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Highway and Rail Transit Tunnel Inspection Manual
2005 Edition
Chapter 4: Inspection Procedures - General Discussion
A. Inspection Of Civil/Structural Elements
1. Frequency
The tunnel owner should establish the frequency for up-close inspections of the tunnel structure based on the age and condition of the tunnel. For new tunnels, this time period could be as great as five years. For older tunnels, a much more frequent inspection time period may be required, possibly every two years. This up-close inspection is in addition to daily, weekly, or monthly walk-through general inspections.
2. What to Look For
This section provides the procedures for inspections as well as the definitions of defects common to concrete, steel, masonry, and timber structures. The identification of structural defects will be accomplished via both visual inspection and non-destructive techniques.
The visual inspection must be made on all exposed surfaces of the structural elements. All noted defects should be measured and documented for location. Severe spalls in the concrete surface should be measured in length, width, and depth. Severe cracks should be measured in length and width. Corrosion on steel members should be measured for the length, width, and depth of the corrosion. The inspectors should clear away debris, efflorescence, corrosion, or other foreign substances from the surfaces of the structural element prior to performing the inspection. Once the defect is noted, it should be classified as minor, moderate, or severe as explained in the following sections.
Particular attention should be paid to determining if differential settlement has occurred in transition areas of the tunnel. Transition areas are those in which the tunnel support conditions change, such as between sections of rock and soil tunneling or between the tunnel and ventilation or station buildings. The location of these areas should be evident from any existing as-built drawings. Differential settlement is often the cause of other defects, which is why extra time should be spent investigation these transition areas.
In addition to visual inspection, structural elements should be periodically sounded with hammers to identify defects hidden from the naked eye. As a result of a hammer strike on the surface, the structural element will produce a sound that indicates if a hidden defect exists. A high-pitched sound or a ringing sound from the blow indicates good material below the surface. Conversely, a dull thud or hollow sound indicates a defect exists below the surface. Such a defect in concrete may signify a delamination is present or that the concrete is loose and could spall off. A hollow sound in timber may indicate advanced decay. Once the defect is found, the surface in the vicinity of the defect should be tapped until the extent of the affected area is determined. This procedure is to be applied to concrete and timber surfaces but should also be used on steel especially where corrosion is evident.
For concrete or masonry surfaces that are accessible, a non-destructive, ultrasonic test method such as "Impact-Echo" may be utilized. Impact-Echo is an acoustic method that can determine locations and extent of flaws/deteriorations, voids, debonding of re-bars, thickness of concrete. The use of this method helps to mitigate the need for major retrofit since the deterioration can be detected at an early stage and repairs performed.
It should be noted that in the 1960s some tunnel owners began to develop maximum allowable rates of water infiltration to be used as a guide to determine original design and subsequent repairs if the amount of infiltration increases. One such owner was the Bay Area Rapid Transit (BART) system in California; they set a limit of 0.8 liters/minute per 75 linear meters (0.2 gpm per 250 linear feet) of tunnel. This translates to 3 liters/minute per 300 linear meters (0.8 gpm per 1000 linear feet) of tunnel. Some tunnel owners have adopted this criteria while still others may use a limit of 3.8 liters/minute per 300 linear meters (1 gpm per 1000 linear feet) of tunnel. These limits are for reference purposes only, with the main emphasis for determining repair needs placed on the location of the leak and the condition of the tunnel components that are affected. For this reason, minor, moderate, and severe leakage rates are given in the following sections for use in classifying individual leaks. Also, it is important for the tunnel inspector to be aware of any tunnel waterproofing system that was installed during the construction of the tunnel. Many of the common civil/structural defects are listed below:
a) Concrete Structures (Refer to ACI 201.1R-92 for representative pictures of these defects)
(1) Scaling
The gradual and continuing loss of surface mortar and aggregate over an area classified as follows:
- Minor Scale - Loss of surface mortar up to 6 mm (¼ in) deep, with surface exposure of coarse aggregates.
- Moderate Scale - Loss of surface mortar from 6 mm (¼ in) to 25 mm (1 in) deep, with some added mortar loss between the coarse aggregates.
- Severe Scale - Loss of coarse aggregate particles as well as surface mortar and the mortar surrounding the aggregates. Depth of loss exceeds 25 mm (1 in).
(2) Cracking
A crack is a linear fracture in the concrete caused by tensile forces exceeding the tensile strength of the concrete. Cracks can occur during curing (non-structural shrinkage cracks) or thereafter from external load (structural cracks). They may extend partially or completely through the concrete member. Cracks are categorized as follows:
- Transverse Cracks - These are fairly straight cracks that are roughly perpendicular to the span direction of the concrete member. They vary in width, length, and spacing. These cracks may extend completely through the slab or beam as well as through curbs and walls supporting the safety walk.
- Longitudinal Cracks - These are fairly straight cracks that run parallel to the span of the concrete slab or beam. They vary in width, length, and spacing. The cracks may extend partially or completely through the slab or beam.
- Horizontal Cracks - These cracks generally occur in walls but may exist on the sides of beams where either encased flanges or reinforcement steel have corroded. They are similar in nature to transverse cracks.
- Vertical Cracks - Vertical cracks occur in walls and are similar to longitudinal cracks in slabs and beams.
- Diagonal Cracks - These cracks are roughly parallel to each other in slabs and are skewed relative to the centerline of the structure. They are usually shallow and are of varying length, width, and spacing. When found in the vertical faces of beams, they signify that a potentially serious problem exists.
- Pattern or Map Cracks - These interconnected cracks vary in size and form networks similar to that of sun cracking observed in dry areas. They vary in width from barely visible, fine cracks to well-defined openings. They are found in both slabs and walls.
- D-Cracks - These cracks are a series of fine cracks at rather close intervals with random patterns.
- Random Cracks - These are meandering irregular cracks on the surface of concrete. They have no particular form and do not logically fall into any of the classifications described above.
All cracks in non-prestressed members may be classified as follows:
- Minor - Up to 0.80 mm (0.03 in).
- Moderate - Between 0.80 mm (0.03 in) and 3.20 mm (0.125 in).
- Severe - Over 3.20 mm (0.125 in).
Any crack over 0.10 mm (0.003 in) in a prestressed member should be classified as severe. Any crack ≤ 0.10 mm (0.003 in) should be classified as moderate.
(3) Spalling
Spalling is a roughly circular or oval depression in the concrete. It is caused by the separation and removal of a portion of the surface concrete revealing a fracture roughly parallel, or slightly inclined, to the surface. Usually, a portion of the depression rim is perpendicular to the surface. Often reinforcement steel is exposed. Spalling may be classified as follows:
- Minor - Less than 12 mm (½ in) deep or 75 mm (3 in) to 150 mm (6 in) in diameter.
- Moderate - 12 mm (½ in) to 25 mm (1 in) deep or approximately 150 mm (6 in) in diameter.
- Severe - More than 25 mm (1 in) deep and greater than 150 mm (6 in) in diameter and any spall in which reinforcing steel is exposed.
(4) Joint Spall
This is an elongated depression along an expansion, contraction, or construction joint. This defect should be classified as described above.
(5) Pop-Outs
These are conical fragments that break out of the surface of the concrete leaving small holes. Generally, a shattered aggregate particle will be found at the bottom of the hole, with a part of the fragment still adhering to the small end of the pop-out cone.
- Minor - Leaving holes up to 10 mm (0.40 in) in diameter, or equivalent.
- Moderate - Leaving holes between 10 mm (0.40 in) and 50 mm (2 in) in diameter, or equivalent.
- Severe - Leaving holes 50 mm to 75 mm (2.0 in to 3.0 in) in diameter, or equivalent. Pop-outs larger than 75 mm (3 in) in diameter are spalls.
(6) Mudballs
These are small holes that are left in the surface by the dissolution of clay balls or soft shale particles. Mudballs should be classified in the same way as pop-outs.
(7) Efflorescence
This is a combination of calcium carbonate leached out of the cement paste and other recrystalized carbonate and chloride compounds, which form on the concrete surface.
(8) Staining
Staining is a discoloration of the concrete surface caused by the passing of dissolved materials through cracks and deposited on the surface when the water emerges and evaporates. Staining can be of any color although brown staining may signify the corrosion of underlying reinforcement steel.
