Water Tunnel Condition Assessment - Jacobs Associates

Water Tunnel Condition Assessment: A Comprehensive Approach to
Evaluating Reliability
By Blake D. Rothfuss, PE, D.WRE
Jacobs Associates
Susan L. Bednarz, RG, CEG
Jacobs Associates
Erin S. Clarke, PE
Jacobs Associates
ABSTRACT: Water tunnels present a unique challenge to asset managers as they are very
difficult to evaluate while they are in-service. Whether the water is used for hydroelectric
production or water supply (and sometimes both), water tunnels are essential infrastructure and
expected to maintain the highest reliability. Unfortunately, assessing the condition of a tunnel
and evaluating its reliability requires taking the tunnel out of service for inspection. Satisfying
operational and customer needs can make tunnel outages difficult to schedule, and at best, short
duration events. Once a curtailment is scheduled, inspecting the tunnel presents unique logistical
and safety challenges, further complicating the condition assessment process.
Asset managers need well-executed tunnel condition assessments to develop fiscal projections
and capital improvement programs for their water tunnels. Water tunnel reliability projections
must be based on a comprehensive understanding of the water tunnel’s current condition that is
developed by experienced water tunnel engineers. The condition assessment team must be
knowledgeable in water tunnel operations, underground safety, concrete and steel lining
evaluation, historic construction methods, and defect interpretation. This comprehensive
understanding enables the inspection team to quickly assess tunnel conditions and identify issues
important to maintaining reliability.
This paper discusses a water tunnel condition assessment methodology that delivers valuable
planning information for asset managers and operations and maintenance (O&M) managers.
Several applications of the methodology will be discussed, including the condition assessment
objectives, tunnel inspection techniques, underground safety procedures, photographic methods,
and overall condition assessment documentation.
BUSINESS SETTING
Surface water reservoirs may not be co-located adjacent to a hydroelectric generating station or
water treatment facility, necessitating the use of aqueducts to convey water long distances
beneath and above ground. A water conveyance system may consist of tunnels, water control
gates and valves, pipelines (low pressure), ditches, canals, flumes, and penstocks, most of which
can be inspected while the system is in-service or routinely during shutdown periods. Tunnels
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and related water controls, however, cannot be inspected while in-service and, depending on a
tunnel’s length, may not be safely inspected during a brief shutdown.
Asset managers are dependent on the condition of the water tunnels to meet their customers’
needs and expectations. Sight unseen, operators trust that water flowing into a tunnel will exit at
the downstream end, and flow into the next conveyance element. Similarly, submerged
mechanical controls—e.g., intake gates, control valves, and turbine shutoff valves—must have
the highest reliability when operated. Tunnels, like other critical infrastructure, will deteriorate
with time; however tunnel problems can arise suddenly and immediately interrupt power
generation or water supply. Confident service reliability is only possible through comprehensive
and well-managed asset-based risk management programs. Understanding the condition of a
water tunnel is a critical component of assessing its reliability and fiscal risk.
CONDITION ASSESSMENT OBJECTIVES
At an asset program level, the primary objective is to assess the tunnel’s condition relative to
current operating demands and identify all future major fiscal needs necessary to maintain the
tunnel’s reliability and asset value. An emerging secondary objective is associated with assessing
the tunnel’s future worth. Consideration of future beneficial uses associated with the hydro
development or water supply system may place greater demands on an in-service tunnel.
Maintaining an accurate as-built record of the tunnel facilitates the planning process without
affecting day-to-day water conveyance. Also, in recent years knowledge transfer between
employee generations has also led to increased emphasis on understanding out-of-sight assets
such as tunnels.
Once the asset program manager has determined that additional information is needed, a projectspecific
water tunnel condition assessment can be planned. Typical objectives include the
following.
