Atch_19 _ETL_04-4 _Trenchless_Technology.pdf

DEPARTMENT OF THE AIR FORCE

HEADQUARTERS AIR FORCE CIVIL ENGINEER SUPPORT AGENCY

MAR 31 2004

APPROVED FOR PUBLIC RELEASE: DISTRIBUTION UNLIMITED

FROM: HQ AFCESA/CES

139 Barnes Drive, Suite 1 Tyndall AFB, FL 32403-5319

SUBJECT: Engineering Technical Letter (ETL) 04-4 (Change 1): Trenchless

Technology (TT) for Crossing Air Force Pavements

1. Purpose. This ETL provides general information and guidance on the use of TT in constructing, reconstructing, rehabilitating, renovating, cleaning, inspecting, locating, and detecting anomalies around underground pipelines, utilities, fuel hydrant lines, or communication lines crossing under Air Force pavements, including runways, taxiways, aprons, overruns, and roadways.

2. Application. All Air Force installations. Consideration of TT is encouraged in all instances where a project involves work on an underground pipeline, utility, fuel hydrant line, or communication line crossing under an Air Force runway, taxiway, apron, overrun, or roadway. When considering the use of TT, input/guidance should be sought from the major command pavement engineer and the appropriate functional engineer for the system involved.

2.1. Authority: Air Force Policy Directive (AFPD) 32-10, Installations and Facilities.

2.2. Effective Date: Immediately.

2.3. Intended Users:

• Air Force major command (MAJCOM) pavement engineers, utility system engineers, and fuel system engineers.

• Base civil engineers (BCE) and others responsible for constructing, reconstructing, rehabilitating, and renovating Air Force facilities (including, but not limited to, underground pipelines, utilities, fuel hydrant lines, and communication lines), or for cleaning, inspecting, locating, and detecting anomalies around Air Force underground pipelines, utilities, fuel hydrant lines, and communication lines.

• United States (U.S.) Army Corps of Engineers (USACE) and Navy offices responsible for constructing, reconstructing, rehabilitating, and renovating Air Force facilities, or for cleaning, inspecting, locating, and detecting anomalies around Air Force underground pipelines, utilities, fuel hydrant lines, or communication lines.

2.4. Coordination: MAJCOM pavement engineers, utility system engineers, and fuels engineers.

3. References:

3.1. Code of Federal Regulations (CFR):

• Title 29, CFR, Chapter XVII, Section 1910.146, Permit-required confined spaces

3.2. Environmental Protection Agency:

• Operation and Maintenance of Wastewater Collection Systems, Volume II, Section 10.320, “Pipeline Rehabilitation Methods,” available online at http://www.epa.gov/OWM/

3.3. Air Force:

• ETL 04-6, Inspection of Drainage Systems, available online at http://www.afcesa.af.mil/Publications/ETLs/default.html

• AFPD 32-10, Installations and Facilities, available online at http://www.e-publishing.af.mil/pubfiles/af/32/afpd32-10/afpd32-10.pdf

3.4. American Society for Testing and Materials (ASTM):

• F2207-02 Standard Specification for Cured-in-Place Pipe Lining System for Rehabilitation of Metallic Gas Pipe, available online at http://www.astm.org/cgi-bin/SoftCart.exe/index.shtml?E+mystore

• F1962-99 Standard Guide for Use of Maxi-Horizontal Directional Drilling for Placement of Polyethylene Pipe or Conduit Under Obstacles, Including River Crossings

• F1871-02 Standard Specification for Folder/Formed Poly (Vinyl Chloride) Pipe Type A for Existing Sewer and Conduit Rehabilitation

• F1867-98 Standard Practice for Installation of Folded/Formed Poly (Vinyl Chloride) (PVC) Pipe Type A for Existing Sewer and Conduit Rehabilitation

• Other ASTM standards related to trenchless technology

3.5. Private Industry:

• Transportation Research Board (TRB), National Cooperative Highway Research Program (NCHRP) Synthesis 242, Trenchless Installation of Conduits Beneath Roadways, 1997

• International Society of Trenchless Technology (ISTT) Web site, http://www.istt.com

• North American Society for Trenchless Technology (NASTT), A Brief History of Trenchless Construction, available online at http://www.nastt.org/

• Australasian Society for Trenchless Technology (ASTT), State of the Industry Report on Trenchless Technologies in Australia, prepared by Australian Water Technologies (AWT) Engineering Pipelines, September 2000, available online at http://www.astt.com.au/AWTReport.htm

• Trenchless Technology: Rehabilitation of Potable Water Pipe, Stuart Wilson, Rural Water, Volume 22, Number 4, Fourth Quarter 2001 http://www.epa.gov/OWM/ http://www.afcesa.af.mil/Publications/ETLs/default.html http://www.e-publishing.af.mil/pubfiles/af/32/afpd32-10/afpd32-10.pdf http://www.astm.org/cgi-bin/SoftCart.exe/index.shtml?E+mystore http://www.istt.com/ http://www.nastt.org/ http://www.astt.com.au/AWTReport.htm

• What is Trenchless Technology Anyway?, Glenn M. Boyce, Trenchless Technology, Volume 5, Number 6, June 1996

• Water Environment Federation (WEF) Manual of Practice (MOP) FD-6, Existing Sewer Evaluation and Rehabilitation (American Society of Civil Engineers [ASCE] Report on Engineering Practice No. 62), Chapter 7, “Pipeline Rehabilitation Methods,” available online at http://www.wef.org/

4. Acronyms and Terms. A glossary of TT terminology is included as Attachment 1.

Note that the lack of standardization of terminology in the TT industry is a significant problem. Identical TT terms vary in meaning with different manufacturers, contractors, researchers, and even with different individuals within the same organization.