(9) Hollow Area
This is an area of a concrete surface that produces a hollow sound when struck by a hammer. It is often referred to as delaminated concrete.
(10) Honeycomb
This is an area of a concrete surface that was not completely filled with concrete during the initial construction. The shape of the aggregate is visible giving the defect a honeycomb appearance.
(11) Leakage
This occurs on a region on the concrete surface where water is penetrating through the concrete.
- Minor - The concrete surface is wet although there are no drips.
- Moderate - Active flows at a volume less than 30 drips/minute.
- Severe - Active flows at a volume greater than 30 drips/minute.
b) Steel Structures
(1) Corrosion
Corroded steel varies in color from dark red to dark brown. Initially, corrosion is fine grained, but as it progresses, it becomes flaky or scaly in character. Eventually, corrosion causes pitting in the member. All locations, characteristics, and extent of the corroded areas should be noted. The depth of severe pitting should be measured and the size of any perforation caused by corrosion should be recorded. Corrosion may be classified as follows:
- Minor - A light, loose corrosion formation pitting the paint surface.
- Moderate - A looser corrosion formation with scales or flakes forming. Definite areas of corrosion are discernible.
- Severe - A heavy, stratified corrosion or corrosion scale with pitting of the metal surface. This corrosion condition eventually culminates in loss of steel section and generally occurs where there is water infiltration.
(2) Cracks
Cracks in the steel may vary from hairline thickness to sufficient width to transmit light through the member. Any type of crack is serious and should be reported at once. Look for cracks radiating from cuts, notches, and welds. All cracks in the steel will be classified as severe.
(3) Buckles and Kinks
Buckles and kinks develop mostly because of damage arising from thermal strain, overload, or added load conditions. The latter condition is caused by the failure or the yielding of adjacent members or components. Erection or collision damage may also cause buckles, kinks, and cuts.
(4) Leakage
This occurs on a region of the steel surface where water is penetrating through a joint or crack.
- Minor - The steel surface is wet although there are no drips.
- Moderate - Active flows at a volume less than 30 drips/minute.
- Severe - Active flows at a volume greater than 30 drips/minute.
(5) Protection System
Steel is generally protected by a paint system, by galvanizing, or by the use of weathering steel. Most existing structures use either paint or galvanized steel. Paint systems fail through peeling, cracking, corrosion pimples, and excessive chalking. The classification of the degree of paint system deterioration is tied to both the physical condition of the paint and the amount of corrosion of the member as follows:
- Minor - General signs of deterioration of the paint system but no corrosion yet present.
- Moderate - Paint generally in poor condition and corrosion is present but not serious. (No section loss.)
- Severe - Paint system has failed and there is extensive corrosion and/or section loss.
c) Masonry Structures3
(1) Masonry Units
The individual stones, bricks, or blocks should be checked for displaced, cracked, broken, crushed, or missing units. For some types of masonry, surface deterioration or weathering can also be a problem.
- Minor - Surface deterioration at isolated locations. Minor cracking.
- Moderate - Slight dislocation of masonry units; large areas of surface scaling.
- Severe - Individual masonry units significantly displaced or missing.
(2) Mortar
The condition of the mortar should be checked to insure that it is still holding strongly. It is particularly important to note cracked, deteriorated, or missing mortar if other deterioration is present such as missing or displaced masonry units.
- Minor - Shallow mortar deterioration at isolated locations.
- Moderate - Mortar generally deteriorated, loose, or missing mortar at isolated locations, infiltration staining apparent.
- Severe - Extensive areas of missing mortar; infiltration causing misalignment of tunnel.
(3) Shape
Masonry arches act primarily in compression. Flattened curvature, bulges in walls, or other shape deformations may indicate unstable soil conditions.
(4) Alignment
The vertical and horizontal alignment of the tunnel should be checked visually.
(5) Leakage
A region on the masonry surface where water is penetrating through a joint or crack.
- Minor - The masonry surface is wet although there are no drips.
- Moderate - Active flows at a volume less than 30 drips/minute.
- Severe - Active flows at a volume greater than 30 drips/minute.
d) Timber Structures
(1) Decay
Decay is the primary cause of timber deterioration and is caused by living fungi, which feed on the cell walls of timber. Molds, stains, soft rot (least severe), and brown or white rot (most severe) are common types of fungi that cause decay. Timber may become discolored and soft and section loss may occur. Any decay should be noted and the amount of section loss should be recorded. Decay may be classified as follows:
- Minor - Discoloration of timber, molds, or stains present.
- Moderate - Timber surface soft with section loss less than 15 percent.
- Severe - Brown or white rot present with section loss greater than 15 percent.
(2) Insects
Any presence of insect infestation should be noted and type of insect recorded, if known. Saw dust or powdered dust on or around the timber member may also indicate the presence of insects and should be noted. Termites and carpenter ants are common types of insects that cause timber deterioration.
(3) Checks/Splits
Checks are cracks in timber, which extend partially through the timber member and are caused by shrinkage due to drying or seasoning of the timber. Cracks that extend completely through the member are called splits. All checks should be noted along with the percentage of penetration through the member. Checks may be classified as follows:
- Minor - Surface checks perpendicular to the plane of stress or isolated checks parallel to the plane of stress.
- Moderate - Checks with less than 15 percent penetration into the timber perpendicular to the plane of stress or isolated checks with less than 40 percent penetration parallel to the plane of stress.
- Severe - Checks greater than 15 percent penetration into the timber perpendicular to the plane of stress or numerous checks greater than 40 percent penetration parallel to the plane of stress.
(4) Fire Damage
Classification is based on the amount of fire damage.
- Minor - Black or charred surface. No appreciable section loss.
- Moderate - Less than 15 percent section loss.
- Severe - Greater than 15 percent section loss.
(5) Hollow Area
A hollow area indicates advanced decay in the interior of a timber member or the presence of insects. All hollow areas should be noted as to size and location.
(6) Leakage
A region on the timber surface where water is penetrating through a joint, check/split, or the timber itself.
- Minor - The timber surface is wet although there are no drips.
- Moderate - Active flows at a volume less than 30 drips/minute.
- Severe - Active flows at a volume greater than 30 drips/minute.
e) Connection Materials
(1) Bolts
The connection bolts on fabricated concrete, steel, and cast iron liners may be discolored due to moisture and humidity conditions in the tunnel. This condition does not downgrade the structural capacity of the bolt. Particular attention should be given to bolts in regions of leakage to ensure that no detrimental loss of section has occurred. If losses in section are observed, such bolts should be noted for replacement. Also, the location of all missing or loose bolts should be noted.
- Minor - Bolts are discolored, but have no section loss.
- Moderate - Bolts are deteriorated with up to 15 percent section loss.
- Severe - Bolts are deteriorated with greater than 15 percent section loss. However, bolts with deterioration approaching 50 percent or more should be replaced.
(2) Gaskets
Gaskets between segmental tunnel liners can be lead, mastic, or rubber. These gaskets can become dislodged from the joint due to infiltrating water or loosening of the joint bolts. They also can fail due to chemical or biological deterioration of the material caused by the infiltrated water. Structural movements of the liner can also tear or otherwise distort the gasket and cause it to leak. All gasket deficiencies should be noted as to extent and location.
3. Safety - Critical Repairs
The inspection may reveal severe defects that could pose danger to the traveling public, tunnel personnel, or inspection team members. When this occurs, this particular severe defect should be categorized for a "critical repair." This categorization would deem that one of the following critical actions be taken:
- Close the tunnel until the severe defect is removed or repaired if such a defect is accessible by vehicles or trains.
- Cordon off the area from public access until the defect can be removed or repaired.
- Shore up the structural member if this is appropriate.
It is imperative that the inspection team coordinates with the tunnel owner in advance and be prepared to take the "critical action." Oftentimes, this type of action is required for delaminated concrete that is on the verge of falling. The inspection team, tunnel personnel, or a specialty contractor could possibly perform the removal. This activity can be very dangerous and all safety precautions should be taken to prevent injury to inspectors and repair personnel.
