To accurately predict soil thermal effects is of great importance for simulations of complex boundary value problems such as the energy foundations and nuclear waste disposal. Existing thermo-mechanical constitutive models only account for clay, and cannot simulate the sand's behaviour under thermo-mechanical conditions. In this study, a unified thermo-mechanical bounding surface (UTMBS) model is proposed for saturated clay and sand. Based on the thermal effects on the isotropic compression line, the model proposes a new unified thermal softening relationship and a plastic modulus for clay and sand, with the thermal cyclic behaviour replicated by a memory surface. The unified model considers the thermal effects on the critical state line and the shape of the bounding surface, accounting for both drained and undrained shearing of clay and sand at different temperatures. In addition, the non-linear elasticity relationship represents the hysteresis loops of the stress-strain relationship in the mechanical cycles. The performance of the proposed model is evaluated against existing experimental results for clay and sand in terms of their thermal cyclic behaviour, drained/undrained triaxial compression, and mechanical cyclic behaviour at different temperatures. It is evident that the UTMBS model is able to simulate various thermo-mechanical behaviours of clay and sand.

The effective cementing of oil and gas wells in deep water weakly consolidated formation is vital for the stable supply of world energy. During the cementing operation, the cement slurry was injected into the formation under pressure differential, and thereby forms a strength transition zone in the adjacent area of wellbore. To properly guide the formation cementing operation, a unified model for predicting the diffusion distance of cement slurry in weakly consolidated formation considering different diffusion patterns was proposed in this paper. The unified model described the diffusion process of cement slurry by the governing equation of compaction grouting, penetration grouting and fracture grouting. The criterion to identify the diffusion pattern was proposed as well. Results show that, when the pump pressure is below the threshold for penetration, compaction grouting is the sole diffusion form, with its distance influenced by the wellbore radius, the shear modulus of the soil, and the stress within the formation boundaries. Exceeding this pressure allows for both compaction and penetration grouting to coexist, where the penetration grouting's diffusion distance depends on the rheological properties of the cement slurry, the formation's physical properties, and operational conditions. Upon reaching the initial cleavage pressure, significant cracking occurs, and the diffusion of the cement slurry extends to the length of these cracks, with the fracture grouting model being based on the Drucker-Prager criterion and influenced by the formation properties and operational factors. The proposed model was validated by numerical simulation results, which showed good performance to predict the diffusion distance of cement slurry. This model provides a costeffective approach to guide the cementing operation of weakly consolidated formation in deep water.

Under the combined effect of rainfall and water level fluctuation, the slope of the reservoir bank is prone to collapse. Ideal elastic-plastic Mohr-Coulomb criterion is used to analyze the stability of reservoir slope, which is difficult to characterize the complex mechanical characteristics of slope soils, such as over consolidation dissipation under wet-dry cycles. It is difficult to analyze the stability of bank slopes under the action of dry and wet cycles to reflect the complex mechanical properties such as overconsolidation and dissipation of slope soils. In this study, focusing on weakly overconsolidated unsaturated red clay at the reservoir bank slope of the Xingan shipping-hydropower junction project in Jiangxi Province, unsaturated direct shear tests were conducted and an overconsolidated unified hardening (UH) model for red clay was constructed. The UH model incorporates the mathematical-physical relationship between suction stress and matric suction using the arctangent function. Subsequently, based on the UH model, an application program of FLAC3D was developed in C++. The SEEP/W module of GeoStudio software was employed to compute the unsaturated seepage field during the rainfall infiltration, and an interface program was created to import FLAC3D data for stability calculations of the reservoir slope. Comparisons between the horizontal displacements obtained from the improved UH model and the classical unsaturated elastic-plastic model revealed significantly larger displacements in the former, suggesting that the improved UH model can provide reasonable predictions of the overconsolidated unsaturated red clay for reservoir slope stability. This research offers valuable insights for similar projects involving analyses of reservoir bank slope.