manhole rehab

Aging Infrastructure & Manhole Rehab in Massachusetts

New England, being one of the first parts of the United States settled, has some of the oldest infrastructure. This is no different for the Town of Hull, Massachusetts.

Recently, the Town put out a multi-million-dollar sewer rehabilitation bid for cured-in-place pipe (CIPP), which also included extensive manhole and structure rehabilitation. This sanitary sewer infrastructure was only 45 years old and is certainly not as old as other sewer systems in New England. Hull is a coastal community with high brackish groundwater and minimal pipe grades, so hydrogen sulfide has been an issue in the collection system, which has increased the rate of deterioration of the system.

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The Town’s 36-in. RCP sanitary sewer interceptor exhibited both corrosion of the concrete due to the presence of hydrogen sulfide gas and infiltration due to high groundwater. This was also the case in the precast concrete manholes on the project. The work for this project included trenchless technologies such as cured-in-place lining of 10,000 ft of 36-in. gravity piping, grouting of service connections, as well as the rehabilitation of more than 1,000 vf of pre-cast manhole structures. Also included was the rehabilitation of a four-barrel inverted siphon, two-barrel lagoon crossings and the concrete structures associated with them. All of the work proposed was required to be completed utilizing trenchless technologies.

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The manholes scheduled for rehabilitation all showed signs of corrosion due to saltwater intrusion and microbiological H2S induced corrosion. Exposed rebar and visible aggregate, as well as heavy infiltration were present in most of the manholes.

The project specifications required the contractor to have a professional engineer prepare, certify, and submit engineering design calculations for the structural rehabilitation of all manholes.

The specifications required the cementitious coating product to have the following minimum structural values based on 28 days curing:

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  • Compressive strength: ASTM C109 >9,000 psi

  • Flexural strength: ASTM C293 >1,600 psi

  • Tensile strength: ASTM C496 >800 psi

  • Modulus of elasticity: ASTM C469 >4,500,000 psi

  • Permeability: ASTM C1202 < 300 coulombs

  • Bond: ASTM C882 >2,000 psi

  • Shrinkage: ASTM C596 0.0% (at 90% RH)

  • Freeze/thaw: ASTM C666 300 cycles

  • Sulfide resistance: ASTM C267 No loss after 90 days

The project specifications also called for the rehabilitation of the manhole inverts. All of the inverts needed to be scheduled when the manholes were bypassed for the CIPP lining unless the liner went through the manhole invert. Other manholes without a CIPP liner needed to have the inverts bypassed with flow through plugs. For the remaining portion of the manhole work, the crews had to go back to each manhole and complete the preparation, infiltration elimination, cementitious coating, and epoxy lining.

Also, all incoming infiltration needed to be eliminated. Green Mountain Pipeline Services (GMPS) used American Chemical Grout Company’s ACG-AG Acrylamide-MBA Premix acrylamide grout on all aspects of this project. GMPS has successfully used this product for more than five years and uses it exclusively in its rehabilitation projects.

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Founded in 2003, Green Mountain Pipeline Services offers a wide range of pipeline inspection and rehabilitation services using trenchless technology. This includes closed circuit TV inspection of mainlines and laterals; cured-in-place pipe mainline and lateral lining; trenchless spot repairs; grouting of mainlines, manholes and laterals; manhole/structure cementitious lining and reconstruction, with epoxy as needed; pipeline/structure cleaning and vacuuming; and smoke testing, manhole inspections, dye testing and flow isolation. Headquartered in Bethel, Vermont, GMPS is a subsidiary of Infrastructure Services Group LLC, which acquires and funds profitable and well-positioned private companies that specialize in water and wastewater pipeline and manhole inspection, maintenance and rehabilitation.

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One of the most important aspects of manhole rehabilitation is preparation. If the manhole is not cleaned and prepared properly no coating or product will last as long as intended. The proper preparation of the manhole walls is key to a successful project.

Strong Seal QSR for manhole patching and repair and Strong-Seal High Performance Mix was used to rehabilitate the manhole walls. Green Mountain Pipeline Services has been using The Strong Company’s products with tremendous success since 1992.

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The photo here shows a manhole that has been prepped. All infiltration has been stopped; the walls have been pressure washed back to sound substrate. Also noticeable is the level of corrosion that has taken place as the aggregate in the concrete is exposed. This manhole has the CIPP liner running through it. The bench will be built up so that the bench slopes back properly to the invert.

The photo on the left is the intermediate stage. The manhole was prepped, all leaks stopped, and patching where needed was completed with Strong-Seal QSR. Here we show the manhole with ½ inch of Strong-Seal High Performance Mix applied. After the product was applied, it was troweled smooth to ensure a good bond to the substrate. Since specifications called for an epoxy to be applied on top of the cement the surface was brushed to radically increase the surface area, which will create a better bonding surface for the epoxy to be applied.

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Because of high H2S levels, the project called for the cementitious liner to have an epoxy applied as a second coat to further protect the manhole from future hydrogen sulfide damage.

The epoxy needed to be solvent-free, 100 percent solids by volume, corrosion resistant formulated for immersion and atmospheric service and needed to exhibit the following properties:

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  • Tensile strength: ASTM D638 >6,900 psi

  • Tensile ultimate elongation: ASTM D638 >1.4%

  • Compressive strength: ASTM D695 >11,900 psi

  • Flexural strength: ASTM D790 >10,900 psi

  • Flexural modulus: ASTM D790 >499,000 psi

  • Shore D hardness: ASTM D2240 >82

  • Adhesion to concrete: ASTM D4541 Substrate Failure

The epoxy product used was Parson SEL-80.

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The final testing of the work consisted of cementitious material physical testing, visual inspection, film thickness measurements, and Holiday or spark testing.

The project was completed on time and on budget. The Town of Hull was pleased with all the work performed by GMPS and included additional change order work onto the contract, consisting of cleaning and inspection of the remaining portions of the interceptor, manhole rehabilitation in other areas of the interceptor, and other CIPP work. As a result of the full-length liner and complete manhole rehabilitation, it is evident that groundwater infiltration has been significantly reduced over the course of the project based on trend data using average daily flows measured at the wastewater treatment facility.

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The work was performed for the Town of Hull Sewer Department with engineering services provided by Woodard & Curran.

Ray Bahr, P.E. is vice president of sales and marketing with Green Mountain Pipeline.

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