Effectiveness of small-diameter timber piles to enhance the bearing capacity of micropiled foundation in soft clays

• Gelam wood ( Melaleuca cajuputi ) and Bornean ironwood ( Eusideroxylon zwageri ) effectively enhance the bearing capacity as micro-pile foundations in soft clays. • Ironwood columns combined with Gelam wood micro-piles (IMP) offer sustainable solutions as alternatives to concrete-based foundation systems. • BCR value of IMP and FMP tends to increase constantly for larger pile number ( n pile > 9). • BCR value of IMP and FMP rise by approximately 2.5 times with greater micropile spacing, and declines at s/D = 9 due to the negative group effect. • The Mohr-Coulomb soil model provides reliable results on load transfer mechanisms and soil-structure interactions in foundation systems. Small-diameter natural timbers like gelam and ironwood have been widely use in constructing micropile foundations, particularly in undrained soft clay. However, the design approaches and analytical methods for micropile foundations using gelam and ironwood remain highly empirical, with limited studies investigating their load transfer mechanism. Their application often depends on empirical knowledge and field experience. In this study, a series of three-dimensional finite element analyses were conducted to simulate the actual arrangement and behavior of micropile systems, focusing on two foundation types utilizing gelam wood micropiles: ironwood with gelam wood micropiles (IMP) and concrete footing with gelam wood micropiles (FMP).The numerical results are initially validated through the field test data. According to the numerical results, for IMP models, load transfer begins with ironwood side friction, followed by tip resistance and additional base support from horizontal Gelam wood, while in FMP models, Gelam wood friction and tip resistance mobilize first, with the footing starting to contribute thereafter, enhancing bearing capacity and reducing settlement. Increasing the number of micropiles more than doubles the bearing capacity for both IMP and FMP models. Additionally, for configurations with four micropiles, a spacing-to-diameter ratio of six is optimal for maximizing bearing capacity and minimizing settlement.