Innovation in Deep Foundations
Any ideas about what’s going into the ground at the job site in this video? If you guessed drilling or driving piles, you’re on the right track. In fact, we’re driving micropiles into the ground at a job site in preparation to build a custom home.
You’ll often hear the term pile when referencing a structure’s foundation. A pile or piling is a vertical, post-like structural element of a deep foundation, which is typically used for homes built on the side of a mountain. Piles can vary in size and in distance from each other. They’re driven or drilled deep into the ground and are used to disburse the foundation’s load to the surrounding rock and soil.
A Quick Physics Lesson
Wait! What’s a load? A load is the weight or force on a joint, connection, beam, column, things like that which are part of the structure. You might be familiar with the term load-bearing wall. One way to think about load is as the downward weight exerted by the roof trusses onto the beam at the top of a load-bearing wall.
Load can be either live or dead. Live load refers to the constantly changing loads on a structure from people inside the building, water flowing through the building, rainwater, ice, or snow on the roof, etc. Dead load is the actual weight of the systems used to form the structure and anything else that doesn’t move. Dead load is the constant, non-changing load on the structure, like an A/C unit, a water heater, appliances, ductwork, pipes, etc.
Each structural element distributes the load, which will eventually be transferred to the surrounding bedrock and soils through the foundation.
Without a strong foundation to hold the load, the walls of a home could collapse. Therefore, the home’s foundation must be built to carry the weight and load of the dead load used in the home and account for variable live loads. And when building on a steep slope where a deep foundation is necessary or in areas with poor soil quality, innovative micropiles are the ideal solution for transferring the load to the bedrock and soil.
Micropiles are small-diameter, high performance post-like structural elements in the deep foundation. They are comprised of high-strength steel casing, rebar, and grout, and these deep foundation elements are typically between 5–12 inches in diameter and can extend to depths of 200 feet and achieve working loads of over 200 tons.
How Micropile Work
Micropiles transfer the structural load through unsuitable soil layers to competent foundation soils. The loads are transferred from the foundation through the steel and grout of the micropile and shed to surrounding rock or soil via high values of friction.
When to Use Micropiles
Micropiles are generally used when there are difficult ground conditions, such as natural or man-made obstructions or pool soil conditions, sensitive ground with adjacent structures, limited access/low headroom and/or karstic geology. Karst geology refers to a type of landscape where bedrock has dissolved, creating sinkholes, sinking streams, caves, springs, and other characteristic features. Karst is associated with soluble rock types such as limestone, marble, and gypsum.
Micropiles are commonly used in green building to reduce the impact of the structure on the land and to replace deteriorating foundation systems. They are often used to reinforce embankments and slopes, as well as to stabilize landslides.
We’ll post more photos as the home takes shape, so stay tuned.
Want to learn more about green building in Asheville? Check out this blog post about reducing your carbon footprint.