4. Condition Codes
Elements will be rated using the guidelines explained below. A numerical rating of 0 to 9 will be assigned to each structural element, 0 being the worst condition and 9 being the best condition. This rating system is a modified form of the one described in the Bridge Inspector's Training Manual published by the FHWA. A general description of the rating system is shown below in Table 4.1 and in Table 4.2 this system is specifically related to different liner types.
If a tunnel owner desires to use this system for mechanical or electrical systems or other tunnel appurtenances, then the codes can be adapted to represent a smaller set of conditions. An example would be to give numbers to the following conditions: excellent, good, fair, poor, and serious. This may be done in order to track conditions through the use of a tunnel management software program.
Table 4.01 - General Condition Codes
| Rating | Description |
|---|
| 9 | Newly completed construction. |
| 8 | Excellent condition - No defects found. |
| 7 | Good condition - No repairs necessary. Isolated defects found. |
| 6 | Shading between "5" and "7." |
| 5 | Fair condition - Minor repairs required but element is functioning as originally designed. Minor, moderate, and isolated severe defects are present but with no significant section loss. |
| 4 | Shading between "3" and "5." |
| 3 | Poor condition - Major repairs are required and element is not functioning as originally designed. Severe defects are present. |
| 2 | Serious condition - Major repairs required immediately to keep structure open to highway or rail transit traffic. |
| 1 | Critical condition - Immediate closure required. Study should be performed to determine the feasibility of repairing the structure. |
| 0 | Critical condition - Structure is closed and beyond repair. |
The rating is dependent upon the amount, type, size, and location of defects found on the structural element as well as the extent to which the element retains its original structural capacity. To judge the extent to which the structural element retains its original structural capacity, the inspector must understand how the element is designed and how the defect affects this design.
To aid the inspectors in evaluating specific conditions for the various kinds of tunnel elements, more specific guidelines are presented hereafter to ensure consistency in assigning condition codes.
5. Tunnel Segments
a) Cut-and-Cover Concrete Box Tunnels and Concrete/Shotcrete Inner Liners
For several highway tunnels and for station areas in rail transit tunnels, the concrete/shotcrete surfaces may be covered with another finish material as described under Tunnel Finishes in Chapter 2, Section A, Part 5. For ceramic tile and epoxy finishes, the general condition of the underlying concrete surfaces is to be evaluated and assessed a condition rating based upon the cracks and leakage through the finish material.
In addition to the descriptions of potential defects presented in Chapter 4, Section A, Part 2, the concrete/shotcrete elements should be rated according to the Condition Code Summary in Table 4.2.
The inspector needs to use good engineering judgment when assessing the overall condition rating of the segment being inspected. Although the specific guidelines presented in Table 4.2 are an excellent tool to ensure consistency of evaluations among different inspectors, the defects presented will not always fall into the categories. For example, if a segment of the cut-and-cover concrete tunnel shows no defects (i.e., no delaminations, no spalls, and no exposed reinforcement steel) other than one severe crack with severe active leakage, the inspector may still want to rate this segment in "poor condition" because a major repair is required to restore the element to good condition.
b) Soft-Ground Tunnel Liners
These liners include fabricated steel, precast concrete, cast iron or masonry liners, as well as connection bolts and gaskets on the fabricated liners.
In addition to the descriptions of potential defects presented in Chapter 4, Section A, Part 2, the inspector should be aware of the following requirements for these liners:
- The ends of precast concrete liners may have an embedded steel plate across the full width of the liner plus steel plate inserts for bolting two end-to-end liners together. The condition of the embedded steel plate is synonymous with the precast liner and therefore should be inspected for degree of corrosion.
- The connection bolts on fabricated concrete, steel, and cast iron liners may be discolored due to moisture and humidity conditions in the tunnel. This condition does not downgrade the structural capacity of the bolt. Particular attention should be given to bolts in regions of leakage to ensure that no detrimental loss of section has occurred. If losses in section are observed, such bolts should be noted for replacement.
- The tunnels should be generally observed for uniform cross-sectional shape from radial soil pressures. As a means of monitoring possible changes in cross section, measurements should be taken at approximately 60 m (200 ft) intervals on the inside face of the liners between spring lines and from the underside of the ceiling/roof at 12:00 to the top of rail for rail transit tunnels or to top of walkway for highway tunnels. Yellow paint should be used to identify the measurement locations.
The ratings for the elements of the tunnel liners are based on the general condition codes in Table 4.1 and for degree of deterioration as shown in Table 4.2.
c) Rock Tunnel Liners
These include cast-in-place concrete and shotcrete liners.
The entire exposed portion of the tunnel liner above the roadway slab or rail transit invert slab should be inspected for typical concrete deficiencies described in Chapter 4, Section A, Part 2. In addition, the lining should be generally observed for uniform cross-sectional shape. As a means of monitoring possible changes in the cross section, measurements should be taken at approximately 60 m (200 ft) intervals between the spring line or vertical sidewalls and from the underside of the ceiling/roof at tunnel centerline to the top of the walkway for highway tunnels or the top of rail for rail transit tunnels. Yellow paint should be used to mark the measurement locations.
The ratings for the rock tunnel, concrete/shotcrete linings are based on the rating scale and descriptions given at the beginning of this section in Table 4.1 for degree of deterioration and as supplemented in Table 4.2.
d) Timber Liners
The exposed portion of the timber liner shall be inspected for typical timber deficiencies described in Chapter 4, Section A, Part 2. The ratings for the timber liners are based on the rating scale and descriptions given at the beginning of this section in Table 4.1 for degree of deterioration and as supplemented in Table 4.2.
Table 4.02 - Condition Code Summary
| Rating | General Description | Cut-and-Cover Box Tunnels and Concrete / Shotcrete Inner Liners | Soft-Ground Tunnel Liners | Rock Tunnel Liners | Timber Liners |
|---|
| 9 | Newly completed construction. | Newly completed construction. | Newly completed construction. | Newly completed construction. | Newly completed construction. |
| 8 | Excellent condition - No defects found. | Excellent condition - No defects found. | Excellent condition - No defects found. | Excellent condition - No defects found. | Excellent condition - No defects found. |
| 7 | Good condition - No repairs necessary. Isolated defects found. | Good condition - No repairs necessary although certain elements contain isolated minor deficiencies and minor presence of efflorescence. No delaminations or spalls are present. | Good condition - No repairs necessary. Steel, precast concrete, cast iron, and masonry liners have isolated minor defects. Steel plates, shapes, and liners have isolated locations of minor surface corrosion but with no section loss. Precast concrete liners and safety walk panels contain not more than one minor crack. Masonry exhibits a minor presence of efflorescence with only minor cracks at greater than 3 m (10 ft) intervals. Connection bolts are discolored, and minor leakage is occurring through the gaskets between liners. | Good condition - No repair necessary. Concrete / shotcrete liner contains minor circumferential cracks at greater than 3m (10 ft) intervals with a minor presence of efflorescence. | Good condition - No repair necessary. Timber exhibits isolated locations of minor checks, minor decay, and minor water leakage. |
| 6 | Shading between "5" and "7." | Shading between "5" and "7." | Shading between "5" and "7." | Shading between "5" and "7." | Shading between "5" and "7." |
| 5 | Fair condition - Minor repairs required but element is functioning as originally designed. Minor, moderate, and isolated sever defects are present but with no significant section loss. | Fair condition - Minor repairs required but element is functioning as originally designed. Concrete elements contain moderate cracks at 1.5 m (5 ft) to 3 m (10 ft) intervals with moderate presence of efflorescence and minor to moderate active leakage. Minor delaminations, spalls, map cracking, and staining exist on the concrete but no reinforcement steel is exposed. | Fair condition - Minor repairs required but liner is functioning as originally designed. Steel, precast concrete, cast iron, and masonry liners have numerous minor defects. Steel plates, shapes, and liners are surface corroded throughout but with no significant section loss. Precast concrete liners and safety walk panels have moderate spalls and more than two minor cracks. Masonry contains moderate cracks at 1.5 m (5 ft) to 3 m (10 ft) intervals with moderate presence of efflorescence and minor to moderate active leakage at isolated locations. Connection bolts (not more than one for every two liner segments) require replacement or retightening. Moderate leakage is present between liners. | Fair condition - Minor repairs are required but element is functioning as originally designed. Concrete / shotcrete lining contains moderate circumferential cracks at 1.5 m (5 ft) to 3 m (10 ft) intervals, not more than one longitudinal moderate crack, moderate presence of efflorescence, and minor to moderate active leakage. Minor delaminations, spalls, map cracking and staining are present but no reinforcement is exposed. | Fair condition - minor repairs required but liner is functioning as originally designed. Timber exhibits numerous minor defects and isolated moderate decay, checks, and moderate leakage. Isolated timber members contain splits. |
