Micropiles are small diameter, drilled and grouted reinforced piles. Micropiles are non-displacement piles, usually 300 mm or less in diameter. The piles have a steel reinforcement achieved with a hi-tensile threadbar. Micropiles are designed as friction piles. EBS installs micropiles with specialized drilling equipment in sizes and configurations to match project scope and requirements.
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Micropiles are not end-bearing piles. They are friction piles. Micropile capacities are based on:
Grout-to-ground bond strength
Mechanical strength of the reinforcing bar
Grouting method used
Minimal Disturbance (adjacent structures & soil)
Ability to work in restricted areas
Large axial loads, moderate lateral loads
Can be installed in all soil types and ground conditions
Unbonded Zone / Overburden
Soil layers that do not have sufficient bearing capacity for the required loads. These layers are isolated from the micropile by the casing, which is usually left in place, and does not impact the capacity of the micropile.
Dense Bearing Strata
This dense soil layer or bedrock has sufficient depth to allow the development of the required bond length.
The casing is usually embedded 30 cm into the dense layer, ensuring isolation from the overburden. This also allows grouting of the micropile without affecting the overburden.
The required loading and the grout-to-soil/rock bond determine the bond length. (see the reference guide for examples) link to reference guide
The threadbar transfers the load from the structure to the bearing strata. Threadbar and couplers allow EBS to couple and terminate sections together in the field as needed without welding. With this modular system, we can adapt to site conditions like low headroom, reach the required depth, and terminate without welding.
MICROPILE DRILLING ACTION
EBS drills micropiles using a down-the-hole hammer and casing. The drill rig pushes the casing down and rotates it, isolating the drilling operation from the surrounding soil and preventing material sloughing into the hole. The down-the-hole hammer is powered by compressed air, which fires the carbide button bit, pulverizing soil and rock in the drill path. The hammering action happens at depth and high frequency, making it more efficient, requiring less power, and developing minimal vibration to surrounding soils and structures. The spoils are forced to the surface through the annular space between the hammer and casing by the high-pressure air.
MICROPILES AND OBSTRUCTIONS
A distinct advantage of micropiles is how they handle obstructions in the soil. Common obstructions like buried concrete and boulders are no problem for micropile equipment. In most cases, the tooling and techniques used to develop the micropile bond length are the same to get through obstructions. Site-specific borehole information prepares EBS for unique site conditions.