Underground Utilities Design Guidance

Considerations

The installation, maintenance, and repair of utilities generally involves a large number of public and private agencies, requiring effort for coordination and integrated planning.

Advance notice and coordination between agencies regarding planned maintenance work is one of the most effective tools for reducing common issues and externalities.

While installing new underground utilities, coordinate the location of other utilities with the relevant agencies as it may conflict with their guidelines. Utility planning, design, and maintenance decisions greatly depend on the design and the operation of the overall system.

For each street, consider soil types and permeability rates, location of bedrock, vegetation, depth to groundwater, water quality and quantity, rainfall, local climate, and temperature extremes such as frost and heat.

Design Guidance

Provide setbacks, spacing, and depth of cover guidelines in accordance with municipality and utility requirements. The depth of cover is measured from the top of pipe or conduit to finished grade.

Install utilities prior to completion of new road and sidewalk surfaces. When introducing utilities under or along sidewalks, medians, parking spaces or buffers, or travel lanes, install them before above-grade street reconstruction and finishing. All building connections should be installed up to the property line.

Place priority utilities in more accessible areas to avoid frequent traffic interruptions, especially to high-capacity lanes. Priority should be given to utilities accessed most frequently:
1. Communication
2. District cooling
3. Gas
4. Wastewater
5. Stormwater

Install flexible, pressurized utilities such as water and gas above gravity-run pipes.

Base utility materials on site-specific and local regulatory requirements. Consider any anticipated loading from the finished grade and select materials accordingly.

Check local soil conditions and water tables for minimum depths of underground utilities. If the minimum depth required cannot be achieved, protect utility lines beneath roadways by encasing them in concrete. Run utilities parallel to the sidewalk or the roadway. Surface elements such as manhole covers and service boxes should sit flush. Design surface elements to hold the weight of large freight vehicles.

Use root barriers in tree pits to direct growth downward. Ensure that pavement surrounding pits is compacted sufficiently to discourage roots from damaging the pavement.