What are the Main Causes of Manhole Deterioration?

After years of rehab and lining work spread across thousands and thousands of manholes, we are regularly asked about the most common issues of degradation we encounter. The two most common are inflow and infiltration (I & I) and corrosion. As discussed in previous blogs, I & I is a biggie because it affects treatment plant capacity. Corrosion commonly refers to Hydrogen sulfide (H2SO4) and MIC (microbial induced corrosion) that eat away at concrete manhole structures or the mortar joint of a brick manhole, causing considerable deterioration if left untreated. The good news in all of this is that the OBIC family of lining products, OBIC Armor Three-Layer System, OBIC 1200, and OBIC 5000 Structural Liner are all designed to stop infiltration and prevent corrosion.

Tree Roots

Tree roots are also a common culprit of severe structural damage to manholes. Trees and woody shrubs have a tap root system that will grow downward deep into the soil in search of moisture. Branches, or secondary roots, grow laterally from the primary root and can grow to several inches in diameter. If these roots find a crack in the manhole wall leading to moisture in the invert, they can exert enough pressure to seriously damage the structure itself, plus they may inhibit flow and cause an overflow. In reality, a sewer manhole is an almost perfect hydroponic environment with warm, nutrient-laden water. Once the roots are mechanically or chemically removed, spray-applied OBIC lining system seals the structure and eliminates the moisture source that attracted the root growth.

Freeze-thaw Cycles

Freeze-thaw cycles in northern climates can have a detrimental effect, particularly on the manhole chimney and cone sections. Soil expansion and contraction caused by freeze-thaw cycles in the top two or three feet of soil cause structure movement and cracking or mortar displacement (in the case of brick chimneys), allowing inflow during a rain event or snow melt. The flexible characteristic of the OBIC Armor System allows the liner to move with the structure, which ensures the prevention of infiltration.

CIP Pipe Rehab

Cured-In-Place (CIP) pipe rehabilitation is a popular method for restoring the sewer pipe at the bottom of the manhole. Recalling that a primary purpose of a manhole is access to the sewer line below, that manhole is used by the CIP company to “shoot” the resin-impregnated liner through the sewer line. It is surprisingly common that when pipe work is done without corresponding manhole work, we find shrinkage or other pipe/invert issues that allow the groundwater, which has diligently been stopped from entering the piping system, to enter the system anyway through the pipe/manhole/invert joint. In situations like this, the OBIC liner system, which adheres well to the CIP material, is used as part of the manhole lining process to complete a watertight, monolithic liner system.

Previous Rehabilitation

An issue that is more common than expected is the repair or redo of previously rehabilitated structures from other companies. We rarely discuss this in public forums because we try to focus on the positives of the OBIC Advantage, but the reality is that about 2% of our work is replacement of previously rehabbed structures with a failed liner. Mostly due to inadequate preparation or poor application, typically, the old, non-OBIC coating has pulled away from the structure wall allowing infiltration and hydrogen sulfide corrosion to occur. On occasion, a large enough piece of old liner falls into the invert restricting the flow. The OBIC Armor Three-Layer System comes with a ten-year warranty that provides confidence that our rehab for the previous non-OBIC rehab will indeed meet customer expectations.

Leaking Pipe Penetrations

Leaking pipe penetrations are also pretty frequent. When the hole was cored into the structure wall to allow insertion of a drain pipe of some sort, the gap between the pipe and wall gets caulked or maybe filled with hydraulic cement, which, of course, eventually works loose resulting in an infiltration groundwater leak. Many times the pipe has been cut flush with the sidewall, in which case the OBIC installer will install a pipe stub so that the flow drops into the manhole instead of behind the liner.

The common denominator of all of these common culprits of manhole deterioration is the OBIC Advantage – that OBIC products are designed to stop degradation and enhance structural integrity for decades without cracking under the pressure of temperature changes or heavy traffic.

If you’d like to learn more about the OBIC advantage, discuss your next project, or schedule a demo, please send an email to info@obicproducts.com or call 866-636-4854 and our team will be happy to help you!