Helical Rigid Inclusion Ground Improvement Systems for Settlement Mitigation in Soft Soils-Paper

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The paper introduces Helical Rigid Inclusion (HRI) systems as an alternative to conventional grout-column ground improvement for limiting settlement in soft, compressible soils. HRIs are steel, helical pile-like elements installed in arrays through weak soils into a competent bearing layer. Unlike foundation piles, they are not connected directly to the structure. Instead, inclusion caps and a granular load transfer platform (LTP) distribute structural loads among the elements and surrounding soil.<br /><br />Design focuses on settlement of the combined HRI–LTP–soil system, alongside checks of each element’s geotechnical and structural capacity. Cap size and LTP reinforcement can be adjusted to improve load transfer and optimize element spacing. Construction typically involves installing the HRIs with hydraulic rotary equipment, setting the caps, and placing and compacting the LTP. Real-time installation torque helps verify capacity and adapt element embedment to variable bearing-layer depths.<br /><br />Potential benefits over conventional rigid inclusions include simpler access to constrained or weak work sites, reduced need for extensive working platforms, smaller equipment and lower mobilization costs, and flexibility in cap and LTP design. Steel shafts may also offer advantages under seismic bending and tensile stresses. However, smaller HRI shafts displace less soil, potentially producing less densification and reduced mitigation of liquefaction risk than larger grout columns. Lateral loading behavior requires further research.<br /><br />A 2021 U.S. highway embankment project used 175 HRIs beneath an LTP reinforced with three geogrid layers. The system was selected because heavy grout-column equipment could not readily access the weak ground and because the competent bearing layer varied in depth. The case illustrates the value of HRIs where site access is difficult and element lengths must be tailored to subsurface conditions. Overall, the paper presents HRIs as a promising alternative whose performance depends on appropriate design, installation tooling, and site-specific assessment.

Keywords

Helical Rigid Inclusion

ground improvement

soft soils

settlement control

load transfer platform

geogrid reinforcement

bearing layer

installation torque

constrained work site

geotechnical design