Hollow Bars in Micropile Construction

Micropiles are rapidly gaining popularity for foundations in urbanized areas or in locations with low headroom and restricted access. They are an ideal choice for underpinning or emergency repairs because they can be installed in virtually any ground condition with minimal vibration and disturbance to existing structures.

Self drilling hollow bolts are ideal for micropiles, soil nails, and tie down and tie back anchors in difficult ground conditions like weathered and decomposed rock, round gravel, sand and clay soils for either permanent or temporary use.

The use of hollow bars in micropiles has greatly increased over the past ten years. Hollow bar micropile construction, also known as self-drilled, is becoming a popular option because it allows faster installation processes and ground improvement at the same time. Despite the growing demand for hollow bar micropiles, little work has been devoted to evaluating the nominal bond strength between the micropile grout and the surrounding soil, especially in clay soils.

The hollow bar, used as both drill rod and grout conduit, is left in the ground as reinforcing steel to transmit compression, tension, and lateral forces. Hollow bars have a larger section modulus than solid bars which increases their bending capacity. With the continuous tremi-grout injection, 100% grout cover and therefore excellent corrosion protection is accomplished, similar to reinforcing steel in concrete.

Hollow bar micropiles are gaining increasing acceptance by engineers and the industry.

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