As the economy evolves, there has been an increasing interest in exploring oceanic resources. However, the complex marine environment poses several geological challenges for offshore engineering endeavors. The presence of gassy soil significantly influences the deformation properties and integrity of the soil, significantly impacting offshore engineering construction. Triaxial shear tests and creep tests were conducted on gassy clay with silt content, prepared using the laboratory zeolite method, to analyze its shear deformation characteristics and long-term resilience. We proposed a prediction model for calculating the long-term resilience of silt-containing clay, accounting for confining pressure and gas content, and verified its efficacy through experimentation. Our findings reveal the following: The stress-strain relationship curve of silt-containing gassy clay is a typical strain hardening curve. The greater the confining pressure or the smaller the gas content, the greater the stress under the same strain and the greater the yield stress; when the gas content is the same, the greater the confining pressure, the greater the long-term strength of the soil; and when the confining pressure is the same, the smaller the gas content, the greater the long-term strength of the soil. The research results can provide theoretical reference for actual complex engineering.

Gassy clay, commonly encountered in coastal areas as overconsolidated deposits, demonstrates distinct mechanical properties posing risks for submarine geohazards and engineering stability. Consolidated undrained triaxial tests combined with cyclic simple shear tests were performed on specimens with varying overconsolidation ratios (OCRs) and initial pore pressures, supplemented by SEM microstructural analysis. Triaxial results indicate that OCR controls the transitions between shear contraction and dilatancy, which govern both stress-strain responses and excess pore pressure development. Higher OCR with lower initial pore pressure increases stress path slope, raises undrained shear strength (su), reduces pore pressure generation, and induces negative pore pressure at elevated OCR. These effects originate from compressed gas bubbles and limited bubble flooding under overconsolidation, intensifying dilatancy during shear. Cyclic tests reveal gassy clay's superior cyclic strength, slower pore pressure accumulation, reduced stiffness softening, and enhanced deformation resistance relative to saturated soils. Cyclic pore pressure amplitude increases with OCR, while peak cyclic strength and anti-softening capacity occur at OCR = 2, implying gas bubble interactions.

Gassy clay deposits are widely distributed in marine sediments. Clarifying the influence patterns of the trapped gas phase on the mechanical properties of gassy clay is of significant importance. Establishing an in -situ strength parameter and consolidation coefficient inversion method based on CPTu is crucial for gassy clay characterization. In this study, gassy clay was prepared using the zeolite method. The variations of strength and consolidation parameters of gassy clay concerning gas content were obtained based on laboratory triaxial and one-dimensional tests. It was observed that the trapped gas phase enhances the undrained shear strength and hinders drainage. Specifically, gassy clay with a gas content of 3.5 % exhibited an 18 % increase in undrained shear strength compared to saturated clay and a 50 % reduction in consolidation coefficient. In addition, laboratory calibration chamber tests were conducted to investigate the cone penetration test (CPTu) in gassy clay with varying gas contents and penetration rates. The drainage effect during the CPTu penetration process in gassy clay was discussed. The reasons behind the variations in static cone penetration parameters under undrained conditions for normally consolidated gassy clay were analyzed by combining the results of triaxial tests and one-dimensional consolidation experiments. A proposed formula for the cone factor N kt was also provided under undrained penetration conditions. The accuracy of conventional methods for estimating the consolidation coefficient of gassy clay was verified, the basic properties of the gassy clay used in the indoor experiment are similar to those of the seabed gassy silt at the project site, and the environmental conditions are similar to those at locations with low initial pore pressure, such as mudflat or shallow sea bed, thereby offering a reference for insitu testing of strength parameters and consolidation coefficients in gassy clay seabed.