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A numerical modeling study is conducted to assess and gain a better understanding of the arching effects of field cemented tailings backfill (CTB). An integrated multiphysics model is developed that can illustrate and capture the changes in the material properties of CTB, consolidation behavior of CTB mass, and the shear behavior at the CTB/Rockwall interface. The predictive capability of the model has been successfully verified with comparisons of the predicted results with monitoring data taken from a series of field studies. The model is then used to simulate a series of applications that are relevant to CTB in practice. [ABSTRACT FROM AUTHOR]

An evolutive elasto-plastic model is developed in this research work to address the vital role of binder hydration in the evolution of the mechanical behavior and properties of cemented paste backfill (CPB). Double hardening/softening parameters, which include effective incremental plastic strain and degree of binder hydration, are adopted. A non-associated plastic potential function based on the dilation angle is employed to formulate the plastic deformation and dilation of CPB. Mechanical parameters, such as cohesion, internal friction and dilation angles, stiffness, and Poisson’s ratio are expressed as functions of the degree of binder hydration. The developed model is implemented in a finite element code, COMSOL Multiphysics, and then validated against experimental data obtained from laboratory tests performed in this study and by other researchers. The validation results show good agreement between the predicted and experimental results, thus confirming the capabilities of the new constitutive model to well capture binder hydration induced evolution of the mechanical behavior and properties of CPB. [ABSTRACT FROM AUTHOR]

To date, only a very few number of models are available to study the shear characteristics of the backfill-rock interface, and none of them have incorporated the effect of the interactions between sulphate ions and cement hydration on the interface shear behaviour. Therefore, a coupled chemo-elastic cohesive zone model (CZM) has been developed to simulate the shear characteristics of the cemented paste backfill (CPB)-rock interface that contains sulphate ions at the early ages. To quantitatively address the influence of sulphate on binder hydration at the early ages, the concept of equivalent chemical age is proposed and integrated into a binder hydration model. Besides, the interface shear properties, fracture toughness as well as shear stiffness are expressed as a function of the equivalent chemical age. By implementing the developed model in COMSOL Multiphysics, the results of the numerical simulation are found to agree with the experimental results. The validated results confirm the capability of the developed model to describe the shear characteristics of the interface that contains sulphate ions. The developed model will contribute to improving the assessment of the shear behaviour of the CPB-rock interface in the field, thus leading to a more economical design of safe CPB structures. [ABSTRACT FROM AUTHOR]

Methane hydrate (MH, also called fiery ice) exists in forms of pore filling, cementing and load-bearing skeleton in the methane hydrate bearing sediment (MHBS) and affects its mechanical behavior greatly. To study the changes of macro-scale and micro-scale mechanical behaviors of MHBS during exploitation by thermal recovery and depressurization methods, a novel 2D thermo-hydro-mechanical bonded contact model was proposed and implemented into a platform of distinct element method (DEM), PFC2D. MHBS samples were first biaxially compressed to different deviator stress levels to model different in-situ stress conditions. With the deviator stress maintained at constant, the temperature was then raised to simulate the thermal recovery process or the pore water pressure (i.e. confining pressure for MH bond) was decreased to simulate the depressurization process. DEM simulation results showed that: during exploitation, the axial strain increased with the increase of temperature (in the thermal recovery method) or decrease of pore water pressure (in the depressurization method); sample collapsed during MH dissociation if the deviator stress applied was larger than the compression strength of a pure host sand sample; sample experienced volume contraction but its void ratio was slightly larger than the pure host sand sample at the same axial strain throughout the test. By comparison with the laboratory test results, the new model was validated to be capable of reproducing the exploitation process by thermal recovery and depressurization methods. In addition, some micro-scale parameters, such as contact distribution, bond distribution, and averaged pure rotation rate, were also analyzed to investigate their relationships with the macroscopic responses. [ABSTRACT FROM AUTHOR]

In order to establish a new bond failure criterion for bonded particles to be used in two-dimensional Discrete Element Modelling, the mechanical behavior of cemented granules with different cement sizes were investigated. In this paper, experimental results of five series of loading tests on cemented granules with four cement widths were presented. Then incorporated the previous experiments with different cement thicknesses, a bond failure envelope dependent on the cement size was proposed. Among a total of about 600 pairs of tested samples, three failure modes were found. Only the failure mode, in which the failure surface was regular and mechanical responses were stable and repeatable, was considered as the representative results and adopted to establish the bond failure model. The experimental results showed that: the peak normal forces in the compression and tension tests are dependent on the cement size; the peak shear forces or peak torsions in the loading tests with complex loading paths, i.e. combined compression shear test, combined compression torsion test and combined compression shear torsion test, are dependent on the normal force and cement size. The peak shear force or peak torsion increases with the normal force when the normal force is smaller than a critical value, while decreases as the normal force is larger than the critical value. The failure envelope in the nomal–shear–torsion space is in an ellipsoidal shape with a cut-off as the normal force reaches the peak compression force. It expands with the cement width and shrinks with the cement thickness. [ABSTRACT FROM AUTHOR]