Papers by Keyword: Discontinuities

Abstract: This paper describes the results of a field investigation with the objective of evaluating the possibility to produce drone-derived 3D digital point clouds sufficiently dense and accurate to determine the rock mass rating (RMR) in the underground mine in Bukit Kachi. Agisoft Photoscan software was used for producing the three-dimensional points cloud from the two-dimensional images' sequences. The rock mass rating was evaluated by using Discontinuity Set Extractor (DSE) and Dips 7.0 in Rockscience software. Results from this research show that 3D digital point clouds, derived from the processing of drone-flight images, were successfully used for reliable representation of discontinuity of the tunnel. According to the results of the analysis, both Tunnel A and Tunnel B are classified as "fair rock." Meanwhile, Tunnel A is failing due to geological conditions of feldspar decomposition that are classified as class I, which is "very poor rock." According to Dips 7.0 analysis, the major direction of discontinuity set of Tunnel A for Window right is N300 – N310, while for Window left is N350 – N360. The most dominant discontinuity direction for Tunnel B Window right is N340 – N350, and the orientation for Window left is N10 – N20. When manual mapping and DSE analysis are compared, both orientations of the discontinuity do not give the same direction due to less data reading in the field and high accuracy from the software.

Abstract: The present study aims to show a novel numerical approach for investigating composite structures wherein inclusions and discontinuities are present. This numerical approach, termed Strong Formulation Finite Element Method (SFEM), implements a domain decomposition technique in which the governing partial differential system of equations is solved in a strong form. The provided numerical solutions are compared with the ones of the classic Finite Element Method (FEM). It is pointed out that the stress and strain components of the investigated model can be computed more accurately and with less degrees of freedom with respect to standard weak form procedures. The SFEM lies within the general framework of the so-called pseudo-spectral or collocation methods. The Differential Quadrature (DQ) method is one specific application of the previously cited ones and it is applied for discretizing all the partial differential equations that govern the physical problem. The main drawback of the DQ method is that it cannot be applied to irregular domains. In converting the differential problem into a system of algebraic equations, the derivative calculation is direct so that the problem can be solved in its strong form. However, such problem can be overcome by introducing a mapping transformation to convert the equations in the physical coordinate system into a computational space. It is important to note that the assemblage among the elements is given by compatibility conditions, which enforce the connection with displacements and stresses along the boundary edges. Several computational aspects and numerical applications will be presented for the aforementioned problems related to composite materials with discontinuities and inclusions.

Abstract: The computational treatment of discontinuities within the framework of the finite element method (FEM) is a requirement for simulations of fracturing of solids and has become a challenging topic in computational mechanics. Particularly popular amongst the advanced schemes is the extended finite element method (XFEM) which is based on enrichment of shape functions and falls within the framework of the partition of unity method. Because there is no simple way to track the interface of discontinuities, the computer implementation of the XFEM is not as straightforward as the FEM. One method to solve the interface tracking problem is the level set method (LSM) which introduces another partial differential equation. The level set equation describes the change of an interface due to a known velocity field. To obtain its solution, the FEM can also be employed. This contribution investigates the XFEM-LSM technique with element enrichment and the integration of discontinuous elements for the modelling of cracks or material interfaces. Numerical experiments illustrate the capabilities and accuracy of the resulting formulation.

Abstract: Discontinuities have an important influence on deformation and failure of rock mass in practical engineering. It is one of the key issues in modern rock mechanics to investigate geometric characteristics of joints and fractures inside the rock mass such as shape, size, location and direction etc. Based on the deep analysis of the above geometric properties, it is proposed that the stochastic fractures in the rock mass can be simulated with the random numbers generated by the Monte Carlo method. The related algorithm is designed and implemented. The correctness and effectiveness of the algorithm is verified with an example of a project. This will lay a solid foundation to further study the cutting problems of discontinuous rock block systems.