AFPD – Air Force Policy Directive AFPET – Air Force Petroleum Office ASCE – American Society of Civil Engineers ASS – advanced support structure ASTM – American Society for Testing and Materials ASTT – Australasian Society for Trenchless Technology AWT – Australian Water Technologies BCE – base civil engineer CCTV – closed circuit television CFR – Code of Federal Regulations CIP – cast iron pipe CIPP – cured-in-place pipe DIP – ductile iron pipe DOT – Department of Transportation EHMWHD – extra-high molecular weight high density EPB – earth pressure balance ERW – electrical resistance welding ETL – Engineering Technical Letter GPR – ground penetrating radar GRC – glass-fiber reinforced concrete GRP – glass reinforced plastic HDD – horizontal directional drilling HDPE – high density polyethylene HQ AFCESA – Headquarters, Air Force Civil Engineer Support Agency IGN – Information Guidance Notes IJS – intermediate jacking station IRT – infrared thermography ISTT – International Society for Trenchless Technology MAJCOM – major command MOP – Manual of Practice MTBM – microtunnel boring machine MWD – measurement while drilling NACE – National Association of Corrosion Engineers http://www.wef.org/

NASTT – North American Society for Trenchless Technology NCHRP – National Cooperative Highway Research Program O&M – operation and maintenance OSHA – Occupational Safety and Health Administration PE – polyethylene POL – petroleum, oil, and lubricants PP – polypropylene PRC – polyester resin concrete PVC – polyvinyl chloride RPM – reinforced plastic mortar RTR – reinforced thermosetting resin SDR – standard dimension ratio SRPC – sulfate resisting Portland cement TBM – tunnel boring machine TRB – Transportation Research Board TT – trenchless technology U.S. – United States USACE – U.S. Army Corps of Engineers VCP – vitrified clay pipe VCT – vitrified clay tile WEF – Water Environment Federation

5. History. The theory and recorded use of trenchless techniques dates back to early Roman times. Visit the North American Society for Trenchless Technology (NASTT) Web site at http://www.nasttglsl.on.ca/english/about.htm for a historical overview of TT.

6. Considerations. TT should be viewed as an alternative construction methodology.

Consider system characteristics, constructability, site conditions, and cost when deciding whether to use TT. Each opportunity to utilize TT must be evaluated on a case-by-case basis.

6.1. System Characteristics. While TT is ideal for straight through runs of pipe, it is less well suited for projects involving characteristics such as numerous service connections, valves, and bends. Additionally, although very good control of grade is possible using TT, exercise caution when considering the use of TT for systems that require very tight grade tolerances, such as lines for petroleum, oil, and lubricant (POL) products.

6.2. Site Conditions. The in situ site conditions and the presence of underground interferences, whether natural (e.g., boulders) or man-made (e.g., underground structures and utilities), should be considered when deciding whether to use TT.

Compared to soil deposits, the presence of natural rock or coral deposits can increase drilling costs, while underground interferences can cause alignment problems (i.e., deflections) during TT operations.

http://www.nasttglsl.on.ca/english/about.htm

6.3. Constructability. The presence of qualified, experienced, certified contractors and equipment operators is essential to the success of a TT project, as is the availability of the proper equipment and materials for the job and site conditions. These factors are more likely to be a problem at overseas, remote, or hostile environment locations.

6.4. Cost. Since TT is an alternative construction methodology, compare its cost to that of conventional techniques such as cut-and-cover (i.e., trenching and backfilling) before deciding to use TT. In the cost analysis, include the indirect costs of conventional construction techniques, such as the need for a longer construction time or the disruption caused by having to close a pavement section.

7. Advantages. For the Air Force, the most important advantage of TT is that it minimizes disruption to both aboveground facilities (e.g., runways, hangars) and belowground facilities (e.g., existing utilities, bunkers). Other important collateral advantages of TT are:

7.1. Size Range. TT can be used to create almost any size range, from a tiny conduit for a fiber optic cable to a multilane vehicle tunnel.

7.2. Pipe Types. TT can use virtually any type of pipe, although some pipe types are better suited for particular TTs. Some pipe types commonly used in TT are:

• Steel pipe

• Polyvinyl chloride (PVC) pipe

• Polyethylene (PE) pipe

• Vitrified clay pipe

• Reinforced concrete pipe

• Polymer concrete pipe

• Fiberglass reinforced pipe

7.3. Pipe Shapes. TT can use a wide variety of pipe shapes. The most commonly used shape is circular, but TT can also use oval, elliptical, and semi-elliptical pipe shapes as well as a variety of box shapes. In addition, modular and other advanced construction techniques can be used to create unusual cross sections.

7.4. Site Preparation. TT can minimize the time needed for site preparation and/or the amount of disturbance. Common TT techniques require either no digging or digging of a drive pit and a receiving pit (adjacent to the ends of the pipe segment, on opposite sides). Even when pits are used, the amount of disturbance is significantly less than for a fully excavated trench. Not only is the disturbance reduced, but it can also be localized to areas that are not mission-critical (i.e., away from the main runways and taxiways).