Work safely. Water tunnels present tunnel inspectors and their support crews with numerous
operational and weather-related hazards. Tunnels should be considered as permit-required
confined spaces, and the tunnel inspection should be carefully planned and executed with
extreme discipline. An injury or illness within a water tunnel can be potentially fatal.
Document the condition of the tunnel. A tunnel may be inspected in a watered or unwatered
state, and at varying levels of detail. The benefits and shortcomings associated with each method
should be considered early in the planning process. These observations can confirm whether the
tunnel and associated mechanical systems can be depended upon or they can identify necessary
improvements, see Figures 1 through 4.
Prioritize any deficiencies relative to potential impacts on reliability and efficiency.
Rockfalls within the tunnel may increase hydraulic head losses and reduce the generating
station’s efficiency. Structural lining defects may influence long-term maintenance costs on
turbines or may create sudden and catastrophic ground instabilities, forcing an outage.
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Develop a plan to access and repair the deficiencies. The repair plan should include
engineered repair requirements, a schedule plan, and outage requirements. Tunnel repairs can
present significant logistical challenges. Repair work should be planned assuming very limited
outage windows and 24-hour workdays. Personnel, materials, and equipment movements should
be carefully choreographed as most of the repairs rely on a single access point and long travel
distances to the repair locations. Cost estimates should include reasonable contingencies for
weather, water control, material availability, design efficiency, and inflation.
Figure 1. Identified leaking intake gate seal
or obstruction in the waterway
Figure 2. Confirmation that the surge tank is
in operable condition
Figure 3. Identification of tunnel lining repairs
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Figure 4. Inspected butterfly valve
Estimate the remaining dependable service life with and without repairs. If consecutive and
comparable tunnel condition assessments are available, a rate of deterioration can be used to
estimate the tunnel’s remaining dependable service life.
Integrate the planning information into the asset management plan. The repair costs may be
easily included in the current work plan or next year’s budget or may require 5 to 10 years to
implement. In some cases, the planning for a replacement tunnel may be appropriate.
UNDERGROUND SAFETY PROCEDURES
Identify Hazards and Mitigation Measures
Safety must be a high priority for all tunnel inspections. Safety regulations applicable to
inspecting in-service water tunnels must be considered during the planning phase of the
condition assessment. In the United States, the provisions of the General Industry Safety Orders
(29 CFR 1910) apply to the inspection of tunnels, and the provision of the Construction Safety
Orders (29 CFR 1926) apply to the construction of tunnels. Three primary hazards, which are
common to all unwatered tunnel inspections, must be considered: tunnel instability, atmospheric
hazards immediately dangerous to life or health (IDLH), and operational hazards. These, and any
other hazards identified through a job hazard assessment, must be mitigated prior to and
throughout the inspection.
Tunnel Instability. Engineers experienced in underground engineering and construction should
watch for localized tunnel instability throughout the inspection. They should look for signs of
structural distress in the rock and structural linings. Crack patterns can often identify hazard
areas that can be avoided during the inspection.
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Atmospheric Hazards. Any source of airborne contaminants or toxic vapors must be kept far
away from the tunnel air inlets to ensure that fresh air is drawn into the tunnel as it is drained.
Exhaust from motor vehicles, generators, and compressors cannot be drawn into the tunnel
during draining. Also, toxic hydrogen sulfide gas (H 2 S) or explosive gas may be encountered
underground. Most atmospheric hazards can be resolved by using fans and natural ventilation.
Table 1 presents an atmospheric monitoring worksheet.
Operational Hazards. The most significant operational hazard on most water tunnel inspections
is the potential for flooding. Flooding can be prevented by effectively using lockout-tagout
(LOTO) protocols that isolate reservoirs from the tunnel being inspected. Two forms of LOTO
exist in most agencies: physical and administrative. Administrative LOTO places a clearance tag
or man-on-line tag (typically paper) on equipment control surfaces. Operators are trained not to
place equipment in service if a tag is present. Physical LOTO requires that equipment be
temporarily disabled or prevented (by locking) from operating. A combination of administrative
and physical LOTO methods is particularly effective in hydro and water supply systems.