| 4 | Shading between "3" and "5." | Shading between "3" and "5." | Shading between "3" and "5." | Shading between "3" and "5." | Shading between "3" and "5." |
| 3 | Poor condition - Major repairs are required and element is not functioning as originally designed. Severe defects are present. | Poor condition - Major repairs are required and element is not functioning as originally designed. Concrete elements contain numerous moderate cracks with extensive efflorescence, severe leakage, and staining. Delaminations and spalls are present over 50% of the concrete surface and exposed reinforcement steel has up to 15% section loss. | Poor condition - Major repairs are required. The precast, steel, and cast iron liner elements exhibit extensive severe deterioration such that the liners can no longer achieve the full original design capacity, although still retaining some degree of their load-carrying capacity. Masonry contains numerous moderate cracks with extensive efflorescence, leakage, and staining. Delaminations of the masonry layers, slight dislocation of certain masonry units, and loose or missing mortar are prevalent at isolated locations. Severe active leakage is occurring through the masonry or between adjacent liner segments at isolated locations. Connection bolts are deteriorated with up to 15% section loss and are loose or missing at isolated locations. | Poor condition - Major repairs are required and element is not functioning as originally designed. Concrete / shotcrete lining has extensive longitudinal and circumferential cracks with extensive efflorescence, leakage, and staining. Delaminations and spalls are present over 50% of the lining surface and exposed reinforcement steel has up to 15% section loss. | Poor condition - Major repairs are required and liner is not functioning as originally designed. Liner elements have numerous moderate defects of decay, checks, splits, and leakage over 50% of the liner area. |
| 2 | Serious condition - Major repairs required immediately to keep structure open to highway or rail transit traffic. | Serious condition - Major repairs required immediately to keep structure open to highway or rail transit traffic. Concrete elements contain extensive severe cracks, delaminations, spalls, and leakage. Exposed reinforcement steel has up to 40% section loss. | Serious condition - Major repairs required immediately to keep structure open to highway or rail transit traffic. The liner elements have extensive, serious material deterioration and are severely deflected such that the elements can no longer support the design loads without immediate repairs. Masonry contains extensive severe cracks, delaminations, and missing masonry units. Severe active leakage is occurring at numerous locations within the tunnel segment. Connection bolts are deteriorated with up to 50% section loss and are loose or missing at several locations. | Serious condition - Major repairs required immediately to keep structure open to highway or rail transit traffic. Concrete / shotcrete lining has extensive severe cracks, delaminations, spalls, and active leakage. Exposed reinforcement steel has up to 40% section loss. | Serious condition - Major repairs required immediately to keep structure open to highway or rail transit traffic. Timber contains extensive severe decay, checks, splits, and leakage over 50% of the timber surface. Numerous timber members are completely deteriorated. |
| 1 | Critical condition - Immediate closure required. Study should be performed to determine the feasibility of repairing the structure. | Critical condition - Immediate closure required. Study should be performed to determine the feasibility of repairing the structure. | Critical condition - Immediate closure required. The liner elements have major deterioration and have lost all capacity to sustain the original design loadings. The masonry is severely deteriorated such that major sections are missing and can no longer support the design loading. Connection bolts are deteriorated in excess of 50% and are loose or missing at several locations. | Critical condition - Lining has extensively cracked and deflected significantly. The lining has lost all capacity to sustain design loads. | Critical condition - Lining has extensively cracked and deflected significantly. The lining has lost all capacity to sustain design loads. |
| 0 | Critical condition - Structure is closed and beyond repair. | Critical condition - Structure is closed and beyond repair. | Critical condition - Structure is closed and beyond repair. | Critical condition - Structure is closed and beyond repair. | Critical condition - Structure is closed and beyond repair. |
e) Track Supports
The track supports in this section are for direct fixation fasteners to concrete plinth pads, continuous concrete pedestals, and the invert slab.
These concrete elements should be inspected for the deficiencies described in Chapter 3, Section A, Part 2 and rated according to the general criteria listed at the beginning of this section.
f) Finishes
As described previously, the primary tunnel finishes include ceramic tiles, porcelain-enameled metal panels, precast concrete panels, and epoxy coatings.
Whereas it does not make sense to use a rating scale of 0 to 9 for such finishes, the inspector could use ratings such as excellent, good, fair and poor condition that follow the general definitions given at the beginning of this section.
For ceramic tiles, the inspector should lightly tap a majority of tiles to determine if they are loose from the substrate. Such tapping will easily reveal a hollow sound if the tiles have been dislodged. Where hollow areas are noted, the inspector should freely define the extent of the hollow area by tapping all adjacent tiles. The area should be so noted in the inspection findings. In addition, the inspector should evaluate the tiles for reflectivity and general condition (broken or missing).
For porcelain-enameled metal panels and precast concrete panels, it is crucial that the attachments to the substrate be carefully evaluated and assessed, as a loose panel would pose a dangerous condition. For metal panels, any corrosion of the panels along the edges or at scrapes/nicks, will indicate a downgrading of the surface condition. For precast concrete panels, careful attention should be given to determine if there are any cracks or delaminated areas in the panels.
Epoxy coatings are not structural in nature, but do offer a protective covering to the concrete for changing environmental conditions or for additional reflectivity to improve visibility in the tunnel. Note the condition of the coating primarily due to peeling or debonding from the substrate.
g) Drainage Systems
It is crucial that the tunnel drainage system be inspected to ensure that it is capable of handling the water flow for which it was designed. This water flow could be ground water from the exterior of the tunnel lining, rain water that enters the portals or vent structures, and drainage from emergency fire protection systems during their use. Failure of this system could result in ponding of the water and subsequent flooding of the tunnel space, thus posing a safety hazard to the tunnel occupants. Transit tunnels are particularly sensitive to this due to the amount of equipment that can reside on the tunnel invert such as the signals and communications equipment, and the third rail power systems. Excessive ponding of water around such equipment can lead to equipment malfunctioning and potential shut down of the system.
Similarly to the tunnel finishes above, it is recommended that the inspector use a rating scale of excellent, good, fair, and poor condition. The rating should be based on the particular system component's ability to convey or store the required amount of water, i.e., whether it is clogged or leaking.
h) Miscellaneous Tunnel Appurtenances
These appurtenances include railings, safety walks, utility supports, CCTV camera supports, enclosures adjacent to the roadway/track etc.
These miscellaneous elements are to be carefully inspected for the degree of deterioration in the elements as well as the extent to which they retain their original design structural capacity. The inspector shall assign a rating for each element based upon the general ratings listed at the beginning of this section and in Table 4.1.
B. Inspection Of Mechanical Systems
1. Frequency
It should be noted that if a proper preventive maintenance program is strictly adhered to, the main purpose of an in-depth inspection is to verify that the mechanical systems are performing as expected. For this reason, recommended preventive maintenance procedures and frequencies for specific mechanical systems and equipment are listed in the accompanying Maintenance and Rehabilitation Manual. Table 4.3 lists the inspection frequencies for highway and rail transit agencies throughout the country for their mechanical systems, which include pumps, fans, motors, etc. Also, a percentage of all the tunnel owners that inspect their mechanical systems are given for each specific frequency.