7.5. Dewatering. While some systems, like POL lines, may need to be protected from contamination from water, mud, salt, and debris, many projects employing TT techniques will require little or no dewatering.

7.6. Safety. TT is safer than conventional trench excavation for several reasons:

7.6.1. Conventional excavating techniques usually require person-entry within the trench to lay the pipe. Even when a conventional trench is shallow, without proper support (e.g., shore jacks, trench “boxes”) there is still a danger of collapse. In addition, even when reinforcement or other safety equipment is required by contract, many workers do not take full advantage of the protection because of the sharp decrease in productivity associated with the use of in-trench safety equipment.

7.6.2. In sharp contrast to conventional construction techniques, most TTs do not require person-entry within the “trench” area. In addition, most TTs only require person-entry in insertion/receiving pits that are relatively easy to reinforce. Even in those TTs that require person-entry within the “trench” area (e.g., tunneling), the person is usually completely enclosed by a supporting pipe with sufficient strength to help guarantee the person’s safety in case of collapse.

7.7. Environmental Impact. Because TT methods minimize soil disturbance and dewatering, environmental damage is correspondingly minimized.

7.8. Replacement of Excavated Materials. Open trenches across an Air Force pavement almost always require replacement of a significant portion of the removed material to maintain pavement strength and stability. Since TTs minimize the disturbance of the in situ materials, the surrounding materials retain their existing strength and stability without material replacement.

7.9. Depth. There is a practical limit to conventional trenching (i.e., the depth a hoe or digger can reach), but virtually no limit to the depth for which TT can be used. In cases where existing underground structures, or even existing underground utilities, create an area of concern, TT can be used to go far beneath the problem.

7.10. Reduction in Operation and Maintenance (O&M) Costs. TT can reduce O&M costs by returning pipe systems to their design capacity (or sometimes even better than design capacity), often at a fraction of the cost of conventional reconstruction.

8. Applicability of Specific TT Methods. No single TT method is best for all cases, and applicability is contingent upon Air Force-specific conditions.

8.1. Local Geology. Local geology/subsurface conditions usually preclude the use of one single TT for all cases. This statement is supported by the Transportation Research Board (TRB), National Cooperative Highway Research Program (NCHRP) Synthesis 242, Trenchless Installation of Conduits Beneath Roadways, which addresses roadway utility crossings. The TRB compiled results of survey responses on TT from the departments of transportation (DOT) in 33 American states and 6 Canadian provinces.

The TRB study had one major conclusion:

No one method is suitable for all types of utilities or all types of soil or site conditions. The selection of compatible methods is site specific and highly dependent on subsurface conditions. Therefore, an adequate soils investigation and an accurate underground utility location program are critical for minimizing subsequent construction problems and claims.

8.2. Time/Mission Disruption. Since mission capability is often the controlling factor in Air Force pavement crossings, there are several other factors related to time or mission disruption that preclude the use of one single TT for all Air Force cases.

8.2.1. Equipment Availability. Equipment availability is a key issue in the use of TT for Air Force pavement crossings. Unlike DOTs (with local jurisdiction), the Air Force has a worldwide jurisdiction, and with force projection comes the possibility of pavement crossing problems anywhere on the globe. Depending on the TT chosen, local equipment may not be available or adaptable to solve a particular problem.

8.2.2. Materials Availability. Local materials availability may affect the choice of TT for a particular problem or location. In this context, “materials” refers to items such as the pipe, pipe liner, grout, and drilling mud. The exact definition of “materials” will vary with the choice of TT method.

8.2.3. Adjacent Area Availability. The availability and usability of adjacent areas may determine the choice of TT. For a technology that requires an insertion pit or a receiving pit, there must be an adjacent area that can be excavated. Other TTs that do not require a pit (e.g., horizontal directional drilling [HDD]) still require a significant staging area, but the staging area does not always have to be adjacent to the pavement.

8.2.4. Specialized Training. The need for specialized training may restrict or eliminate the choice of some TTs for a particular need in a particular area (e.g., in a dangerous area). The engineer who considers the choice of a TT must also consider that the same personnel who can perform a wide range of other construction activities may not be capable of operating, for example, a computer-controlled directional drilling machine.

The issue of training may not be as critical for peacetime construction performed by a qualified civilian contractor, but it could be a controlling issue in a force-projection environment. In any event, a TT contractor for an Air Force pavement crossing must have adequate training and experience to ensure a safe and satisfactory result, and any TT equipment operator must be properly and specifically trained on the TT equipment that will be used by that operator.

8.2.5. Use of Sleeves. For any pressurized utility or fuel line crossing under an active Air Force pavement (runway, taxiway, apron, overrun, or roadway), a TT which includes the use of a protective sleeve is highly recommended when extreme loadings may cause undue stresses on the pipeline. (Note: Such situations can usually be mitigated through the use of an increased pipe wall thickness and/or a greater depth of pipeline cover.) When a sleeve is used, the sleeve material should be of a type and strength that will minimize the risk of external leakage in the event of a breach in the main pipeline, since external leakage could cause environmental contamination, structural weakening of the pavement support system, or other danger (e.g., fire). In addition, the sleeve system should have adequate venting to maintain integrity and safety at all times, specifically to include the case of a breach in the main pipeline. Specific design and performance criteria (e.g., the need for protective coatings and cathodic protection) and venting requirements for the sleeves will depend on the TT chosen, the type of pressurized pipeline, and the material to be transported within the pressurized pipeline.