Differing Site Conditions. The job hazards assessment should identify all of the potential
hazards tunnel inspectors may be exposed to; however, in tunnels that have not been recently
inspected, actual site conditions may be different than anticipated. The lead inspector should be
authorized to postpone or alter the inspection plan in the event that actual conditions are too
hazardous. In most cases, well-prepared inspectors can adapt to different conditions, as was the
case when very slippery mud was encountered in a water tunnel (see Figure 5).
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Table 3-1
Table 1. Atmospheric Monitoring Record
Station Time Air Speed*
(fpm)
Air Flow
(cfm)
O2
(%)
CO
(ppm)
H2S
(ppm)
LEL
(%)
Temp
( o F)
Press.
(mm Hg)
Exterior, Adit 1 0728 N/R N/R 20.9 0 0 0 40 27.85
Interior, Adit 1 0728 N/R N/R 20.7 0 0 0 N/R N/R
Sta. 566 0813 N/R N/R 20.4 0 0 0 N/R N/R
Sta. 600 0830 No radio contact with adit
Sta. 682+50 0858 N/R N/R 20.9 0 0 0 N/R N/R
Sta. 700 0908 180 4,500 20.7 0 0 0 56 27.9
Sta. 730 1020 170 4,250 20.9 0 0 0 61 27.9
Sta. 756 1058 92 2,300 20.7 0 0 0 56 N/R
Sta. 764+71 1111 N/R N/R N/R N/R N/R N/R N/R N/R
Sta. 800 1145 N/R N/R 20.7 0 0 0 N/R N/R
Sta. 819 1215 N/R N/R 20.7 0 0 0 N/R N/R
Weep hole @ 3 o’clock producing water + gas
Sta. 856 1258 130 3,250 20.7 0 0 0 55 27.8
Sta. 900 1428 150 3,750 20.7 0 0 0 57 27.8
Sta. 968+30 1649 N/R N/R 20.9 0 0 0 56 N/R
Adit 2 1823 N/R N/R 20.9 0 0 0 N/R N/R
* Natural ventilation only.
N/R = Not Recorded
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Figure 5. Very slippery mud encountered in a water tunnel
Six inches (150 mm) of mud in this unlined tunnel were an unanticipated hazard and created
continuous slip and fall hazards for several miles. Inspectors used walking sticks to help
maintain their stability.
Safety Preparations
Communication
Communication between the surface support team and tunnel entrants is typically problematic
during long in-service water tunnel inspections. The inspection team should carry radios for
voice communication, but the range may be limited to less than about 1.6 miles (2.5 km) and will
be significantly affected by tunnel bends. Air horns have been used effectively in concrete-lined
tunnels to signal safety team members, but a horn’s effectiveness can be significantly affected by
unlined rock tunnel surface irregularities.
To safeguard the inspection team in the event that communication is lost during an underground
emergency, the inspection party should include at least two people trained in first aid. The
inspection team should be large enough that two entrants could be sent for help if needed, while
the remainder of the inspection team can attend to an injured inspector.
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Safety Instruction
Prior to entering the tunnel, all tunnel entrants and the support team should participate in an
extended safety tailgate meeting. The agenda includes the following topics: purpose of
inspection, access, anticipated conditions, safety procedures, communication, accident
prevention, and emergency response procedures.
Personal Protective Equipment
Personal protective equipment for the tunnel entrants is selected to protect against the identified
hazards. A comprehensive list of the required personal protective equipment is included in
Appendix A.
Pre-entry Activities and Monitoring during Inspection
Prior to entering the tunnel, a permit required confined space permit must be completed. The
permit includes essential information about the inspection, including the hazards assessment,
incident action plan, communication plan, LOTO procedures, personnel accountability plan,
personal protective equipment list, and atmospheric monitoring equipment list. A sample permit
is included in Appendix B.
