Helical piles install into soils much the same way screws install into wood. The purpose of any pile is to transfer structure loads to a depth below grade where soil moisture content is stable and the soil strata is suitable for load bearing. Helical piles are unique because of their installation method. As the piles are installed, the torque required for advancement is monitored and recorded. Decades of empirical testing has documented that there is a correlation between the installation torque and the piles’ capacity. Once the structure’s loads have been determined, we can mathematically determine the minimum installation torque energy required to achieve pile capacities to support the structure including a factor of safety. In some cases, usually larger commercial projects, the design engineer may require physical load testing of a percentage of the piles to be installed. VersaGrade owns pile test frames, hydraulic testing equipment and measuring instrumentation to perform both compression and tension testing. Helical piles can be used in tension or compression, and are used for approximately 75% of foundation repairs.
Micropiles and soil nails are essentially the same thing; the difference is in their application. Micropiles are used in tension and compression as load bearing tendons. Soil nails are typically used in steep slope or wall stabilization where the nails are installed beyond the soils' failure plane (angle of internal friction). Both applications utilize a hollow bar steel tendon with a sacrificial cutting bit that is installed with a rotary-percussion hammer. During installation, a neat cement and water mixture is pressure injected down the hollow bar and through the cutting bit into the soils surrounding the hollow bar/tendon. This method of installation is called Injection BOring (IBO). IBO piles and soil nails develop their strength, in both compression and tension, by the summation of the steel tendon plus the strength of the annular soil-cement bond with its surrounding soils, referred to as the area of influence.
The area of influence is the annular area in which the soils are cemented together. Micropiles and soil nails can be installed in almost any soil condition with excellent load bearing characteristics which makes them an ideal alternative in rocky or high blow count (high density) soils where helical pile installations are not conducive.