When a sleeve is used for a cathodically protected pipeline: (1) the carrier pipe should be centered in the sleeve using non-metallic devices, and (2) the annular space should be filled with clean, non-corrosive fill material to allow cathodic protection current to reach the entire surface of the carrier pipe. A corrosion control specialist certified by the National Association of Corrosion Engineers (NACE) should be consulted when designing such work.

9. Performance Specifications. A growing number of DOTs are using performance specifications rather than product specifications for most, if not all, of their TT contracts for roadway crossings. With the growing number of methods and materials available, it is becoming harder and harder to write a good product specification that will allow contractors to use the best TT for a particular job (i.e., one that will maximize benefits and minimize cost), whereas performance specifications place the responsibility on the contractor to deliver a finished product with adequate performance characteristics to satisfy mission needs. For mission critical systems, like POL lines, the use of product specifications may still be preferable.

10. TT Types. Attachment 2 illustrates the major types of TT currently available.

Hybrids of the major methods create a plethora of choices for a given TT application;

however, the various methods can be separated into four major groups, three of which can be considered structural (new construction or reconstruction, renovation, and rehabilitation) and two non-structural (cleaning and inspection [to include pipeline location and anomaly detection]).

10.1. New Construction or Reconstruction. Construction methods may be categorized as either surface-launched or not surface-launched.

10.1.1. Surface-launched. In general, surface-launched TTs start by drilling a pilot hole that is then expanded by “backreaming” (i.e., pulling an enlarging cutting head back through the pilot hole) before pulling in the pipe. Backreaming can be done separately from, or in conjunction with, pipe pullback. An alternate method uses the pilot hole as a guide, with a cutting head and pipe being pushed along the guide path (similar to microtunneling). The main surface-launched TTs are HDD and guided boring; a hybrid type, the midi rig, is often referred to as a third type.

10.1.1.1. In the TT industry, the term “guided boring” is sometimes used generically to mean any horizontal boring with any degree of control over the drill head; however, the term is more commonly used to describe a type of small-scale, surface-launched boring rig that has a limited capability for guiding the auger-head. Guided borings are often used by utility companies for highway crossings and are particularly cost effective when several crossings need to be made in a single geographical area. The major advantage over traditional (horizontally oriented) rotary drilling methods is that no drive pit or receiving pit is needed. The major disadvantage is the mobilization cost of the specialized equipment and operators, which is why this method is often used only for multiple crossings.

10.1.1.2. HDD is, essentially, a larger-scale, higher-technology version of guided boring, usually with computerized remote control over the drilling head. (In fact, some vendors refer to a guided boring rig as a “mini HDD.”) In sharp contrast to guided boring rigs, the largest HDDs are capable of traveling several miles underground with remotely controlled guidance (using radio-driven locator technology to track the drilling head).

The major advantage of HDD is the relatively large depths and relatively long distances that can be traversed. HDD has been used for crossings under rivers, lakes, multi-lane highways, and airports. Mobilization costs remain the major disadvantage of this method, even more so than for guided boring.

10.1.1.3. Many vendors consider midi rig boring, a hybrid TT technique, a separate surface-launched method. The size of a midi rig varies, but it falls somewhere between a guided boring rig and an HDD rig. Similarly variable, the remote location and guidance capabilities of a midi rig would usually be thought of as better than a guided boring rig, but not as effective as an HDD rig; it is essentially a “supercharged” guided boring rig or “scaled-back” HDD rig. The advantages and disadvantages of a midi rig are similar to those of guided boring (paragraph 10.1.1.1) and HDD (paragraph 10.1.1.2).

10.1.2. Non-surface Launched. These methods may be divided into several types:

boring/coring, push/pull (includes pipe jacking, pipe pullback, and pipe pulling), compaction, pipe ramming, water pressure, tunneling, and microtunneling. In TT terms, tunneling and microtunneling are considered “stand-alone” technologies; the other methods are used in conjunction with other TT methods to produce installed pipelines.

10.1.2.1. Boring/Coring. Boring/coring refers to traditional auger boring/coring rigs mounted horizontally. In TT terms, this is distinguished from guided boring or HDD by a lack of directional control at the cutting head. In traditional boring/coring, a receiving pit is used to “catch” the drilling apparatus so localized directional control is not required.

10.1.2.2. Push/Pull. Push/pull methods such as pipe jacking, pipe pullback, and pipe pulling use hydraulic, mechanical, or air jacks to push or pull a pipe through a horizontal stratum.

10.1.2.2.1. “Pipe jacking” is a term that has various meanings and usages within the TT industry and is sometimes even used to refer to any TT method. Though this ETL explains and categorizes pipe jacking methods, be aware that the term “pipe jacking” can have widely differing meanings depending on the source (see paragraphs 10.1.2.3 and 10.1.2.4). The most common use of the term “pipe jacking,” however, is to describe any of several methods that use jacks to push or pull an open pipe through a horizontal stratum, with spoil removal either before or after inserting the pipe.