In inverted siphon tunnels, provisions to pump out the tunnel and remove residual leakage may
require significant planning and involve water discharge permits. Figure 6 illustrates a
submersible pump and backup required to drain a tunnel for inspection.
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Figure 6. Submersible pumps may be required to unwater a tunnel prior to inspection
TUNNEL INSPECTION TECHNIQUES
The inspection team may consist of two functional groups—a survey group and a condition
assessment (CA) group.
The survey group is responsible for the inspection navigation. It leads the inspection
team, identifies significant hazards, and establishes tunnel stationing.
The CA group is responsible for assessing the condition of the tunnel. It interprets the
geologic conditions; sounds out the concrete lining to identify structurally inadequate
concrete sections and voids behind the lining; classifies the defects; counts defects and
voids; measures water infiltration flows; records the sizes and orientations of defects and
cavities; and photographs and videotapes the tunnel’s condition.
SURVEY METHODOLOGY
The survey group leads and sets the pace for the inspection team, stations the tunnel, and warns
the CA group of any significant hazards. Based upon as-built drawings and landmarks (see
Figure 7) within the tunnel, the survey group stations the tunnel and locates key features. This
effort aligns the inspectors’ observations with the tunnel stationing. At 100-foot (33.3 m)
intervals, the tunnel stationing should be marked on the walls with spray paint (NSF 61
compliant) or crayons. Tunnel stations should also be determined for the beginning and end of
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each concrete tunnel section. The survey group may also install permanent station markers to
assist future inspections.
The inspection team’s pace will vary dramatically depending upon the tunnel invert’s condition
and the distribution of defects. Inspection paces for unlined tunnels range between 1,500 and
2,000 feet per hour (f/h) (457 and 610 m/h). Inspection rates for lined tunnels range between
2,500 to 3,500 f/h (762 and 1,067 m/h). Figure 8 compares the planned pace with the actual
inspection pace for a tunnel inspection where the number of defects per 100 feet (33.3 m)
increased in the downstream tunnel reach.
Figure 7. Tunnel station marker installed during construction and used by tunnel inspectors
during the condition assessment
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6:00 AM
7:00 AM
8:00 AM
9:00 AM
10:00 AM
11:00 AM
12:00 PM
1:00 PM
2:00 PM
3:00 PM
4:00 PM
5:00 PM
6:00 PM
7:00 PM
8:00 PM
Time
Stationing
239+00 339+00 439+00 539+00 639+00 739+00 839+00 939+00
Team 1, Planned
Team 1, Actual
Figure 8. Comparison of planned and actual inspection pace
CONDITION ASSESSMENT METHODOLOGY
To improve consistency among all the tunnel inspectors, a key to descriptive terms is used to
describe the observations. The key provides multiple descriptive terms for: orientation
(inspection direction and dimensioning); tunnel configuration (circular, horseshoe, or
rectangular); lined/unlined tunnel characteristics (lining type, lining condition, dimensions,
surface roughness, corrosion, water infiltration, defect classification, rock joint patterns, and rock
integrity).
Defect Classifications
Four categories of defects and voids are defined to allow the inspectors to consistently document
their observations. Defects are defined as any failure of the structural lining system, ranging from
a shallow pocket to a hole in the unreinforced concrete lining. A void or cavity is defined as any
space between the rock-side of the concrete lining and the rock surface. Defects are classified
into four types, ranging from the least significant (Type I) to the most significant (Type IV). To
further refine the defect descriptions, the team may choose to add descriptors such as rock
pockets or sloped defects. A rock pocket is a portion of the lining in which poorly cemented
aggregates are visible and readily removed by hand. Rock pockets are typically Type I, II, or III
defects. A sloped defect, typically associated with concrete placement inconsistencies, is oriented
at an angle of between 15 and 30 degrees to the horizontal and may be a Type II, III, or IV
defect. Figures 9 through 12 illustrate the defect types, and Figures 13 and 14 illustrate how the
defects were distributed in one inspected water tunnel. This type of analysis is essential to rating
the condition of the tunnel by reach and developing a repair cost estimate.
