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Micro (Mini) Piles
Micropiles are small diameter piles that can be installed in almost any type of ground where piles are required, with design loads as small as three tons and as high as 500+ tons. Also known as minipiles, pin piles, needle piles or root piles, micropiles can offer a viable alternative to conventional piling techniques, particularly in restricted access or low headroom situations.
Important Terms
Structural Connections:The various connection details that attach micropiles to structures.
Soil/Rock Load Transfer Mechanism: The various means by which the load is transferred from the pile shaft to the soil or rock bearing strata.
Design Load: The working load of the pile. Test piles are usually tested to two times the static design load.
Types of Micropiles
• Pushed or Driven
• Compaction Grouted
• Jet Grouted
• Post Grouted
• Pressure Grouted
• Drilled, End Bearing
Micropile Applications
• Supporting New Loads in Congested Areas
• Seismic Retrofit
• Arresting Structural Settlement
• Resisting Uplift/Dynamic Loads
• Underpinning
• Excavation Support in Confined Areas
• Reticulated Pile Wall
Important Micropile Parameters
• Soil characteristics at pile shaft/soil interface
• Rock at pile tip
Micropile Design Steps
1. Geotechnical study
2. Determine load to be supported
3. Design pile-to-structure connection
4. Design pile-to-soil or rock load transfer
5. Develop a pile testing program
Typical Micropile Programs Involve
• Drilling holes, 2 inch to 12 inch diameter
• The construction of a pile shaft consisting of structural steel pipes, grout, steel sections and/or placement of reinforcing steel, as required by design
• The filling of the hole with high-strength cement grout
Micropile Quality Assurance/Quality Control
Test selected piles to two times the static design load using standard ASTMD113 pile load test criteria
Benefits of Micropiles
• High-performance
• Design loads from 3 to 500+ tons
• Can be readily designed for tension/uplift loads
• Appropriate for a wide range of ground conditions
• Suitable for low headroom and restricted access
• Low noise and vibration
• Can penetrate obstacles
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