10.1.2.2.2. Pipe pullback is usually distinguished from pipe jacking by the location of the jack relative to the pipe insertion; that is, when the jack is located behind the pipe insertion so that the jack puts the pipe in compression, the method is usually referred to as pipe jacking. When the pipe is pulled back through a previously drilled borehole so that the pipe is put in tension, the method is usually referred to as pipe pullback. In the case of a pipe being pulled directly behind the cutting heads using a cable through a previously bored guide hole, there is no clear consensus on which term (i.e., pipe jacking or pipe pullback) should be used, even though the pipe is clearly being put in tension.

10.1.2.2.3. Usually pipe jacking is the method preferred in collapsible strata, whereas pipe pullback is preferred in self-supporting strata, although the preference may also depend on equipment availability. Either technique may be used in boreholes that are stabilized with fluid (e.g., driller’s mud).

10.1.2.2.4. Pipe jacking is not limited to circular or elliptical cross sections. Box-shaped cross sections may be used in soft strata, or even in stiff strata, if oversize cutting heads are used ahead of the jacked pipe. Modular jacking has been used to build up support for structural components (such as bridge abutments) out of modular units jacked into soft soil. In addition, pipe jacking may be used to create an advanced support structure (ASS). The ASS is an enclosing support environment created by a series of closely spaced jacked pipes that form walls and/or ceilings, or often an archway, before excavation inside or underneath the ASS. In some cases, grout or glue is injected to fill the spaces between pipes; in other cases, the pipes are reinforced during or after excavation; and in some cases, particularly for temporary use, the ASS is used without interior reinforcement.

10.1.2.2.5. Though pipe pulling is a traditional utility industry TT technique, the term “pipe pulling” is frequently misused as a synonym for pipe pullback. In pipe pulling, an existing pipe is removed simultaneously with new pipe installation by a single pulling action. Because of side friction, this method is usually limited to very small diameter pipes with relatively short runs. While this technique is often overlooked in TT discussions (it is “low-tech” and has limited application), it is probably the best TT method in cases where its use is viable.

10.1.2.3. Compaction. Compaction methods are usually distinguished from jacking methods because they do not remove spoil (the term “pipe jacking” is sometimes used generically to describe these methods as well); that is, the soil around the pipe is compacted in situ, and remains around the installed pipe. When a closed pipe is driven, compaction is generically called “piercing.” When a mechanical or hydraulic jacking system is used, piercing is often referred to as the push rod method; when a percussive system is used to drive the pipe, piercing is often referred to as impact moling; and when a horizontally mounted pile driver is used to drive the pipe, piercing is usually referred to as pipe ramming (paragraph 10.1.2.4). The use of auger-like cutting heads that both dislodge and compact the soil is often referred to as the rotary method or “cutting.”

10.1.2.4. Pipe Ramming. The term “pipe ramming” is often generically used for any insertion of a pipe using a percussive device, particularly if the device is a horizontally mounted pile driver; therefore, the term “pipe ramming” is sometimes used in place of “pipe jacking” (i.e., spoil removed), but also sometimes used in place of “piercing” (i.e., spoil compacted in place).

10.1.2.5. Water Pressure.

10.1.2.5.1. Fluid-assisted Boring. Fluid-assisted boring uses a combination of mechanical drilling and pressurized fluid jets to provide the cutting action. This method is commonly used in rock coring or boring through extremely stiff soils.

10.1.2.5.2. Jet Cutting. Jet cutting (sometimes referred to as “jetting”) is a specialized piercing method, particularly useful in sandy soils, in which a water jet is used to “liquefy” the soil in advance of the inserted pipe (i.e., it makes the sand “quick”). As with pipe pulling, this method is limited to relatively small diameter pipes with relatively short runs because side friction acts on that part of the pipe that is not in the vicinity of the jet head. Use of the term “jetting” as a synonym for jet cutting can lead to confusion because the term “jetting” is also used to describe a pipe-cleaning method (paragraph 10.4.1.1.3).

10.1.2.5.3. Slurry Shield. The slurry shield method uses a mechanical tunneling shield with a closed face, and uses a liquid (usually water) to remove the excavated material and balance the ground water pressure. In another confusion of terminology, however, “slurry boring” is also used generically to describe any auger boring with driller’s mud;

that is, “slurry boring” and “auger boring,” respectively, are sometimes used to distinguish “wet” drilling from “dry” drilling.

10.1.2.6. Tunneling. Tunneling methods include any technique that involves excavating soil or rock at the leading edge of a shield or boring machine and erecting a lining system from within the excavated space. Traditional tunneling methods range from removal by hand to sophisticated excavators. Hand-bolted segmental rings are frequently used in traditional tunneling, although shotcrete/gunite (i.e., blown concrete) is gaining in popularity for larger tunnels because of increased productivity (i.e., faster advance rates). The modern tunneling method uses a tunnel boring machine (TBM).

TBMs are currently used worldwide to create large tunnels (e.g., for subways or highway tunnels). The distinguishing feature of all tunneling methods is that they allow person-entry during excavation and lining.

10.1.2.7. Microtunneling. Microtunneling installs pipe using a microtunnel boring machine (MTBM). The term “microtunneling” refers to the fact that person-entry is not required (in fact, it is usually not possible) during tunneling. The term “microtunneling” is frequently misunderstood and misused because it refers to the remote control aspect of the method (i.e., no person-entry needed), not the size of the tunnel. In fact, microtunnels can be quite large. MTBMs typically use pipe jacking to insert pipe just behind the cutting head (the jacked pipe continuously supports the tunneling operation), but in self-supporting strata (especially rock), pipe pullback is an alternative (paragraph 10.1.2.2.2).