Table 4.03 - Mechanical Inspection Frequency
| Type of Agency | Daily | Weekly | Twice / Month | Monthly | 3 Months | 6 Months | 12 Months | 24 Months | 36 Months | 84 Months | 120 Months |
|---|
| Highway | X | X | | X | X | X | X | X | X | X | X |
|---|
| 4.0% | 4.0% | | 28.0% | 4.0% | 4.0% | 20.0% | 24.0% | 4.0% | 4.0% | 4.0% |
| Rail Transit | X | | X | X | X | X | | X | | | |
|---|
| 8.3% | | 8.3% | 50.0% | 8.3% | 16.7% | | 8.3% | | | |
The inspection frequencies shown should only be used as a guide to what is currently done, not as a suggestion of what should be done. It is up to the tunnel owner to determine the frequency of these in-depth inspections. They can be performed concurrently with the civil/structural inspections or as deemed necessary by the owner because of the age of the mechanical equipment and the amount of equipment needed for proper tunnel operation. It is difficult to determine from the data provided in Table 4.3 the actual scope of the inspection being conducted. It can be assumed that a frequent inspection (generally less than semi-annually, but dependent on the equipment being inspected) is typically a walk-through visual inspection in which the inspector is only looking at critical mechanical equipment to verify that it is functioning properly. On the other hand, a less frequent inspection (generally semi-annually or greater) should be an indicator of a full, in-depth inspection in which every piece of mechanical equipment is inspected and its condition assessed to ensure proper operation.
2. What to Look For
The mechanical inspection will consist of verifying the condition and operation of tunnel equipment and systems. The inspection will include a review of the physical condition of each piece of equipment for damage due to environmental and operational conditions. Any procedures involving the operation of system components must be coordinated with the tunnel owner prior to performing any testing. Each system or piece of equipment should be checked for operation, unless operation of the equipment would cause damage to equipment and/or inspection personnel, or significant disruption to the operation of the tunnel. Any equipment that cannot be operated should be identified, its physical condition noted, and such information immediately reported to the tunnel owner. The inspection should encompass the following systems: tunnel ventilation, air conditioning, heating, controls, plumbing, tunnel drainage, fire protection, and wells/septic systems. Each system should be inspected as follows:
a) Tunnel Ventilation
The inspection of the tunnel ventilation system should include, as a minimum, the following items:
- Review the maintenance records for each piece of equipment and note any special or frequent previous maintenance problems.
- Note the physical condition of each fan, airway, louver, motor-operated dampers, and drive trains.
- Verify that each fan and the associated motor-operated dampers and components are operational.
- Engage a special testing firm to perform vibration analysis on the fans, motors, and bearings during typical fan operations and inspect the fan drive system and bearings.
- Ensure that the airways, where accessible, are free of obstruction and debris.
- Test the operation of the CO monitoring equipment (if such a system exists in highway tunnels).
b) Air Conditioning
The inspection of the air conditioning systems in control rooms, etc., should include the following items:
- Review the maintenance records for each piece of equipment and note any special or frequent previous maintenance problems.
- Note the physical condition of air handling units, condensing units, packaged units, chillers, pumps, cooling towers, exposed air distribution systems, cooling piping, and terminal units.
- Verify that the system is operational. The temperatures at the time of the inspection may dictate if the system is able to be in operation.
- Engage a special testing firm to perform vibration analysis and inspections on chillers, cooling towers, and pumps.
- Engage a special testing firm to perform lube oil analysis on all bearing lubricants.
c) Heating
The inspection of the support area heating system should include the following items:
- Review the maintenance records for each piece of equipment and note any special or frequent previous maintenance problems.
- Note the physical condition of air handling units, pumps, steam and water distribution systems, terminal units, boilers, exposed air distribution systems, heating piping, and steam converters.
- Engage a special testing firm, preferably one that is commissioned by the National Board of Boiler and Pressure Vessel Inspectors, to analyze the boilers to determine their operating efficiency and to inspect the boiler breeching for corrosion and holes.
- Verify that the system is operational. The temperatures at the time of the inspection may dictate if the system is able to be in operation.
d) Controls
The inspection of the tunnel controls should include a visual observation that the control panel indicators represent the operating condition(s) of the equipment each control serves.
The use of a SCADA (Supervisory Control and Data Acquisition) System often controls the entire facility. These systems operate with a minimal amount of hardware maintenance, with the exception of the component level sensors. Software changes for additional programming and periodic upgrades are required to maintain flexibility and reliability of system operation.
e) Plumbing
The inspection of the support area plumbing system should be conducted according to any applicable plumbing code requirements and should also include the following:
- Review the maintenance records for the plumbing system and note any special or frequent maintenance problems.
- Note the physical condition of the bathroom fixtures, water heaters, and drainage system.
- Verify that the plumbing fixtures are operational and the piping is free of leakage.
- Look for watermarks on tunnel surfaces to identify locations of leaks in plumbing system.
f) Tunnel Drainage
The tunnel drainage system including sump pumps should be inspected to determine if the tunnel drains are clear of debris to permit water runoff to flow freely through the drains.
g) Fire protection
The inspection of the fire protection system should include the following items:
- Review the maintenance/inspection records for the system and note any unusual maintenance issues.
- Note the physical condition of the fire protection system in the tunnel and tunnel support areas. This will include the fire extinguishers, hose connections, pumping systems, piping, circulating pumps, and hose reels.
- Note the physical condition of the fire protection storage tanks, alarms, and level switches.
- Check fire control panel for faulty detectors, signals, and wiring.
C. Inspection Of Electrical Systems
1. Frequency
As with the mechanical systems, it should be noted that if a proper preventive maintenance program is strictly adhered to, the main purpose of an in-depth inspection is to verify that the electrical systems are performing as expected. For this reason, recommended preventive maintenance procedures and frequencies for specific electrical systems and equipment are listed in the accompanying Maintenance and Rehabilitation Manual. Table 4.4 lists the inspection frequencies for highway and rail transit agencies throughout the country for inspecting electrical systems. Also, the percentage of tunnel owners that inspect their electrical systems is given for each specific frequency.
Table 4.04 - Electrical Inspection Frequency
| Type of Agency | Daily | Weekly | Monthly | 3 Months | 6 Months | 12 Months | 24 Months | 36 Months | 84 Months | 120 Months |
|---|
| Highway | X | X | X | X | X | X | X | X | X | X |
|---|
| 3.1% | 3.1% | 15.6% | 3.1% | 3.1% | 28.1% | 34.4% | 3.1% | 3.1% | 3.1% |
| Rail Transit | | X | X | | X | X | X | | | |
|---|
| | 15.4% | 61.5% | | 7.7% | 7.7% | 7.7% | | | |
These frequencies should only be used as a guide to what is currently done, not what should be done. It is up to the tunnel owner to determine the frequency of and which items should be checked during these in-depth inspections. They can be performed concurrently with the civil/structural inspections or as deemed necessary by the owner because of the age of the electrical equipment and the amount of equipment needed for proper tunnel operation. It is difficult to determine from the data provided in Table 4.4 the actual scope of the inspection being conducted. It can be assumed that a frequent inspection (generally less than semi-annually, but dependent on the equipment being inspected) is typically a walk-through visual inspection in which the inspector is only looking at critical electrical equipment to verify that they are functioning properly. On the other hand, a less frequent inspection (generally semi-annually or greater) should be an indicator of a full, in-depth inspection in which every piece of electrical equipment is inspected and its condition assessed to ensure proper operation. Further recommendations on inspections are given in NETA MTS 1 and NFPA 70B.
2. What to Look For
The electrical system inspection will consist of verifying the condition and operation of all of the following systems: power distribution, emergency power, lighting, fire detection, and communication. Each of these systems are described herein and are to be inspected for the specific requirements listed below and the following general items:
- Visibly inspect wiring systems for damage and corrosion.
- Ensure that all enclosures and box covers are in place and secure.
- Check for conformity to NFPA 70, 70B, 70E, 72, 130, and NETA MTS 1.
- Check that all disconnects are properly identified as to the items they disconnect.
- Check that all loads are properly identified as to the source or means of disconnect.
- For all large power systems, Electrical Safety Operating Diagrams should be posted to comply with OSHA and NFPA 70E.
a) Power Distribution System
This system consists of the electrical equipment, wiring, conduit, and cable used for distributing electrical energy from the utility supply (service entrance) to the line terminals of utilization equipment. The system would include equipment such as transformers, switchgear, switchboards, unit substations, panelboards, motor control centers, starters, switches, and receptacles. Specific inspection includes:
- Take voltage and load readings on the electrical system using any of the installed meters.
