• Title/Summary/Keyword: rock failure

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A Comparative Study of Simplified Probabilistic Analysis Methods for Plane Failure of Rock Slope (암반사면의 평면파괴해석을 위한 간이 확률론적 해석 비교연구)

  • Kim, Youngmin
    • Tunnel and Underground Space
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    • v.31 no.5
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    • pp.360-373
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    • 2021
  • Many sources of uncertainty exist in geotechnical analysis ranging from the material parameters to the sampling and testing techniques. The conventional deterministic stability analysis of a plane failure in rock slope produce a safety factor but not a probability of failure or reliability index. In the conventional slope stability analysis by evaluating the ground uncertainty as an overall safety factor, it is difficult to evaluate the stability of the realistic rock slope in detail. This paper reviews some established probabilistic analysis techniques, such as the MCS, FOSM, PEM, Taylor Series as applied to plane failure of rock slopes in detail. While the Monte - Carlo methods leads to the most accurate calculation of the probability of safety, this method is too time consuming. Therefore, the simplified probability methods could be alternatives to the MCS. In this study, using these simple probability methods, the failure probability estimation of a plane failure in rock slope is presented.

Comparative Study on the Rock Failure Criteria Taking Account of the Intermediate Principal Stress (중간주응력을 고려한 선형 및 비선형 암석파괴조건식의 비교 고찰)

  • Lee, Youn-Kyou
    • Tunnel and Underground Space
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    • v.22 no.1
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    • pp.12-21
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    • 2012
  • Although the Mohr-Coulomb and Hoek-Brown failure criteria have been adopted widely in rock mechanics, they neglect the ${\sigma}_2$ effect. The result of true triaxial tests on rock samples, however, reveals that the ${\sigma}_2$ effect on strength of rocks is considerable, so that rock failure criteria taking into account the influence of ${\sigma}_2$ are necessary for the precise stability evaluation of rock structures. In this study, a new nonlinear 3-D failure criterion has been suggested by combining the Hoek-Brown criterion with the smooth octahedral shape function taken from Jiang & Pietruszczak (1988). The performance of the new criterion was assessed by comparing the strength predictions from both the suggested criterion and the corresponding linear 3-D criterion. The resulting fit of the new criterion to the true triaxial test data for six rock types taken from the literature shows that the criterion fits the experimental data very well. Furthermore, for the data sets having data taken in the low ${\sigma}_3$ range, the nonlinear failure criterion works better than the linear criterion.

The investigation of rock cutting simulation based on discrete element method

  • Zhu, Xiaohua;Liu, Weiji;Lv, Yanxin
    • Geomechanics and Engineering
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    • v.13 no.6
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    • pp.977-995
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    • 2017
  • It is well accepted that rock failure mechanism influence the cutting efficiency and determination of optimum cutting parameters. In this paper, an attempt was made to research the factors that affect the failure mechanism based on discrete element method (DEM). The influences of cutting depth, hydrostatic pressure, cutting velocity, back rake angle and joint set on failure mechanism in rock-cutting are researched by PFC2D. The results show that: the ductile failure occurs at shallow cutting depths, the brittle failure occurs as the depth of cut increases beyond a threshold value. The mean cutting forces have a linear related to the cutting depth if the cutting action is dominated by the ductile mode, however, the mean cutting forces are deviate from the linear relationship while the cutting action is dominated by the brittle mode. The failure mechanism changes from brittle mode with larger chips under atmospheric conditions, to ductile mode with crushed chips under hydrostatic conditions. As the cutting velocity increases, a grow number of micro-cracks are initiated around the cutter and the volume of the chipped fragmentation is decreasing correspondingly. The crack initiates and propagates parallel to the free surface with a smaller rake angle, but with the rake angle increases, the direction of crack initiation and propagation is changed to towards the intact rock. The existence of joint set have significant influence on crack initiation and propagation, it makes the crack prone to propagate along the joint.

Dynamic mechanism of rock mass sliding and identification of key blocks in multi-fracture rock mass

  • Jinhai Zhao;Qi Liu;Changbao Jiang;Zhang Shupeng;Zhu Weilong;Ma Hailong
    • Geomechanics and Engineering
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    • v.32 no.4
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    • pp.375-385
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    • 2023
  • There are many joint fissures distributed in the engineering rock mass. In the process of geological history, the underground rock mass undergoes strong geological processes, and undergoes complex geological processes such as fracture breeding, expansion, recementation, and re-expansion. In this paper, the damage-stick-slip process (DSSP), an analysis model used for rock mass failure slip, was established to examine the master control and time-dependent mechanical properties of the new and primary fractures of a multi-fractured rock mass under the action of stress loading. The experimental system for the recemented multi-fractured rock mass was developed to validate the above theory. First, a rock mass failure test was conducted. Then, the failure stress state was kept constant, and the fractured rock mass was grouted and cemented. A secondary loading was applied until the grouted mass reached the intended strength to investigate the bearing capacity of the recemented multi-fractured rock mass, and an acoustic emission (AE) system was used to monitor AE events and the update of damage energy. The results show that the initial fracture angle and direction had a significant effect on the re-failure process of the cement rock mass; Compared with the monitoring results of the acoustic emission (AE) measurements, the master control surface, key blocks and other control factors in the multi-fractured rock mass were obtained; The triangular shaped block in rock mass plays an important role in the stress and displacement change of multi-fracture rock mass and the long fissure and the fractures with close fracture tip are easier to activate, and the position where the longer fractures intersect with the smaller fractures is easier to generate new fractures. The results are of great significance to a multi-block structure, which affects the safety of underground coal mining.

