Contents lists available at ScienceDirect Computers and Geotechnics journal homepage: www.elsevier.com/locate/compgeo Research Paper Simulation of the inclined jointed rock mass behaviors in a mountain tunnel excavation using DDA Trong Nhan Do, Jian-Hong Wu ⁎ Department of Civil Engineering, National Cheng Kung University, Tainan, Taiwan ARTICLE INFO Keywords: Asymmetrical loading Trap-door test Discrete element ABSTRACT Assessing the stability of a mountain tunnel in complex geological conditions during construction is a challen- ging task. Although the Discontinuous Deformation Analysis (DDA) method has been applied in many rock engineering problems, its accuracy as a tool for analysis of tunnel excavation in a complex geological condition (e.g., involving sloping ground and jointed rock mass) needs further validation. In this paper, the DDA simu- lations of a tunnel excavation under various conditions (e.g., different dip angles and locations of the tunnel in the slope) were verified with physical tests (e.g., “trap-door” tests) in two main aspects, the sloping ground subsidence and the stress distribution of the jointed rock mass induced in the excavation. The results showed that the DDA was able to simulate, accurately, the mechanical behaviors of the inclined jointed rock strata in a tunnel excavation. The applicability of the DDA in such tunnel excavation projects is implicated. 1. Introduction Despite of the successful experiences in tunnel constructions [1–4], mountain tunnel excavations are challenging tasks. Complicated geo- logical conditions with a sloping ground surface and jointed rock mass make it difficult to predict rock mass movements in mountain tunnel excavations. In addition, the locations of the tunnels within the slope of the mountain affect the rock mass displacements, and the stability of the tunnel with very shallow overburden is threatened by natural dis- asters as surface erosions and landslides [5]. The unexpected stress concentrations and surface subsidence, which is induced by tunnel excavations, can result in the destruction of the superstructures and a loss of life [6–10]. Therefore, the engineers highlighted the urgent re- quirement to develop theory and the methods to ensure the rock mass stability during a tunnel excavation. The empirical method [11], analytical solution [12], and numerical simulation method [13] have been proposed to clarify the mechanical behaviors of the ground, including the yielding stress and the ground subsidence, during underground excavation [14–18]. The topography of the ground and the dip angle of the rock strata are two essential governing factors for the mechanical behaviors of the rock mass [19–21]. Different cases involving these factors have been studied: (1) Horizontal ground surface with horizontal excavation [7,17,19,22–28]. (2) Sloping ground surface with horizontal excavation [29-32]. In those studies, most of the researches mainly focused on the former, which highlighted the effect of the dip angle of the strata on the deformation tendency of the surrounding rocks in horizontal ground surface [17,19,28]. The later corresponding to mountain tunnels having different geology characteristics as compared to the former with re- gards to complicated topography of surface ground as well as dipping angles of the strata is one of the most challenging for engineering [21]. In some cases, the location of tunnels must be considered due to geo- logical conditions [5], the effect of superstructures [33], and so on. Changing the location of mountain tunnels lead to the change of the overburden, which clearly affects the mechanical behaviors of the ad- joining rock mass. Therefore, this research figures out the effects of the location of the tunnel and the dipping angle of the rock mass to the surface subsidence and the stress concentration in the mountain tunnel with sloping ground. The Distinct Element Method (DEM) [34] and Discontinuous De- formation Analysis (DDA) [35] are two well-known methods for ana- lyzing the block contact problems in a blocky assemblage with a large displacement. The DEM is an explicit time integration method, while the DDA is equipped with an energy-based implicit algorithm. Thus, the numerical stabilization of the DDA is higher than that in the DEM for the same time step [36,37]. The DDA has proven its key role in rock mechanics with great achievements including landslide hazards https://doi.org/10.1016/j.compgeo.2019.103249 Received 1 May 2019; Received in revised form 4 August 2019; Accepted 6 September 2019 ⁎ Corresponding author. E-mail address: jhwu@mail.ncku.edu.tw (J.-H. Wu). Computers and Geotechnics 117 (2020) 103249 0266-352X/ © 2019 Elsevier Ltd. All rights reserved. T