Manhole Information

We receive questions regarding the location of manholes or damaged/displaced concrete around manholes.  Here are some important facts to understand about manholes:

A manhole is a huge structure.

One of the major components of the storm sewer drainage system and the sanitary sewer collection system are manholes. From the surface, manholes appear to be just a round metal disk (about the same diameter as a car tire), with the words “Storm Sewer” or “Sanitary Sewer” stamped on the top. But, below the surface, the subsurface structure is typically about 5 feet in diameter and can be up to 20 feet deep in the ground. The manhole and subsurface infrastructure weigh several thousand pounds and are typically installed with a large piece of construction equipment to connect them with pipes used to transport rainwater or wastewater. They are massive structures and do not move without significant external force. Below is a picture of a typical manhole installation.

Manholes are installed prior to any sidewalks, driveways, or other structures.

When a developer establishes a neighborhood, one of the first steps is the installation of utilities, including the water, drainage, and sanitary sewer systems. This installation includes manholes. After utilities, streets are typically constructed. Once utilities and streets are completed, the neighborhood then has vacant lots waiting for homes to be built.

The homebuilders then purchase the vacant lots from the developer and choose how to position the homes on the lot, as well as choosing the location of the driveway. The homebuilders then build the house, driveway, sidewalks, etc. Sometimes the homebuilder locates sidewalks or driveways on top of the existing manholes and other District facilities.

The manhole rarely cause sidewalks to crack or move.

As stated, manholes are massive structures that are connected to significant pipe structures. They do not move except in rare circumstances. However, sidewalks and driveways are typically only about 4 inches thick with some steel reinforcement and are built to lay on top of flat ground.  Concrete is rigid and does not bend as the ground moves. The two most common forces that move the ground, and thereby impact sidewalks or driveways, are tree roots and water flow. Tree roots tend to attempt to lift a sidewalk, which causes cracking. Water flow from either sprinkler system leaks or water drainage from gutters tends to erode the ground below the concrete, creating a sunken section. In some cases, both forces are working in the same area.

There are options for a damaged sidewalk or driveway.

If your sidewalk or driveway is damaged, look first for water leaks, water flow or tree root infiltration. Until those problems are addressed, it won’t be effective to repair the concrete. After that investigation is completed, if the concrete is solid, it is generally less expensive to inject a slurry mixture to lift or level the driveway or sidewalk. The concrete can be re-poured, but that is generally the most expensive option. Contact TNG, MUD 341’s operator, if you plan to make a sidewalk or driveway repair near a manhole or if you have questions. They will inspect the area and can provide you the appropriate Harris County specifications.