between the Optical Fiber Sensing Cable
strain sensing cables are not standard tight buffer telecom
and the Sensing Instrument:
cables but those that require special manufacturing processes
7.3.1.1 Optical Fiber Connectors:
ensuring that all the layers are tightly bonded together.
(1) An optical fiber connector terminates the end of an
7.2.2 Strain Sensor—A strain sensing optical fiber cable.
opticalfiber,andenablesquickerconnectionanddisconnection
7.2.3 Temperature Sensor—A temperature sensing optical
than splicing. The connectors mechanically couple and align
fiber cable.
thecoresoffiberssolightcanpass.Betterconnectorslosevery
7.2.4 Maximum Strain—The maximal strain (in tension and
little light due to reflection or misalignment of the fibers. In all,
compression) an optical fiber sensing cable may experience
about 100 optical fiber connectors have been introduced to the
before its functionality is affected by attenuation or mechanical
market. The most common connectors used in optical fiber
failureorscalefactorchange(forexample,slippageofthefiber
sensing technology are: ferrule (FC), lucent (LC) and standard
within the protection layers).
(SC).
7.2.5 Strain Range—The difference between the maximal
(2) A basic connector assembly consists of an adapter and
strain in elongation and compression.
two connector plugs. Due to the polishing and tuning proce-
7.2.6 Maximum and Minimum Temperature—The maximal
dures that may be incorporated into optical connector
and minimal temperature a sensing cable may experience
manufacturing, connectors are generally assembled onto opti-
before its functionality is affected by attenuation or mechanical
cal fiber in a supplier’s manufacturing facility. The assembly
failure (for example, melting of the protection layers).
and polishing operations involved, however, can be performed
7.2.7 Temperature Range—The difference between the
in the field, for example, to make cross-connect jumpers to
maximal and minimal allowable operational temperature of the
size. Most optical fiber connectors are spring-loaded, so the
optical fiber sensing cable.
fiber faces are pressed together when the connectors are mated.
7.2.8 Mechanical Parameters of the Optical Fiber Sensing
The resulting glass-to-glass or plastic-to-plastic contact elimi-
Cable—Mechanical property of the optical fiber sensing cable
nates signal losses that would be caused by an air gap between
depends both on the material composition of the jacket of the the joined fibers.
fiber and on the other sensor parts in contact with the external
(3) Measurements of these parameters are now defined in
media.
IEC standard 61753-1. The standard gives five grades for
7.2.9 Protection Features—The environmental demands an insertionlossfromA(best)toD(worst),andMformultimode.
The other parameter is return loss, with grades from 1 (best) to
optical fiber sensing cable is able to resist, for example,
hydrostatic pressure, chemicals, crush load, temperature. In 5 (worst). A variety of optical fiber connectors are available,
addition to the loose-tube construction technique discussed but SC and LC connectors are the most common types of
above, armoring of the cable is commonly done to increase its connectors on the market. Typical connectors are rated for 500
resistance to environmental abuse. Cables can be of single or to 1000 mating cycles. The main differences among types of
double armor construction—and have various armor configu- connectors are dimensions and methods of mechanical cou-
rations for strength and flexibility.Aparticularly strong type of pling. Generally, organizations will standardize on one kind of
armor is “wire armor” where the armor is constructed of a connector, depending on what equipment they commonly use.
tightly wound wire covering—like a spring surrounding the (4) Features of good connector design include:
cable. Rodent damage to cables is a significant threat, and (a) Low insertion loss,
armor is the first defense against it. But excessive armoring (b) High return loss (low amounts of reflection at the
may decrease the resolution of the sensing cable, for example interface),
when detecting small strains. Optical fiber sensing cable can (c) Ease of installation,
include other protection components, for example textile. (d) Low cost,
(e) Reliability,
7.2.9.1 BendingPerformance—Theminimalradiusofbend-
(f) Low environmental sensitivity, and
ing shall meet the following minimum criteria: for bend-
(g) Ease of use.
insensitivefibertheminimumbendradiusis0.2in.(5mm),for
normalsinglemodefibertheminimumbendingradiusis0.8in. 7.3.2 Interface Between the Optical Fiber Sensing Cable
(2 cm). Cables typically need a minimum bending radius of at and the Structure or the Soil—The fixation needs to assure that
least10to20cablediameters.Thesevaluesarespecifiedbythe the optical fiber sensing cable is tightly connected to the object
cable producer. under investigation. If the object is a structural component,
F3079 − 14 (2020)
fixation may be achieved by attaching the optical fiber sensing lengths typically 3.28 ft to 32.8 ft (1 m to 10 m), DOFSS
cabletotheobjectbyscrewing,welding,gluing,usingmagnets sensors are directional measuring the strain projected along
or any other means of fixation. The fixation can be realized their axis. Most cables are also sensitive to the acoustic
overthewholelengthoratdiscretelocations.Alternatively,the pressure around them, as well as the strain, so at higher
optical fiber sensing cable may be embedded directly into the
frequencies, their response is not exactly that of an ideal
structure. If the object under investigation is the soil itself, a extended strain sensor. If the optical fiber sensing cables are
tight connection of the optical fiber sensing cable to the soil is
used for qualitative measurements, for example, to only
required. This may be achieved, however, by friction between identify locations with high levels of strain, either a simpler
the optical fiber sensing cable and the soil or by placing
calibration procedure or the use of generic calibration coeffi-
micro-anchors at intervals along the optical fiber sensing cable. cients shall be sufficient. Calibration shall meet the minimum
An alternative is to embed tightly the sensing cables onto a
requirement of 1 µstrain.
geotextile with high friction properties with the surrounding
8.4.1 Simultaneous Determination of Strain and Tempera-
soil. The failure force of the fixation has to be chosen in a way
tureCoeffıcientsoftheSensingCable—Calibrationofthestrain
that either the fixation fails before the optical fiber sensing
and temperature coefficients, c and c , shall be performed
ε T
cable fails at the force corresponding to maximum allowable
according to 8.4.1.2 by the integrator in case the intended fiber
strain in the optical fiber sensing cable or that the fixation force
optic cables (that is, sensors) were not characterized by the
is larger than the optical fiber sensing cable force at the
cable manufacturer. The process described in 8.4.1.2 can also
maximal allowable strain. It is sometimes desirable that the
be used for quality control of reported values by fiber manu-
connection between the optical fiber sensing cable and the
facturers as described in 8.4.1.3. These calibration coefficients
object under investigation loosens at high level of strain to
can be defined as:
avoid breakage of the sensing cable. This means that not all of
] ν ] ν
B B
the strain will be transferred to the cable from the surrounding
∆ν 5 ∆ε1 ∆T
U U U U
B
] ε ]T
T5const ε5const
medium and hence not all of the strain will be measured.
(3)
] ν ] ν
B B
c 5 ;c 5
U U U U
ε T
] ε ]T
8. Details of Instrumentation T5const ε5const
8.4.1.1 Calibration Setup—The process shall be performed
8.1 Fixation and Installation Procedures—Fixation and in-
stallation procedures need to be laid out in detail so that all using a calibration setup which consists of the following
components and configuration (schematically shown in Fig.
involved personnel are able to follow these procedures to
assure consistent quality of the installation. In add
...