Effectiveness of Head-Enlarged CDM Columns in Evaluating Settlement of Improved Grounds-Paper

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The paper evaluates Point Foundation (PF), an improved cement deep mixing (CDM) method that creates columns with enlarged heads, tapered transitions, and narrower tails. Unlike conventional constant-diameter CDM columns, PF columns place more reinforcement in the shallow, weaker soil layers, where footing-induced stresses are greatest.<br /><br />The authors introduce a simple procedure for selecting PF column dimensions while keeping column volume equal to that of a conventional CDM column. They compare predicted footing settlements using two established methods: three-dimensional elastic strain integration and the Schmertmann method.<br /><br />The case study examines a footing at the Jincheon Energy Factory project in South Korea. For the comparison, the footing, soil profile, loading, number and stiffness of columns, and column volumes were held constant. Results show that PF columns can reduce settlement relative to conventional CDM columns. For the analyzed footing, the best-performing configurations produced settlements approximately 90–93% of those for CDM columns—about a 7–10% reduction. The optimal head-to-tail diameter ratio was around 1.5 across the column spacings considered. The two settlement methods showed similar trends when calculations extended to two footing widths below the foundation.<br /><br />The authors also assessed material savings. To achieve the same settlement as conventional CDM columns, optimized PF columns required roughly 10% less mixed material in the case study; estimated savings varied with column spacing and reached approximately 11.5–12.5% in the analyses.<br /><br />Overall, head-enlarged PF columns can improve settlement performance or reduce material use beneath shallow foundations. The findings are based on analytical comparisons for a specific footing and soil profile, so performance and savings may differ under other site conditions.

Keywords

point foundation

cement deep mixing

settlement reduction

head-enlarged columns

shallow foundation

soil improvement

footing settlement

column geometry

material savings

Korean case study