Micropiles / Tie-downs
Micropiles are small-diameter (usually less than 12 inches in diameter), drilled, and grouted foundation elements with design loads ranging from 50 to 400 tons. The structural load is principally carried in steel reinforcement and transferred by friction into the surrounding ground. Micropiles support both tension and compression loading and are cast into pile caps for load transfer to the above-grade structure. The piles typically comprise heavy reinforcing bars (up to 3.5 inches in diameter) grouted in place, with steel casing extending from the pile cap to the top of load-bearing soils. Specialized drill rigs allow construction in limited-access conditions. The equipment can pass through building doorways and operate in a headroom of 9 feet, making Micropiles ideally suited for structural upgrades, seismic retrofit, and underpinning of existing structures.
Tie-down anchors are small-diameter friction elements designed and constructed for only tensile loading. Structural capacity is provided by either reinforcing bar or high-strength strands, which are grouted for load transfer to load-bearing formations.
Tie-downs are typically pre-loaded against structures and locked off to maintain resistance against uplift loads.
Micropiles and Tie-downs are constructed using similar equipment. Rotary hydraulic drills advance the bored hole using sectional lengths of drill steel. Rush thread jointed steel casing can be advanced simultaneously as needed to maintain the hole’s stability. The core reinforcing is placed into the drilled hole and tremie grouted. The casing is typically withdrawn to the top of the bond zone for Micropiles, and completed extracted for Tie-down applications. This construction method permits installation in almost any ground conditions, including cohesive and caving granular soils below groundwater as well as rock. Downhole percussion hammers are used for drilling through high-strength formations. Leveraging design-build expertise, Malcolm Drilling delivers efficient foundation solutions tailored to each project, including cost-effective alternatives like Micropiles and Tie-downs, suitable for challenging geotechnical conditions.