10.2. Renovation. In this ETL, renovation is defined as a repair technique that depends, in part, on the original pipe for support after the upgrade is completed. That definition was adopted for this ETL for two reasons: (1) that definition is commonly used in the TT industry; and (2) that definition is convenient for grouping TT methods. Note, however, that it is also common within the TT industry to use the terms “renovation” and “rehabilitation” interchangeably. Renovation, as defined in this ETL, is most often used in pipes large enough for person-entry. The two main types of renovation are spot repairs and applied linings. For POL lines, repair and liner materials must be capable of withstanding exposure to both the product and any additives, and should be approved by the Air Force Petroleum Office (AFPET).

10.2.1. Spot Repairs. Spot repairs are usually either formed and cured in situ or prefabricated and inserted.

10.2.1.1. Traditionally, formed and cured in situ spot repairs were limited to manually formed repairs on large concrete storm sewers. More recently, however, the term “formed and cured in situ repairs” refers to a number of techniques that involve the use of a “packer” (sometimes called a “balloon”), which is cylindrical in shape, pulled into the area to be repaired and then inflated, sometimes bridging a damaged joint. The packer is then used as a form to hold a polymer concrete or other specialized grouting material that is injected through the packer and into the damaged pipe (and sometimes into the surrounding fill material).

10.2.1.2. In TT terms, “prefabricated and inserted repairs” refers to a number of methods in which pipe segments are grouted or glued in place. Although most prefabricated and inserted repairs are done by person-entry, there are two exceptions:

cured-in-place repairs and sophisticated robotic repairs.

10.2.1.2.1. Cured-in-place Repairs. Cured-in-place repairs are patches that are inserted in a reduced or deformed (i.e., folded) shape and then expanded by one of several different methods to fit the inside of the pipe in the distressed area, and then held in place until cured.

10.2.1.2.2. Sophisticated Robotic Repairs. Although most cured-in-place repairs use some robotic components to complete the repairs, the term “sophisticated robotic repairs” refers to a highly specialized area of TT that is most commonly used in the nuclear industry and that has prohibitively high costs. The description of sophisticated robotic repairs is beyond the scope of this ETL, but it is important to note that the term “robotic repair” is sometimes used generically in the TT industry to describe any repair done by remote control, especially if a closed-circuit television (CCTV) camera is used.

10.2.2. Applied Linings. Grouts, glues, polymers, or other exotic materials that are applied by spray or flooding are considered “applied linings.” Due to the traditional need for surface preparation, most applied lining renovations are in large pipes with person-entry; however, recent advances in chemical (polymer) grouts have reduced the requirements for surface preparation, and recent equipment advances have improved the ability to deliver the lining material into smaller pipes. Chemical stabilization is a renovation method used to simultaneously repair a pipe defect and stabilize the surrounding soil; that is, the polymer flows out through the pipe defect into the surrounding soil, and when the polymer sets, it both stabilizes the soil and patches the pipe defect. Even with these advances, however, small pipe applied linings are usually not cost-competitive when compared with other TT methods, particularly in terms of the life-cycle cost. The exception may be in potable water lines, particularly metal pipes, where the combination of pigging (paragraph 10.4.1.2.1) and spray lining can be a cost-effective way to remove tuberculations (chemical deposits usually associated with “red water”) and return the pipe to a nearly new condition. Both cement mortar and polymer lining systems are currently available for renovating potable water lines.

10.3. Rehabilitation. In this ETL, “rehabilitation” is defined as a repair technique that does not depend on the original pipe for support after the upgrade is completed. This definition was adopted here because it is commonly used in the TT industry and because it is convenient for grouping TT methods. As noted in paragraph 10.2, however, it is also common within the TT industry to use the terms “renovation” and “rehabilitation” interchangeably. As defined in this ETL, rehabilitation methods can be further divided into three groups: applied lining methods, prefabricated lining methods, and upsizing. Both of the lining methods have the disadvantage of causing a reduction in pipe capacity (in addition to the disadvantage of usually needing person-entry).

Upsizing, as its name implies, can return the pipe to its original capacity, or even increase its capacity, without person-entry. Still, there are many cases where a pipeline requires less than its original capacity (e.g., if a conventional communications cable was being replaced with a fiber optic cable), and in those cases, lining methods remain a useful rehabilitation alternative. For POL lines, liner materials must be capable of withstanding exposure to both the product and any additives, and should be approved by AFPET.

10.3.1. Applied Lining. Applied linings for rehabilitation are usually restricted to large pipes, with installation techniques similar to those for renovation linings (paragraph 10.2.2), but usually with thicker application and/or stronger material. Gunite/shotcrete (i.e., blown concrete) is gaining in popularity for large-pipe rehabilitation, particularly using advanced concrete mixes such as fiber-reinforced concrete.

10.3.2. Prefabricated Lining. There are four main rehabilitation methods using prefabricated linings: insert renewal, modified sliplining, spiral wound linings, and segmented linings. All four techniques are sometimes referred to generically as sliplining, but the term sliplining is properly applied only to insert renewal and modified sliplining.

