Manholes are an important part of wastewater collection systems. They provide access to the wastewater collection system pipelines for maintenance, inspection, and renovation. The term manhole derives from the fact that these structures were designed to provide worker entry for cleaning and inspection. Although most access to wastewater collection system pipelines in the United States is by manholes, other types of access points are also found such as small diameter cleanouts (and/or lamp holes) and large junction boxes.
Technologies for the renovation of manholes are many. They include specialty products installed to primarily stop leakage; a variety of coatings for leakage control, structural enhancement and corrosion protection.
These materials are either spray (low pressure) or trowel applied. They have a long, established history with recent improvements in fast setting high strength corrosion resistant mortars. Some are reinforced with fibers for added tensile strength and crack resistance.
Specialty products such as mechanical seals, hand applied coatings, external wrap materials, etc. are designed to address specific infiltration and/or inflow concerns such as leaks between the manhole casting and the chimney and usually can be applied with a minimum of labor and equipment.
These systems utilize a variety of resins. They are used for renewal of the manhole structure, have excellent chemical resistance and strong, long-term physical properties. Typical methods and equipment for installation can line diameters from 2 ft to 10 ft and up to 60 ft deep. Liners are typically designed for full depth hydrostatic head conditions and to withstand earth pressure and traffic loading. They can also be designed as a stand-alone structure.
The CIPMH (cured-in-place manhole) liner is a unique one-piece liner made to fit all manholes including barrel sections, eccentric and concentric cones constructed of brick and mortar, pre-cast or block. CIPMH for chimney or full-depth manhole repair eliminates infiltration & inflow through manhole walls. The universal sized manhole liner is engineered to resist freeze-thaw cycles and create a watertight, corrosion resistant lining.
Solvent free (100% solids) coatings are operator and environmentally safe and require no evaporative curing process making them ideal for underground coating applications. These high build coatings are either spray or trowel applied and can be specified at structurally enhancing thicknesses. Current generations of epoxy coatings will adhere to moist or damp substrates and have excellent chemical resistance and long-term physical properties.
These materials are typically spray applied. Many variations are available from elastomeric to rigid formulations. Generally, they are 100% solids only used for underground coating, but can be adapted to use in environments where UV exposure exist. They have good to excellent chemical resistance and elastomeric qualities that range from rigid formulations to highly flexible. Urethanes generally have strong long-term physical properties. A hallmark of the urethane family is their quick-curing capacity which allows for a rapid “return to service” for the structures that are coated.
Generally, the top of the old manhole is cut off and removed and the interior is pressure washed to remove any debris and loose material. The channel is typically removed and replaced after the installation of the pre-cast inserts. If this is not possible, the precast manhole inserts can be shaped to fit the existing bench configuration. The precast inserts typically come in either one continuous section or in different lengths for easy assembly.
Geopolymer cements can be used to restore a manhole’s structural integrity and permanently stop infiltration and corrosion. A variety of structural and corrosion resistant products are on the market.
Leakage control technology that is injected into the ground surrounding the manhole. The chemical grout is injected through the manhole structure to mix with the surrounding soil to provide a waterproof seal and prevent infiltration from entering the manhole. A variety of grouts are available for specific applications.
Used to seal the casting/chimney and wall area against leakage into the manhole. Capable of withstanding surface traffic impact and freeze/thaw pressures.
Plastic panel that is glued to the manhole wall with a pre-applied mastic on the structure. Generally unaffected by water vapor pressure, characteristics include resistance to corrosive environments, monolithic protective coating, encapsulation all areas of the manhole structure, is pin-hole free, stops infiltration and is bonded to the host structure.
Poured-in place concrete manhole reconstruction includes the formation of a new integrated liner wall within the existing manhole structure. The new manhole liner wall generally conforms to the existing inside dimension and is often combined with epoxy coating, or a plastic (HDPE or PVC) liner for corrosion protection.
These systems have an extensive installation history. Excellent chemical resistance with both PVC and HDPE sheet materials; they are typically used with cementitious or polymer mastic basecoats.