Gas hydrates are found in coarse-grained and fine-grained soil worldwide, within deepwater marine sediments and beneath permafrost. Natural gas hydrates can be formed within fine-grained marine sediments as sub-vertical complex fibrous vein structures. A better understanding is required of the geomechanical behaviour of fine-grained hydrate-bearing soil that resemble fracture-hosted natural deposits, as they have the potential to pose a significant geohazard. This thesis presents a simple, repeatable laboratory procedure for the formation of simplified, vertical, cylindrical, synthetic tetrahydrofuran hydrate veins centred within fine-grained soil. The geomechanical impact of the different-sized tetrahydrofuran hydrate veins was then determined by carrying out consolidated and unconsolidated undrained compression tests on specimens. These results were then used to develop relationships between the hydrate vein size and the strength and stiffness of the fine-grained specimens. The application of these relationships to natural fine-grained sediments hosting gas hydrate veins is then discussed.