- Check that all indicator gages on the transformers show that fluid levels, temperatures, and pressures are within range.
- Check for signs of damage and overheating of all equipment.
- Check that adequate working space is provided in accordance with NFPA 70, Article 110 and is clear in front of equipment with no material stored in the working space.
- Evaluate the condition of enclosures and conduit and ensure that all enclosures and box covers are in place, conduits are not broken, etc.
- Visibly inspect wiring systems for damage and corrosion.
- Check power distribution system for conformity to NFPA 70 and NFPA 130.
- Check that all disconnects are properly identified as to what items they disconnect.
- Check that all loads are properly identified as to the source or means of disconnects.
- Check all motor controllers for proper operation.
- Have a NETA testing agency perform a thermographic (infrared) inspection for hot spots and an internal inspection, and note any deficiencies. Have this same agency review the previous maintenance records to see if prior discrepancies were corrected. Verify that all tests meet industry standards, including NETA MTS1.
b) Emergency Power System
This system consists of the electrical equipment, wiring, conduit, and cable used for providing electrical power in case of utility service failure. Equipment included in this system consists of emergency generators or uninterruptible power supply (UPS) systems, transfer switches, and other equipment supplying emergency power.
- Ascertain the ability of the emergency power system to operate when the normal power fails, by disabling the normal power supply (i.e., the supply that supplies any transfer switch or other means of transferring loads) and operating the emergency system with selected emergency loads for a sufficient period to evaluate its condition.
- Have a NETA testing agency perform an internal inspection and an inspection for hot spots, and note any deficiencies. Have this same agency review the previous maintenance records to see if prior discrepancies were corrected. Verify that all tests meet industry standards, to include NETA MTS1 and NFPA110.
c) Lighting System
This system consists of the electrical equipment, wiring, conduit, cable, luminaries, sensors, and controllers used to provide lighting for the tunnel.
- Measure the light levels within highway tunnels using an Illuminating Engineering Society (IES) LM-50 device and compare the results against the requirements of IES RP-22.
- Measure the light levels at intervals suggested by IES LM-50.
- Measure the light levels at emergency egress exits and compare with the IES Handbook recommendations.
- Inspect all lighting that is above the roadway surfaces for visible damage, to include corroded or damaged housings, loose attachments, broken lenses, and burnt out bulbs. Also, note if lenses should be cleaned.
- Verify the operation of the lighting controls for the different ranges of nighttime and daylight illumination.
- For transit tunnels, verify that all emergency and continual-use lighting is operational and provides the required amount of illumination.
- For transit tunnels, test operation of Emergency Trip Switch (ETS) lighting, which is linked to the third rail power system to indicate when third rail power is properly shut off. These lights are typically spaced every 240 m (800 ft).
d) Fire Detection System
This system consists of control panels, initiating devices (heat and smoke detectors, pull-stations, etc.), notification appliances (strobes, horns, etc.), wiring, conduit, and cable used to detect a fire in the tunnel.
- Inspect the fire detection system by operating the drill switch and assuring that all of the annunciators and notification appliances operate.
- Check existing records to determine if the system has been tested at regular intervals in accordance with NFPA 72. NFPA 72 requires that a copy of the records for the last seven years be available.
e) Communication System
This system consists of the communication equipment (SCADA, CCTV cameras, telephones, radios, etc.) used to provide communication within and from the tunnel.
- Verify the operation of the SCADA system by ensuring a positive indication is received for each required operation.
- Verify that the CCTV cameras, telephones, radios, or other communication devices are operational.
- Inspect traffic signals for proper operation during all phases.
- Verify that any over-height detectors are not triggering at any heights just below the desired setting and also verify that they are triggering at or just above the desired setting.
D. Inspection Of Other Systems/Appurtenances
1. Inspection of Track Elements
It is recommended that rail transit owners require their internal inspectors, outside consultants, or specialized testing agencies be familiar with and follow the recommended procedures established by their own internal guidelines or the current revision of the US DOT's Federal Railroad Administration - Office of Safety's, Code of Federal Regulations for Title 49, Track Safety Standards Part 213 Subpart A to F, Class of Track 1-5 (TSS Part 213)4. The current revision of this document is dated June 9th, 2001. In fact, it is recommended that each inspection team be required to have a copy of this "pocket-size" book and any owner's specific requirements available when conducting track inspections.
TSS Part 213 provides the following guidelines for class of track and maximum operating speeds for passenger trains shown in Table 4.5.
Table 4.05 - Passenger Train Operating Speeds
| Class of Track | Maximum Allowable Operating Speed for
Passenger Trains, km/h (mph) |
|---|
| Class 1 | 25 (15) |
| Class 2 | 50 (30) |
| Class 3 | 100 (60) |
| Class 4 | 130 (80) |
| Class 5 | 140 (90) |
It is not the intent of this manual to duplicate the material in TSS Part 213. Rather, key elements of track will be described and the general deficiencies that an inspector must look for and evaluate when conducting track inspections will be listed.
a) Frequency
TSS Part 213 Subpart F describes the frequencies for inspecting various classifications of track. It also explains how such inspections can be performed by vehicle or on foot. Inspection frequencies vary from twice weekly for typical rail transit Class 4 and 5 track to weekly for lower speed track (Classes 1 through 3). TSS Part 213 Subpart F also provides inspection frequency guidelines for switches, track crossings and lift rail assemblies or other transition devices on moveable bridges. These requirements include monthly visual inspections on foot and the physical operation of mechanized switches every three months. In addition, TSS Part 213 requires that the rail on all Class 3 and higher track be inspected for rail or rail joint defects with specialized rail defect detection equipment at least once a year.
The questionnaires sent out revealed that rail transit owners perform track inspections that vary from daily to yearly based upon their internal procedures. The established frequencies need not change unless the requirements of TSS Part 213 are not being achieved.
b) What to Look For
This section provides general guidance on defects that occur in track elements as listed in TSS Part 213, Subparts C, D, and E. Specifically, these Subparts cover the following track elements:
- Subpart C - Track Geometry (Gage, Alignment, Curves - Elevation and Speed Limitations, Elevations of Curved Track - Runoff, and Track Surface).
- Subpart D - Track Structure (Ballast, Crossties, Gage Restraint Measurement Systems, Defective Rails, Rail End Mismatch, Continuous Welded Rail, Rail Joints, Torch Cut Rail, Tie Plates, Rail Fastening Systems, Turnouts and Track Crossings, Switches, Frogs, Spring Rail Frogs, Self-Guarded Frogs, and Frog Guide Rails and Guard Faces - Gage).
- Subpart E - Track Appliances and Track-Related Devices (Derails).
An inspection program should ensure that each of the track elements in each Subpart are reviewed and evaluated to maintain safe operation of the trains. A brief description of the inspection required for some of the major track elements is as follows:
(1) Rail
Inspect the rail for horizontal and vertical cracks in the steel, horizontal and vertical split heads, transverse and compound fissures, fractures, split web, piped rail, bolt-hole crack, head web separation, broken base, detail fracture, engine burn fracture, broken or defective weld, and surface defects. See TSS Part 213 and the Rail Defect Manual5 compiled by Sperry Rail Service for explanation of these defects. The severity of these defects range from minor to major.
(2) Gage
The gage of the track is the distance from the center to center of rail heads measured at right angles to the rails in a plane five-eighths of an inch below the top of the rail head. The gage may deviate from construction over time, thus exceeding tolerances for tangent and curved tracks. TSS Part 213 gives the appropriate gage distance according to classification of track as follows in Table 4.6.
