Development of a high-pressure, temperature-controlled calibration chamber for cone penetration tests in hydrate-bearing sand

Natural gas hydrate is recognized as both a potential energy resource and an environmental hazard, underscoring the necessity to estimate the strength and stiffness of hydrate-bearing reservoirs for safe exploitation. The cone penetration test (CPT) is widely used in offshore geotechnical investigations, and extensive empirical correlations estimate soil properties from cone resistance. However, only a limited number of CPTs in hydrate-bearing sediments have been reported publicly. To address this gap, a high-pressure, temperature-controlled calibration chamber is developed for CPT in hydrate-bearing sediments. The apparatus allows independent application of confining and axial stresses, efficient hydrate formation in soil, and up to four penetration tests in a single sample. The sample is cooled by combined liquid and condensing-tube cooling, reaching about 2 °C within 30 h. The apparatus performance is evaluated comprehensively, and the effects of hydrate saturation, confining stress, and soil relative density on cone resistance are investigated through 32 tests. The experimental results indicate that existing empirical correlations between cone resistance and the relative density of pure sand may not directly apply to hydrate-bearing sands.