Frequently Asked Questions

Looking for quick answers about manhole production, design, and installation? Search our frequently asked questions tool below.

Where are manholes typically installed?
Manholes are typically installed near the start of a branch sewer in low-traffic areas, along sewer lines, or near key areas which require accessibility.
Why are manhole covers round?

Simply put, round covers cannot inadvertently fall into the hole.

What is meant by shallow, normal, and deep manholes?

A shallow manhole is meant for depths of two to three feet. This is sometimes referred to as an inspection chamber, as it is very shallow. It is often chosen for sites near the start of a branch sewer in low-traffic areas.

A normal manhole is the most commonly placed manhole as the name suggests, and is meant for depths of five feet. These pieces can be square or round shaped.

A deep manhole is meant for depths of greater than five feet and is often wider than other manholes, as well. A heavy safety lid is required for deep manholes.

Why should I use precast manholes for my next project?
Installation is fairly simple. In contrast to poured in place structures, precast installation can be completed with simple machinery and a small group of professionals.
What are some design considerations pertaining to manholes?
  • Water flow rates based upon sewer line use and location
  • Sediment volume, density, and re-suspension
  • Anticipated surcharge loading on the structure
  • Soil bearing capacity below the structure
  • Ease of access for future maintenance and/or cleaning
What are some advantages of precast that designers need to know?
  • Unmatched durability and strength
  • High quality concrete mix designs
  • Documented QA/QC programs
  • Easily customizable to meet project needs
What are the main considerations in sizing manhole parameters?
The main consideration when properly sizing a precast manhole is the size, quantity, and angle in which the intersecting pipes must enter the manhole. Additionally, the overall depth of the manhole will be determined by the invert elevations of the inflow pipes versus the outflow pipes.
When should you choose a round manhole design and when should you choose a square or rectangular one?

Round manholes offer flexibility in the angle of intersecting pipes as well as design advantages. The wall thickness of round manhole structures doesn’t increase nearly as much with increasing depth due to the inherently strong nature of round structures.

The primary advantage of square and rectangular manholes is the ability to accommodate larger pipes intersecting at 90 degree angles without significantly increasing the overall size of the structure.

How complicated is precast manhole installation?
Most products can then be installed in just one day with the use of small equipment.
What are the steps of installation?

Basic instructions for typical installation can be found here.

What equipment and supplies are necessary for precast manhole installation?
  • Excavator or backhoe
  • Vibratory compactor and/or sheep’s foot roller
  • Any proper bracing that is required
  • Sealants, grouts, and mastic as required
  • All proper safety equipment and PPE
What are some advantages of precast that installers need to know?
  • Ease and speed of installation
  • In-stock availability of many standard sizes
  • Customization to fit project needs
  • Compelling upfront costs as many required materials are supplied by producers (ie. Sealants, grates, mastic)
  • Dedicated and knowledgeable sales staff

Need more info?

Rethink Precast Marketing has an experienced team that is equipped to help you weigh the considerations of installing a precast concrete manhole. They can also guide you to a qualified supplier near you. Reach out today for more information.