What is a Micropile?
Micropiles are small diameter (usually less than 12 inch 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 surrounding ground. Micropiles support both tension and compression loading and are cast into pile caps for load transfer to above grade structure. The piles typically comprise a heavy reinforcing bar (up to 3.5 inch diameter) grouted in place with steel casing extending from pile cap to top of load bearing soils. Specialized drill rigs allow construction in limited access conditions. The equipment can pass through building doorways and operate in headroom of 9 feet, making Micropiles ideally suited to structural upgrades, seismic retrofit and underpinning of existing structures. Our design-build expertise allows us to provide owners with the most efficient foundation solution for every project in the most difficult ground conditions. Tiedown 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.
Tiedowns are typically pre-loaded against structures and locked off to maintain resistance against uplift loads.
Micropiles and Tiedowns 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 stability. The core reinforcing is placed into the drilled hole and tremie grouted. The casing is typically withdrawn to top of bond zone for Micropiles, and completed extracted for Tiedown applications.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. Micropiles and Tiedowns can provide a cost effective alternate to hand mined underpinning, conventional drilled piers or augercast piling methods in challenging geotechnical conditions.