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Type I Defect
Defects do not affect the operational reliability, watertightness, or structural integrity of
the tunnel.
Defects may include closed or tight circumferential temperature shrinkage cracks and
shallow voids in the structural concrete lining.
Figure 9. Type I Defect: Sloping defects along concrete placement layers
Type II Defect
Defects are generally not considered to affect the operational reliability. Depending on
the distribution and frequency, clusters of this defect type may reduce the structural
capacity of the tunnel lining system.
Defects may include circumferential cracks that are open and sharp edged. Voids may
extend well into the structural lining system.
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Figure 10. Poorly cemented concrete at a construction joint
Type III Defect
If isolated, this defect type is not considered to affect the operational reliability. However,
if clustered, this defect type may have compromised the tunnel’s structural support
system locally.
The structural support system has been interrupted by a void or defect, preventing the
effective resolution of ground and water loads. A void in the concrete tunnel liner is of
full thickness, and the rock or soil is exposed.
Figure 11. Poorly cemented concrete has eroded through the full liner thickness
Type IV Defect
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This defect type will affect the operational reliability and has compromised the tunnel’s
structural support system.
The structural support system has been interrupted by a void or defect, preventing the
effective resolution of ground and water loads. This defect type is characterized by the
presence of a cavity behind the tunnel liner coupled with a full thickness void in the
concrete tunnel liner. This condition creates asymmetrical loading on a compromised
structural support system.
Figure 12. Defect and outlined cavity behind liner in a concrete-lined pressure tunnel, circa 1925
construction
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Figure 13. Defect distribution per 100 feet (33.3 m)
Figure 14. Estimated volume of defects and voids per 100 feet (33.3 m)
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Water Infiltration Classifications
Leaks in the tunnel identify breaches in the lining watertightness. During normal operations, the
differential pressure between the in-service tunnel and the groundwater will govern whether
water is infiltrating or exfiltrating from the tunnel. Infiltrating water may affect the tunnel’s
water quality, and exfiltrating water may affect groundwater levels or create localized ground
instability. Locating these features relative to surface structures should be considered in the
condition assessment. The inspectors should classify and measure the leakage.
Condition Assessment Ratings
The overall condition assessment rating will depend on the type, size, distribution, frequency,
and location of defects or anomalies found in the tunnel. Evaluating the significance of a defect
demands a comprehensive understanding of how the tunnel or specific structural element in the
tunnel was designed and its intended function. Water tunnel reaches are rated as excellent, good,
fair, poor, and critical depending upon the tunnel’s condition. For water tunnels, the qualitative
rating is based on the following.
Structural integrity of the waterway which considers condition of the concrete lining,
steel lining, timber supports and lining, or rock integrity;
Hydraulic performance of the waterway which considers the hydraulic roughness,
obstructions, and transitions;
Remaining capacity of rock traps, sumps, and drain lines;
Watertightness which considers water loss or gain, and the potential for hydraulic piping;
Operability of mechanical systems like slide and roller gates, gate and butterfly valves,
and pumps;
Operability of instrumentation and control systems like flow meters and water level
meters;
Erodible material which may be mobilized and scour concrete inverts, erode penstock
linings, or increase wear in pumps or turbines.
This rating system was adapted from the U.S. Highway and Rail Transit Tunnel Inspection
Manual (2005). Figures 15 through 19 illustrate how the condition assessment ratings can be
applied to an in-service water tunnel.
Excellent Condition
The in-service tunnel is in a like-new condition and is functioning as originally designed.
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There are no identified defects or anomalies.
The tunnel is watertight. This level of service assumes that minor seepage may be present
at tunnel portals and adits.
