are small-diameter deep foundation elements that bypass poor bearing soils and transfer loads into a competent bearing stratum or rock. Individual micropile capacities can be as large as 400+ tons. Micropiles are capable of resisting both lateral and axial loads. They are particularly advantageous where low headroom or restricted access precludes conventional pile-driving equipment, where vibrations are of concern, or where deep foundations are to be installed through difficult ground conditions such as dense glacial till, boulders, karst or uncontrolled fill.
High strength steel casing (generally 4 to 12 inches in diameter) is drilled to design depth. A reinforcing element, typically a single steel threadbar, is placed in the casing extending the full length of the micropile. Cement grout is tremied in place using gravity. Often following tremie grouting, micropiles are grouted under pressure as the casing is extracted from the bottom of the bond zone to its final elevation. These are called pressure grouted or “Type B” micropiles and are typically used in sands or slightly compressible soils. The intent of pressure grouting is to achieve a larger bond zone surface area for a higher bond capacity.
On rare occasions, micropiles may undergo further grouting, called post grouting, after the primary cement-grout has started to set. These piles are referred to as “Type C” or “Type D” micropiles.
- New building foundations
- Bridge piers and abutment foundations
- Retrofit of existing structures to withstand increased loading
- Structural settlement control
- Counteraction of uplift potential of tower structures
- Tank and crane pad foundations
- Seismic retrofit
- To function as soldier piles for earth retention.
- High capacities achievable
- Low noise and vibration installation
- Able to penetrate subsurface obstructions
- Can be installed in low headroom limited access and within building interiors
- Can be installed through water
- In most instances, facility operations can continue uninterrupted during the micropile program
Hollow Bar Micropiles
Hollow bar micropiles, as the name implies, are formed in a continuous operation by pressure injecting cementitious grout through an all-thread hollow bar. They are advantageous where a new foundation system must be installed in very close proximity to existing foundations that could be undermined should the foundation soils be loosened by conventional auger cast or micropile installation.
Moretrench has completed numerous micropile foundation projects, ranging from Flagler Bridge emergency stabilization in West Palm Beach County, FL, to foundation systems for the first SHARON denitrification facility in the United States.
If you have any questions, or would like to discuss partnering with Moretrench on your next micropile project, please fill out our contact form, and we will be happy to get back to you as soon as possible.