With the rapid development of nuclear power in China, the disposal of high-level radioactive waste (HLW) has become an important issue for nuclear safety and environmental protection. Deep geological disposal is internationally accepted as a feasible and safe way to dispose of HLW, and underground research laboratories (URLs) play an important and multi-faceted role in the development of HLW repositories. This paper introduces the overall planning and the latest progress for China's URL. On the basis of the proposed strategy to build an area-specific URL in combination with a comprehensive evaluation of the site selection results obtained during the last 33 years, the Xinchang site in the Beishan area, located in Gansu Province of northwestern China, has been selected as the final site for China's first URL built in granite. In the process of characterizing the Xinchang URL site, a series of investigations, including borehole drilling, geological mapping, geophysical surveying, hydraulic testing and in situ stress measurements, has been conducted. The investigation results indicate that the geological, hydrogeological, engineering geological and geochemical conditions of the Xinchang site are very suitable for URL construction. Meanwhile, to validate and develop construction technologies for the Beishan URL, the Beishan exploration tunnel (BET), which is a 50-m-deep facility in the Jiujing sub-area, has been constructed and several in situ tests, such as drill-and-blast tests, characterization of the excavation damaged zone (EDZ), and long-term deformation monitoring of surrounding rocks, have been performed in the BET. The methodologies and technologies established in the BET will serve for URL construction. According to the achievements of the characterization of the URL site, a preliminary design of the URL with a maximum depth of 560 m is proposed and necessary in situ tests in the URL are planned.

The Beishan underground research laboratory for geological disposal of high-level radioactive waste in China: Planning, site selection, site characterization and in situ tests

A micro-mechanics based plastic damage model for quasi-brittle materials under a large range of compressive stress

The identification of crack stress thresholds and damage evolution from circumferential strain control triaxial tests are presented in this paper. As underground excavations become deeper to exploit mineral resources or construct civil projects, it has become increasingly important to determine the full stress–strain and damage evolution behaviours of brittle rock. Therefore, post-peak reaction of Class II rock or ‘snap-back’ behaviour must be captured to show the response of the material under self-sustaining failure. To investigate this, a series of triaxial compression tests were carried out for a granite sourced from over 1000 m depth. The tests were controlled using the feedback of lateral strain gauges attached to the Hoek cell membrane, to allow for constant, slow dilation of the specimen. The test results were then input to existing methods along with two new techniques, to identify the crack stress thresholds of crack closure, crack initiation and damage. It was found that although the crack closure threshold is comparable for axial and lateral control testing, the crack initiation and damage thresholds are significantly higher for the tests conducted in this study compared to most existing research. This result highlights the importance of the circumferential strain control method in triaxial tests when determining the post-peak behaviour and damage evolution of brittle rock. This was made easier with the strain gauged membrane proposed in this study, which provides reliable measurements throughout the duration of rock testing. Therefore, full stress–strain and damage evolution data can be obtained for use in damage-plasticity constitutive models.

Experimental Study on the Damage Evolution of Brittle Rock Under Triaxial Confinement with Full Circumferential Strain Control

A coupled elastoplastic damage model for brittle rocks and its application in modelling underground excavation

A Plastic Strain-Induced Damage Model of Porous Rock Suitable for Different Stress Paths

Based on experimental investigations, we propose a coupled elastoplastic damage model to simulate the mechanical behavior of granite under compressive stress conditions. The granite is taken from the Beishan area, a preferable region for China’s high-level radioactive waste repository. Using a 3D acoustic emission monitoring system in mechanical tests, we focus on the cracking process and its influence on the macroscopic mechanical behavior of the granite samples. It is verified that the crack propagation coupled with fractional sliding along the cracks is the principal mechanism controlling the failure process and nonlinear mechanical behavior of granite under compressive stress conditions. Based on this understanding, the coupled elastoplastic damage model is formulated in the framework of the thermodynamics theory. In the model, the coupling between damage and plastic deformation is simulated by introducing the independent damage variable in the plastic yield surface. As a preliminary validation of the model, a series of numerical simulations are performed for compressive tests conducted under different confining pressures. Comparisons between the numerical and simulated results show that the proposed model can reproduce the main features of the mechanical behavior of Beishan granite, particularly the damage evolution under compressive stress conditions.

Damage and Plastic Deformation Modeling of Beishan Granite Under Compressive Stress Conditions

Titanium and its alloys are widely used as implant biomaterials due to their well mechanical properties and biological compatibilities. Nb and Mn are well‐known alloying elements with biological potential. Herein, the Ti–Mn–Nb phase equilibria at 900 °C (Ti‐rich region) is determined and published. According to the β single‐phase field in this phase diagram (at 900 °C), Ti–xMn–yNb (x = 4, 10, 16; y = 2, 8, 14, at%) alloys are selected and fabricated which are suited for solution heat treatment. The Ti–Mn–Nb alloys are investigated by optical microscopy (OM), X‐ray diffraction (XRD), and mechanical testing. A unique diffraction pattern (interpreted as occurrence of a transition phase) is observed by transmission electron microscopy (TEM) in Ti–10Mn–2Nb. In the in vitro evaluation, the human osteoblasts (MG63) adhere well and proliferate on the surface of Ti–xMn–yNb (x = 4, 10; y = 2, 8, 14, at%). According to cell culture experiments, the alloys are nontoxic to human osteosarcoma cells in comparison with pure titanium. Based on a performed screening study, different titanium alloys Ti–4Mn–yNb (y = 2, 8, 14) appear as the biomaterial with the highest potential around 700 MPa ultimate tensile strength and 9–10% elongation.

A New Kind of Biomedical Ti–Mn–Nb Alloy

Experimental investigation and thermodynamic calculation of the phase equilibria in the Fe-Nb-Ti ternary system

Phase Equilibria in the Fe-Al-Sn Ternary System

Experimental investigation of phase equilibria in the Co–Si–Zr ternary system

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