The tunnel is in-service at full capacity. Confidence is high that the tunnel’s operational
reliability will remain high over the tunnel’s life.
Figure 15 is an image of a tunnel in excellent condition.
Figure 15. Tunnel transition from unlined to lined reaches
Good Condition
The in-service tunnel is no longer in like-new condition and is functioning as originally
designed.
Isolated defects are present but there are no observed systemic patterns to any defect
distribution or frequency. Defects may include circumferential temperature shrinkage
cracks or isolated single rock falls. Repairs are not warranted.
The tunnel is watertight. This level of service assumes that minor seepage may be present
at tunnel portals and adits.
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The tunnel should be re-inspected within 10 years.
The tunnel remains in-service at full capacity. Confidence is high that the tunnel’s
operational reliability will remain high over the tunnel’s life.
Figures 16 (a) and (b) are images of a tunnel in good condition.
Figure 16. (a) Typical lined horseshoe tunnel section
Figure 16 (b). Typical concrete-lined tunnel section
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Fair Condition
The in-service tunnel or section of tunnel is functioning as originally designed.
Defects or anomalies are present and may be systemic. Defect size and frequency may
range from minor and random (Type 1 defect), to moderate and repeating (Type 2
defect), to severe and isolated (Type 3 or 4 defect). Circumferential cracks may be open
and sharp edged. Longitudinal cracks may be present but do not show active movement.
Localized erosion or scour areas may be present. Rock falls may be present on the tunnel
invert but do not obstruct the flow.
Repairs may not be required immediately but should be planned for within 5 to 10 years.
The tunnel is moderately watertight. Leakage should be measured and monitored
routinely. This level of service assumes that leakage may be present at tunnel portals and
adits.
The tunnel should be re-inspected within 5 years to assess the rate of defect deterioration.
The tunnel remains in-service at full capacity. Confidence is moderate that the
tunnel’s operational reliability will be sustainable over the tunnel’s life.
Figure 17 is an image of a tunnel in fair condition.
a
b
Figure 17. (a) Tubercle over cement mortar-lined (CML) steel tunnel liner; (b) revealed pit
corrosion beneath tubercle and CML
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Poor Condition
The in-service tunnel or section of tunnel is not functioning as originally designed.
Significant and numerous defects are present, jeopardizing the continued operation,
watertightness or structural integrity of the tunnel.
Defect size and frequency may range from minor and random (Type 1 defect), moderate
and repeating (Type 2 defect) to severe and repeating (Type 3 or 4 defect).
Circumferential and longitudinal cracks may be open and sharp edged. Open cracks my
produce significant volumes of calcite, silty sand or clay. Localized erosion or scour
areas may be present. Unlined tunnel instability has generated rock falls that affect water
flow.
Immediate mitigation is prudent and should include developing a risk assessment of the
tunnel operations, implementing a monitoring plan to evaluate the operating
characteristics, designing a contingency plan, and planning for a repair outage within 5 to
10 years.
The tunnel may not be watertight. Leakage at tunnel portals and adits maybe excessive.
Unexplained water courses near portals or along low-cover portions of the tunnel may be
telltale signs of a tunnel breach, sinkhole, or other ground instability.
The tunnel should be re-inspected within 2 years to assess the rate of defect deterioration.
The tunnel remains in-service at full or partial capacity. Confidence is low that the
tunnel’s operational reliability will be sustainable over the tunnel’s life without repairs.
Figure 18 shows a void and cavity that are suspected of being the source of leakage daylighting
near the tunnel’s downstream portal. Longitudinal cracks run upstream and downstream. This
water tunnel was inspected by a remotely operated vehicle (ROV) because system demands
prevented an outage.
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Figure 18. Void and cavity, located in the tunnel’s crown
Critical Condition
The in-service tunnel or section of tunnel is not functioning as originally designed.
Critical defects are present, jeopardizing the continued operation, watertightness or
structural integrity of the tunnel.
