Smart Soil Improvement: The Use of Rigid Inclusion for the Soil Consolidation-Paper

Paper

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Rigid inclusions improve soft ground by installing concrete or cement-mortar columns that are substantially stiffer than the surrounding soil. Typically 300–800 mm in diameter, they occupy only about 2–10% of the treated soil volume. They are constructed using continuous flight auger (CFA) or displacement pile (DP) techniques; concrete is pumped through the hollow drilling tool as it is withdrawn. The method can use large rigs or smaller equipment suitable for restricted urban sites.<br /><br />The paper describes two applications. In Florence, rigid inclusions helped restore the Lungarno Torrigiani embankment after its river wall collapsed in 2016, displacing soil toward the Arno. Small rigs installed 764 columns, each 300 mm in diameter and approximately 7.5 m long, to consolidate the displaced backfill and provide a stable working platform for subsequent repairs. These works formed part of a broader scheme to support and protect the historic wall and nearby structures.<br /><br />At the Orogel plant in Cesena, 486 CFA columns, 800 mm in diameter and up to 36.6 m deep, were installed beneath a mat foundation for a 30 m-high automated cold store. The inclusions were designed to reduce and control total and differential settlement, rather than to act as structural foundation elements. The project demonstrated rapid production, with a 36.6 m column drilled and cast in about 37 minutes.<br /><br />The cases show that rigid inclusions can be adapted to both emergency remediation and large new developments. The paper highlights their efficiency, versatility, and suitability for urban settings, as well as environmental advantages: limited site installation, no drilling fluids, and no contamination of excavated soil by support fluids.

Keywords

rigid inclusions

soft ground improvement

concrete columns

cement-mortar columns

continuous flight auger

displacement pile

settlement control

embankment stabilization

mat foundation

urban ground remediation