تجزیه و تحلیل حساسیت از پارامترهای موثر بر ثبات حفره زیرزمینی

In order to analyze the stability of the underground rock structures, knowing the sensitivity of geomechanical parameters is important. To investigate the priority of these geomechanical properties in the stability of cavern, a sensitivity analysis has been performed on a single cavern in various rock mass qualities according to RMR using Phase 2. The stability of cavern has been studied by investigating the side wall deformation. Results showed that most sensitive properties are coefficient of lateral stress and modulus of deformation. Also parameters of Hoek–Brown criterion and σc have no sensitivity when cavern is in a perfect elastic state. But in an elasto-plastic state, parameters of Hoek–Brown criterion and σc affect the deformability; such effect becomes more remarkable with increasing plastic area. Other parameters have different sensitivities concerning rock mass quality (RMR). Results have been used to propose the best set of parameters for study on prediction of sidewall displacement.

At present, a variety of numerical methods are available for stability analysis of rock masses. There are many factors and parameters that affect the rock mass stability. Many authors have carried out sensitivity analysis on parameters influencing stability of underground openings using numerical methods. Shuangjian et al. investigated the sensitivity of factors, influencing the strength of jointed rock [1], [2], [3] and [4]. Starzeca and Andersson studied sensitivity of geometric parameters of probable blocks in underground openings [5]. Bhasin and Hoeg studied sensitivity of joint parameters in a large cavern in Himalaya [6]. Schlueter and Pruess performed sensitivity studies on gas release from an underground rock cavern [7]. Kabala and Milly studied sensitivity of flow in unsaturated heterogeneous porous media [8]. McElwee et al. performed analyses on influencing parameters in slug test [9]. Yeung and Tinucci carried out sensitivity analysis of the conceptual design of a repository in rock salt to ascertain influences of maximum salt temperature, maximum entry temperature, and entry closure [10]. Beiki et al. applied sensitivity analysis using neural network to estimate the deformation modulus of rock mass [11]. Brunton et al. identified influencing parameters in sublevel caving material flow behavior, and ore recovery and dilution [12]. Determining priority of these parameters can be very useful during computation and estimation of them. Sensitivity of these parameters varies from case to case. The parameters can also be utelized in a probability risk analysis in further studies [13]. Change in rock mass properties or change from elastic to elastoplastic behavior causes a change in priority of parameters sensitivity. This paper attempts to determine the priority of sensitive parameters effecting underground opening stability, using RMR rating system.

In this paper considering different rock qualities in RMR rating system, a sensitivity analysis was performed on cavern stability. Results showed that parameters sensitivity in addition to case conditions in a specific project, depend on formation of plastic zone around cavern. σc and parameters of Hoek–Brown criterion have no sensitivity in elastic state and gradually affect the stability when plastic area occurs in rock mass surrounding the cavern. Also in elastic state two most important parameters in stability analysis are coefficient of lateral stress and modulus of deformation respectively and in plastic state the main parameters concerning cavern stability are modulus of deformation and coefficient of lateral stress respectively. The presented table showed the priority of all parameters in elastic and plastic states.