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As ground improvement has become a more commonly accepted tool by construction professionals and engineers, ground improvement experts have made advancements in technology that have pushed the industry forward. These advancements now allow ground improvement to be used in practically every soil and groundwater condition, and ground improvement is now a resource to not only take a site from poor to good, but also to make good sites great for shallow footing support. When good sites become great, this means that foundations can be designed for considerably high-bearing pressures.

Building foundations are subject to compressive loads from dead loads and live loads, in addition to other loading factors. Wind loads and seismic loading conditions can result in uplift (tensile) loads on foundations. Structural engineers designing foundations for high bearing pressures on ground improvement sometimes up-size foundations to resist these uplift forces using the weight of the foundation. This limits the cost savings of foundation construction that ground improvement can provide, due to additional concrete and steel for foundations and/or additional ground improvement elements to realize a minimum area of coverage across a foundation footprint.

A means of maximizing the value of ground improvement is to include uplift resistance as a part of their scope. Most ground improvement contractors have methods to accommodate uplift forces which will allow the bearing pressure to be fully realized. Some contractors may employ embedded anchors in their ground improvement elements, and others may use helical “screw” piles or micropiles. Although including uplift resistance in the ground improvement scope will increase the cost of the ground improvement contract, the savings in foundation construction often eclipse these added costs.

There are several considerations to address when designing a project for high bearing pressures and accommodating uplift.

  • Partner with companies that have ground improvement experts on staff and not merely sales personnel or contractors.
  • Treat ground improvement partners as valued members of the project team and engage their input early in the project.
  • Connect the geotechnical engineer and structural engineer with the ground improvement expert. This keeps everyone abreast of design approaches and project requirements (such as loading conditions), since all will have a professional stake in the project outcome.
  • Make sure that uplift resistance is provided uniformly across a foundation. For example, if two ground improvement elements are required beneath a foundation to resist compressive loads, but uplift resistance can be fully accommodated in one ground improvement element, then both ground improvement elements should be used for uplift resistance for purposes of eccentricity.

If a significant number of ground improvement elements will be used to resist uplift, perform an uplift load test to confirm ground improvement design approach.

Using ground improvement on projects to resist uplift loads as well as to increase bearing pressures for shallow footings is an innovative way to save project costs in foundation construction and schedule. For projects with relatively small uplift loading demands (less than 5 to 8 kips), it can oftentimes be more cost effective to up-size foundations to resist these loads. For other circumstances, let a ground improvement expert design a solution to help the project.

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