Application of MBC analysis for support design of underground cavern (original) (raw)
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International Journal of Rock Mechanics and Mining Sciences, 2004
An analysis method that can grasp the behavior of a rock mass is necessary to establish a rational method for designing and constructing large-scale caverns. In underground excavation, sliding and opening of joints due to stress relaxation are considered to be the governing mechanisms of the behavior of a jointed rock mass. In the present study, a micromechanics-based continuum model of a jointed rock mass is proposed and an analysis method for underground excavation is developed. To examine the performance of the proposed method, the excavation of Shiobara power station cavern constructed by the Tokyo Electric Power Co., Ltd. is analyzed and results are compared to measured data. In numerical results, for instance, displacement of the measurement facilities during excavation are in good agreement with measured data. r
Parameter analysis of MBC model for underground cavern
The accurate analysis of rock with joints is urgently needed to improve the predictions of rock behavior and to design the support of underground caverns in rock reasonably. Horii and Yoshida proposed a Micromechanics Based Continuum (MBC) model that enables to take the opening and shear slip of joints into account by replacing the rock mass containing joints with an equivalent continuum. This study applied the MBC model to a cavern excavation analysis and examined its applicability using joint and quantity of support as parameters. ' ' tan J n J s J n
International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1997
The governing mechanism of behaviors of rock mass during excavation of a large scale cavern is found to be sliding and opening of joints initially closed by earth pressure. A constitutive model of jointed rock mass is proposed applying MBC (micromechanics-based continuum) approach. The model reflects the behaviors of joints in the analysis of a large-scale cavern. The problem of excavation of a large-scale underground power station cavern constructed by Tokyo Electricity Power Company in Japan is analyzed, and numerical results are compared with measurement data. derived from a relationship between average stress and average strain over a representative volume element (R.V.E) which contains a lot of microstructures. This theory is suitable for the analysis of rock mass containing a number of joints.
Coupling Analysis of Deformation and Flow in Jointed Rock Mass during Cavern Excavation
Mechanical behaviors of geological material are governed by the existences and behaviors of microstructures such as joints or microcracks in rock mass. During cavern excavation, not only the mechanical properties but also permeability of jointed rock mass are changed due to joint deformation. In this article, the coupled modeling of deformation and flow of jointed rock mass is carried on the basis of the Micromechanics-Based Continuum approach (MBC approach). The derived model is implemented into the MBC analysis, which enables us to carry the excavation analysis of a cavern and obtain the distribution of displacement, stress, strain and permeability of rock mass and the deformation of joints.
Simulation of excavations in jointed rock masses using a practical equivalent continuum approach
International Journal of Rock Mechanics and Mining Sciences, 2002
A simple practical equivalent continuum numerical model previously presented by Sitharam et al. (Int. J. Rock Mech. Min. Sci. 38 (2001) 437) for simulating the behaviour of jointed rock mass has been incorporated in the commercial finite difference programme fast Lagrangian analysis of continua (FLA C). This model estimates the properties of jointed rock mass from the properties of intact rock and a joint factor (Jr), which is the integration of the properties ofjoints to take care of the effects of frequency, orientation and strength of joint. A FISH function has been written in FLA C specially for modelling jointed rocks. This paper verifies the validity of this model for three different field case studies, namely two large power station caverns, one in Japan and the other in Himalayas and Kiirunavara mine in Sweden. Sequential excavation was simulated in the analysis by assigning null model available in FLACto the excavated rock mass in each stage. The settlement and failure observations reported from field studies for these different cases were compared with the predicted observations from the numerical analysis in this study. The results of numerical modelling applied to these different cases are systematically analysed to investigate the efficiency of the numerical model in estimating the deformations and stress distribution around the excavations. Results indicated that the model is capable of predicting the settlements and failure observations made in field fairly well. Results from this study confirmed the effectiveness of the practical equivalent continuum approach and the joint factor model used together for sol',ing various problems involving excavations in jointed rocks. (t)
Parametric study for a large cavern in jointed rock using a distinct element model (UDEC—BB)
International Journal of Rock Mechanics and Mining Sciences, 1998
Parametric studies are performed using the distinct element computer program UDEC-BB for a large cavern in the Himalayas. The studies provide insights into some important deformation mechanisms in a numerical system of blocks. The sensitivity studies involving changes in joint spacings (block size) revealed that the deformations around an opening are dependent on the size or the number of blocks adjacent to the excavation. Large size blocks deform mainly through translational shear upon which rotational shear may occur. In a model in whieh the block size is small compared to the tunnel dimensions, the tendency to dilation across an increased number of non-planar joints may contribute to interlocking of blocks. The BB joint behavioural model which allows the modelling of the dilation accompanying shear and hence the build-up of higher normal stresses, predicts smaller deformations than the Mohr-Coulomb model in which the dilation angle is constant. The sensitivity studies involving changes in key BB joint shear strength parameters have shown that, within the range of values considered, the model output is relatively insensitive to assumed joint strength parameters joint roughness coefficient and (at. However, an increase in the joint wall compressive strength contributes to an increase in the joint shear strength resulting in a marked reduction of displacements around the opening.
Stability Analysis and Design of Rock Support for Tunnel and cavern of Kathmandu University Geo-lab
Kathmandu University Journal of Science, Engineering and Technology
This study focuses on the design and stability analysis of underground structures in the Lesser Himalayan Region of Nepal. The rock support design for such opening depends upon the rock mass strength. In this study a proposed Kathmandu University Geo-Lab tunnel and cavern, which passes through weak rock mass conditions, was used as a case study. Existing empirical and analytical methods for the stability of the proposed tunnel and cavern are used for the estimation of support pressure and design support. A detailed numerical study was carried out in 2D finite element analysis to design the tunnel in such region. The results of analysis showed that the support pressure and deformation can be predicted very well from the numerical analysis.Kathmandu University Journal of Science, Engineering and TechnologyVol. 13, No. 1, 2017, page: 1-19
Rock mechanics or rock engineering was developed since the 1960s, but the underground excavation in rocks is still at its infant stages. The construction and maintenance of underground rock tunnel or caverns require prudent and detailed designs in the excavation process. To be able to predict the effects of the excavation process and estimate the effectiveness of the support designs, one has to understand the properties of the rock materials and their likely behaviour with the physical elements. This places great importance on the study of the deformation of the rock tunnel during excavation, particularly because deformations such as inward displacement can influence its stability. In this project, using stress analysis, investigations on the extent of deformation of rock tunnels during excavation will be conducted. Also uncover out the factors that contribute to the instability and displacement of underground excavations.
International Journal of Rock Mechanics and Mining Sciences, 1997
The paper discusses the results of a numerical study which examines the influence of joint constitutive models on the response of a specific jointed rock mass made up of an anisotropic rock (slate). It presents a comparison between predicted convergences and displacements of rock mass surrounding a pilot gallery, and those measured during field investigations. To perform this analysis, the two-dimensional Distinct Element Method code, UDEC, is used and three joint laws are compared. Based on field investigations for site characterisation, two models are constructed according to fracture density (MODEL A and MODEL B). For each of them, the influence of joint constitutive law on the stability of the gallery is examined, and comparisons between the investigations and predictions are made. Examination of the results shows that there is no noticeable change in stress magnitudes between laws. The displacement magnitudes depend on (1) the constitutive law, (2) the input model parameters and (3) the fracture density. A parametric study in the case of MODEL A indicates that a relatively good match between predicted and measured displacements around the gallery can be observed in certain areas.