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• An analytical viscoelastic model is established to solve stress based on RSR method. • The explicit stress on interfaces of rock-grout and grout-transducer was obtained. • The stress first increases and then keeps constant as diameter ratio increases. • The rheological time increases as viscosity coefficient and the modulus ratio increase. The rheological stress recovery (RSR) method was proposed to measure the in-situ stress of rock mass with time-dependent property by drilling a hole and embedding transducers into it. To solve the stress distribution on the transducer, a viscoelastic axisymmetric plane model was firstly built considering an arbitrary stress boundary condition. The analytical solution was developed by dividing the stress boundary conditions into axisymmetric and anti-axisymmetric combining with Laplace transformation technique. The explicit stress expressions on interfaces of rock–grout and grout–transducer was obtained using Burgers and Boltzmann viscoelastic models, respectively. Furthermore, the variations of transducer surface final stress, which is related to rheological time, geometric and mechanical properties of rock mass, grout parameter, and transducer materials, was proposed for calculating the measured stress by RSR method. For both of Burgers and Boltzmann viscoelastic model, final stress increases as elastic modulus ratio increases when elastic modulus ratio under 20, and the final stress could be ignored when diameter ratio is over 1.4. The rheological time increases with increasing of viscosity coefficient and the modulus ratio, but decreases as the shear modulus increases. The results in here provide a simple method for stress analyzing and have great value for understanding the relationship between the initial stress of rock mass and the measured stress for the RSR method. [ABSTRACT FROM AUTHOR]

The combined finite-discrete element method (FDEM) is an advanced finite and discrete element coupling method. This study further applies it to the problem of stress wave propagation in the jointed rock mass. Firstly, the fundamental theory of FDEM is briefly described and the methods commonly used in FDEM to characterize structural planes are comprehensively analyzed. Then, based on the viscous boundary condition (VBC), the viscous-spring boundary condition (VSBC) is added to absorb the reflected wave at the artificial boundary and restore the residual displacement to meet the actual engineering. In addition, the application range of the VBC and VSBC is verified, which indicates that the VBC and VSBC in the improved FDEM can be well applied not only to the continuum range but also to the case of the new fracture formed. Finally, several classic models are solved to verify the stress wave propagation across different types of joints by FDEM. The results reveal that results from FDEM agree well with analytical solutions based on the displacement discontinuity model and numerical solutions from universal distinct element code (UDEC), which means that the improved FDEM can capably and accurately simulate wave propagation in the jointed rock mass. [ABSTRACT FROM AUTHOR]

Thermal cracking widely exists in many geoengineering practices (e.g., geothermal exploitation, nuclear waste disposal and CO 2 sequestration), and highly affects the efficiency and safety of the engineering applications. Some of these projects are constructed in shale formations with anisotropic thermal/mechanical properties, which affect the thermal cracking behavior. It is therefore imperative to understand and correctly model the thermo-mechanical (TM) coupling behavior of anisotropic shale rocks for better and safer designs. In this paper, a novel anisotropic TM coupled model, named as Y-TM aniso , is proposed to study the heat transfer and thermal cracking process in the anisotropic shale formations based on the combined finite-discrete element method (FDEM). In particular, some inherent characteristics of the shale formations (e.g., material anisotropy, pre-existing discontinuities and multiple layers) can be well handled in this model. The performance of this model on temperature field calculation and thermal cracking modelling are confirmed by numerical tests with analytical or experimental solutions. An application test concerned with the thermal cracking in a shale formation is investigated. The results show that the proposed Y-TM aniso has implications in the application and design of TM coupling problems in anisotropic shale formations. [ABSTRACT FROM AUTHOR]

To investigate the mechanism of tunnel supports for large squeezing deformation hazards, the explicit cohesive element-based numerical manifold method (ECo-NMM) is extended. First, for modeling the compound effect of the artificial supports and tunnel face, a layer-based tunnel support algorithm is proposed to simulate the interaction between the supports, tunnel face and surrounding rock mass and represent the geometric and mechanical properties of the tunnel supports. Then, to investigate the influence of tunnel support timing, a mapping algorithm is proposed to correlate simulated processes with real excavation processes, based on which the installation timing of tunnel supports is characterized. In addition, a reconstruction algorithm is proposed to illustrate 2D simulation results in 3D. To validate the accuracy and applicability of this improved method, numerical cases are conducted using the developed method, and the predicted results are compared with analytical solutions, test observations and original numerical results. Finally, this improved method is applied to investigate the influence of the tunnel support timing, and the predicted results indicate that the squeezing stress acting on the tunnel supports first decreases and then increases with the continuous increase in the delay in the tunnel support, based on which the tunnel support timing is optimized. [ABSTRACT FROM AUTHOR]

For tunnelling in a deep soft rock mass, rock rheology and the advancing process significantly affect the induced pressures on the support system and the long-term safety of the tunnel. In this study, coupled analytical solutions, which take both the rock rheology and tunnel face advancement effects into consideration, are proposed to predict the mechanical behavior of deep-buried circular lined tunnels in a soft rock mass. To account for different rheological behaviors of rocks, five types of viscoelastic models are adopted in the theoretical derivations. The analytical solutions are validated by comparing the predicted results with corresponding existing solutions and those predicted by finite difference simulations. According to parameter degradation, the proposed solutions can be simplified to the classic viscoelastic solution without consideration of tunnel face advancement and the elastic solution with consideration of tunnel face advancement. Based on the proposed coupled solutions, the characteristics of convergent displacements of unlined tunnels with or without consideration of the tunnel face advancement, are studied. In addition, for lined tunnels, the influences of the initial stress release parameter, influence radius of the tunnel face, excavation rate and liner installation time on rock stress and displacement and support pressure are systematically investigated. Finally, the proposed solution is successfully applied to analyze the time-dependent behavior of the Lyon-Turin Base Tunnel, and good agreements are achieved between the theoretically predicted values and corresponding field monitoring data. [ABSTRACT FROM AUTHOR]