Combined Finite–Discrete Numerical Modeling of Runout of the Torgiovannetto di Assisi Rockslide in Central Italy Francesco Antolini 1 ; Marco Barla 2 ; Giovanni Gigli 3 ; Andrea Giorgetti 4 ; Emanuele Intrieri 5 ; and Nicola Casagli 6 Abstract: The combined finite–discrete-element method (FDEM) is an advanced and relatively new numerical modeling technique that com- bines the features of the FEM with those of the discrete-element method. It simulates the transition of brittle geomaterials from continua to dis- continua through fracture growth, coalescence, and propagation. With FDEM, it is possible to simulate landslides from triggering to runout and carry out landslide scenario analyses, the results of which can be successively adopted for cost-effective early warning systems. The purpose of this paper is to describe the results of the FDEM simulations of the triggering mechanism and the evolution scenarios of the Torgiovannetto di Assisi rockslide (central Italy), a depleted limestone quarry face where a rock wedge with an approximate volume of 182,000 m 3 lies in limit equi- librium conditions, posing relevant issues in terms of civil protection. The results obtained demonstrate that the FDEM is able to realistically sim- ulate the different phases of such a complex slope’s failure as well as to estimate both its runout distances and velocity, key features for landslide risk assessment, and management. DOI: 10.1061/(ASCE)GM.1943-5622.0000646. © 2016 American Society of Civil Engineers. Author keywords: Numerical modeling; Finite–discrete-element method (FDEM); Rockslide; Triggering; Runout. Introduction Today, rock slope stability analyses are routinely performed to assess the equilibrium conditions of landslides. A wide range of modeling tools capable of back-analyzing and/or predicting the behavior of rock slopes are available to engineers and geoscientists. Limit equilibrium analysis represents the most simple and common solution adopted in rock engineering. Major rock slope instabilities, however, involve complex internal deformation and fracturing, bearing little resemblance to the two-dimensional (2D)/three- dimensional (3D) rigid block assumptions adopted in most limit equilibrium analyses (Stead et al. 2006). Furthermore, important limitations of the limit equilibrium method include the limited pos- sibility to take into account progressive failure and deformability of the rock material along with the strength degradation related to the sliding mass deformation. Nowadays, numerical methods offer improved tools to study the complexities related to the geometry, material anisotropy, nonlinear behavior, in situ stress conditions, and coupled processes. Different methods are currently available for rock slope stability analysis. These can be subdivided into the following: • Continuum methods [e.g., FEM, finite-differences method (FDM), boundary elements method (BEM), etc.]; • Discontinuum methods [e.g., distinct-element method (DEM), discontinuous deformation analysis (DDA), particle flow method (PFM), etc.]; and • Hybrid continuum–discontinuum methods [e.g., combined finite–discrete-element method (FDEM), hybrid DEM/BEM methods, other hybrid FEM/DEM methods, etc.]. The continuum and the discontinuum numerical methods can be considered as conventional modeling techniques because of their widespread diffusion among the scientific and technical commu- nity. The concepts of continuum and discontinuum should not be considered as absolute, but instead they are relative and problem- specific, highly depending on the problem scales. As a conse- quence, continuum modeling is best suited for analysis of intact rock behavior at the small scale and for analysis of good and very good quality rock masses [typically with a geological strength index (GSI) ≥ 60] or very jointed rock masses or soil-like material (GSI ≤ 30) at the slope scale. Special joint elements can only allow the modeling of a few discontinuities inside the rock mass. Discontinuum modeling is hence more appropriate when the slope evolution is strictly controlled by the relative movements of joint- bounded blocks and the intact rock deformation between them. This is generally more common when the rock mass quality expressed in terms of GSI is between 30 and 60. With the discontinuum, model- ing large relative displacements can take place at the contact between each distinct element. Even though the continuum and discontinuum methods are also capable of simulating certain aspects of the progressive failure of geomaterials, they often fail to realistically capture and simulate the progressive failure of rock slopes and, in particular, the dynamics of kinematic releases accompanying the distortion, stress concentra- tion, fracture initiation, and subsequent propagation. The need to include the concepts of fracture mechanics has emerged in the last few years as a key issue for rock slope modeling (Stead et al. 2004). The first attempts to address the influence of fracture mechanics on a numerical code date back to the 1980s, when several authors (i.e., 1 Research Assistant, Dept. of Structural, Building and Geotechnical Engineering, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy (corresponding author). E-mail: francesco.antolini@polito.it 2 Research Associate, Dept. of Structural, Building and Geotechnical Engineering, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy. 3 Research Associate, Dept. of Earth Sciences, Univ. degli Studi di Firenze, Via La Pira 4, 50121 Firenze, Italy. 4 Associate Professor, Dept. of Electrical and Information Engineering Guglielmo Marconi, Univ. di Bologna, Viale del Risorgimento 2, 40139 Bologna, Italy. 5 Research Assistant, Dept. of Earth Sciences, Univ. degli Studi di Firenze, Via La Pira 4, 50121 Firenze, Italy. 6 Professor, Dept. of Earth Sciences, Univ. degli Studi di Firenze, Via La Pira 4, 50121 Firenze, Italy. Note. This manuscript was submitted on August 6, 2014; approved on December 18, 2015; published online on February 26, 2016. Discussion period open until July 26, 2016; separate discussions must be submitted for individual papers. This paper is part of the International Journal of Geomechanics, © ASCE, ISSN 1532-3641. © ASCE 04016019-1 Int. J. Geomech. Int. J. Geomech., 04016019 Downloaded from ascelibrary.org by DIP Idraulica/Trasporti E on 03/03/16. Copyright ASCE. For personal use only; all rights reserved.