10.3.2.1. Insert Renewal. Insert renewal is the simplest and most commonly used type of sliplining, particularly in pipes that have no internal tees. As its name implies, a finished pipe is inserted inside the original pipe. While the simplest of the sliplining methods both in concept and in execution, it is often not the ideal solution because it typically is also the method that most reduces pipe capacity.

10.3.2.2. Modified Sliplining. Modified sliplining involves slipping a lining with a reduced diameter inside the existing pipe and then expanding the lining. Modified sliplining is usually separated into cured-in-place pipe (CIPP), and fold and form pipe, although both of these methods involve curing the lining in place.

10.3.2.2.1. CIPP. CIPP is installed as a flexible insert (sometimes referred to as a “sock”), then expanded and cured. CIPP is typically resin-impregnated, but other exotic materials are also used. Many CIPP installation procedures require that the insert be subsequently pulled inside-out. CIPP has recently become a more popular rehabilitation technique, but price remains a concern because of the expense of the materials required to produce the blend of thinness, flexibility at insert, and strength after curing.

Other benefits, however, such as less installation time or less disruption of mission capability, may offset the higher material costs of CIPP.

10.3.2.2.2. Fold and Form Pipe. Also known as deformed and reformed pipe, fold and form pipe is usually distinguished from CIPP although they are closely related. The most common type of fold and form pipe is folded at roughly the midline of the liner, so that the insert forms a “U” shape. (In some products, the “U” shape is folded again so that the liner is flat for insertion.) The folded pipe is either pushed or pulled through the original pipe and then inflated/expanded and cured in-place. Fold and form pipe is easier to insert and cure in specific sections of pipe than other modified sliplinings and therefore lends itself better for rehabilitation of pipes that have internal tee joints (that is, it can be used as a very long spot repair between the tees). Unfortunately, like other types of modified sliplining, fold and form inserts tend to be expensive. As with CIPP, however, other factors (e.g., less installation time or less disruption of mission capability) may offset the higher material costs.

10.3.2.3. Spiral-wound Lining. This technique uses a ribbed plastic strip that is spirally wound by a winding machine to form a liner. The liner is sometimes grouted, and sometimes expanded and cured in place. In large-diameter pipes, the strips are sometimes formed into panels and installed by hand (which would probably be more properly categorized as a segmented lining but usually is not).

10.3.2.4. Segmented Lining. The term “segmented lining” is used to describe either the use of short pieces of flexible (or folded) pipe insert (similar to spot repair liners) installed as overlapping panels that are either grouted or glued in place to form a continuous pipe liner, or the use of segments of pipe that are butted and either grouted or glued in place to form a continuous pipe liner. Typically these methods are used only in large-diameter pipes that allow person-entry. Segmented linings are becoming less favored because they have the disadvantages of spot repairs but none of the installation advantages of seamless lining systems.

10.3.3. Upsizing. Upsizing can be further subdivided into two types: pipe eating and pipe bursting. These two methods are conceptually similar in that both put a pipe of the same or larger size back in the position where the defective pipe was located and both cause minimal disturbance of surface assets, but the mechanics of the methods are dissimilar: Pipe eating is a tunneling technique (with spoil removal), and pipe bursting is a compaction technique.

10.3.3.1. Pipe Eating. Although MTBMs are used most often in new construction, they can also be used in a rehabilitation technique known as pipe eating, in which the MTBM is run along the axis of a defective pipe to remove the defective pipe with the near-surrounding soil (while the replacement pipe is inserted). While technically this method would qualify as a reconstruction technique, the TT industry typically refers to pipe eating as a rehabilitation technique (a logical designation for practical purposes [i.e., for bidding] even though it is technically incorrect). Before being “eaten,” the defective pipe is sometimes pre-filled with grout, which can improve the performance of the MTBM but increases the need for crushing capability during the “eating” process (this variation of pipe eating is sometimes referred to as pipe crushing). In addition, some pipe-eating systems employ a proboscis-like device to seal the pipe in front of the MTBM shield to collect and divert existing flow, thus allowing a sanitary sewer, for example, to remain "live" during the rehabilitation process.

10.3.3.2. Pipe Bursting. Pipe bursting is rapidly becoming the method of choice for pipe rehabilitation, particularly in spans of pipe that have no internal tee joints. In this technique, a splitting tool (typically called a “bullet”) is pulled by cable through the original pipe, along with a replacement pipe. The bullet may simply rely on its geometry to transfer the cable force to the pipe for splitting, but more sophisticated bullets are mechanized to actually expand outward to create splitting tensile forces (usually used only as needed). The principal advantage of pipe bursting over sliplining techniques is that pipes that are as large or larger than the original pipe can be inserted. This means that the pipe can be returned to its original capacity, or more, and that exotic replacement pipe materials are not required. An additional advantage of pipe bursting over most other rehabilitation techniques is that no surface preparation or even pipe cleaning is needed (although constrictions/blockages of sufficient size and strength to “stop the bullet” have to be addressed prior to beginning bursting). Pipe bursting usually has a minimal effect on surface assets since the amount of material being compacted is usually small compared to the original pipe’s cross section. Even so, pipe bursting is a compaction method, and the amount of surface disturbance depends to some extent on the quantity and quality of the original backfill material, the depth of burial, and the surrounding soil conditions, and depends to a great extent on the increase in size of the upsized pipe compared to the original pipe.