Immediate action is prudent and should include implementing an operations contingency
plan and repairs, as appropriate.
The tunnel should be re-inspected within 2 years to assess the rate of defect deterioration.
The tunnel poses a high level of risk if it remains in-service at full or partial
capacity.
No photograph is available of a tunnel in critical condition.
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PHOTOGRAPHIC METHODS
Documenting a tunnel condition assessment using photographs and videography can
significantly enhance a comprehensive water tunnel condition assessment. The high quality of
the images in this paper is the result of the photographers’ experience, equipment, and technique.
Asset managers, operators, engineers, and contractors all benefit from high-quality, underground
photographs that accurately represent the condition and and accessibility of the underground
facilities. The challenge is to take high-quality inspection photographs while walking through a
slippery, pitch-black tunnel with a foot or two of water in the invert plus water spraying in from
the sidewall and crown.
Many common underground photo problems can be minimized through equipment and technique
adjustments.
Equipment
Camera. Using a digital SLR camera and high-quality lenses greatly improves the quality of the
underground images; however, point-and-shoot cameras can also take excellent images under
optimum conditions. Both systems have problems photographing reflective, moving subjects in
dark, humid, or dusty environments.
Media Storage. One of the benefits of using digital photography is the ability to take an
“infinite” number of pictures then selectively choose the best ones. Prior to the tunnel inspection,
obtain several large-capacity media storage cards and seal them in double zip-lock plastic bags to
waterproof them. Multiple cards provide redundancy storage media in the event a card is
damaged during the inspection.
Auxiliary Flash. Insufficient camera flash will light only a small portion of the scene. Auxiliary
flashes are usually more powerful than integrated camera flashes. Connecting an external strobe
flash to your camera will increase light output and scene illumination. Powerful strobe flashes
that can light up 40 feet (12 m) of tunnel are lightweight and portable. Pivot head flashes also
allow the photographer to vary flash illumination to accent specific tunnel or mechanical
equipment features.
Wide Angle Lens. Sometimes the scene is too big to fit into the viewfinder, as is the case with
the surge tank in Figure 2. Most point and shoot cameras don’t have integral wide angle lenses
that can capture the entire scene. Select a camera or lens that has the widest possible focal length.
A 16 mm focal length lens provides an adequate field of view for most underground
photography.
Protecting Equipment. Long tunnel inspections require the underground photographer to carry
all of his or her equipment for long durations. Damaged equipment is useless and a burden.
Protect equipment from water vapor and spraying water by using a waterproof or water resistant
camera, lenses, and strobe flash. Enclosing equipment in a watertight camera bag or a bag with a
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waterproof cover also helps, as does using a walking stick to probe ahead for depressions when
water is present on the tunnel invert.
Technique
Choosing the “Right” Shot. The underground photographer will be documenting elements of
the tunnel that few people will ever see in person. Consider the interests the asset manager or
bureau chief may have when planning for and justifying tunnel rehabilitation projects. Frame the
pictures to show the general condition of the tunnel, and provide sufficient detail to reassure
those who will not have the opportunity to be in the tunnel that it is in excellent condition or to
convince them that the deteriorated condition is real and may jeopardize future reliability.
Camera Stabilization. Blurry images caused by camera shake or moving equipment and
workers can ruin a photograph. Mount the camera on a tripod to eliminate camera shake. New
cameras and lenses with image stabilization help to reduce camera shake. To reduce blurring
from moving equipment and workers, increase the ISO setting and open the lens aperture to its
widest opening. Use a minimum shutter speed of 1/125th second for hand-held photographs to
reduce motion blur.
Image Clarity. Dust, tiny airborne water droplets, water vapor, and exhaled breath can obscure
the image with spots or reflections. To solve the problem, use an external flash that is connected
to the camera by a cord and aim the flash at an angle to the axis of the photograph. The flash no
longer reflects off the dust and water vapor into the lens and the reflections disappear. Exhaling
and brief breath holding will allow exhaled breath to move away from the flash and reduce the
“white-out” in an image.
