Micropiles

Micropiles are small-diameter deep foundation elements that bypass poor bearing soils and transfer loads into a competent bearing stratum. They can be installed through almost any type of subsurface condition from sands to clay to bouldery soils to rock. Micropiling is accomplished using low-vibratory drilling techniques, a critical consideration when working around sensitive structures.  A history of successful design and installation makes Moretrench the micropile contractor of choice for many of our clients.

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/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.

Installation

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, micropile contractors grout the micropiles 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.

Applications

  • New building foundations
  • Bridge piers and abutment foundations
  • Retrofit of existing structures to withstand increased loading
  • Structural settlement control
  • Counteraction of uplift forces on structures
  • Tank and crane pad foundations
  • Seismic retrofit
  • To function as soldier piles for earth retention.
  • Slope stabilization
  • A-frame earth retention.

Advantages

  • 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 installed 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.