Reliability-Based Analysis for Rock Slopes Considering Failure Modes (파괴형태를 고려한 암반사면의 신뢰도해석)

  • 이인모;이명재
    • Journal of the Korean Geotechnical Society
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    • v.15 no.6
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    • pp.3-16
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    • 1999
  • This paper presents the results of sensitivity analysis based on an example study to verify a newly developed reliability-based model for rock slopes considering uncertainties of discontinuities and failure modes-plane, wedge, and toppling. The parameters that are needed for sensitivity analysis are the variability of discontinuity properties (orientation and strength of discontinuities), the loading conditions, and the rock slope geometry. The variability in orientation and friction angle of discontinuities, which can not be considered in the deterministic analysis, has a great influence on the rock slope stability, The stability of rock slopes including failure modes is more influenced by the selection of dip direction of cutting rock face than any other design variables, The example study shows that the developed reliability-based analysis model can reasonably assess the stability of rock slope.

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Analysis of Empirical Failure Criteria and Suggestion of New Equation for Intact Rocks (경험적 파괴조건식의 해석과 새로운 수식의 제안)

  • Park, Chul-Whan
    • Tunnel and Underground Space
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    • v.6 no.3
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    • pp.234-238
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    • 1996
  • Three empirical criteria of rock failure are analyzed in order to understand the meaning of coefficients. Transformation of equations is discussed to apply in the numerical analysis. New failure criterion for intact rocks is proposed in this study, which can be used directly in programming. New equation has the form of parabolic curve($\alpha$=0.5~1.0), and is based on Mohr's shear failure using data from triaxial tests. Its validity will be discussed in the next report.

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Simple Evaluation Method of Uplift Resistance for Frictional Shallow Anchors in Rock

  • Kim, Daehong;Lee, Seungho
    • Journal of the Korean GEO-environmental Society
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    • v.23 no.1
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    • pp.15-23
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    • 2022
  • This paper presents the results of full-scale load tests performed frictional anchors to various lengths at several sites in Korea. Various rock types were tested, ranging from highly weathered shale to sound gneiss. In many tests, rock failure was reached and the ultimate loads were recorded along with observations of the shape and extent of the failure surface. Laboratory tests were also conducted to investigate the influence of the corrosion protection sheath on the bond strength. Based on test results, the main parameters governing the uplift capacity of the rock anchor system were determined. By evaluation of the ultimate uplift capacity of anchor foundations in a wide range of in situ rock masses, rock classification suitable for structural foundation was developed. Finally, a very simple and economical design procedure is proposed for rock anchor foundations subjected to uplift tensile loads.

Rockfall and Toppling Failure Simulation of Rock Slopes using 3-Dimensional Discontinuous Deformation Analysis (3차원 불연속변형해석법을 이용한 암반사면의 낙석과 전도 파괴 시뮬레이션)

  • Hwang, Jae-Yun;Ohnishi, Yuzo
    • Tunnel and Underground Space
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    • v.22 no.3
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    • pp.181-187
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    • 2012
  • Many researches on disaster prevention using computer simulation methods can be performed to minimize the damage of property and to protect human life. Discontinuous deformation analysis (DDA) is a new computer simulation method to analyze the behavior of discontinuous rock masses. Since most rock slope problems are 3-dimensional in nature, 2-dimensional deformation analysis has limited application. In this study, the basic principles of 3-dimensional discontinuous deformation analysis are described. The newly developed 3-dimensional discontinuous deformation analysis method is proposed as the computer simulation method for discontinuous rock masses. Then, the failure behavior of rock slopes are simulated using 3-dimensional discontinuous deformation analysis. The simulation results are compared and examined with the failure behavior at the rock slopes. The results show the applicability of 3-dimensional discontinuous deformation analysis to analyze the deformation and failure mechanisms of rock slopes.

A plastic strain based statistical damage model for brittle to ductile behaviour of rocks

  • Zhou, Changtai;Zhang, Kai;Wang, Haibo;Xu, Yongxiang
    • Geomechanics and Engineering
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    • v.21 no.4
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    • pp.349-356
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    • 2020
  • Rock brittleness, which is closely related to the failure modes, plays a significant role in the design and construction of many rock engineering applications. However, the brittle-ductile failure transition is mostly ignored by the current statistical damage constitutive model, which may misestimate the failure strength and failure behaviours of intact rock. In this study, a new statistical damage model considering rock brittleness is proposed for brittle to ductile behaviour of rocks using brittleness index (BI). Firstly, the statistical constitutive damage model is reviewed and a new statistical damage model considering failure mode transition is developed by introducing rock brittleness parameter-BI. Then the corresponding damage distribution parameters, shape parameter m and scale parameter F0, are expressed in terms of BI. The shape parameter m has a positive relationship with BI while the scale parameter F0 depends on both BI and εe. Finally, the robustness and correctness of the proposed damage model is validated using a set of experimental data with various confining pressure.

A Case Study on Joint System Simulation Results Application to Rock Slope Design (절리계 모사결과의 암반사면설계 적용 사례)

  • Kim, Dong-Hee;Jung, Hyuk-Il;Kim, Seouk-Ki
    • Proceedings of the Korean Geotechical Society Conference
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    • 2005.10a
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    • pp.669-680
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    • 2005
  • It is very difficult to determine the failure block scale in great rock slopes. Especially, postulating entire slope domain as a failure block without attention to discontinuity trace lenth makes very confuse and difficult to design rock slopes. In this paper, we estimate realistic failure block scale using joint system simulation method and introduce the application procedures on rock slope analysis. Besides, presenting how joint characteristics measurement and statistical analysis results are applicated to slope stability analysis design flow.

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