Commonly used to design excavations in rock, empirical rock-mass classification systems make design recommendations on the basis of experience in similar geologic conditions and are generally ...considered conservative. Numerical methods make it possible to develop design procedures, in which the influence of joint properties and other variables can be assessed directly. This study examined the mechanical response of a jointed rock mass around a supported circular tunnel, using the distinct element code UDEC. This response was compared to that predicted by continuum analysis, using properties derived from empirical systems. The Rock Mass Rating (RMR) system, Bieniawski 1976, and the Hoek-Brown failure criterion, Hoek, Brown 1980, were examined in this study. Five rock mass parameters were varied: orientation, spacing, condition, location of the joints, and the state of stress. Data from numerical models suggested that, for most of the rock mass models, RMR provided reasonably conservative results except in cases when the orientation of the joints caused the models to behave anisotropically. In such cases, continuum models, using material properties predicted by RMR, overestimated the rock mass strength predicted by discontinuum models.
After long-term sedimentary structure effect, the coal face roof rock itself appeares various fractures and after mining the coal, owing to mine pressure appeared, part of goaf overburden rock ...gradually become distortion,delamination even fall. Due to the collapse of roofs, formation of air disasters are related to the caving height. Therefore, study the caving height is a key factor of realizing mine safe and effective production. This paper bases on the background of One Mine, using UDEC to study 5-3s soft rock mine working face of goaf caving height, first weighting interval and cycle weighting interval. By analyzing the simulation results, it reflects the relationship between advancing degree of working face and the goaf caving height. The conclusion provides a reference for resolving the problem of mine roof collapse in similar mine.
The article took Chang Gou yu coal mine for example. Based on the scene investigation and the ore presses monitor, According to the geological conditions of Chang Gou yu coal mine,we made the ...numerical simulation of mining face. After analyzed the abutment pressure and it's coverage of the first caving, the old roof first weighting and the old roof periodic weighting, Combined with the mine pressure monitoring data and the mine pressure appear law of the mining face, the article can take some reference for safety, high production, and efficiency exploitation.
This project determines the tensile strength of lithophysal analog rock and presents failure criteria that can be used by geotechnical engineers to evaluate underground structures in rock. The ...physical and mechanical properties that are related to the failure criterion, such as porosity, compressive strength and modulus of elasticity, are also discussed. Experimental tensile tests were made using direct uniaxial and indirect Brazilian tests. Three 4-inch specimens were fabricated and tested in direct uniaxial tensile tests using Hydro-Stone TB. The results showed that the elastic tensile modulus of elasticity was within two percent of existing data for the compressive modulus of elasticity. The direct tests were not successful in determining the ultimate tensile strength, as failure occurred at the connections. Twenty 4-inch diameter by 2-inch long specimens were fabricated and tested using the indirect Brazilian tensile test method. Hydro-Stone TB was also used as the analog material in the Brazilian indirect tests. The Brazilian tests were successful in determining the splitting tensile strength and the effect of porosity on the ultimate tensile strength of the Hydro-Stone TB specimens. Results showed that the tensile strength of the specimens was approximately 10 percent of the compressive strength. New test data were obtained for 0 (solid), 6.2, 12.5 and 18.7 percent porosities. Photographs, figures and graphs are shown for the test setups and results. Computer simulations of both direct and indirect tensile testing were made using Itasca's UDEC 2D, 3.1 computer program. The computer results were then compared with the experimental data. The results showed that the UDEC computer models can successfully predict the cracking patterns of the experimental test specimens. Results of the experimental tensile tests were combined with existing compressive test data and the Mohr-Coulomb, Mohr-Coulomb in s-t Space, Griffith and Power Failure Criteria were then formulated from these test data. Also, the four criteria were used to show the effect of porosity on the failure strength of the analog rock material for porosities between 0 and 18.7 percent.
Le mécanisme de fauchage gravitaire est l’un des phénomènes évoqués pour expliquer des glissements dans des roches stratifiées, schistosées ou foliées présentant un pendage opposé à la pente du ...talus. Ce processus est souvent suggéré comme première étape du développement du glissement de terrain de La Clapière dans les Alpes-Maritimes. Des modélisations numériques par éléments distincts ont été effectuées afin de représenter ce mécanisme. Leur but était d’analyser si ce scénario descriptif et qualitatif était mécaniquement admissible et quelles étaient les conditions dans lesquelles il pouvait se réaliser. Des modèles simples, « conceptuels » du phénomène de fauchage gravitaire sont présentés. Ils permettent de mettre en évidence certaines conditions nécessaires pour amorcer le phénomène de fauchage gravitaire. La modélisation bidimensionnelle, par éléments distincts du site de La Clapière est ensuite exposée. Le mécanisme de fauchage n’a pas pu être simulé sur ce versant avec les paramètres introduits dans le modèle. Cette constatation a conduit à s’interroger sur la légitimité de cette hypothèse.
The mechanism of gravitational toppling is often mentioned to explain movements in layered, schistosed or foliated rocks with respectively bedding planes, shistosity or foliation dipping steeply into the slope. This mechanism is in particular suggested as the beginning of the « La Clapière » landslide situated in the south part of the Alpes. Distinct elements numerical modelling was carried out in order to represent this mechanism. The aim of these simulations was to analyse if the descriptive and qualitative scenario put forward was mechanically acceptable and what were the conditions under which it could have occurred. Initially, simplified « conceptual » models of gravitational toppling are presented. They highlight some of the conditions required to start the gravitational movement. Two-dimensional modelling of the site is then presented. With the geometrical and geotechnical parameters introduced, it was not possible to simulate a toppling phenomenon. This outcome led to the reconsideration of this hypothesis.
Taking the fragment ore section of orebody No. 105 with the high value in Gaofeng mine in Guangxi province for example, three representative kinds of goafs in all scales were selected on the basis of ...the differences of goaf scale, surrounding rock conditions and situ stress field, and their stability were calculated by the universal distinct element code (UDEC). The calculation results showed as follows: 1) with the increase of goaf scale, the tensile stress scope in the goaf roof expanded from 12 m to 60 m; 2) the tensile failure mode of joints surfaces was primary, and that of ore block was auxiliary; 3) the maximum principal stress peak could reach 40.3 MPa which exceeded rock body tensile strength 38.07 MPa, but the influence on goaf stability was small because the peak was far away from goaf; 4) the plastic zone in roof changed from 7 m to 12 m because of the increased scale, so the goaf stability became worse gradually; 5) the objective principles that the whole plastic zone distributed on the left part of goaf roof and no plastic zone in pillar provided reference for choosing proper position of filling wellhead.
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