Published in Geostrata: ‘Under-Slab Utility Installation With Aggregate Piers’

Deanna Chambers, PE, LEED AP, M.ASCE and Charles Allgood, PE, LEED AP, M.ASCE, co-authored an article for ASCE’s Geostrata Magazine about under-slab utility installations before or after ground improvement.

We recently published an article in the peer-reviewed journal, Geostrata, a magazine by and for geotechnical engineers from the American Society of Civil Engineers (ASCE). It was a pleasure to write the article and share our experience and techniques with ground improvement when a project includes under-slab utilities.

The article emphasizes specific coordination and planning for project scenarios involving utility lines installed within and adjacent to an improved building pad. To read the full article in Geostrata’s Sept./Oct. 2019 issue, please click here.”

If you have a minute, here is an excerpt:

“When excavations are needed for utility construction beneath a building supported on improved ground, the improved footing and floor subgrade support can be compromised. So without proper planning, there can be costly time delays and repairs, and in the worst case, the ground improvement and/or utilitycontractors might need to remobilize to the site. This means the designer and general contractor must review any subgrade excavation that’s needed after aggregate pier construction has been completed.

“Many under-slab utilities, such as electrical and gas services, and shallow water and sewer piping, are placed within the upper foot or so below the floor slab. These are not usually a concern for ground improvement. Of course the utility trenches must be backfilled with engineered fill to maintain good support of the overlying slab.

“Problems can occur, however, when utilities are installed more than 2 ft below the floor slab or that enter or exit the building below the bearing elevations of footings. Typically, these utilities are gravity sanitary and storm sewer lines and water line connections. Some northern U.S. regions can have water line connections at depths over 7 ft below grade to place them below the frost depth…These deep utilities founded below footing bearing elevations may be installed before or after ground improvement. Each approach requires planning for utility layout and protection.”

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