http://hdl.handle.net/10453/35200 2026-08-10T03:25:09Z http://hdl.handle.net/10453/195400 Title: A NOVEL MULTILAYERED SOIL CONSOLIDATION SOLUTION BASED ON THE SPECTRAL METHOD TO PREDICT LONG-TERM SETTLEMENT Authors: Xu, B; Indraratna, B; Rujikiatkamjorn, C; walker, R Abstract: ABSTRACT: The consolidation of soft soils is a critical consideration for infrastructure stability, particularly in coastal regions where soft ground typically comprises multiple layers with varying properties. Creep plays a significant role in consolidation and is essential for accurately predicting long-term settlement in viscous soils. Accurate settlement prediction is influenced by loading patterns, soil stratification, and drainage boundary conditions. Despite advancements in theoretical approaches, comprehensive analytical solutions that integrate the effects of multilayered soil profiles and general drainage boundaries remain limited. This study presents a general spectral-based method for analysing the consolidation behaviour of multilayered soils under various loading patterns and drainage boundary conditions, including scenarios with or without prefabricated vertical drains (PVDs), impeded drainage, and time-dependent drainage conditions. The spectral-based solutions employ matrix operations to express the excess pore water pressure (EPWP) as unified solutions across multiple soil layers, effectively capturing the effects of complex boundary conditions. Based on this framework, a simplified Hypothesis B method is proposed to calculate long-term consolidation settlement. The proposed methods are validated against previous analytical solutions for special cases and field data, demonstrating their accuracy and flexibility in predicting EPWP dissipation and settlement. The study provides a more realistic representation of consolidation behaviour by incorporating general drainage conditions expressed as Robin Boundary Conditions (RBCs). The findings offer practical insights for optimizing engineering designs and improving settlement prediction in layered viscous soil foundations, offering a versatile and robust tool for geotechnical engineers to address the complexities of multilayered soil systems under diverse loading and drainage conditions. 2026-06-14T00:00:00Z http://hdl.handle.net/10453/195399 Title: Subgrade Soil Fluidization under Cyclic Loading of Heavy-haul Trains and Preventive Measures Authors: Indraratna, B; Atapattu, S; Rujikiatkamjorn, C; Arivalagan, J; Singh, M; Kelly, R Abstract: ABSTRACT: Soft soil deposits along Australia’s low-lying coastal regions pose significant challenges for the safety and stability of rail infrastructure. The undrained instability of these often saturated formations exacerbated by excess pore water pressure (EPWP) in tandem with upward hydraulic gradients under dynamic wheel loading is the primary cause of soil fluidization (mud pumping). This paper identifies critical ground (subgrade) conditions prone to fluidization and proposes novel solutions to ensure an efficient and safe operation of rail tracks. Using an iconic custom-built Dynamic Consolidation Apparatus (DCA) capable of assesiing the fluidization potential, laboratory testing under cyclic loading was conducted to investigate: (i) the occurrence of subgrade instability under various drainage conditions and intermittent cyclic loading with rest periods, (ii) the role of drainage geotextiles in stabilising the subgradeballast interface, and (iii) the effectiveness of a combined system of a prefabricated vertical drain (PVD) and a geocomposite (i.e. an impervious membrane sandwiched between two drainage geotextiles). Experimental results indicated that prior to fluidization, the water content in the upper soil layer approached its liquid limit due to internal moisture redistribution, effected by very fine particles from the bottom half of the test specimen migrating towards the top surface. This unique failure mechanism, characterized by fluidised soil (slurry) being pumped to the surface under high EPWP gradients, differs from traditional cyclic undrained yielding. The inclusion of the geocomposite at the ballast-subgrade interface could effectively impede particle migration by reducing the EPWP gradients. The findings also revealed that longer rest periods between loading cycles could reduce the likelihood of mud pumping. Additionally, PVDs on their own significantly reduce EPWP build-up in thicker soil layers. A case study at the town of Sandgate, NSW, demonstrated the effectiveness of relatively short PVDs (approx. 