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Characterization of underground rock masses employing structure from motion: Application to a real case
Published in Daniele Peila, Giulia Viggiani, Tarcisio Celestino, Tunnels and Underground Cities: Engineering and Innovation meet Archaeology, Architecture and Art, 2020
R. García-Luna, S. Senent, R. Jurado-Piña, R. Jimenez
A good knowledge of the discontinuity network in a rock mass is fundamental for the design and control of tunnels under construction, as discontinuities are surfaces of weakness that control the occurrence of unstable blocks in the tunnel and the loads imposed by the blocks on the excavation support (Goodman 1976, Hudson & Harrison 1997). However, characterizing these discontinuities using manual methods (i.e. direct measurements made with compass) can impose a risk on the safety of the operators who take the data, as the (unsupported) tunnel face is the area of the tunnel with a higher risk of collapse (Slama et al. 1980, Health and Safety Executive 1996). In addition, the results obtained manually are often very subjective, depending on factors such as the access conditions to the outcrop, the number of measurements made, the worker´s ability, the time available and the scale of the problem.
Rock strength properties and their measurement
Published in Duncan C. Wyllie, Christopher W. Mah, Rock Slope Engineering, 2017
Duncan C. Wyllie, Christopher W. Mah
The actual shear performance of discontinuity surfaces in rock slopes depends on the combined effects of the surface roughness, the rock strength at the surface, the applied normal stress and the amount of shear displacement. This is illustrated in Figure 4.12 where the asperities are sheared off, with a consequent reduction in the friction angle with increasing normal stress. That is, there is a transition from dilation to shearing of the rock. The degree to which the asperities are sheared will depend on both the magnitude of the normal force in relation to the compressive strength of the rock on the fracture surface, and the displacement distance. A rough surface that is initially undisturbed and interlocked will have a peak friction angle of (φ+i). With increasing normal stress and displacement, the asperities will be sheared off, and the friction angle will progressively diminish to a minimum value of the basic, or residual, friction angle of the rock. This dilation–shearing condition is represented on the Mohr diagram as a curved strength envelope with an initial slope equal to (φ + i), reducing to φr at higher normal stresses.
Modeling material failure in large concrete structures: recent computational developments
Published in Günther Meschke, René de Borst, Herbert Mang, Nenad Bićanić, Computational Modelling of Concrete Structures, 2020
S. Blanco, A.E. Huespe, J. Oliver, M.D.G. Pulido
In recent years increasing achievements have been reached on numerical modelling of cracking of concrete. New techniques, like the strong discontinuity modelling using finite elements with embedded discontinuities, E-FEM, X-FEM etc., have overcome important numerical problems like mesh size and mesh bias dependencies of the results (Oliver & Huespe 2004a) allowing larger elements than with alternative techniques (smeared approach, non-local and gradient approaches etc.) and opening a door to numerical modelling of larger and more realistic concrete structures. However, many times robustness issues still limit the applicability of the existing techniques to reduced size specimens. When material failure at large, three dimensional, concrete structures is aimed at being modelled, two principal obstacles are found (Oliver et al. 2005, Jirasek 2000) The lack of robustness of the existing techniques, requiring very skilful procedures, like arc-length methods combined with automatic time step reductions, which increase the computational costs up to unaffordable values.Loss of convergence of the non-linear computations, which cannot be achieved in many occasions. In those cases, the critical (collapse loading) and post-critical ranges of the structural behaviour cannot be reached, and one of the main goals of the failure analysis (the assessment of the safety factor of the structure) cannot be fulfilled.
Analytical and numerical assessment of a preliminary support design – a case study
Published in Cogent Engineering, 2021
Sylvanus Sebbeh-Newton, Shaib Abdulazeez Shehu, Prosper Ayawah, Azupuri A. Kaba, Hareyani Zabidi
For the entire project, scanline surveys and drilled cores according to ISRM (2015) were used to describe the discontinuities and define the rock quality designation (RQD). The discontinuity studies comprised width and infill type, degree of weathering, orientation, persistence, opening, roughness, and spacing of measured discontinuities. Dip and dip direction measurements were processed with Dips 7.0 software based on equal-angle stereographic projection (Figure 3) to identify the joint sets for each section. The joint sets in NATM-1 have close to very close spacing with occasional wide spacing, medium persistence, very tight to tight opening, rough to smooth planar roughness, slickenside, and moderate to high weathering characteristics. The attitudes of the identified joint sets in the various sections are listed in Table 1. Laboratory experiments including unit weight (γ), uniaxial compressive strength (σci), Young’s modulus (Ei,), Poisson’s ratio, and triaxial test were conducted on the core samples drilled from rock blocks of all the geological units based on techniques suggested by ISRM (2015).
Applicability of the classical fracture mechanics criteria to predict the crack propagation path in rock under compression
Published in European Journal of Environmental and Civil Engineering, 2020
Mahmoud Alneasan, Mahmoud Behnia, Raheb Bagherpour
It is worth to be mentioned that most of studies associated with LEFM were focused on the initial extension angle, but by taking into account crack trajectory from the crack tip to material boundary or a specific point in the material, previous criteria may show important differences. Therefore in this study it is focused on the predicting of crack propagation path under mixed mode loading I–II by employing a numerical model which takes into consideration σ, G and S criteria. For numerical model, displacement discontinuity method which is a branch of boundary element method was implemented in this study. This method considered as a powerful numerical method for modelling cracking problems and has been extensively used in fracture mechanics (Aliabadi & Rooke, 1991; Castelli & Scavia, 2004; Crouch, Starfield, & Rizzo, 1983). A numerical code (TDCPC) (Behnia et al., 2012) is developed in this study to predict crack propagation path under σ, S and G criteria.
Analytical stochastic analysis of rock wedge stability using a JDRV method considering the residual factor as a random variable
Published in Geomatics, Natural Hazards and Risk, 2020
Chao Hu, Danqing Song, Zhuo Chen
In the field of rock slope engineering, the peak and residual strength of discontinuity planes can usually be obtained by the direct shear test. However, a suitable method that can determine the value of R for the discontinuity planes has rarely been reported in the literature. Fortunately, a method that can estimate the mean value of R in strain-softening soils can inspire us. In this method, the mean of R can be estimated as the ratio of the length under the residual shear strength to the total length of a slip surface (Metya et al. 2019). In fact, a formula could obtain from rewriting Equation (6). Moreover, Af is assumed to be the area of the discontinuity planes at the peak strength, and A is the total area of the discontinuity planes. Therefore, the average strength of the discontinuity planes should be given by To compare the two formulas, a simple conclusion could be derived, i.e., R is essentially identical to the ratio of the areas at the peak strength to the total areas of discontinuity planes. According to this opinion, we may find a simple method to determine the value of R.