###### Abstract  
Gas hydrate has gradually become a new potential energy resource. However, some engineering and environmental problems related to the mechanical properties of gas hydrate-bearing sediments (GHBS) during gas recovery may occur. Many studies have been carried out on the basic mechanical properties of GHBS samples based on laboratory tests, but their evolution characteristics and suitable models require further research. Based on a series of data analyses of published laboratory experimental results on GHBS samples with different hydrate saturations under various confining pressures, the evolution characteristics of strength and dilation parameters were investigated. It was found that cohesion (\(c\)) increases quickly to a peak value and then decreases gradually to a residual value with an increasing plastic shear strain, and the samples with higher hydrate saturations have higher initial values, peak values, and residual values of cohesion (\(c\)). The internal friction angle (\(\varphi\)) increases quickly with increasing plastic shear strain and then becomes stable at a residual value for all the samples with different hydrate saturations. The dilation angle (\(\psi\)) increases from negative to positive values with increasing plastic shear strain and then becomes stable at a residual value. These characteristics are likely to be related to the compaction occurring at the early stage of compression before expansion due to dilation. In this paper, a non-linearly fitted model is proposed considering the evolution of the mechanical parameters, and the verification tests show that the proposed model can simulate the stress-strain behaviors of the GHBS samples well. This model is also adopted in the stability analysis of submarine slopes containing hydrate reservoirs. The analytical approach is developed, accompanied by the strength reduction method. gas hydrate-bearing sediment; evolution characteristics; strength parameter; dilation angle 20242517  
Nevertheless, the strength parameters in these studies are always obtained based on the peak strength of the specimens under various confining pressures [19; 22; 23]. This is enough for building a strength criterion or a perfect elastoplastic constitutive model. However, the test results show that strain hardening and softening behaviors are very common for most GBHS samples [15; 18; 23; 24]. The previous studies also demonstrate that the strength parameters should be mobilized instead of being constant during the process of plastic deformation and damage [25; 26]. In order to describe the post-yielding behaviors of geomaterials, the evolution of strength parameters is introduced into the constitutive model. On the one hand, some studies assume that both cohesion and the internal friction angle decrease with increasing damage [27; 28; 29]. On the other hand, based on some experimental observations and analyses, some studies argue that cohesion will drop while the internal friction angle may increase during the yielding and damage process. Thereafter, the CWFS (Cohesion Weakening Friction Strengthening) model was proposed and applied in engineering modeling [30; 31; 32; 33; 34]. However, most of these studies were conducted on rock specimens. The evolution characteristics of the strength parameters of the GHBS samples should still be determined. The dilation angle is also an important parameter to describe the stress-strain behaviors of geomaterials. Instead of using a constant value of the dilation angle, as in many studies [23; 34; 35], some studies have demonstrated that the dilation angle should also be mobilized during the damage process, and some mobilized models of dilation angle for rock have been proposed [36; 37; 38]. Nonetheless, the evolution characteristics of the dilation angle of GHBS samples still need to be studied. [PERSON] et al.