Table 4.06 - Track Gage Distances
| Class of Track | Gage must be at least | But not more than |
|---|
| Class 1 | 1400 mm (4' - 8") | 1450 mm (4' - 10") |
| Class 2 and 3 | 1400 mm (4' - 8") | 1444 mm (4' - 9 ¾") |
| Class 4 and 5 | 1400 mm (4' - 8") | 1438 mm (4' - 9 ½") |
(3) Alignment
Alignment of tracks may not deviate from uniformity more than the amounts shown in Table 4.7:
Table 4.07 - Track Alignment
| Class of Track | Tangent Track | Curved Track |
|---|
| The deviation of the mid-off-set from a 18.6 m (62 ft) line1 may not be more than ___ mm (inches) | The deviation of the mid-ordinate from a 9.3 m (31 ft) chord2 may not be more than ____ mm (inches) | The deviation of the mid-ordinate from a 18.6 m (62 ft) chord2 may not be more than ___ mm (inches) |
|---|
| Class 1 | 125 (5) | N/A3 | 125 (5) |
| Class 2 | 75 (3) | N/A3 | 75 (3) |
| Class 3 | 43 (1 ¾) | 43 (1 ¾) | 43 (1 ¾) |
| Class 4 | 37 (1 ½) | 25 (1) | 37 (1 ½) |
| Class 5 | 18 (¾) | 12 (½) | 15 (5/8) |
- The ends of the line shall be at points on the gage side of the line rail, 15 mm (5/8 in) below the top of the railhead. Either rail may be used as the line rail; however, the same rail shall be used for the full length of that tangential segment of track.
- The ends of the chord shall be at points on the gage side of the outer rail, 15 mm (5/8 in) below the top of the railhead.
- N/A - Not Applicable
(4) Curves
The maximum crosslevel on the outside rail of a curve may not be more than 200 mm (8 in) on Track Classes 1 and 2 and 175 mm (7 in) on Classes 3 through 5.
(5) Fasteners/Bolts/Spikes
Each of these elements is extremely important for safe operation of the rail transit system, especially in securing the gage of the track. Spikes should be inspected to ensure they are tight and snug against the rail if they are used for lateral restraint of the rail. Fasteners include special clips or attachments on both regular jointed and continuous welded rail (CWR) and should be inspected for missing, broken, or loose fasteners. For CWR, fasteners can also serve as longitudinal restraint.
Special testing of the fasteners is required to ensure the proper clamping force is being applied to restrain the rail. Bolts are used at rail joints for splicing the rail or for attaching tie plates to the underlying anchorage system, whether ties or direct fixation. They should be inspected for condition and missing, loose, or broken fasteners.
(6) Tie Plates
Tie plates are used to distribute the rail uniformly to the supporting tie or concrete bearing system with grout. These should be inspected for condition and to determine if uniform bearing is being achieved. If point loading on the tie plates is prevalent, this may affect the gage of the rail, alignment, or curvature.
(7) Crossties
Crossties support and secure the rail. They are typically made of timber or precast concrete although fiber reinforced plastic ties are currently being manufactured or used to rehabilitate existing timber ties. They should be inspected for condition and for effective support in accordance with TSS Part 213, Subpart D, Section 213.109.
Timber crossties should be inspected to insure that they are not: broken through, split or otherwise impaired such that ballast can work through or spikes and rail fasteners cannot be held, so deteriorated that the tie plate or base of rail can move laterally 12 mm (½ in) relative to the crosstie, or cut by the tie plate through more than 40 percent of the crosstie's thickness.
For concrete crossties, they should be inspected for cracks, deteriorated concrete, spalls, etc.
(8) Ballast
Inspect the ballast for condition. Insufficient or fouled ballast is described as any ballast that will not a) transmit and distribute the load of the track and railroad rolling equipment to the subgrade; b) restrain the track laterally, longitudinally, and vertically under dynamic loads imposed by railroad rolling equipment or thermal conditions; c) provide adequate drainage for the track; and d) maintain proper track crosslevel, surface, and alignment.
(9) Rail Joints
Rail joints occur where the ends of two rails meet and are spliced together with bolts to maintain vertical integrity of the rail. These joints should be inspected for cracks or loose joint bars; worn joint bars (such that excessive vertical movement is permitted); broken joint bars; and missing, broken, or deteriorated bolts. The proper number of crossties in the vicinity of the rail joint is also critical and should be reviewed in accordance with crossties mentioned before.
2. Inspection of Power Systems (Third Rail/Catenary)
a) Third Rail Power System
(1) Frequency
It is recommended that visual inspections of the third rail system be performed for normal tunnel sections or at crossovers in tunnels on a monthly basis. This visual inspection should be made on foot and should note any defects that would affect the movements of the electric rail transit vehicles. In addition, it is recommended that testing equipment such as ohmmeters; a direct current power supply, generator, or equivalent alternating current supply; and miscellaneous leads be used to test resistance of rail joints on a yearly basis. Any deficiencies should be repaired during this testing period.
(2) What to Look For
The third rail system provides power to electric rail transit vehicles via direct contact with the third rail from current collectors (shoes) attached to the transit vehicles. The third rail system is comprised of the steel contact rail, protection boards, protection board brackets, insulators, insulator caps, anchors, and negative running rail bonded joints as shown in Figure 2.19. A brief description of the inspection required for some of the major third rail system elements is as follows:
- a. Steel Contact Rail
The contact rail should be inspected to determine if it is resting evenly and uniformly on all insulators, for excessive wear and damage on the contact surface, to determine if its alignment follows the same radius as any curve in the tunnel, and to ensure that all ends are terminated with end approach castings.
- b. Contact Rail Insulators
The contact rail should be inspected to verify that insulators are present, that they rest directly on each bracket, and that they are held in place by a centering cup that forms an integral part of the bracket. Each insulator shall be covered with an insulator cap. This cap is held in place by the lug hole, which is an integral part of the insulator. Inspect each insulator for condition. Those that are dirty should be thoroughly cleaned; any that are broken or chipped should be replaced.
- c. Protection Board
Protection boards should be of sufficient length to be supported by not less than two brackets. On curves these boards should be cut to conform to the radius of the curve. Inspect these boards to ensure they are in good condition, properly attached, and cover the contact rail.
- d. Protection Board Brackets
For timber ties, inspect the protection board brackets to determine if the brackets are placed on the long timber ties, that they are horizontally gaged accurately, that they rest directly on the tie, and that they are fastened by two lag screws. Also, verify that no brackets are installed on ties supporting joints in the running rail. For concrete base supports, the brackets are to be fastened with bolts and a 3 mm (1/8 in) thick polyethylene pad is to be placed between the steel bracket and the concrete for isolation purposes.
- e. Contact Rail Splices
All contact rail splice joints, except joints at end approaches, should have a bonded joint. Two bonds are required at each bonded joint, one on each side of the contact rail. Inspect this bonded joint by performing a resistance test on a two-foot length across the joint with a length of solid rail necessary to give an equal resistance. The solid rail reading should not be greater than 800 mm (32 in). Use the following testing equipment to perform the test:
- Ductor, low resistance ohmmeter.
- Direct Current (D.C.) power supply.
- Miscellaneous leads.
- Generator or equal for Alternating Current (A.C.) supply.
- f. Negative Running Rail Bonded Joints
Inspect all negative running rail bonds, impedance bond locations, turnout and crossover bonds to complete a continuous negative circuit. Ensure that no defective joints exist. Perform a resistance test on a 750 mm (30 in) length of rail across the joint with a length of solid rail necessary to give an equal resistance. The solid rail reading should not be greater than 1200 mm (4 ft). Use the same equipment as described for the contact rail splice test.
- g. Third Rail Insulated Anchor Arms
Inspect all bolts, insulators, contact clamps, and anchor plates used at contact rail anchor locations. Inspection should note loose or worn bolts, nuts or clamps, broken insulators, or any removal of assemblies.
b) Catenary Power System
(1) Frequency
It is recommended that the catenary inspection include two levels - a visual inspection and an in-depth inspection. Two agencies have specific frequency requirements that may be indicative of other rail transit agencies and are discussed herein. These agencies include Metro-North Commuter Railroad and AMTRAK.
Metro-North recommends that a visual inspection of the catenary system be made on foot at bi-monthly intervals. They also recommend that an in-depth inspection be made from a track vehicle with a high-level platform bi-annually. On the other hand, AMTRAK recommends that a visual inspection of the catenary system be made from the head end of a train on a weekly basis. AMTRAK also requires a quarterly geometry car inspection, a yearly catenary car inspection, and a bi-annual up-close inspection and repair be made from the top of a catenary car, wire train, or highway-rail vehicle.