Abstract: An approach for modeling and numerical simulation of planar components using the edge line concept is developed. With this method, we develop an efficient modeling technique for microstrip discontinuities. The structure presents an arbitrary number of ports, each one with different orientation and dimensions. This article presents a hybrid method based on multimode contour integral and mode matching techniques. The process is based on segmentation and dividing the structure into key building blocks. We use the multimode contour integral method to analyze the blocks including irregular shape discontinuities. Finally, the multimode scattering matrix of the whole structure can be found by cascading the blocks. Therefore, the new method is suitable for analysis of a wide range of waveguide problems. Therefore the present approach can be applied easily to the analysis of any multiport junctions and cascade blocks. The accuracy of the method is validated comparing with results for several complex problems found in the literature. CPU times are also included showing the efficiency of the new method proposed.

Abstract: Seepage properties of fractured rock mass are of prime importance for hydraulic engineering and accurate description of rock fracture geometry parameters is an important and basic task in rock hydraulics. In this paper, an improved K-means clustering algorithm for structural plane of fractured rock mass was first brought forward and the corresponding Matlab program for discontinuity orientations partitioning was compiled and then used in the fitting analysis of dominant orientations of certain dam foundation rock mass. On this basis, combining calculation formulas of multi-group fractures, the permeability tensor and principle value was calculated for the actual dam foundation. The results provide a theoretical and computational reference for other similar projects.

Abstract: Obajana Limestone Mine is operated by Obajana Cement Plc, the largest cement company in West Africa. The mine is located in Obajana town 49km North-West of Lokoja, Kogi State, Nigeria within the Igara-Kabba-Lokoja Schist belt with coordinates N07⁰ 55^l 00^ll and E06⁰ 26¹ 00¹¹. An assessment of the mine pit slope face was carried out in order to evaluate bench slope stability conditions with a view to providing a consistently safe and effective mine pit working environment. Scanline method was used in the geologic mapping of a section of the northern pit-wall of the mine. Empirical method was used to determine rock strength parameters relevant to design and analysis. Factors of safety values - the primary indices for assessing the probability or remoteness of slopes to failure were determined by the traditional limit equilibrium analysis; a most accepted and widely used method among geotechnical engineers. Roclab and RockPack III Software were used as tools for the analyses. Results from kinematics analysis i.e stereographic projections, stereoplots and stereo-analysis identified four sets of pole concentration with three of these lying within the friction cone (Critical area). This implies that the set of discontinuities with these poles will negatively influence stability conditions of the mine pit slope face.

Abstract: By using space-harmonic analysis method, the characteristics of vibrational power flow and sound radiation of an infinite submerged cylindrical shell with internal rings and bulkheads are studied analytically. The harmonic motion of the shell and the pressure field in the fluid are described by Flügge shell equations and Helmholtz equation, respectively. The coupling condition on the outer surface of the shell wall is introduced to obtain the vibrational equation of this coupled system. Both four kinds of forces (moments) between rings and shell and between bulkheads and shell are considered. The solution is obtained in series form by expanding the system responses in terms of the space harmonics of the spacings of both ring stiffeners and bulkheads. The vibrational power flow and radiated sound power are obtained and the influences of various complicating effects such as the ring, bulkhead and fluid loading on the results are analyzed. The analytic model is close to engineering practice, which will give some guidelines for noise reduction of this kind structure.

Abstract: Rock slope failure mechanisms were assessed in this study using KOPEC and RCC quarries as case studies in Oyo state. Discontinuities such as joints and bedding planes were obtained through face mapping and scanline survey of the excavated slopes of the quarries. Stereographic projections of the discontinuities were generated using ROCKPACK III and the stereonets analyzed in accordance with Markland’s plane failure analysis. The results of the analyses show that there are possibilities of plane failures in the south- east region of KOPEC quarry slope face and south –west region of RCC quarry slope face. It is therefore recommended that constant monitoring of the slope failure should be done and the slope angle should be less than 700 and 600 for KOPEC quarry and RCC quarry respectively.