In the 2017 Infrastructure Report Card, the American Society of Civil Engineers (ASCE) issued a grade of D+ for the condition of the country’s wastewater systems. ASCE classifies wastewater to include sewage treatment plants, sanitary sewer pipelines and collection systems, storm water management, and combined sewer overflows (CSOs). The aged and decaying state of wastewater systems is not unique to the United States, but is also a global concern.
While many local and federal agencies around the world have begun to develop asset management plans for their wastewater systems, and thousands of pipeline rehabilitations are conducted annually, large-diameter wastewater pipelines are areas of key concern. Typical dig-and-replace technologies often are not practical, because in most urban areas, these degrading pipes are located directly under critical infrastructure such as major roadways or other assets. As the diameter of these pipes becomes larger (more than 36 in.), the cost of many traditional trenchless technologies, such as cured-in-place pipe, becomes exponentially more expensive and often requires significant excavation around access points that present additional issues related to community disturbance, traffic control, noise and general disruption. Other techniques, such as slip-lining, would require an even greater excavation diameter for an access hole to install new liners. Additionally, other issues related to either the shape (round, arched, elliptical) or the layout (straight, curved, bends of various radii) can make these repair technologies impractical.
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