To exploit the resource of methane hydrate, it is crucial to understand the mechanical behavior of hydrate-bearing sediments. In this paper an elastoplastic constitutive model is developed for describing the mechanical behavior of gas hydrate–bearing soils (GHBS). To address the effect of the hydrate occurrence habits, the concept of the effective degree of saturation of the gas hydrate is introduced, and the effective stress stresses are redefined for describing the mechanical response of the GHBS. Within this context, a yield or loading function is developed while considering the bonding effect of gas hydrate; thus, the yield function can expand or shrink as gas hydrate forms or dissociates. To describe more realistically the mechanical behavior of the GHBS, a nonassociative flow rule is proposed by assuming the dilatancy to be a function of bonding stresses, suction stress, and stress ratio. The proposed model is applied to analyze the mechanical responses of the GHBS with different hydrate occurrence habits under different environmental loadings. It is demonstrated that the proposed model can well capture the main features of the mechanical behavior of GHBS, including the hydrate-induced enhancements of stiffness, strength and dilatancy, the unsaturation-related characteristics, and the hydrate occurrence habits dependency, showing that the proposed model is capable of describing the mechanical behavior of GHBS due to hydrate dissociation or under other environmental loadings.

The effects of basalt fiber incorporation on the mechanical properties of red clay soils were investigated. Through the direct shear test, unconfined compressive strength test, and microstructure test, the shear strength curves and stress–strain curves of basalt fiber-modified red clay soils were obtained under different basalt fiber incorporation rates and different soil dry density conditions. The results showed that: (1) the shear strength and compressive strength of the soil were significantly increased after the incorporation of basalt fiber; (2) the strength increase was greatest at 0.3% of basalt fiber incorporation, which was the optimum incorporation level; (3) the damage form of the soil changed, and the red clay soil incorporated with basalt fiber changed from brittle damage to ductile damage; and (4) the microscopic electron microscope pictures showed that, at the appropriate amount of fiber incorporation conditions, the fiber bond with the soil particles and form a fiber‒soil column. When subjected to external forces, the discrete fiber‒soil columns interact with each other to form an approximate three-dimensional fiber‒soil network, which acts to restrain the displacement and deformation of the soil particles, which is the main reason for the improved mechanical properties of the improved soil. The experimental research on the improvement of red clay soil with basalt fiber can provide a theoretical basis for engineering practice and help provide an environmentally friendly and efficient method of road base treatment in engineering.

Marine hydrate exploitation may trigger the seabed geological disaster, such as seafloor collapse and landslide. It is critically important to understand the mechanical properties of hydrate‐bearing sediment. Strain‐softening observation is a typical behavior of hydrate‐bearing sediment (HBS) and exhibits more significant at higher hydrate saturation. This paper performed a series of triaxial compression tests on methane hydrate‐bearing sand to analyze the influence rule and mechanism of hydrate saturation on the strain‐softening characteristic, stiffness, and strength and introduced the strain‐softening index to quantificationally characterize the strain‐softening behaviors of HBS with different hydrate saturations. Based on the analyses on the mechanical behavior of HBS, the Duncan–Chang model is extended to address the stress‐strain curves of HBS. Two empirical formulas with hydrate saturation embedded are used to characterize the enhanced initial modulus and strength for HBS, respectively. To address the strain‐softening behavior of HBS, the modified Duncan–Chang model introduced a damage factor into the strength of HBS. To validate the modified Duncan–Chang model, four different triaxial compression tests are simulated. The good consistence between simulated result and experimental data demonstrates that the modified Duncan–Chang model is capable of reflecting the influence of hydrate saturation not only on the stiffness and strength but also on the strain‐softening characteristics of HBS.

Many engineering problems, such as soil stabilization, nuclear waste storage, and oil and gas extraction, require understanding and modeling of the coupled chemomechanical behavior of soils. Based on the framework of the Barcelona basic model (BBM), a constitutive model (BBM-C) for addressing chemomechanical coupling behavior of saturated soil is proposed. By replacing matric suction with osmotic suction, the analogous yield function, hardening law, and flow rule are introduced for the BBM-C. This study also presents a parameter calibration method for the proposed constitutive model. To validate the BBM-C, three oedometer tests, in which the specimen was subjected to mechanical loading with constant osmotic suction, were used to calibrate the model parameters. Two other oedometer tests, including (1) mechanical loading at constant osmotic suction and (2) alternative chemical and mechanical loading, were used as blind tests to verify the proposed BBM-C with the calibrated model parameters. A comparison between experimental data and predicted results demonstrated that the BBM-C was able to capture the main features of the chemomechanical coupling behavior of saturated soil.