We drive and walk by manholes every day. There are 20 million manholes in the U.S. and thousands of manholes throughout Delaware (45,000 in New Castle alone), but we don’t give them much thought until there is a problem. Manholes require attention as a vital part of Delaware’s infrastructure. Manholes have existed since before the Civil War and have seen the evolution of the streets around them from brick to pavement. Inspections must be performed to ensure aged materials are cared for or replaced.
Yes, original brick and stone can still be found around manholes in areas of the country with a long history, like Delaware – the first state. This speaks to American craftsmanship and innovation; however, nothing lasts forever, and manholes will crumble if not maintained. If a manhole lasts 50 years, it means we should pay particular attention to manholes created in the 60s and 70s right now in addition to having a maintenance schedule for all manholes. When manholes fail, it creates a host of problems. So the critical question before we address what manhole rehabilitation means is, what causes manholes to fail?
Why Do Manholes Fail?
Manholes are the gateway for ground and surface water to enter the sewer systems. Water flowing over and into manholes creates wear and tear, leading to deterioration. Manholes should be inspected and maintained regularly to address compromised areas. Inspection and maintenance avoid corrosion and cave-ins. This is one-way manholes incur damages. Another is hydrogen sulfide.
Manhole inverts are susceptible to leaks due to the sloped floor between the invert and the barrel wall. The entire structure is prone to corrosion and abrasion, which invites instability. The manhole ring is exposed to natural elements such as freezing and heat, not to mention the weight of traffic. A deteriorated manhole can fail and cause road hazards, sewer blockage, and other safety issues. The most common enemies are:
- Asphalt deterioration
- Root invasion
- Water erosion
- Ground settlement or earthquakes
- Weather (i.e., ice, rain, extreme heat)
Maintaining structural integrity and curing defects is as essential as street maintenance to avoid more significant problems that overburden city populations with additional costs. So, what can we do to be cost-effective, efficient, and prevent failure? Inspections.
Manhole Inspections
Standard Pipe Services’ best practice is to utilize a CCTV camera to monitor, record carefully, and inspect manholes thoroughly to locate and resolve structural or wear and tear problems. Ensuring timely, scheduled, documented inspections is crucial to infrastructure health. In addition, performing required maintenance for prevention is vital. If the area passes muster, it is recorded and archived, but if it doesn’t, entry into the confined space is necessary to investigate further. The camera is an excellent method to keep costs down and lower the necessity of confined space entry.
NASSCO has established documentation procedures and a Manhole Assessment Certification (MACP) that has contributed to the safety and uniform documentation procedures for long-term collaborative solutions in preventative maintenance. Documentation includes detailing structural defects, recording O&M and I/I ratings, and dimensions. Consistently recording and archiving this data builds a roadmap to identify the proper rehabilitation or replacement needs.
Manhole inspections should be conducted when the groundwater level is high. In setting your schedule, take note of wet weather conditions ad plan November through May inspections. Manhole inspections include:
- Identifying any inflow and infiltration issues
- Inspecting material and structural conditions
- Removing debris to check the integrity properly
Standard Pipe Services is certified in NASSCO’s two inspection protocols:
Level One Manhole Inspection
Basic condition assessment with information to evaluate the general condition.
Level Two Manhole Inspection
Detailed documentation of defects to determine condition and provide specifics for rehabilitation.
NASSCO has assigned grades based on deterioration severity:
Manhole Rehabilitation
Solutions to remedy a manhole problem usually are found in rehabilitation methods rather than replacing the structure. Rehabilitation provides sufficient protection by reinforcing and revitalizing the existing structure. In addition, rehabilitation protects against inflow and infiltration issues (I/I) which are the primary reasons for failure. The cost and type of rehabilitation will vary depending on the location and the issue to be addressed.
- What is the substrate condition? Its tensile strength? Is the concrete flaking off?
- What are the infiltration issues? (at the chimney, the Mainline Connections, or Joints)?
- What is the impact on the area? (noise, vibration, dust)
- What gases are coming from the manhole? (hydrogen sulfide)?
- What are the material requirements (adhesion, abrasion)?
- What are the application conditions (dust, water, small spaces)?
- Will there be a need to divert traffic?
- Is the manhole easily accessible?
- Is there root intrusion?
Once these questions are answered, solutions to the defect are addressed about liners, cementitious coatings, or a combination.
Cementitious Manhole Relining
Cementitious manhole relining is the area’s most common type of repair. Standard Pipe Services utilizes this method in most cases when we see brick manholes or manholes precast with concrete deterioration. This method typically requires minimal surface preparation beyond high-pressure cleaning. We reline manholes with a Calcium Aluminate that contains fiberglass flakes. This concentration helps reduce corrosion and increase structural integrity. Manholes are lined using a spin cast machine or sprayed by hand from inside the manhole. The thickness will vary depending on the job and the amount of deterioration.
Manhole Grouting
When the manhole is in fair condition but has several leaks, Standard Pipe Services recommends Curtain Grouting. Curtain Grouting seals the manhole with Acrylamide Grout. In addition, an external barrier wall is created around the manhole to protect it from infiltration for years to come.
Epoxy Manhole Relining
The use of epoxy is becoming popular in the industry. The material is conducive in areas with high concentrations of hydrogen sulfide or active infiltration. Epoxy can be hand applied or spray applied depending on the area’s difficulty. Another factor in Epoxy relining is the structural integrity of the manhole. Depending on the number of cracks or voids, a cementitious backing may be installed before the final epoxy coating.
Other Manhole Repairs
Raising Manholes
Manholes are often paved over and forgotten about. Eventually requiring the manhole chimneys to be raised.
Frame & Cover Replacement
With wear and tear, manhole covers may break or become loose, creating infiltration issues in the manhole.
Manhole Steps
Many manholes with severe deterioration will require new manhole rungs.
Manholes Benches & Inverts
This part of the manhole sees the most sewage. Because of this, they often deteriorate and need cementitious repairs.
Not only are manhole inspections performed to identify sources of Inflow & Infiltration and determine the structural condition of the manhole, but manhole inspections also help verify or correct existing sewer maps.
In Closing: Let’s Talk about Delaware Infrastructure
In discussing maintenance, rehabilitation, and infrastructure, it is essential to know how Delaware compares to the rest of the nation. An infrastructure report card is given annually by the American Society of Civil Engineers. It can be found [here]. The nation moved from a D to a C-, so there has been consistent improvement in recent years.
As taxpayers, paying attention to what we spend on replacement or repair is important because it provides insight into what we could be doing better to lower costs. One of these crucial costs is infrastructure, including manhole replacement and rehabilitation. Preventative maintenance and proactive action are always more cost-effective than being caught by surprise when a manhole or other infrastructure fails. Wondering how Delaware stacks up? Here are a few facts from the ASCE site:
According to their website:
Success in a 21st-century economy requires serious, sustained leadership on infrastructure investment at all levels of government. Delaying these investments only escalates the cost and risks of an aging infrastructure system, an option that the country, Delaware, and families can no longer afford.
Standard Pipe Services is committed to being a driving force in infrastructure improvement, access, and sustainability. There are grants to assist municipalities and homeowners in achieving sound infrastructure that can be found [here].
Standard Pipe Services can assist you in manhole inspection, maintenance schedules, and rehabilitation. Call or email today and start your maintenance plan journey with an expert in the field! Follow us on LinkedIn for more tips.
