Long-term extraction sequence optimization is an essential step in the development of mining projects. However, for dredge mined heavy mineral sands deposits this process still done manually as available software solutions are tailored to conventional open pit mines and are not applicable due to the constraints that come with dredge mining and the heavy mineral sands market. In this research an extraction sequence optimization model was developed that can take into account the mining and market constraints that come with the dredge mining of heavy mineral sands, based on flexible meta-heuristic methods. A comparison between the ant colony optimization and genetic algorithm methods showed better performance for the genetic algorithm. The genetic algorithm was validated using synthetic validation models and applied to a real dataset in a case study. The results show that the developed genetic algorithm model can take into account the necessary objectives of a spatially continuous mining path, maximum capacity of extraction and processing equipment, and fixed product offtake rates. The genetic algorithm model showed good performance and consistency at identifying the mining direction and the optimization of production and stockpiling profiles. However, errors between the optimized and ideal extraction sequences are still present in the validation study and the extraction paths show significant variance between different model runs. The developed model is in its current form a potentially useful tool for the selection of equipment and optimizing operational parameters such as the offtake rate. Through further work the accuracy of the optimization model can be improved and the variance in results be reduced. Furthermore, through extension of the optimization scope a broader optimization model could be created that does not just save time and labour, but also provides additional insights into risk and robustness. Additionally, through the implementation of additional factors a model could be created that not just optimizes the mining operation economically, but simultaneously minimizes the negative impacts of mining.

dataset: https://doi.org/10.4121/1d3885ff-dc9c-4d05-9e4d-2d8f562d9c8d ... Read more

Jet trenching operations in sandy seabeds have been extensively studied and are well understood, offering a preferred method for offshore cable installation due to its relatively low environmental impact. However, the transition to clay seabeds presents significant challenges, demanding a deeper comprehension of jet trenching dynamics in cohesive soils. Recognizing this need, DEME NL Offshore, a Dutch company specializing in offshore operations, seeks to develop a predictive model tailored for jet trenching in cohesive soil environments.

This thesis addresses the complexity of jet trenching in clay seabeds through a comprehensive computational fluid dynamics (CFD) modelling approach. Beginning with an extensive literature review, various methods for modelling jet trenching processes are explored, highlighting the critical parameters influencing trenching outcomes. While existing models primarily focused on jet penetration depth, this study identifies the need to integrate fluid dynamics principles and particle behavior to achieve a better understanding of jet trenching dynamics. A CFD model is developed to cover the fluid dynamics in the trench behind the jetting sword. Subsequently, a langrangian model is applied to determine the trajectory of cohesive particles of different diameter in the trench.

Key Findings:
• For the scenarios considered in this thesis, jet trenching in clay soils is not feasible by the accumulation of particles at the trench bottom before the cable touchdown point.

• Particle diameter significantly influences trenching outcomes, underscoring the importance of further investigation.

• Existing models inadequately account for clay block formation and behavior, indicating a gap in understanding.

• Empirical validation and field testing are essential to enhance model accuracy and reliability.

• Integration of field observations and experimental data can refine the model for real-world scenarios.

In response to these findings, recommendations for future research endeavors are proposed, emphasizing the importance of empirical validation and field testing to enhance model accuracy and reliability. By integrating field observations and experimental data, trenching models can be refined to better predict real-world trenching scenarios, thereby optimizing offshore cable installation processes.

In conclusion, this thesis contributes valuable insights into the challenges of jet trenching operations in cohesive seabeds and lays the groundwork for future research in the field. By addressing the recommendations outlined herein, future endeavors can advance trenching methodologies, ultimately improving the efficiency, reliability, and sustainability of offshore cable installation. ... Read more

Deep-sea mining (DSM) of polymetallic nodules involves the use of Seafloor Mining Tools (SMTs) that collect nodules from the seabed while separating and discharging excess water and sediment. This discharge generates sediment plumes, which can adversely affect deep-sea ecosystems through elevated concentrations of suspended particles. Understanding the parameters that control sediment plume formation is critical for developing responsible mining practices and minimizing environmental impacts before commercial exploitation begins.

This research investigates the influence of source velocity and release conditions on sediment plume dynamics, using a controlled experimental setup at the TU Delft Dredging Laboratory. To replicate realistic DSM scenarios, the existing setup was extended with a moving cart to simulate the SMT traversing the seabed, a factor identified as significant in recent studies on turbidity current generation. Unlike prior research that relied on dye tracers, this study employed actual sediment particles—glass beads suspended in water—allowing for more representative observations of plume behavior.

The experimental setup consisted of a 25 m³ modular tank, with the moving cart connected to vertical supports holding various diffuser configurations. Sediment mixtures were prepared in a separate tank to ensure constant suspension. Key variables included source velocity, sediment mixture concentration, discharge geometry, and discharge velocity. A total of 18 experiments were conducted to capture the effects of cart speed and sediment concentration while maintaining a constant sediment flux. Measurements included ultrasonic velocity profiling for turbidity currents, sediment traps for quantifying deposition, and video documentation for visual inspection.

Results show that source velocity significantly affects the formation and propagation of sediment plumes. At lower source velocities, observed trends aligned with previous research, with sediment plumes forming and advancing along the seabed. However, at higher source velocities, a new regime emerged: turbidity currents were not observed, and sediment remained suspended higher in the water column. In a real DSM scenario, this could lead to passive sediment transport over longer distances, potentially increasing ecological exposure. Furthermore, none of the experiments exhibited turbidity currents advancing ahead of the impingement zone, suggesting reduced direct interaction between the SMT and the sediment plume.

These findings indicate that controlling SMT source velocity and discharge conditions could mitigate the lateral spreading of sediment plumes, offering a pathway toward more environmentally responsible mining operations. The study contributes empirical data on plume dynamics under varying operational conditions and highlights the importance of including moving-source effects in experimental assessments. This knowledge can inform guidelines for DSM deployment, aiding both regulators and industry in minimizing environmental impact while advancing technological feasibility.
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