R.B. Wang

Experimental studies on hydro-mechanical properties of metamorphic rock under hydraulic pressures

The research on the hydro-mechanical coupling of metamorphic rock is of great importance in rock engineering. The main purpose of this study was to investigate the hydro-mechanical properties of metamorphic rock based on the experimental data from triaxial compression tests. Metamorphic rock samples taken from an underground oil storage facility were tested under different hydraulic pressures using a rock servo-controlled triaxial rheology test system. The results indicated that hydraulic pressure had impact on the strength, deformation and permeability of the metamorphic rock. Based on the test results, the stress–strain behaviour and permeability evolution of the rock samples show three stages. The mechanical properties of the metamorphic rock are presented in detail for the three stages in the whole stress–strain process. The derived mechanical parameters are correlated to the division of the phases. The relationship between hydraulic pressure and axial strain, lateral strain, volumetric strain and permeability are analysed and discussed, especially the influence of hydraulic pressure on various parameters in the hydro-mechanical process. The influence of the hydraulic pressure on the failure mode of the rock under coupled conditions is described.

Permeability Evolution of Granite Gneiss During Triaxial Creep Tests

Permeability is an important factor for seepage analysis of rock material, and a key factor in ensuring the safety of underground works. In this study, the permeability evolution of granite gneiss during triaxial creep tests was investigated. In the context of an underground oil storage cavern in China, a series of hydro-mechanical coupling creep tests were conducted on rock cores of granite gneiss at three different pore pressures to reveal the effect of pore pressure on the permeability evolution and to investigate the correlation between the permeability and volumetric strain during the creep process. During the creep tests, the permeability decreases in the initial loading phase. At all deviatoric stress levels, the permeability remains stable in the steady creep stage and increases rapidly in the accelerated creep stage. Based on the test data, the initial permeability, steady permeability and peak permeability at various stress levels are defined. The effect of pore pressure on the permeability is captured by a linear model. In addition, the relationship between permeability and volumetric strain can be described as a process divided into three phases, with different functions in each phase.

Deformation and control engineering related to huge landslide on left bank of Xiluodu reservoir, south-west China

This paper reports a comprehensive investigation on the deformation characteristics, failure mechanism and stabilisation treatment of Baitieba slope on the left abutment of Xiluodu hydropower plant on the downstream reach of Jinsha River. In the first two years following the excavation, the development of the slope movement after rainfall became a threat to the water inlet and spillway tunnels constructed beneath it, as well as to the construction of the plant. On the basis of field investigation and real-time monitoring, the deformation characteristics and the failure mechanisms of the slope were investigated. There are two sliding surfaces in the slope: a shallow one which is a rotational slide; a deep one as a result of the reactivation of the ancient slip zone induced by excavation which is a translational slide. The deep sliding surface is dominant in translating the global soil mass to move. Based on the analysis of the movement tendency and stabilities, the efficacies of the used stabilisation measures, including reinforcements, piles, concrete protections, drainages and infiltration protection are assesses. It has been found that the used treatments effectively retarded the deformation of the slope to a very slow creep rate of .33–.64 mm/month in the last two year. The slope is gradually stabilised.

A nonlinear creep damage model for brittle rocks based on time-dependent damage

Many experiments conducted under the three-dimensional stress condition reveal that damage of brittle rocks shows obvious deformational and time-dependent effect. Based on triaxial rheological test results, the creep behaviours and creep rupture characteristics of metamorphic volcanic fine conglomerate were investigated. It is found that the test results agree well with numerical curve, and the relationship between creep damage variable and loading time can be fitted by an exponential function. By analysing the tertiary creep, a new nonlinear viscoplasticity model on the basis of creep damage was proposed, and then, the three-dimensional nonlinear creep damage constitutive equations were deduced and validated by tests. Comparisons between numerical predication and test data show that this nonlinear creep damage model is valid and reasonable. Therefore, it can better describe the complete creep phases of the metamorphic volcanic fine conglomerate, which include primary creep, secondary creep and tertiary creep.

