Mechanical And Acoustic Behaviours Of Biomediated Residual Soil In Comparison With Sand

Lim, Jun Xian (2021) Mechanical And Acoustic Behaviours Of Biomediated Residual Soil In Comparison With Sand. PhD thesis, UTAR.

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Abstract

Microbial-induced calcite precipitation (MICP) emerged as an innovative and sustainable soil stabilisation technique. The progression of MICP research on soils containing fines is relatively slow compared to clean sands. No study prioritizing microstructural formation and deformation of MICP-treated residual soil was found. There is also no comparative study on the behaviours of MICP-treated residual soil and sand. The aim of this research was to investigate the microstructural formation (e.g. anisotropy and distribution of calcites) and deformation behaviours of MICP-treated residual soil in comparison with sand. In this research, a practical MICP treatment method for residual soil was suggested. Influences of consolidation stress on MICPtreated soils, and the progressive changes in deformation behaviours of MICPtreated soils were also examined through isotropic consolidation and undrained shearing in triaxial tests with mechanical and acoustic emission (AE) measurements. Microscopic and acid washing tests were conducted to examine micro-structural formation of soils. It was found that the deformation behaviour of MICP-treated residual soil was inherently anisotropic but MICPtreated sand behaved as an isotropic material, owing to their different soil fabrics. The consolidation properties of residual soils were markedly improved by MICP treatment. However, MICP only slightly altered the consolidation properties of sand due to the low cementation level in dense sand (Dr  82 %). As the consolidation stress reached 120 kPa (exceeding pre-consolidation pressure), the compressive resistance was contributed by calcite densification. In undrained shearing, MICP-treated residual soils experienced three changes namely: yielding (calcite de-bonding), instability by grains mobilization, and ultimate failure. MICP-treated sand manifested strain hardening with less significant shear strength improvement. This was attributed to the particle arrangement of dense sand which had more dominant effect compared to the weak calcite bonding by MICP. Major mobilizations in sand included the plastic slippage over adjacent particle surfaces and incipient dislocation at the interlocking point contacts.

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