Reducing Safety Vest Reflections. There are three approaches to avoid photographs in which
the only the reflective vest stripes are visible. They include not using a flash, moving the flash
off the camera, and using a high-end, camera-mounted strobe flash that compensates for the
reflective stripes.
Scale the Image. Sometimes the photographed feature lacks a scaling feature, making the
interpretation and analysis difficult. Include a photographic scale, a black and white scale rod,
measuring tape, or other object to provide scale and perspective to the scene. The scale also
provides a convenient focal point for many auto focus camera lenses.
Earmark the Image. Log the pictures taken during the inspection and include the camera’s
image number and tunnel station where the picture was taken. The combination of the date/time
stamped image and the tunnel station allow the tunnel engineer to produce an accurate as-built
record and condition assessment.
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SUMMARY
Many of the existing conveyance systems in North America are approaching the sunset of their
original design life without formal assessment of their current condition. There may be some
systems that have not been thoroughly inspected since they were put in service. Thorough
condition assessments provide essential planning information for asset management programs.
Unwatered tunnel inspections allow tunnel inspectors to obtain extensive observational and
nondestructive information of an in-service water tunnel. The inspection can be accomplished
safely and at an acceptable cost when properly planned and executed. These programs can
greatly increase a utility’s ability to provide reliable service, anticipate future fiscal demands,
and meet customer expectations.
REFERENCES
American Society of Civil Engineers Task Committee, “Guideline for the Evaluation of Water
Conveyance Tunnels”, (Draft)
NSF/ANSI Standard 61, “Drinking Water System Components” (1988).
“Occupational Safety and Health Standards,” Code of Federal Regulations. Title 29, Pt. 1910
(2010).
“Safety and Health Regulations for Construction,” Code of Federal Regulations. Title 29, Pt.
1926 (2010).
U.S. Department of Transportation. 2005. U.S. Highway and Rail Transit Tunnel Inspection
Manual (2005).
ACKNOWLEDGEMENTS
The authors appreciate the support of the San Francisco Public Utilities Commission, Seattle
City Lights, Puget Sound Energy, and the South Central Connecticut Regional Water Authority.
BIOGRAPHIES
Blake Rothfuss is a Lead Associate and Corporate Safety Manager with Jacobs Associates
where he specializes in hydroelectric project design and construction, and water tunnel
rehabilitation. Over his career, Blake has had extensive experience in water resources
engineering, underwater inspection and construction, and managing heavy construction projects.
Sue Bednarz is a Project Geologist with Jacobs Associates where she specializes in field
exploration and design for tunnels, pipelines, and highways. Sue is a recognized expert in
construction and inspection photography.
Erin Clarke is a Staff Engineer with Jacobs Associates where she specializes in the design and
construction of underground structures.
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APPENDIX A: RECOMMENDED TUNNEL INSPECTOR’S
PERSONAL PROTECTIVE EQUIPMENT
Individual equipment that should be worn or carried
Hard hat
Hard hat mounted light (700 lumen output recommended)
Backup flashlights and spare batteries
Safety glasses, clear
Gloves, mechanics style, synthetic
Warm clothes, synthetic or wool (no cotton)
Water repellant jacket
Walking sticks (required in unlined tunnels, useful in lined tunnels)
Sturdy boots (hip or chest waders recommended)
Emergency whistle
Personal first aid kit (blister kit, bleeding control kit)
Snacks and water
Hand cleaner/sanitizer
Extra ziplock plastic bags, 1 gallon
Group equipment
Atmospheric monitoring meters (O 2 , CO, H 2 S, LEL)
Air speed meter
Communication: Air horns and radio
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APPENDIX B: SAMPLE TUNNEL AND CONFINED SPACE ENTRY PERMIT
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