The growing demand for large-scale geological hydrogen storage has driven the exploration of resource-efficient methods for repurposing existing underground infrastructure. This study assesses the technical feasibility of converting underground oil storage caverns into lined rock caverns (LRCs) for hydrogen storage and evaluates the material costs associated with two proposed design schemes. Two retrofit schemes were analyzed numerically using parameters derived from an existing LRC demonstration project. The ultimate and maximum operating gas pressures were determined using the uplift failure model, considering cavern burial depth and the mechanical properties of the surrounding rock mass. Structural responses under pressurization were evaluated, followed by a comparative assessment of concrete and steel liner costs. The results indicate that dividing the original cavern into multiple lined sub-caverns separated by concrete pillars improves structural performance and reduces the maximum tensile stress in the steel liner, although tensile-stress concentrations may develop in the concrete pillars. Meanwhile, the proposed Single-cavern scheme offers significantly higher hydrogen storage capacity with lower concrete requirements but a larger steel liner area. A supplementary short-term cyclic thermo-mechanical analysis revealed response-dependent differences from the corresponding static analysis. The static analysis overestimated the maximum tensile stress in the steel liner and the plastic-zone volume in the concrete liner, while underestimating the plastic-zone volumes in the rock-mass and total system. These findings highlight the importance of cyclic thermo-mechanical effects on LRC response while supporting the applicability of static analysis as a preliminary assessment approach, provided that an adequate safety margin is adopted when determining the maximum operating gas pressure. Additionally, in both schemes, the tensile-stress level in the steel liner remains low, suggesting significant potential for liner optimization in material selection and liner thickness. Overall, the results indicate that repurposing oil storage caverns as LRCs is a technically feasible retrofit option, while overall economic feasibility should be further evaluated through life-cycle cost analysis.

With mines reaching into greater depth, problems with violent failures become more prevalent, such as rockbursts. To assess the potential for such occurrences, understanding energy dynamics is crucial. This study delves into the impact of excavation shape, aspect ratios, inclined angles and in-situ stress on dissipated plastic energy and released kinetic energy through numerical simulations. Detailed analyses of plastic zone around rectangular and elliptical excavations, varying in aspect ratios, unveiled the distinct patterns of tensile and shear plastic zone. Quantitative assessments of dissipated plastic energy and released kinetic energy highlighted contrasting behaviors between rectangular and elliptical excavations across various aspect ratios. Although the relationships between these energies and excavation parameters are found to be intricate, it becomes evident that: with an increase in the aspect ratio, both shear and tensile plastic zones exhibit a growing trend, and their distribution shows a high degree of consistency with regions of energy concentration. When the aspect ratio is below 1.5, elliptical excavations release slightly less kinetic energy than rectangular ones. Beyond 1.5, this relationship reverses. Moreover, upon exploring inclined angles, critical angles were identified, delineating points where the influence of aspect ratio nearly diminishes. Under the given in-situ stress conditions, approximately 50° and 20° serve as the critical angles for dissipated plastic energy and released kinetic energy, respectively. Changes in the degree of in-situ stress anisotropy have a limited impact on the overall energy trends but significantly alter the critical values of aspect ratio and inclination angle. When the in-situ stress ratio matches the excavation aspect ratio, both forms of energy reach their minimum values. These findings illuminate the complex interplay between excavation geometry and energy dissipation, offering invaluable insights for designing effective excavations and devising strategies to mitigate failures.

Large-scale underground hydrogen storage is expected to play an important role in balancing variable renewable energy supply and future hydrogen demand. In regions dominated by hard rock, lined rock caverns (LRCs) provide a potential storage solution. Repurposing existing underground oil storage caverns could further reduce the need for new excavation; however, these caverns were not originally designed for high-pressure gas storage and commonly have shallow cover and elongated geometries that differ substantially from conventional LRCs. This thesis investigates the feasibility and key engineering considerations of converting such oil storage caverns into LRCs for underground hydrogen storage.

The research is developed through three interconnected numerical studies. The first provides a geological foundation by investigating how in-situ stress and rock mass discontinuities influence anisotropic cavern deformation during excavation. The results demonstrate that joint orientation and stiffness can substantially modify both the magnitude and spatial distribution of cavern deformation, highlighting the importance of geological structures in assessing existing caverns. The second study serves as a pilot geometric-design investigation, examining the effects of cavern-bottom geometry and sliding layer stiffness on steel liner stress and interface displacement. Smoother bottom transitions generally reduce local liner demand, particularly when interface restraint is high, although reductions in stress and interface displacement do not necessarily coincide. These two studies provide geological and geometric understanding for the central investigation of oil-cavern repurposing.