6m) in enhancing the stability of a track built on deep estuarine clay deposits (> 15m). 2026-06-14T00:00:00Z http://hdl.handle.net/10453/195299 Title: Enhanced dewatering of municipal activated sludge using aluminum formate: Performance and mechanisms Authors: Chen, C; Guo, Y; Lu, Y; Zhang, X; Nghiem, LD; Liu, Q Abstract: The efficient dewatering of municipal activated sludge (MAS) remains a critical challenge, primarily due to the intricate water-binding forces within extracellular polymeric substances (EPS) and pore blockage of sludge colloids. Conventional agents like polyaluminum chloride (PAC) and aluminum sulfate (AS) offer limited effectiveness due to the instability of hydrolyzed aluminum species and the aggregation of sludge colloids that block pores. To tackle this problem, this study introduced aluminum formate (AF) as a novel conditioner, with AF agents synthesized at various HCOOH/Al molar ratios (1.5-4.0). Among these, AF-2.5 (with an HCOOH/Al molar ratio of 2.5) demonstrated optimal performance, remarkably reducing water content (WC) from 85.3 ± 2.3 % to 43.3 ± 2.1 %, capillary suction time (CST) from 89.5 ± 2.0 s to 8.9 ± 1.5 s, and bound water content from 2.09 ± 0.3 g/g dry solids (DS) to 0.53 ± 0.2 g/g DS. Mechanistic investigations revealed that the formate anions in AF play a crucial role in stabilizing the highly charged Keggin-Al<inf>13</inf> species during hydrolysis. This stabilization enables multiple synergistic effects: enhanced charge neutralization, the formation of a structural skeleton, and disruption of EPS. The three-dimensional (3D) porous structure of AF promotes water release while effectively preventing pore clogging. Tafel analysis further revealed that AF-2.5 exhibited the lowest corrosion current (1 ×10^-9A/cm²), significantly outperforming PAC and AS (∼1 ×10^-8 A/cm²), indicating superior corrosion resistance and reducing the risk of infrastructure degradation. This research highlights AF-2.5 as a sustainable alternative to traditional agents, offering both superior dewatering efficiency and excellent ecological compatibility. 2025-10-01T00:00:00Z http://hdl.handle.net/10453/195264 Title: Effects of Hydraulic Retention and Inorganic Carbon During Municipal Wastewater Treatment Using a Microalgal Bacterial Consortium Authors: Thiruchchelvam, T; Johir, M; Krishna, KCB; Sathasivan, A Abstract: Municipal wastewater (MWW) was treated using a microalgal–bacterial consortium without mechanical aeration. An inoculum for the reactor was prepared by acclimatizing Chlorella vulgaris to MWW and supplementing with a small amount of activated sludge. The hydraulic retention time (HRT) and solids retention time (SRT) were progressively reduced from 6.67 to 1.17 d and from 10 to 6.67 d, respectively, to test the process robustness under realistic MWW operation. The COD removal efficiency was 88% at 0.23 kg-COD/m3/d. Mass balance suggested the major nitrogen and phosphorus removal mechanism as assimilation. A high percentage (80%) of oxidized nitrogen indicated an efficient nitrification at all HRTs. Inorganic carbon (IC) balance calculation explained the observed IC dynamics. The chlorophyll a-to-mixed liquor volatile suspended solids (MLVSS) ratio and percentage of nitrite responded to IC limitation and supplementation. The mixed liquor exhibited excellent settleability (sludge volume index: 42 mL/g) with dense algal–bacterial flocs. An increased organic loading rate, however, reduced daytime dissolved oxygen, suggesting limitation under non-aerated conditions. These findings demonstrate the potential of microalgal–bacterial systems to achieve efficient COD removal and nitrification at realistic HRTs without aeration while emphasizing the importance of IC management. 2026-12-24T00:00:00Z