Neelima Satyam

Soil reinforcement is a potential solution to mitigate wind‐induced sand erosion. Previously, microbiologically induced calcite precipitation (MICP) has been used to control sand erosion and enhance the strength of soil particles. However, it has limitations. The present study explores the effectiveness of an alternative biologically inspired method, enzyme‐induced carbonate precipitation (EICP), in enhancing the stability and strength of aeolian sand. The novelty of this study lies in the identification of an optimal dosage through a multiscale evaluation of EICP performance, specifically targeting high‐velocity erosion resistance (up to 30 m/s), surface strength uniformity, penetration depth, mechanical reinforcement and the explicit characterization of calcite thermal stability. Plant‐based Jack bean urease was used at varying concentrations with a 1‐M cementation solution. To mitigate wind‐induced sand erosion, surface treatment was performed using the spray method. The treated specimens were subjected to a wind tunnel test, a surface strength test, a calcite test, scanning electron microscopy (SEM) analysis and energy‐dispersive X‐ray spectroscopy (EDX) analysis. To evaluate the strength of soil particles, unconfined compressive strength (UCS) and split tensile strength (STS) samples were treated using the stopped and gravity flow methods and were tested for UCS, STS, ultrasonic pulse velocity (UPV) and calcite formation. Additionally, to assess the thermal behaviour of the formed calcite, thermogravimetric analysis (TGA) was performed. The study demonstrated that the EICP method effectively mitigates erosion up to a wind speed of 30 m/s and achieves optimal soil strength, with a maximum UCS value of 756 kPa and 5% calcite formation. However, practical implementation considerations, including extended treatment duration and long‐term durability under field conditions, require further investigation before large‐scale application.

The frequency of extreme precipitation events is increasing globally, leading to more frequent catastrophic debris flows. The high velocity and long runout distances of debris flows cause damage to infrastructure and loss of life. Despite ongoing scientific efforts, understanding the debris‐flow initiation mechanisms and developing reliable early‐warning thresholds remain challenging due to the limited availability of data from extreme historical events. This study develops a numerical modelling framework to analyse the initiation and runout dynamics of an extreme‐precipitation‐induced debris flow and to derive corresponding Intensity‐Duration (ID) thresholds. The 6 August 2020, Pettimudi, Kerala, debris flow is used as a case study. The model correctly reproduces the debris‐flow arrival time, peak velocity (~9 m/s), and deposit thickness (7–8 m). The resulting ID thresholds reflect the unique characteristics of extreme events and differ noticeably from regional thresholds derived from historical cases. In addition, the framework developed in this study can help derive ID thresholds for debris flows in the absence of historical data.

The large-scale generation and improper disposal of Iron Ore Tailings (IOT) pose significant environmental and geotechnical challenges, necessitating sustainable reuse strategies. This study investigates the geopolymer-based stabilization of IOT using alkali-activated binders composed of Ground Granulated Blast Furnace Slag (GGBS) and Fly Ash (FA). The IOT content was fixed at 90%, while FA and GGBS (10% total) were varied in three proportions: 90:2.5:7.5, 90:5:5, and 90:7.5:2.5 (IOT: FA: GGBS). Sodium hydroxide (NaOH) solutions of 2.5 M and 5 M were combined with sodium silicate (Na₂SiO₃) at NaOH: Na₂SiO₃ ratios of 1:1 and 2:1. Mechanical testing revealed that the 90:2.5:7.5 mix activated with 5 M NaOH at a 1:1 ratio achieved the highest 28-day strengths of 11.14 MPa (UCS) and 0.93 MPa (STS). Statistical analysis (ANOVA) confirmed curing duration and NaOH molarity as the dominant parameters governing strength development. Microstructural investigations (XRD, SEM, EDS) demonstrated that enhanced performance is associated with the formation of hybrid C-A-S-H and N-A-S-H gel networks, resulting in matrix densification and improved interparticle bonding. Toxicity Characteristic Leaching Procedure (TCLP) results verified reduced heavy metal leachability within regulatory limits. The findings establish that geopolymerization enables effective transformation of IOT into a high-performance, cement-free geomaterial, offering a sustainable pathway for large-scale tailings valorization and construction applications.

Entrainment significantly modifies the dynamics and runout of debris flows, yet the combined influence of water content, bed properties, and particle-scale characteristics remains poorly constrained. Building on our previous flume-based framework, this study integrates mesoscale flow experiments with micromechanical analysis of debris materials including grain shape, roughness, and fragmentation using X-ray micro-CT imaging. A series of controlled flume experiments were performed using erodible sand beds (4 cm thick) prepared via mist pluviation to minimize segregation. Sixteen flow tests were conducted across a range of volumetric water contents (20–50%), capturing high-speed flow kinematics, entrainment depth, and deposit morphology. Complementary micro-CT imaging of fluvial and colluvial grains enabled quantification of particle shape (sphericity, aspect ratio, surface irregularity) and its potential role in erosion thresholds.Results show distinct morphological transitions with increasing water content. At low w/c (20–24%), flows exhibited limited mobility and formed short, conical lobes with minimal scouring. Around intermediate w/c (~28%), reduced bed dilatancy and moderate pore pressure generated thicker but shorter deposits, indicating partial suppression of entrainment. At higher w/c (30–50%), enhanced lubrication and basal shear promoted deeper scouring, larger entrainment volumes, and substantially longer runouts with wide, flattened deposits. A parabolic relationship emerged between bed water content and entrainment rate, highlighting the nonlinear coupling between fluid fraction, granular collisions, and bed resistance. Deposits exhibited poor sorting and layered structures similar to natural debris flows, confirming dynamic similarity. Preliminary micro-CT analyses suggest that more angular and elongated grains exhibit larger contact stresses and higher resistance to dislodgement, whereas smoother grains mobilize earlier potentially explaining material-dependent variability in erosion observed across tests. Ongoing work aims to link shape descriptors directly with measured entrainment rates. This combined experimental–micromechanical approach advances our understanding of debris-flow erosion by bridging particle-scale processes and mesoscale dynamics. The results provide new insights for improving entrainment parameterization in debris-flow models and for developing more reliable runout predictions in geophysical hazard assessments.