Geometric model Construction of the main discontinuities using the Discrete Fracture Network method, A Case Study of the Pirtaghi dam site, Northern Iran

Accurate characterization and geometric modeling of rock mass discontinuity networks are fundamental for assessing the strength, mechanical, and hydraulic behavior of jointed rock masses, a critical aspect in geotechnical engineering. This is especially crucial for large infrastructure projects where discontinuities influence structural stability and potential seepage. At the Pirtaghi Dam site, a comprehensive understanding of the main discontinuity network is essential for stability evaluation and seepage path prediction,. This research constructed a 3D stochastic geometric model of the main fracture network using the Discrete Fracture Network (DFN) method. Extensive geological mapping in the dam abutments collected field data on fracture location, orientation, trace length, and density. From this collected data, appropriate probability distribution functions (PDFs) for geometric parameters were determined. A 3D fracture network model was then simulated via the Monte Carlo method and a custom 3DEC code, effectively incorporating these derived PDFs. Goodness-of-fit tests revealed that the main joint sets at the Dam site consistently follow uniform (orientation), exponential-lognormal (spacing), and power (trace length) probability distributions. Quantified 3D density values (P32=1.5 to 2.3 m²/m³) and trace length exponent values (a = 2.3 to 2.5) were also obtained. This developed DFN model, with its quantitative geometric parameters, provides reliable, site-specific input for advanced numerical modeling, such as distinct element method simulations using 3DEC. This validated model significantly enhances the ability to comprehensively analyze and predict the complex hydraulic and mechanical behavior of the discontinuous rock mass at Pirtaghi Dam, offering a critical tool for informed engineering design and risk assessment.