Improved Settlement Modeling of Leca Column–Raft Systems in Soft Clay: Influence of Friction Angle and Material Properties

Abstract

Stone columns are widely recognized as an effective ground improvement technique to enhance the bearing capacity of soft clay, reduce compressibility, and accelerate consolidation by providing drainage for excess pore water. Conventional columns are typically filled with coarse aggregates, but increasing attention is now given to sustainable and lightweight alternatives. This study investigates the use of Lightweight Expanded Clay Aggregate (LECA) as filler material in column raft systems. Numerical modelling was performed in PLAXIS 3D (2020), with LECA represented by the Mohr-Coulomb model and soft clay by the Hardening Soil model. Drained analysis was adopted to capture long-term settlement behaviour. A comprehensive parametric study examined the effects of area replacement ratio, raft thickness, and internal friction angle on settlement performance. The novelty of this research lies in the development of two predictive models for estimating settlement in LECA-filled column raft systems. Unlike previous studies, the proposed models extend the existing Settlement Prediction Model (IP_CR-2019_0349) by incorporating a wider range of LECA properties, including internal friction angle and modulus, which vary with production sources. The validated design chart provides practical guidance for engineers in applying LECA columns to improve soft clay foundations. Overall, the study demonstrates that LECA is a lightweight, durable, and environmentally friendly alternative to conventional aggregates, with strong potential for sustainable ground improvement.