Building on these preliminary studies, the main investigation evaluates two concepts for converting shallow, elongated oil storage caverns into hydrogen-storage LRCs: a Multi-cavern scheme, in which the existing excavation is divided into multiple lined sub-caverns, and a Single-cavern scheme, in which one continuous lined volume occupies the existing cavern. A modified uplift failure model is used to obtain a preliminary maximum operating gas pressure estimate, after which numerical analyses evaluate liner stress, yielding of the concrete and surrounding rock, storage capacity, material demand, and sensitivity to key geological and design parameters. Short-term cyclic thermo-mechanical analyses are additionally performed to examine the implications of hydrogen injection and withdrawal.

The results reveal a clear trade-off between structural performance and storage/material efficiency. At the benchmark pressure of 3.3 MPa, the Multi-cavern scheme reduces the maximum steel liner tensile stress from 32.4 MPa to 25.4 MPa and has a total plastic-zone volume approximately 18% of that of the Single-cavern scheme. In contrast, the Single-cavern scheme provides approximately twice the effective gas-storage volume and a substantially lower indicative material cost per unit mass of stored hydrogen. Rock mass quality strongly influences structural response, demonstrating the importance of geological conditions in retrofit assessment. The cyclic analyses further show that static loading at the maximum operating gas pressure does not conservatively bound all response quantities: compared with the cyclic cases examined, it produces higher steel liner stress and concrete yielding but lower rock mass and total yielding.

Overall, the thesis demonstrates that repurposing existing oil storage caverns using LRC technology is a technically promising option, but that retrofit feasibility cannot be assessed from storage volume or pressure capacity alone. Geological conditions, LRC geometry, global uplift resistance, liner response, material demand, and operational loading need to be considered together. The work establishes a preliminary assessment framework and identifies the principal issues requiring further development toward project-specific design. In particular, the continuing PhD research will extend the geological investigation to construction and pressurized operational stages and develop more detailed performance-based and coupled analyses for shallow LRC hydrogen storage.

The Stability Graph Method (SGM) is an empirical approach for open stope design, originally developed from extensive case histories in Canada and Australia. It has been applied in Boliden’s Garpenberg and Zinkgruvan mines, providing efficiency in preliminary design and guidance for data collection on key influencing factors. However, uncertainty remains a significant challenge. Geological data are often incomplete at the design stage, and even with detailed geological surveys, heterogeneity in rock mass quality and complex jointing hinder precise parameter quantification. This study develops a probabilistic Stability Graph Method, which integrates probabilistic analysis into the conventional framework. Rather than requiring exact input values, the method uses parameter ranges derived from available geological information. The outputs include probability distributions of stability numbers, providing upper and lower bounds as well as mean values. Combined with empirical stability and caving curves, this approach enables prediction of both stope stability and caving probability. Application to the Garpenberg Mine demonstrates that predicted caving extents agree well with observed performance, validating the method’s effectiveness in supporting risk-informed stope design under uncertainty.

In the present paper the problems of the nonlinear debonding of anchorage interface, the strain-hardening and rupture of rockbolt, and the progressive damage of heterogeneous rock for the fully grouted rockbolt under axial loads are studied. A micromechanical numerical model is developed and implemented into the finite difference programme, to analyze the load transfer mechanism and damage evolution by introducing the bi-exponential shear slip model of interface, bilinear strain-hardening model of rockbolt and elastic damage model of rock. The close agreement between the simulation results of the proposed model and the theoretical and experimental data validates the model's capability for accurately characterizing the pull-out behavior of the grouted rockbolt. Failure type strongly depends on the strength of rock and anchorage interface, as well as the anchorage length. In particular, when rock strength is low, strain energy is predominantly dissipated through rock damage, leading to the interface failing to fully mobilize its load transfer effect, especially at a relatively long anchorage length. Moreover, the excessive interfacial adhesion performance causes a large range of serious damage in rock near the interface and leads to peak pull-out load even lower than the rockbolt with poor interfacial bonding properties. Finally, the critical anchorage length is investigated and the load transfer mechanism of the fully grouted rockbolt is clarified by comparing the case with or without rock damage. It is therefore very useful of the developed micromechanical model, since it provides an essential understanding of the load transferring capacity and failure type of the fully grouted rockbolt, especially under rock damage.

The stability graph method is a widely used empirical method for dimensioning open rooms/stopes and support design based on stope geometry and stability number. This paper presents a rigorous investigation employing numerical models featuring multiple joint sets to replicate the structurally controlled failure of open stopes. The equivalent linear overbreak/slough (ELOS) in the model is calculated based on the volume of the detached blocks identified by defining thresholds for normal and shear displacements on joint planes. Modified Factor B values are proposed based on analyses of numerical models with varying critical joint set angles. It is found that the numerical simulation results align well with stability graph outcomes when using modified Factors A and B. This research has improved the understanding of the empirical stability graph method and promotes its reliability in predicting the stability state and unplanned dilution in open stopes.