Experimental Investigation of the Anisotropic Mechanical Properties of a Columnar Jointed Rock Mass: Observations from Laboratory-Based Physical Modelling

Because of the complex geological structure, determination of the field mechanical parameters of the columnar jointed rock mass (CJRM) was a challenging task in the design and construction of the Baihetan hydropower plant. To model the mechanical behaviour of the CJRM, uniaxial compression tests were conducted on artificial CJRM specimens with geological structure similar to that found in the actual CJRM. Based on the test results, the anisotropic deformation and strength were mainly analysed. The empirical correlations of evaluating the field mechanical parameters were derived based on the joint factor approach and the modulus reduction factor method. The findings of the physical model tests were then used to estimate the field moduli and unconfined compressive strengths of the Baihetan CJRM. The results predicted by physical model tests were compared with those obtained from the field tests and the RMR classification system. It is concluded that physical model tests were capable of providing valuable estimations on the field mechanical parameters of the CJRM.

A study on the fractal characteristics of displacement time-series during the evolution of landslides

Abstract Landslides are one of the major natural disasters that are frequently occurring in southwestern China. The main objective of this study is to investigate the relationship between failure of landslide and fractal dimension using displacement time-series. Taking two slopes in southwestern China as examples, we estimate the fractal parameters of displacement time-series and analyze the relationship between fractal dimension and the stability of the slope during the evolution of landslides. The result shows that the fractal dimension increases when a landslide undergoes a transition from stability to failure, but decreases during the evolution from active to stable. Fractal dimension has a critical value of 1.10 in the transition between active and stable, which indicates that fractal dimension is an important nonlinear parameter in the evaluation of the stability of landslides, although more studies and in situ data are required for validation.

Robust equivalent tunnelling Mohr–Coulomb strength parameters for generalised Hoek–Brown media

A novel robust method for estimating equivalent tunnelling Mohr–Coulomb strength parameters in elastic–plastic or elasto–brittle–plastic media satisfying Hoek–Brown failure criterion is proposed. Based on the best uniform approximation technique, this method consists of explicit and closed-form formulae in terms of elementary functions, making the estimation of equivalent parameters more convenient than other methods. A simple code is provided and a series of benchmark test cases are performed for validation. When the tunnel support is accurately known, the performance estimates of this method are better than estimates of best fitting in an artificial stress range and best fitting in the existing range methods, but not as accurate as the performance of equating model responses method and that proposed by Jimenez et al. However, when the estimation of support pressure is poor, this method is the most robust among all methods. In elasto–brittle–plastic rock mass, the advantage of robustness of this method is even more obvious. Considering both accuracy and robustness, this method can be employed as a preferable alternative.

Mechanism of continuous movement and long-term safety analysis of Baitieba landslide based on field monitoring data and numerical simulation

Baitieba landslide, located on the left bank of Xiluodu reservoir, is an ancient landslide. The landslide slides along the shallow and deep sliding surfaces after excavation. Sliding along the shallow sliding surface has become stabilised by and large; whereas sliding along the deep sliding surface still continues after some effective and systematic treatments. Based on the data of inclinometer boreholes observed in the field, a detailed investigation into the mechanism of continuous sliding along the deep sliding surface is carried out. It is found that slow creep of the ancient sliding zone is a predominant factor, and its creep deformation has undergone two stages: attenuation of creep deformation and linear increase of creep deformation. A numerical simulation, considering creep behaviour of the ancient slip zone, is also conducted to verify the mechanism of movement of the landslide inferred from the monitoring data of inclinometer boreholes. Using the monitoring data, long-term stability of the landslide is analysed and it is concluded that the landslide is stable overall.

A Coupled Elastic-Plastic Damage Model for Rock Material

With complex mechanics character and under the action of compression and tension in tri-direction, rock will show coupled plastic-damage mechanism as its basic character. Phenomenological coupled elastic-plastic-damage constitutive model with internal variable is proposed based on thermal mechanics theory, elastic law and macro damage mechanics. Numerical experiments on this model and analyze the model character. The result shows that the coupling model could realize rocks softening behavior brought about by damage and strength enlargement caused by confining pressure increasing.

Modeling Coupled Flow-Stress-Damage during Creep Deformation

In order to reflect the tertiary rheological characteristics of hard rocks at the high stress states, a new nonlinear visco-elastic-plastic model is proposed on the basis of linear visco-elastic-plastic model and nonlinear visco-elastic-plasticity. And then the corresponding constitutive model are deduced, which can be used for describing rocks’ long-term strength characteristics and their creep deformational behavior and time-dependent damage under interaction of coupled seepage-stress field in rock engineering. At last, considering the time effect of rock damage in the process of tertiary creep, a coupled seepage -stress creep damage model for investigating the whole creep deformation behavior, including tertiary creep failure process is established, and the related equations governing the evolution of stress, creep damage and rock permeability along with the creep deformation of rock is introduced.