Evaluation of Rock Mass Strength Using Potential Discrete Fracture Network (PDFN) in Voronoi Technique-DEM

Document Type : Research Article

Authors

Dept. of Mining, Petroleum & Geophysics, Shahrood University of Technology, Shahrood, Iran

10.29252/anm.2019.1632

Abstract

Summary
Almost all of the proposed models of Discrete Fracture Networks (DFN) embedded within rock masses are discontinuities with zero tension strength. While, potential discontinuities and weak surfaces such as rock bridges, veinlet, and schistose surfaces are a candidate for breakage under stress and have also a significant effect on rock mass strength. Simultaneously with geometrical parameters, this geomechanical heterogeneous nature of fractures is crucial for understanding rock mass behavior and characteristics. This paper focuses on the probabilistic effect of potential discontinuity properties on the rock mass strength using Potential Discrete fracture networks (PDFN)-bonded block models (BBM) framework. The cohesive crack model is used to define block contact behavior. A comparison of the results indicates the importance of the proposed model for the assessment of realistic rock mass strength instead of traditional DFN.
 
Introduction
Analysis of discrete fracture network (DFN) employing the complex nature of fracture patterns plays an important role in understanding the micro and macromechanical behavior of rock mass. Rock mass behavior analyses have traditionally been undertaken for discontinuity with zero tension strength along DFN to calculate mechanical properties. In point of this view, such methods regardless of geometrical parameters generally assume the same possibility of failure for all fractures in the rock mass. The distribution of the DFN strength parameter in Potential DFN can result in important changes in the strength of rock mass and remains a challenge in rock engineering design. The term of PDFN is used for those fracture network with tension and shear strength. Detailed analysis of the employed PDFN which elaborately highlights the role of the distribution of input strength property of each fracture that controls the real strength of rock mass has been presented in this research.
 
Methodology and Approaches
In the BBM-DEM, the Voronoi tessellation scheme is employed and the material is simulated as assemblies of several particles bonded together at their contact areas. In order to define contact law of BBM, a cohesive crack model (CCM) is implemented in the UDEC. The calibration process is carried out to obtain contact properties. DFN is written in c++, in which the probability distribution of cohesion, friction angle, and tension strength is considered. The sensitivities of the rock mass strength calculated using SRM e.g., UDEC-DFN to the variability of the input parameter are investigated. A discussion of results is then made base on a reference simulation performed without a distribution method. 4 different P21 are investigated.
 
Results and Conclusions
The cohesive crack model is implemented in UDEC to define contact law among generated BBM through the Voronoi tessellation technique. In order to assess the effect of the distribution of mechanical parameters in PDFN on the strength of rock mass, DFN is written and this feature is added. The results indicate the importance of the proposed model for the assessment of realistic rock mass strength in engineering applications.

Keywords

Main Subjects


توده‌سنگ به طور معمول به دلیل ساختارهای تشکیل دهنده مانند ناپیوستگی‌ها (مانند ترک، درزه، سطوح ضعیف، گسل) ماهیت ناهمگن پیچیده‌ای دارد. رویکرد شبکه شکستگی مجزا ماهیت پیچیده‌ای از الگو و توزیع شبکه شکستگی‌ها را در نظر می‌گیرد و نقش بسیار مهمی در فهم رفتار میکرومکانیکی[1] ماکرومکانیکی[2،3] توده‌سنگ دارد. در برخی موارد مانند روش‌های معدنکاری تخریب توده‌ای و آتشکاری نیاز به ایجاد و توسعه ناپیوستگی‌ها در توده‌سنگ است. برای مثال در روش معدنکاری تخریب توده‌ای، برآورد تخریب‌پذیری و خرد شوندگی توده‌سنگ و در نتیجه خارج شدن مواد معدنی از نقاط تخلیه، از نظر موفقیت‌آمیز بودن عملیات معدنکاری بسیار حایز اهمیت است[4]. در مقابل، مسایل مکانیک سنگی دیگری نیز وجود دارند که در آنها اصرار بر کاهش توسعه ناپیوستگی‌ها و عدم تشکیل ناپیوستگی‌های جدید است. برای مثال، ملاحظات مربوط به ارزیابی پایداری شیب‌های معادن روباز و پایداری فضاهای زیرزمینی از این دسته مسایل هستند.

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