Manhole Rehabilitation

Replacement Manhole Covers

PERMAFIX® is a rehabilitation system that seals, protects and structurally enhances defective sewer manholes and chambers. A Portland cement mortar fortified with micro silica is applied centrifugally to the manhole walls with a spinning head to the desired finished thickness. PERMAFIX® seals, protects and structurally reinforces them in a safe and cost effective manner.

Click to see how Permafix Manhole Rehabilitationworks.

Benefits

  • Structurally reinforced to extend its useful life . The mortar cures to 80% its ultimate flexural strength within 24 hours. Full strength is achieved within 28 days
  • Fully encapsulated interior prevents erosion damage from ground water
  • Full containment of sewage wastes
  • More effective and less expensive than partial spot repairs
  • Safe - hazardous entry avoided
  • Cures quickly at high strengths for a speedy return to service
  • Flows maintained during procedure
  • No excavation or surface disruption
  • Quick - no traffic inconvenience
  • Corrosion protected

Problem

Manholes are underground chambers built to provide man-entry access to service and maintain sewer and drain lines, water valves and meters, and communication and power equipment. They are subject to erosion from ground water intrusion, corrosion from liquids and gases, dynamic traffic loads as well as general deterioration from age and wear. Out of sight, their degradation is not easily monitored. When neglected, complete collapse is likely.

Occurring at least every 100 to 300 feet (50-100 meters), they become an integral part of each piping system. Studies in the USA show that more than half of all pipe defects occur within 10 feet (3m) of either side of manholes. And, since they are in direct contact with the surface, they are often the first segment of the sewer system to result in major damage.

With the advent of effective pipe repair technologies, the defects and problems in manholes are now receiving increased attention. The leaks that are prevented by lining pipes are redirected to the next weakest part of the system, which usually the manholes. Engineers and cities worldwide are realizing the benefit of effective repairs to manholes. They know that neglecting such an integral part of the system, by concentrating on the pipe, only shifts the problem. Having any part of the system fail means that the whole system has failed. The good news is that manholes are the easiest segment to investigate and the most effective and least costly to repair.

Inspection & Evaluation

A visual inspection should be made to determine the location and extent of all defects. Common areas are the bench, channel, wall and mortar joints, the casting, and the casting-chimney joint and pipe/wall penetrations.

The four major criteria for determining the thickness of the new liner are:

  • Diameter
  • Depth
  • Degradation
  • Deterioration (Corrosion)

The most appropriate thickness can be selected based upon the condition and size. Since cementitious liners depend on the underlying integrity of the existing manhole, surface preparation and application are just as critical to effective repairs as the material to be used.

Criteria for material selection should include:

  • 3000 psi minimum compressive strength in the first 24 hours
  • Quick setting for rapid sealing
  • High flexural strength for resistance to buckling
  • Independently tested and certified
  • Factory trained applicators

Procedure

Once the interior surface has been prepared, pipe inlets entering at any point higher than the bench should be temporarily plugged. The mortar is mixed while the robotic spinner head is positioned within the center of the chamber next to and slightly above the bench.

As soon as a batch is properly mixed, it is pumped to the spinner head and centrifugally cast onto the interior wall. The spinner head is then raised and lowered through the center axis of the manhole, casting a uniform and dense layer of PERMAFIX® mortar evenly throughout. Multiple passes can be made until the specified thickness is attained.

Because of the patented capabilities of PERMAFIX®, the thickness can be easily varied from one manhole to another or verified at any point within the same manhole. For instance, immediate traffic loading requires a thicker wall in the top 18” (600mm) near the casting. In deep manholes, ground water pressures require thicker walls in the bottom portion.

When the specified thickness is obtained throughout, the operator may enter the manhole to make bench repairs, remove any temporary pipe plugs and perform a final interior inspection. The lid is immediately repositioned to prevent accelerated evaporation of the mix water.

The newly lined manhole provides the very best prepared surface possible since bacterial regeneration has not begun and since the textured mortar surface provides an interlocking surface for the epoxy to bond. Both the mortar and the epoxy then cure together to form an impermeable barrier against future corrosion.