10.4. Non-structural Methods. Non-structural TT methods are overlooked often in technical discussions of TT methods even though they are the most common use of TT.

Non-structural TT methods can be divided into two groups: cleaning and inspection (to include pipeline location and anomaly detection).

10.4.1. Pipe Cleaning. Although there are many variations and combinations of the individual cleaning techniques, all commonly used pipe cleaning methods can be grouped as either hydraulic or mechanical.

10.4.1.1. Hydraulic Cleaning. There are two types of hydraulic cleaning: flushing and jetting; however, a variant of flushing called the “air hammer method” is often classified separately (paragraph 10.4.1.1.2). Hydraulic cleaning is not suitable for POL lines, where contamination of the fuel by residual water is a possibility and where lines must be vapor-free to prevent the possibility of fire or explosion before pressurized air is introduced.

10.4.1.1.1. Flushing. Flushing is using of a relatively large volume of water, flowing through the pipe, to induce cleaning. A fire hydrant is commonly used as the water source for this method since it provides an adequate volume of water with an adjustable flow rate. Ironically, flushing is the most common form of pipe cleaning but often the least effective. While loose debris is almost always flushed from the pipe (giving the appearance that the pipe has been cleaned), more firmly held debris, sediments, chemical deposits, and other materials that have become embedded or affixed to the pipe walls will usually not be removed by flushing. Still, the method is easy and requires no special equipment or training and provides a tangible benefit in most cases.

10.4.1.1.2. Air Hammer. The air hammer method is variant of flushing. The term “air hammer” is a misnomer, however, because the method uses an injected air bubble to create a “water hammer” that increases the cleansing ability of the flushing water. (Most people are familiar with the water hammer effect because of the loud noise and vibration in faucets and toilets after the water has been turned off and later turned back on and air is in the water lines.) The cleansing effect is increased because the water hammer (directly behind the air bubble) moves with great turbulence. This effect is similar to a massaging showerhead that sends out intermittent jets of water.

10.4.1.1.3. Jetting. The term “jetting,” when associated with pipe cleaning, refers to any method that delivers pressurized water to a tip, or head, for thorough cleaning. Jetting requires more equipment than flushing since the jet head must be pulled through the pipe. Jetting can provide greatly improved cleaning compared to flushing, particularly when used in conjunction with CCTV inspection, but still cannot always break the mechanical bonds for complete removal of all deposits.

10.4.1.2. Mechanical Cleaning. There are two types of mechanical cleaning: pigging and manual cleaning.

10.4.1.2.1. Pigging. Pigging is the pulling of a slug, or “pig,” through the pipe for cleaning. The advantage of pigging is that it can break the mechanical bonds of deposits in smaller pipes that other cleaning methods cannot. In addition, pigging can be used in conjunction with any of the other methods for improved cleansing. There are a wide variety of pigs, with varying sophistication. At the low-technology end, the pig may be a rubber, plastic, or metal slug. At the high-technology end, the pig may be a mechanical scrubbing machine. In between, there are many different pigs with various types of abrasive surfaces, studs, or brushes. For small pipes with severe clogging, pigging may be the only alternative to reconstruction.

10.4.1.2.2. Manual Cleaning. Large pipes may be cleaned manually. A wide range of techniques fall within this category, principally limited only by the available equipment and the diameter of the pipe. All variants on manual cleaning have the same two disadvantages, however: person-entry is required and small pipes cannot be cleaned by this method.

10.4.2. Inspection. Inspection methods can be divided into two groups: internal inspection and location/anomaly detection. See ETL 04-6, Inspection of Drainage Systems, for a more detailed study.

10.4.2.1. Internal. Internal pipe inspection is usually done by one of two methods. If the pipe is large, the inspection is done by person-entry; if the pipe is small, the inspection is done by CCTV.

10.4.2.1.1. Person-entry. The main advantage of a person-entry inspection is that it incorporates the oldest and most reliable method of inspection: the human eye. During a person-entry inspection, the inspector can get first-hand information about internal pipe conditions that are impossible to obtain by any other method. In addition, videotape records or photographs, guided directly by the inspector, can be used to supplement and document the inspector’s findings. Measurements and samples can be taken directly. In every way, when practicable, person-entry is the best method of inspection;

however, safety considerations require that a pipe be of an appropriate size and condition before person-entry is allowed. See Occupational Safety and Health Administration (OSHA) rules on confined space entry in Title 29, CFR, Chapter XVII, Section 1910.146, Permit-required confined spaces.

10.4.2.1.2. CCTV. CCTV is the only proven technology for internal inspection of small pipes. A key factor for the success of a CCTV inspection is establishing proper reference points so the video can be tied to exact locations in the pipe being inspected.

The biggest disadvantage of CCTV is that the quality of the data is highly dependent on the operator’s experience and skill. In addition, and particularly when videotape is used for analysis, the results are highly dependent on the quality of the equipment, its degree of maintenance, and the timeliness of hardware and software updates. There is a wide range of equipment for CCTV inspections, usually grouped by the size of pipe to be inspected. In addition to inspecting the internal condition of the pipe, CCTV can be used to estimate the infiltration/inflow of water due to leaks in the pipe.

10.4.2.2. Location/Anomaly Detection. While some aspects of location/anomaly detection can be satisfied during an inspection, this paragraph describes methods that can be used apart from an inspection to simply locate the pipe or locate specific anomalies in the general area of the pipe.