By Gerhard “Gerry” P. Muenchmeyer, PE Muenchmeyer Associates LLC
Editor’s Note: This is the first in an occasional series of articles discussing long-term performance needs, capabilities and requirements of various rehabilitation technologies.
For almost 40 years, the trenchless rehabilitation industry has rapidly expanded with new products becoming available in the United States and most other parts of the world. Many of these products are installed in conjunction with innovative technologies, generally provided with guidelines and standards, and are intended, in good faith, to ensure consistent application quality and long-term product performance.
What is application quality? It has many different definitions. It can be generally defined as industry and/or customer expectations for long-term performance. The performance is based on known facts, installation experience, technology standards and associated product history, as defined by the technology provider, product manufacturer and contractor.
In addition, let’s also define “long-term product performance” as a product’s capability to achieve its design and service life over an expected period of time in accordance with manufacturer’s recommendations.
It’s difficult to ascertain the longevity of a product unless it has a documented installation history. If that’s not available, there must be standard guidelines complete with good common sense and an understanding of what needs to be accomplished and what products will meet the challenge. It’s not because a salesman says so, but because sound technical information has been assembled and proven – over time – based on quality field applications for similar infrastructure that we wish to successfully rehabilitate.
Typical sewer system
Let’s examine a typical sewerage collection system that has deteriorated over time and contains pipelines that are cracked, corroded and infiltrating; manholes that are corroded; and leaking and root-clogged house service connections that have not been maintained by the system owner for many years. These conditions result in costly treatment of extraneous water at the treatment plant, and accelerate the deterioration and failure of the pipeline infrastructure. In many cases, this is the result of not only many years of neglect, but a collection system that has outlived its useful design life.
In the past, a common approach was to merely dig-up, remove and replace the old pipeline with new and better corrosion resistant pipe materials. The installation of these new products alone, however, was not the entire solution. In order for the new pipe to be watertight at the joints between pipe sections, an engineered seal or compression gasket had to be installed in every joint to prevent groundwater leakage during subsequent ground movement. The seals or gaskets were designed to function over the service life of the pipe product.
The consequence of pipe removal and replacement, however, is that it’s extremely disruptive to residents, the general public, businesses and utilities, such as gas, water, fiber optics, telephone, etc., located in proximity to the pipeline being replaced.
An alternative is to rehabilitate or replace the collection system components using proven trenchless methods and technologies. However, it is important to understand each technology’s capabilities not only for the expected design life of the product, but also the effective service life of the installation.
Design life can be defined as the physical longevity of the installed material; service life defines how long the installed materials provide the intended functional service.
One such technology is cured-in-place pipe (CIPP), which was developed and first installed in England nearly 50 years ago. In the United States, it has evolved into a multi-billion-dollar industry saving municipalities and industries billions of dollars in construction costs. In 2002, several samples were removed from a 30-year old lined pipe and tested for flexural properties by a third-party testing company in England. The results showed that the strength of these samples exceeded the specification at the time by 50 percent.
Additionally, extensive accelerated life testing at the Trenchless Technology Center (TTC) at Louisiana Tech University showed that CIPP life expectancy should exceed 50 years of service under normal use. Ongoing research in the UK and at institutions such as the TTC have definitively proven the accuracy of claims that a pipeline rehabilitated with CIPP has a useful life of 50 years or longer.
To reach acceptance as the premier technology in the U.S., CIPP has undergone extensive ASTM reviews and standard approvals. For instance, one of the earliest approved ASTM standards for CIPP was F1216. Through extensive third-party testing of CIPP materials meeting this standard, the short-term and long-term capabilities have been confirmed and documented for more than 45 years
Why has this unique technology grown so rapidly and become accepted almost universally? It has 45 years of successful installation history, can structurally rebuild an existing pipeline, stop future corrosion of the pipe material and prevent excessive infiltration from entering the system, yet its capabilities are sometimes totally misunderstood.
CIPP must be installed correctly to manufacturer’s standards and confirmed by good inspection to achieve the projected design life. In order to meet end-user expectations, including both the design and service life for a sewer collection system, additional complementary products may, however, be required for a complete and successful project
Dealing with leakage
Based on such a long history, a cured-in-place pipe will provide a structurally sound, corrosion-proof solution for the reconstruction of pipelines offering a predictable and proven design life. The technology, however, does not always result in effective leakage control. Groundwater pressure may cause continued water infiltration into the system, particularly when a house service connection is cut open in the CIPP and where the new CIPP enters the manhole structure. Additional solutions for eliminating groundwater leakage into the newly rehabilitated pipeline must, therefore, be designed and combined with the CIPP rehabilitation technology.
Specific areas of leakage concern typically include the following:
Leakage between the host pipe and the CIPP where it penetrates the manhole structure. (Fig. 1)
Leakage between the host pipe and the CIPP at the house service connection where an opening has been cut into the CIPP to again provide service to the home. (Fig. 2)
Anywhere else water can flow between the CIPP and the host pipe, contributing to extraneous flow into the collection system.
To provide both a design- and service-life solution, the CIPP product technology must incorporate an effective and predictable sealing technology to address leakage. Since it is impractical and virtually impossible to permanently bond two materials in a wet, greasy and dirty sewer environment, either mechanically or chemically, the installation of a new CIPP pipe may, by itself, fail to stop leakage into a pipeline system for the expected service life of the product.
In sewer pipeline excavation and replacement construction, pipe materials are installed in sections and each section is connected at a joint which contains a compressible, long-term proven, rubber gasket. The gasket in the joints allows the new pipe to move and shift in the imbedded soil without breaking or cracking, and the compressible rubber gasket prevents the moving or shifting joint from leaking.
This same approach can be applied to the CIPP technology to provide not only a long-term design life, but also a leak-proof, long-term service life. In order to achieve this, the products installed when rebuilding a collection system must:
Have a proven history in similar collection system applications.
Be able to be commercially installed in a repeatable manner in a field construction environment.
Provide a long-term solution for both design and service life.
Be verifiable by the system owner during and after installation, and during the service life.
Available products that can be used in conjunction with the CIPP technology include grouts, resins, liquid sealants and manufactured compressible rubber seals. Each type of sealing technique must be evaluated and selected for its recommended application and proven long-term installed capability for the recommended application.
Compressible, hydrophilic rubber seals are designed as part of the product installation and are typically installed to prevent future long-term leakage, much like the rubber seals used in the joints for new pipe construction. These products are factory produced in dimensionally standard sizes and cross-sections, allowing for consistent and repeatable installation and performance in the field.
When a CIPP is installed without the required seals or gaskets and leakage occurs, alternate solutions have been successfully applied. Grouts, resins and liquid sealants, hydrophilic or non-hydrophilic in characteristic, are typically applied when a leak becomes apparent after the product is installed. The material must be flowable, such as a cartridge contained grout or paste which is applied by injection into the void area to stop the leak.
Trenchless technologies and associated products such as CIPP, are a long-term proven, cost-effective and a minimally intrusive approach for rebuilding the underground pipeline infrastructure. However, when applied, the long-term service life, in addition to long-term design, must be considered and a technical sound approach developed to achieve total solution.
Understanding a product’s capability to achieve the intended project goals and adding other products as applicable, provides a system solution and is a key factor in a project’s ability to perform as required and meet end-user expectations.
About the author: Gerhard “Gerry” P. Muenchmeyer is a licensed professional engineer and principal of Muenchmeyer Associates, headquartered in North Carolina. Throughout his impressive career as a leader and manager for a municipality, contractors, vendor and consulting engineers, Muenchmeyer has diligently worked to address and improve quality control in the rehabilitation market.