Geopier X1 Rammed Aggregate Pier (RAP) Elements are ground improvement elements that reinforce unsuitable soils to provide improved bearing capacity and settlement control for conventional shallow footing and slab-on-grade support. X1 RAPs consist of stiff columns of rammed aggregate and are the newest type of Geopier RAP in our ground improvement “arsenal”. They are constructed with a patented mandrel and compaction chamber that allows us to install RAPs faster and more efficiently than ever before. X1 RAPs can be installed using a pre-augered “drill-and-fill” replacement construction method OR a fully displacement method that does not require pre-augering. The selected construction method is a function of the site-specific subsurface conditions. For sites with non-caving soils such as silty or clayey soils, the drill-and-fill (replacement) construction method is more appropriate and consists of predrilling an augered cavity and filling it with successive compacted lifts of imported aggregate. For sites with caving soils such as clean sand or gravel soils, the displacement method is more appropriate and allows the existing site soils to cave into the mandrel and “self-serve” as the RAP aggregate (how efficient!). Imported aggregate can be added to the displacement method to supplement the site soils as needed. Both X1 construction methods compact the lifts of aggregate with direct vertical ramming energy that results in high-stiffness engineered elements. The vertical ramming action also increases the lateral stress and improves the surrounding soils. The end result is an improved subgrade that is ready to receive traditional shallow footings designed for higher bearing pressures and a slab-on-grade.