Experimental investigation of creep behavior of clastic rock in Xiangjiaba Hydropower Project

There are many fracture zones crossing the dam foundation of the Xiangjiaba Hydropower Project in southwestern China. Clastic rock is the main media of the fracture zone and has poor physical and mechanical properties. In order to investigate the creep behavior of clastic rock, triaxial creep tests were conducted using a rock servo-controlling rheological testing machine. The results show that the creep behavior of clastic rock is significant at a high level of deviatoric stress, and less time-dependent deformation occurs at high confining pressure. Based on the creep test results, the relationship between axial strain and time under different confining pressures was investigated, and the relationship between axial strain rate and deviatoric stress was also discussed. The strain rate increases rapidly, and the rock sample fails eventually under high deviatoric stress. Moreover, the creep failure mechanism under different confining pressures was analyzed. The main failure mechanism of clastic rock is plastic shear, accompanied by a significant compression and ductile dilatancy. On the other band, with the determined parameters, the Burgers creep model was used to fit the creep curves. The results indicate that the Burgers model can exactly describe the creep behavior of clastic rock in the Xiangjiaba Hydropower Project.

Experimental study and modeling of hydromechanical behavior of concrete fracture

In this study, the hydromechanical behavior of a concrete fracture under coupled compressive and shear stresses was investigated. A special experimental device was designed to create a planar fracture in a cylindrical sample and to carry out different kinds of hydromechanical tests on the fracture. Four series of laboratory tests were performed on an ordinary concrete sample. Hydrostatic compression tests were first conducted to characterize the normal compressibility of the fracture. In the second series, direct shear tests were conducted on the fracture under different normal stresses. The maximal shear stress of the fracture was determined as a function of the normal stress. In the third series, fluid flow tests were carried out in view of characterizing the overall hydraulic conductivity of the fracture as a function of its opening and closure. Shear tests with a constant fluid pressure were finally performed to investigate the influence of fluid pressure on the deformation behavior of concrete fractures. Based on the experimental investigation, an elastoplastic model is proposed. This model takes into account the nonlinear elastic behavior of a fracture under normal compression and the plastic deformation and failure due to shear stress. The model was coupled with the classical Darcy's law to describe the fluid flow along the fracture by considering the variation of permeability with fracture aperture. Numerical results agree with experimental data from various laboratory tests.

Elastoplastic cup model for cement-based materials

Based on experimental data obtained from triaxial tests and a hydrostatic test, a cup model was formulated. Two plastic mechanisms, respectively a deviatoric shearing and a pore collapse, are taken into account. This model also considers the influence of confining pressure. In this paper, the calibration of the model is detailed and numerical simulations of the main mechanical behavior of cement paste over a large range of stress are described, showing good agreement with experimental results. The ease study shows that this cup model has extensive applicability for cement-based materials and other quasi-brittle and high-porosity materials in a complex stress state.

Numerical analysis of thermo-hydromechanical process related to deep geological radioactive repository

This paper addresses numerical analysis of thermo-hydromechanical processes in the context of deep geological disposal of radioactive waste.The emphasis is put on modeling of damaged zones induced by excavation,pore pressure and temperature changes.The theoretical background of thermo-poroelasticity for saturated porous media is first recalled.The framework for modeling initiation and evolution of induced cracks is then presented by using a variational approach of phase-field method.A specific model with two crack phase fields and considering thermo-hydromechanical interaction is proposed.A particular attention is paid on the description of shear cracks.The proposed model is implemented in the standard finite element method.An example of application is finally presented on the analysis of thermo-hydromechanical responses and cracked zones evolution around a typical disposal repository in the context of French concept for high level waste disposal.

Advances in peridynamics modeling of deformation and fracturing of brittle geomaterials

Peridynamics(PD)is an emerging method that establishes a theoretical framework based on non-local theory to describe material mechanical behavior with spatial integral equations.It gives a unified expression of the me-dium including state transformation and characterization in different scales.It is showing great potential for evaluating the complicated mechanical behaviors of brittle solids.In the past two decades,peridynamics has been showing its great potential and advantages in modeling crackings of brittle materials although there are many challenges.The present paper summarizes firstly the theoretical framework and advantages of peridy-namics for modeling fracturing.It introduces then the theoretical improvements to address challenges of peri-dynamics in modeling brittle solid crackings including the release of Poisson ratio limit,different fracture criteria,contact-friction models,coupled constitutive models,and computing accuracy.Afterward,the extension of peridynamics is introduced to the coupled modeling with the other methods such as finite element method,phase field method,and particle-like method before its applications in static and dynamic cracking as well as those under impacts.Meanwhile,some contents that require further exploration are briefly summarized.Finally,the blind spots and future development of peridynamics are analyzed and discussed for the deformation and fracturing modeling of brittle geomaterials.