Jiuchang Zhang

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.

Testing and modeling of the mechanical behavior of dolomite in the Wudongde hydropower plant

ABSTRACT In order to understand the mechanical behaviours of the surrounding rocks in the underground caverns of the Wudongde hydropower plant, triaxial tests are performed on a type of dolomite. It is revealed that damage induced by crack development is the main factor controlling the nonlinear plastic deformation and failure behaviour of the dolomite in both pre- and post-peak regimes. Based on this understanding, a coupled elastoplastic damage model is developed for capturing the dolomite’s mechanical behaviours. In the model, the effects of plasticity and damage on rocks is described by introducing plastic hardening and damage softening commonly in the plastic yield surface. Which are both derived from a suitable Helmholtz free energy function. The model is used to simulate the triaxial tests. Comparisons between test results and the numerical modelling show that the developed model is capable of describing the macro mechanical behaviours of the Wudongde dolomite.

Study on Accelerated Creep Properties and Creep Damage Constitutive Relation for Volcanic Breccias

In order to know about the accelerated creep properties of volcanic breccias, triaxial compression rheological experiments are carried out on rock servo-controlled triaxial rheology equipment. Based on the experimental results, the accelerated creep phase of creep curve of volcanic breccias is analyzed. It is shown that the strain rate increases sharply, the rock damage rapidly increases; the acoustic emission dramatic increases with the increase of time during the stage of accelerated creep, and the accelerated growth of rock damage leads to the sharp increase of creep rate. Then based on the accelerated creep deformation, the relation of damage variable versus time is obtained, and and the creep damage constitutive equation of volcanic breccias is established. It is shown that the established nonlinear creep damage models based on time function is correct and reasonable.

An Elasto-plastic Model and Its Return Mapping Scheme for Anisotropic Rocks

Based on an anisotropic failure criterion that includes a scalar parameter in terms of the mixed invariants of the stress and micro-structure tensors, an elasto-plastic model is suggested for the description of mechanical properties of transversely isotropic rocks. And on the basic principles of return mapping, we deduce the formulations of return mapping suit for transversely isotropic rocks, especially the second derivative of plastic potential function and unsymmetrical consistent constitutive matrix. For application, an experimental program is conducted and several tests of argillite specimens are simulated with various confining pressures and loading orientations. The comparison reveals that the proposed model and its return mapping scheme are suitable for describing the mechanical properties of argillite.

Temporal and spatial distribution of the grout pressure and its effects on lining segments during synchronous grouting in shield tunnelling

Abstract The advance of tunnel shield creates void between the lining segments and the surrounding rock at the tail part of the tunnel shield. Grout is continuously injected into that void, to control the ground subsidence and maintain the segments stability. The grouting process must be precisely controlled and monitored to prevent any undesired significant subsidence or segment damage. In this work, a novel model to characterise the temporal and spatial distribution of the grout pressure in the rock-segment void is proposed, based on the theory of group diffusion and consolidation. The temporal variation of the grout viscosity is also considered in the proposed model. The proposed model is verified against field monitored data of the grout pressure, and exhibits quite good performance. Then a three-dimensional finite element model of the lining segments is developed to study the effects of the grout pressure on the mechanical response of the lining segments. The mechanical responses of the lining segments, in terms of internal force, moment and stress profile, are thoroughly analysed. These mechanical responses are also verified against the field monitored data, to further validate the proposed model of grout pressure distribution.

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.