Micropiles - Threaded Bar

Micropiles are foundation elements of small diameters up to 300 mm, which transfer tension, compression as well as alternating loads into the soil through skin friction. They are usually not tensioned and act as a passive foundation system. Micropiles are in accordance with EN 14199 and FHWA-NHI-05-039.
Micropiles have specific advantages over the conventional systems. Typical applications are uplift control, foundations, underpinning, installations in confined spaces and near existing structures, restricted access areas, remote locations, places where vibration or noise needs to be minimized and in contaminated soils (less spoil due to small diameters).
Depending on the design working life and aggressiveness of the environment, micropiles can be broadly classified as Temporary (up to 2 years) and Permanent (100 years).

Standard Corrosion Protection (SCP)

Solid bar (mono), hot rolled, with continuous thread serves as the steel reinforcement (tendon). SCP micropiles can be used for permanent application in low corrosive environment for compression load case. For tensile load case in low corrosive environment, it can be used for temporary application with full load capacity, or for permanent application with reduced load capacity (due to crack width limitation). Corrosion protection is achieved by grout cover thickness and crack width limit.

Double Corrosion Protection (DCP)

For permanent applications where design working life is more than 2 years or sufficient protection is not possible by SCP system due to aggressive soil conditions, a Double Corrosion Protection (DCP) shall be used.
By using a DCP system, micropiles can be used for permanent application (more than 100 years) irrespective of corrosiveness of environment and direction of load. Threaded solid bar placed inside a HDPE or PVC corrugated sheathing which is factory grouted serves as the reinforcement bar (tendon).
Micropiles

Benefits of Threaded Bar System

  • Steel bars can be cut and coupled without any additional threading at site to connect couplers
  • Splicing of threaded bars using coupler is simple
  • Threads being hot rolled and with coarse pitch make it screw-able even when make it screw-able in challenging site conditions, thus making it suitable for geotechnical applications.
  • High relative rib area provides maximum bond stress between steel bar and cement grout

Threaded Bar Types

  • 500/550: Ø16 - 75 mm
  • 550/620: Ø20 - 75 mm
  • 670/800: Ø18 - 75 mm
  • 950/1050: Ø18 - 75 mm
For more details on Threaded BarClick Here

Other Corrosion Protection Systems

Apart from SCP and DCP systems, other corrosion protection systems are available. This is to enhance the design working life compared to an SCP system and can be considered as a semi-permanent system.

  • Hot dip galvanizing of threaded bars in accordance to EN 1461, BS729 or ASTM A153
  • Epoxy coating of threaded bars in accordance to BS 7295, ASTM A934 or ASTM A775

Minimum Drill Hole Diameter

SCP & DCP micropiles depend on ground conditions, drilling equipment setup and design considerations. See below the minimum drill hole diameters.
table-micropiles