(2) What to Look For
There are at least two documents available that give specific requirements for inspection of the catenary system. These include the Catenary System Inspection Procedures for the Metro-North Commuter Railroad6 and the Catenary Inspection Manual for AMTRAK7. Since Metro-North was included in the inventory for this project, some of their recommended procedures will be briefly defined herein. However, this would not preclude an owner from using his own or even AMTRAK's recommended procedures. A brief description of the inspection required for some of the major catenary system elements is given below. Note that a particular element may have different procedures for a visual inspection than for an in-depth inspection.
- a. Visual Inspection
In addition to noting general observations for the following elements, a walk-through inspection should record excessive arcing in a matrix that shows location, train speeds, number and type of pantographs, direction of travel, climatic conditions, and any unusual circumstances. This will help determine if arcing is due to equipment mal-adjustment or to a pattern of circumstances.
- Support and Registration Insulators - Check for broken sheds and any build-up of deposits that could cause tracking. Insulator support steel should be checked for missing or loose nuts and any evidence of movement.
- Hangers - Check that alignment is vertical. Hangers consistently leaning one direction indicate that stretch or slippage has occurred and this should be investigated immediately. Make note of detached hangers and determine cause; this may be due to loose or damaged carbons on pantographs. Check contact wire clip for evidence of impact.
- Jumpers - Check "C" jumpers and full section continuity jumpers at overlaps for loose clamps, movement or evidence of burning and that they do not sag below contact wire level.
- Pull-Off Arrangements - Check for evidence of clamp slippage and ensure that heel settings are higher than the contact wire and that the drop bracket is vertical. Verify that the messenger is positioned vertically over the contact wire at pull-off locations.
- Anchors - Check to see if the anchors supporting the catenary system within the tunnel are in good condition and anchored firmly to the substrate. Note any deficiencies.
- b. In-depth Inspection
The in-depth inspection will be used to perform the following inspection tasks as well as give inspection personnel the opportunity to complete general repairs and preventive maintenance.
- Contact Wire Wear - Check contact wire wear at each registration point with particular attention to phase gaps and overlaps. Verify that vertical thickness of contact wire does not measure less than 11 mm (0.42 in). If this is not the case, then the contact wire should be replaced in that location.
- Clamped Electrical Connectors - Randomly remove and check clamped connections at "C" jumpers, feeder points and full section overlap jumpers for corrosion or burning. If the above conditions are found, the clamps should be removed, cleaned, and tightened. In addition, high melting point grease should be applied to stranded conductors.
- Hangers - Check for evidence of mechanical wear or electrical arcing. Inspect neoprene sleeves between the messenger and the retainer.
- Messenger Supports - Check for electrical tracking across the insulator and check stainless steel wire and thimbles for signs of mechanical wear; replace as necessary.
- Registration Assembly - Check registration components at same location as messenger assembly for wear. Open contact wire clamps, check for wear, and regrease. Inspect hinge pin, clevis pin and all bolted connections. Tighten or replace as necessary.
- Support and Registration Insulators - Check for contamination, signs of electrical tracking, and broken or chipped sheds. Check tightness of fixing bolts into ends of insulators.
- Overlaps - Verify the contact wire profiles at overlaps to ensure efficient transition of the pantographs. Inspect underside of contact wires for signs of arcing and adjust, if necessary.
- Section Insulators - Check for evidence of burning of the skids and arcing horns. Adjust turnbuckles on the support hangers of each unit to keep units level and vertically in line with contact wire.
- Disconnect Switches - Open and close to ensure operation of switches.
3. Inspection of Signal/Communication Systems
Similarly to track inspections, it is recommended for inspection of signal systems that rail transit owners require their internal inspectors, outside consultants, or specialized testing agencies be familiar with and follow the recommended procedures established by their own internal guidelines or the US DOT's Federal Railroad Administration - Office of Safety's, Code of Federal Regulations for Title 49, Part 236 - Rules, Standards, and Instructions Governing the Installation, Inspection, Maintenance, and Repair of Signal and Train Control Systems, Devices, and Appliances8, further referred to as FRA Part 236. For communication systems, the same office of the Federal Railroad Administration has produced Title 49, Part 220 - Railroad Communications9, further referred to as FRA Part 220. However, this publication contains little in regard to inspection and testing and more on actual operations of such systems.
It should be noted that there is no current requirement for rail transit tunnel owners to follow the guidelines in FRA Part 236 or Part 220, but in lieu of developing their own, many transit agencies have adopted these as standards.
Given the complexity of FRA Part 236, it will not be reproduced in this manual in its entirety, but rather key sections have been identified and generalized to give basic direction for inspection of signal systems. To establish a comprehensive signal system inspection program, it is recommended that a copy of FRA Part 236 be consulted directly.
a) Frequency
(1) Signal Systems
Specific inspection procedures outlined in FRA Part 236 for the various components of the signal system range in frequency from 1 month to 10 years. Some of these frequencies include the following:
| Switch circuit controller | - | 3 months |
| Switch obstruction | - | monthly |
| Semaphore/searchlight | - | 6 months |
| Relays (type dependent) | - | 2 years |
| Ground tests (power supplies) | - | 3 months |
| Insulation tests (cables) |
| New | - | 10 years |
| Resistance < 500,000 ohms | - | yearly |
| Timing devices | - | yearly |
| Interlocking tests | - | 2 years |
| Trip stops |
| Height and alignment | - | monthly |
| Operation | - | 6 months |
(2) Communication Systems
Specific frequencies for inspection of communication systems range from continuously (by use) to monthly. Examples of these frequencies are shown below:
| Emergency telephones | - | monthly |
| Radiating cables | - | prior to work |
| Backbone cables | - | continuously (by use) |
| Communications equipment | - | per manufacturer. |
As another source of frequency recommendation, a survey of current rail transit tunnel owners showed actual inspection frequencies for both signal and communication systems that range from daily to every six months, with monthly being most common.
b) What to Look For
(1) Signal Systems
Comprehensive and timely inspections of signal systems are necessary due to the possible consequences if a component of the system fails. According to FRA Part 236; "When any component of a signal system, the proper functioning of which is essential to the safety of train operation, fails to perform its intended signaling function or is not in correspondence with known operating conditions, the cause shall be determined and the faulty component adjusted, repaired or replaced without undue delay." In addition to the visual and operative inspection procedures given in the above frequency section, a brief description of the inspection required for some additional signal system elements is as follows:
- Verify that legible and correct plans are kept at all interlockings, automatic signals, and controlled points.
- Verify that open-wire transmission lines operating at voltage of 750 volts or more shall be placed not less than 1,200 mm (4 ft) above the nearest crossarm carrying signal or communication circuits.
- Verify that each wire is tagged or marked so that it can be identified at each terminal. Also, verify that tags and wires do not interfere with moving parts of any signal apparatus.
- Test the operating characteristics of all parts of semaphores or searchlights.
- If a block signal system is being used, then verify that each signal governing train movements into a block will display its most restrictive aspect when any of the following conditions are met within the block:
- Occupancy by a train, locomotive, or car.
- When points of a switch are not closed in proper position.
- When an independently operated fouling point derail-equipped with switch circuit controller is not in derailing position.
- When a track relay is in de-energized position or a device which functions as a track relay is in its most restrictive state; or when signal control circuit is de-energized.
- Verify that insulated rail joints are maintained to prevent sufficient track circuit current from flowing between the rails separated by the insulation to cause a failure of any track circuit involved.
- Verify that the trip stop arm is maintained at the height above the plane of the tops of the rails and the horizontal distance from its center line to gage side of the nearest running rail are in accordance with the specifications of the carrier.
- Ensure that results of all tests performed are recorded on preprinted or computerized forms provided by the rail transit authority and are retained until the next record is filed or for one year, whichever is greater.
(2) Communication Systems
As with signal systems, it is critical that communication systems be kept in good working condition; therefore, accurate and frequent verification of working condition is pertinent. In addition to the procedures described in the above frequency section, the following actions are suggested:
- Verify that all emergency telephones are in proper operating condition by placing a call from each location.
- Test signal strength of radiating cable.
- Visually inspect backbone cables for signs of degradation.
- Follow all manufacturers' recommendations for inspection and preventive maintenance of communications equipment.
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