Macro and micro properties of organic matter in hydraulic mud consolidation

Abstract

Due to the co-existence of multiple organics and multiple length scales of the structure, quantitative characterization of the microstructure of organic matter in hydraulic mud consolidations, and understanding the impact on its mechanical properties have been challenging topics. This article attempts to tackle the challenge using lab experiments and a data-constrained modelling (DCM) approach combined with multi-energy synchrotron-based X-ray micro-CT (computed tomography). In this paper, scanning electron microscopy (SEM) and other different technical means were combined to study the microstructure of hydraulic mud composition and distribution. One unmodified hydraulic mud and four remolded samples were analyzed in vacuum preloading tests corresponding to organic matter contents of 1.65%, 3.75%, 5.15%, 8.65%, and 11.15%, respectively. Organic matter plays a significant role in hindering the shear strength of consolidation. Macro- and microstructure under different pressures could be extracted by the DCM and X-ray CT. The DCM-reconstructed microstructure of fine-grained soil from hydraulic mud is presented by four groups: organic matter, two groups of minerals, and pores. Different groups are displayed with different colors, which could clarify the distributions and density degrees of each component (group). The macro- and microstructures and the distribution of organic matter were quantified and compared among groups. It was demonstrated that the mechanical properties of the organic matter were closely correlated to the meso- and nano-scale clusters of porosity and minerals. The variation of organic clusters with loading pressure, and the number of sub-macro organic clusters, were small. Three scales of organic cluster (40-400 μm, 4-40 μm, and 0.4-4 μm) changed visibly in consolidation at 200 kPa and 800 kPa. The analysis has shown that pressures of 100 kPa and 400 kPa could be used as two characteristic values of structure change of hydraulic mud, which perhaps matched the turning points of destruction. The DCM approach, combined with multi-energy synchrotron-based X-ray micro-CT presented here, are applicable in studying the relationship between the microstructure and macro-properties for various other engineering materials.