Micro-piles, also known as mini-piles, (and less commonly as pin-piles, needle-piles, or root-piles) are deep foundation elements constructed using high-strength small-diameter steel casing and/or threaded bar. Capacities vary depending on the micro-pile size and subsurface profile. Allowable micro-pile capacities in excess of 1,000 tons have been achieved.
The micro-pile casing generally has a diameter in the range of 3 to 10 inches. Typically, the casing is advanced to the design depth using a drilling technique. Reinforcing steel in the form of an all-thread bar is typically inserted into the micro-pile casing. High-strength cement grout is then pumped into the casing. The casing may extend to the full depth or terminate above the bond zone with the reinforcing bar extending to the full depth. The finished micro-pile resists compression, uplift/tension, and lateral loads and is typically load tested in accordance with ASTM D 1143 (compression), ASTM D 3689 (uplift/tension), and ASTM D 3966 (lateral). The technique has been used to support most types of structures. Linde-Griffith Construction Company’s micro-pile drill rigs allow installation in restricted access, low headroom interiors, permitting facility upgrades with minimal disruption to normal operations.
Linde-Griffith Construction Company has the capability of combining our micro-pile technology with one or more of our other ground modification techniques to meet unique or complex project requirements cost-effectively and efficiently. Lines of micro-piles spanned by wooden lagging can be ideal where excavation walls are required in low headroom and other confined areas. Post-grouting within the bond length can increase frictional forces with surrounding soils, thus achieving greater capacity. Micro-piles can serve to “stitch” the soil together, within predicted shear zones to enhance mass stability. In liquefiable profiles micro-piles can transfer loads to competent bearing strata to conform to seismic design requirements. Foundation underpinning is often performed using micro-piles or other deep foundation techniques adjacent to planned excavations.
For planned foundations in areas with multiple underground utilities the cost of a cast-in-place piling system may often be substantially increased by the expense of utility re-routing, creation of adequate access, and sometimes even a shutdown of facility operations. With Linde-Griffith Construction Company’s micro-piles these complications are rarely an issue when performing foundation repair. Small diameter micro-piles can be installed while avoiding existing utilities. Linde-Griffith Construction Company works closely with engineers, contractors, and owners to help to ensure that micro-pile installation minimizes impact on facility operations. Moreover, micro-piles greatly alleviate the quality assurance concerns associated with cast-in-place piling in weak soils.