Consultants, designers, and contractors know that Geopier Rammed Aggregate Pier® ground improvement systems are a great way to save the owner money and time for a wide variety of projects. Design and construction professionals also know that Geopier systems often require testing to verify subgrade conditions at the site and to validate the Geopier site-specific design parameters. What many design and construction professionals don’t know is that there are best practice methods for performing aggregate pier load tests, and that improper selection of maximum applied loads can lead to unconservative test results.
A Geopier load test, or modulus test, is performed on single test pier typically constructed in the “worst” area of the site (i.e. area containing the softest soil conditions). Furthermore, modulus tests are conducted to a pressure equal to at least 150% of the maximum design top of pier stress to assure a reasonable level of safety that supports long term settlement control and demonstrates that the Geopier element has adequate strength. Performing modulus testing beyond the limit state top of pier stress meets the intent of the International Building Code (IBC) and local building codes with respect to shallow foundation support.
Geopier Technical Bulletin No. 12 provides a best practice method to make sure that field modulus testing properly represents the loading conditions that aggregate pier systems will experience during actual structural loading.