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Distinctions Between Vertical Structures and Horizontal Structures for Effective I&I Abatement
Michael Caputi, Vice President of Epoxytec
When addressing inflow and infiltration (I&I), the first critical phase entails a comprehensive condition assessment to gain insights into the impact of corrosion and leaks within the system. Whether proactively managing an I&I abatement maintenance program or reacting to mandates (such as EPA consent decrees), effective planning and execution can only take shape once the relevant data is collected. Understanding which assets contribute the most to I&I, why such occurrences have taken place, and anticipating future challenges is paramount.
Organizations like WEF, AWWA, NASTT, NASSCO, EPA, AASHTO, and AMPP provide guidance on I&I and trenchless lining options, covering standards and education for condition assessment, lining design, and product selection. After a thorough condition assessment, a plan to target specific structures can then be formulated. Some of these structures are discussed in greater detail below.
Distinctions in Underground Buried Assets
Lining methods demonstrate success when using products specifically designed for achieving monolithic watertight sealing for mitigating I&I. When lining both horizontal and vertical structures, should the technologies differ, it is important that they can interface together effectively to deliver seamless monolithic lining in unison.
When evaluating buried collection lining systems, the assessment should consider two main categories of assets: horizontal pipe systems and vertical assets, which include structures like manholes and pump stations.
Each category experiences distinct forces and stresses, often requiring different technologies and performance requirements. Technologies, specifications, surface preparation standards, contractor qualifications, and execution may differ, especially when comparing horizontal pipe lining with vertical structure (manhole and lift station) lining.
In horizontal conditions, for example, liners often need greater strength and wall thickness when the host is deficient due to certain conditions or forces, requiring the liner to bear load and/or resist internal pressure assumptions. With manholes, on the other hand, the directional forces may not be the same and other host assumptions are factored differently. With vertical structures, film thickness is often calculated purely to hold back I&I as the main intention, with consideration at times for low pressure effective lateral earth stresses when the walls have deteriorated severely.
Horizontal Pipe Lining
Horizontal pipe lining can be tackled using a variety of proven technologies.
Cured-in-place pipe (CIPP) and pull-in place lining are often the selected for large projects and long lengths of work due to their cost-effectiveness for long runs of pipe. These technologies preserve existing pipe that has been damaged by leaks, cracks, intruding roots, and corrosion.
The pipe bursting method is used on pipes that are severely damaged, for replacing an entire system, or for repairing larger sections of sewer pipeline. The installers begin by placing a “bursting head” at the access point on the one end of the pipe. Hydraulic power is used to drag the head through the pipe. As it makes its way through the system, it breaks the old pipe apart and draws a new seamless pipe behind it.
Sliplining is one of the oldest methods of trenchless rehabilitation of existing pipelines. It is used to repair leaks or restore structural stability to an existing pipeline. It is completed by installing a smaller, “carrier pipe” into a larger “host pipe,” grouting the annular space between the two pipes, and sealing the ends. The most common material used to slipline an existing pipe is high-density polyethylene (HDPE), but fiberglass-reinforced pipe (FRP) and PVC are also common.
Spray-in-place pipe (SIPP) lining is a process where high-build, high-strength applied and bonded polymer systems are utilized to fill dry cracks and surface imperfections, creating a watertight seal once cured. SIPP is an option often sought out for irregular shaped pipe, culverts, or shorter runs when other lining methods may have limitations.
Vertical Lining (manholes, wet wells, lift/pump stations)
The buried forces affecting vertical structures differ, requiring a diverse range of lining solutions. These solutions vary due to distinct conditions and lining intentions, and are distinct from those associated with horizontal pipe lining.
Certain liners aim to prevent hydrogen sulfide (H2S) corrosion as the main design parameter. However, when the project requires more than corrosion protection—specifically, resistance to and mitigation of I&I forces like hydrostatic pressure—a watertight, monolithic high-strength liner is essential.
Vertical manhole lining, though not as high strength as horizontal pipe lining, confronts distinct forces, such as effective lateral earth forces and hydrostatic pressure which are lower pressure forces. This technology is typically applied and bonded to endure these pressures unique to vertical assets.
Numerous manhole rehab and lining options offer benefits based on specific situations:
Zero/Low I&I: For cost-effectiveness, cementitious lining may provide a cost benefit due to its use of inexpensive raw materials and ease of application. And in some cases, where H2S levels are low and I&I abatement is not the main concern, these lining systems can be selected for sewer lines where a full monolithic I&I abatement program or lining job is not necessary and therefore the intent is to simply restore the profile.
High I&I: When manholes necessitate a comprehensive, vacuum-tested, sealed monolithic I&I abatement lining system, advanced technologies may be more suitable. For instance, ultra-high build, high-strength, bonded polymer lining systems are ideal when seeking secure, watertight sealing from manhole to manhole; this approach can integrate seamlessly with CIPP or other pipe lining technologies when choosing certain epoxy-based polymer liners. Here it is imperative to seek a technology that bonds well to avoid the creation of annular space and interfaces, and bonds well to horizontal liners. Because of this requirement, polymer technology is a better choice than cementitious technology. Moreover, due to the advantages of epoxy adhesion over other kinds of polymers (such as polyurethane or polyurea) which may not be sufficient, many epoxy polymer liners, such as Epoxytec CPP, are designed for optimal bonding at their termination to mate or tie-in vertical assets (manholes and lift stations) to horizontal pipes.
The benefits of applied and bonded, ultra-high build, high strength epoxies are summarized below.
- Zero Annulus Design:
- The epoxy system’s intended design and polymer type advantage prevents the creation of annular space, eliminating any potential redirection of flow channeling to weaker points. This feature enhances the overall integrity of the lining system and prevents vulnerabilities.
- Versatility in Tie-In:
- The system demonstrates compatibility by easily tying into a variety of construction materials, including cured-in-place pipe and other liners. This versatility enhances its applicability in diverse environments and projects, especially when needing to interface and bond with other horizontal lining system to deliver seamless monolithic integration.
- High Repairability and Maintainability:
- An epoxy system facilitates high repairability and maintainability without the need for complex equipment. This attribute allows for efficient and cost-effective upkeep, minimizing downtime and operational disruptions.
- High Surface Tolerance:
- Many epoxy systems exhibit high surface tolerance, enabling effective application and adhesion to different substrate conditions. This characteristic is crucial for ensuring uniform coverage and long-lasting performance.
- Good “Wet” (SSD) Adhesion:
- The epoxy system typically shows good adhesion to wet (saturated surface dry – SSD) surfaces. This is particularly valuable in applications where exposure to moisture or water is commonplace, ensuring reliable performance in wet environments.
- High Flexural and Tensile Strengths:
- A formulated structural epoxy system boasts high flexural and tensile strengths, providing robust resistance to side wall pressures. This strength is essential for maintaining the structural integrity of the lining system, especially in scenarios where pressure variations may occur or unintended spanning is required.
The use of epoxy-amine resins in these systems is the key to their capability to provide durable, long-lasting, structurally sound solutions in challenging and dynamic environments.