Another winter is coming and drivers know that by spring there will be a new crop of potholes coming up that will need to be rehabbed. Manhole rehabilitation is a growing segment of the trenchless sector and will continue to grow with numerous manholes that require attention every year.
An engineer gauges the current condition of the manhole to determine the rehab design that will be used by taking into account the main reason for failure. This is necessary for the rehab to be a success. If poor specs or material is selected that does not properly match the current conditions for that particular manhole, the project will fail.
Engineers have a lot of information available as they design manhole rehabilitation projects. Recent technological advances mean that manhole inspection software can synchronize between GIS systems to give them the most recent view of pipeline and manhole networks. One database can contain links to GPS points, traffic needs, manhole locations, flow conditions maintenance history and real time data of everything involving a particular manhole. This gives the contractor and engineer what they need to do the job correctly with less error.
Ask the right questions
- You must be sure to consider all the facts to select the appropriate method to rehab the manhole. Such as:
- What are the owner requirements regarding noise, vibration, and dust?
- What are the application conditions such as dust, water, and small spaces?
- What are the material requirements such as abrasion, adhesion, and chemical resistance?
- What is the condition of the substrate, for example, it’s tensile strength and a material that inhibits bond?
- Evaluate environmental conditions, including gasses, sewer flows, bypassing criteria and traffic control
- Material selection determined largely by controlled elements such as live flow, low oxygen, constant moisture or high levels of hydrogen sulfide
After evaluating the conditions of the manhole and evaluating the rehab methods next comes determining the best technique for that particular manhole environment and these include:
- Prevents water from entering structure
- Stretchable epoxy coated polyester
- Eliminates inflow and infiltration (I/I),
- Provides structural reinforcement
- Able to be installed without confined space entry on simple structures
- Increases structural integrity of manhole
- Best for locations a potential infiltration cannot be addressed in a timely manner
- Tends to give the best performance with close to 100% calcium aluminate
- For manholes with .5”-2” of concrete deterioration
- Good where bypass pumping or limited flow control
- Typically require minimal surface prep
- Calcium aluminate additive provides pH buffer, reduces rate of concrete degradation when hydrochloric acid is present
- Some additives such as fiberglass flakes, help protect against corrosion
- Increase structural integrity
- Can be spray applied, pumped and troweled or spin cast
Mechanical Seals, Inserts, and Liners
- Good for large diameter manholes
- Physical barrier against corrosion
- Record longevity when applied properly
- Materials range from PVC, fiberglass, and HDPE
- Usually grouted in place after installation by applying mortar to ½” thick and physically pushing liner to the surface
- Moves into existing annular space and is the mechanism to lock liner in place and provide the desired level of adhesion
- Can be more expensive
Polymer Modified Coatings
- Spray application has better coverage due to gun reaching angles in manhole
- Can be sprayed, trowel or spin cast
- Good for oddly shaped structures with atmosphere control
- Does not require super-smooth surface for good adhesion
- Possible to apply up to 250 mils, reduces pinole concern
- Requires environmental controls and stringent surface prep
- Full-time inspection recommended
- Moisture and temperature sensitive, can pinhole on concrete if not in properly controlled environment
Be sure to create a decision matrix that includes manhole conditions and needs, available materials and technology, project management and quality control requirements, inspection and grading protocol. Use the appropriate material and technique for the long life of the male and cost efficiency. The method should be a long-term solution and contractor -friendly. Investigate case histories and work with a contractor with experience in the chosen material with a proven track record. All of this information will provide you with the best approach for a long lasting manhole rehabilitation. Remember, as part of your manhole maintenance or rehab, the frame and lid should be adjusted prior to other remedial action. Consider the benefits of the Mr. Manhole system for frame and lid adjustment.