Search

This paper investigates the feasibility of a proposed underground gas storage facility. Based on S gas storage, a large-scale 2D hydromechanical coupling FEA model is established to explore the geo-mechanical properties of S gas storage under a multi-cycle alternating injection and production and validated by the interference logging test. To account for the damage development of fault damage area under the influence of seepage-stress coupling, the soil adopts the Mohr–Coulomb constitutive assumption. Additionally, a zero-thickness cohesive element is proposed as a mechanical model to simulate the fault gouge. The mechanical parameters of zero-thickness cohesive elements are verified by a ring shear test and a preliminary FE model. Thereafter, another refined conceptual finite element (FE) model considering the fault damage area, fault core, water-containing damaged area, overburden damaged area, and the contact model between different damaged areas of the fault and the fault core is developed and validated. The simulation results demonstrate that the initial seal ability of the caprock and faults remains intact. Specifically, (i) the maximum caprock and ground displacements are 8.5 cm and 5.4 cm, respectively. (ii) The most significant slip distance is 0.125 mm, indicating that, leakage under the action of multi-period alternating injection–production, the S aquifer structure had no fault activation and caprock. (iii) The risk of fault activation is higher for high-angle faults compared to low-angle faults. Low-angle faults are more susceptible to shear slip. Providing a scientific reference for the feasibility study of gas storage. [ABSTRACT FROM AUTHOR]

Energy accumulation and energy release are typical characteristics during the whole deformation process of layered rocks. To reveal the characteristics of the energy evolution and failure mechanism of layered rocks, uniaxial compression tests are carried out on layered shale samples. The anisotropic properties of layered rocks are studied. The energy indexes, namely, the elastic energy, dissipated energy, and total input energy of the specimens, are further investigated, revealing the energy damage evolution mechanism of the layered rocks. The experimental results show that the mechanical properties and failure modes of layered rocks are obviously anisotropic. The failure modes of layered rocks can be divided into three types, and the uniaxial compression strength typically shows “U” shaped with the increasing orientation of bedding planes. The energy reserve of the layered rock mass is also anisotropic due to the influence of bedding planes. Before the peak strength, the energy evolution of the layered rock samples is nearly similar, dominated by energy accumulation. The energy dissipation and energy release predominated after the peak strength. In the postpeak stress stage, the elastic strain energy (Ue) is released suddenly, while the dissipated energy (Ud) increases significantly. After that, the elastic-dissipated energy ratio (Ud/Ue) of the layered rocks is studied. The elastic-dissipated energy ratio slowly decreases with strain in the elastic stage, while it increases significantly in the postpeak fracture stage, which has a mutation point. The mutation point is defined as the critical elastic-dissipated energy ratio (Kc), which also shows a typical “U” shape with the orientation of bedding planes. Therefore, the strength failure criterion according to the energy mutation is proposed, which does not need to consider the tensile or shear failure mode of the layered rocks. The failure criterion is validated by the experimental results of other layered rock samples made of similar materials in the laboratory. The criterion is useful for the strength prediction of layered rocks under uniaxial compression. [ABSTRACT FROM AUTHOR]

With the resource exploitation from the shallow to the deep, how to effectively control the deformation and floor heave of roadway in soft rocks has become an important factor affecting the safe mining of resources. For deep mining, the serious supporting problems and destruction of the surrounding rock are widespread. This paper takes a testing gallery in China’s Huainan mining area as an example to study the deformation and failure behavior for deep roadway in soft rocks. Combining the geological environment characteristics of the roadway, the indoor creep test of soft rock and the large-scale triaxial creep tests on site are carried out, and the nonlinear creep constitutive model of soft rock and its numerical realization method are proposed. Then, the nonlinear creep model is applied to a particular case of the testing gallery in soft rocks. According to the long-term deformation monitoring data of surrounding rock, the mechanical parameters of loose zone are determined by the orthogonal design method. The results show that the deformation and floor heave of the roadway is mainly due to the obvious creep deformation caused by the weak surrounding rock under the high ground stress level. The model proposed in this paper can better reflect the creep characteristics and nonlinear characteristics of soft rock under different stress levels. The research results have important reference value for long-term deformation prediction and supporting system optimization of deep roadways in soft rocks. [ABSTRACT FROM AUTHOR]