Manholes are used in both sewage and stormwater applications to provide service workers with access to these systems during maintenance and repair operations. They were primarily made of brick and other masonry materials from the 1800s until the late 1990s. However, these manholes degrade over time, causing the bricks to eventually collapse. Concrete manholes are also subject to failure due to microbial-induced corrosion (MIC) from sanitary sewer gasses, especially hydrogen sulfide (H2S).
Engineers are currently in the process of rehabilitating manholes in utility systems by lining them with advanced materials. Here’s all the information you need on fixing manholes and carrying out rehabilitating projects.
What is Manhole Rehabilitation?
Manhole rehabilitation is a process that protects and reinforces existing sewage manholes rather than replacing them; it helps companies save time and money. The process begins with engineers assessing the current conditions of the manhole, which often requires vacuum excavation.
The National Association of Sewer Service Companies (NASSCO) has developed a Manhole Assessment Certification Program (MACP) as the standard in North America for identifying and assessing defects. Inspectors must ensure manholes meet Occupational Safety and Health Administration (OSHA) standards, including Confined Space Entry (CSE). They use a variety of utility locator methods to accomplish this goal, including video pipe inspection, ground-penetrating radar (GPR) and light detection and ranging (LiDAR) technology.
Manhole Rehabilitation Options
The variety of options available for rehabilitating a manhole makes the selection of material a complex one. The choices can generally be classified into cementitious materials, polymers and cured-in-place pipe (CIPP).
Cementitious materials primarily include Portland cement (OPC) and calcium aluminates (CACs). The primary advantages of these materials are that they’re easy to apply, more cost-effective than other materials and generally provide adequate protection from chemical reactions. CACs have greater resistance to MIC than OPC, so they’re usually better choices for rehabilitating manholes. However, the best choice depends on a variety of factors such as the project budget, condition of the manhole and ability to dry the manhole.
Polymer manhole linings are composed of epoxies, polyurethanes or polyureas, which workers can apply by hand or spray applied. These materials provide the greatest resistance to chemical corrosion of all liner materials, but they’re also more expensive and difficult to apply. The lining system must be fully intact, which requires it to dry completely. This step is crucial for polymer linings because the interior surface of the manhole must be absolutely dry for the lining to provide complete protection. Meeting this requirement can be challenging because manholes are close to water.
A manhole with significant corrosion will also require repair before applying the polymer, which generally involves using a cementitious mortar to rebuild the manhole back to its original shape. This process requires several days to complete because high-strength cement is required to support the polymer lining. Proper curing also requires a certain humidity and temperature range, so weather conditions are critical for this step.
Workers must also spark test linings to ensure they don’t have any pinholes. This process involves the use of a metal rod connected directly to the manhole. Any pinholes in the lining will complete an electrical circuit with the rod, causing it to spark. Pinholes prevent the liner from being as chemically resistant as it should be and will require workers to repair the liner before placing it into service. If installation proceeds as planned, however, polymer linings provide manholes with greater protection than other options.
A CIPP rehabilitation typically requires the manhole to be at least 3 ft in diameter. It must be large enough to accommodate the entire system in addition to the larger crew and equipment required. Workers must seal the bottom of the manhole to keep material out of the space between the manhole and CIPP liner during the installation. A CIPP liner also needs a wet outlet over the manhole, and some installations require workers to remove the manhole chimney to allow access to the manhole’s full diameter.
The CIPP method is less common than other alternatives because it creates a greater ecological footprint. However, it’s still the most viable option for some projects.
A complete replacement may be a better option for a manhole that’s badly damaged and has poor structural integrity. This process requires workers to dig out the manhole and replace it with an entirely new structure, which is usually made of precast concrete or high-density polyethylene (HDPE).
Reliable Underground Services – SoftDig
SoftDig is highly experienced in Utility Locating and Subsurface Utility Engineering projects. Check out some of our recent work with manhole catch basin details. Contact us today to learn more about how we can help you with your project. Contact us today at (610) 738-8762 or request an estimate online.