Use of fuzzy set theory for minimizing overbreak in underground blasting operations – A case study of Alborz Tunnel, Iran Mohammadi Mohammad a,⇑ , Hossaini Mohammad Farouq b , Mirzapour Bahman a , Hajiantilaki Nabiollah a a General Mechanic Co., Tehran 1465865163, Iran b Faculty of Mining Engineering, Engineering University College, University of Tehran, Tehran 14395-515, Iran article info Article history: Received 23 September 2014 Received in revised form 18 November 2014 Accepted 20 December 2014 Available online 20 April 2015 Keywords: Fuzzy model Overbreak Regression analysis Underground blasting Alborz Tunnel abstract In order to increase the safety of working environment and decrease the unwanted costs related to over- break in tunnel excavation projects, it is necessary to minimize overbreak percentage. Thus, based on regression analysis and fuzzy inference system, this paper tries to develop predictive models to estimate overbreak caused by blasting at the Alborz Tunnel. To develop the models, 202 datasets were utilized, out of which 182 were used for constructing the models. To validate and compare the obtained results, determination coefficient (R 2 ) and root mean square error (RMSE) indexes were chosen. For the fuzzy model, R 2 and RMSE are equal to 0.96 and 0.55 respectively, whereas for regression model, they are 0.41 and 1.75 respectively, proving that the fuzzy predictor performs, significantly, better than the statistical method. Using the developed fuzzy model, the percentage of overbreak was minimized in the Alborz Tunnel. Ó 2015 Published by Elsevier B.V. on behalf of China University of Mining & Technology. 1. Introduction Despite the intrinsic destructive characteristic, drilling and blasting method is the most satisfactory tool for excavation of rocks. This excavation method needs lower capital investment and is characterized by high progress rate for underground excava- tion works [1]. More than 85% of the energy produced in the blast is not used in the process of fragmentation and displacement of the rock. This energy causes the structural strength of the surrounding rock mass to be weakened. This is demonstrated by overbreak, leaving the fractured mass in a potential state of collapse [2]. Therefore, overbreak is defined as the ratio of the difference between the theoretical and real areas of the cross sections from the perimeter of the tunnel cross section, excluding the floor [3]. Controlling the overbreak in underground excavations is of great importance due to both economic and safety reasons. Many studies have been performed in order to identify the causes of overbreak in underground excavations. Chakraborty et al. investigated the effect of rock mass quality and joint orienta- tion on tunnel blasting performance with regard to pull, frag- mentation and overbreak [4]. Germain and Hadjigeorgiou, studied the influence of stope geometry and blasting patterns on overbreak [5]. The effects of rock mass quality on overbreak were investigated by Innaurato et al. [3]. The work of Singh and Xavier showed that proper planning and high accuracy in drilling have a significant role in decreasing the overbreak percentage [6]. Kim et al. used numeri- cal methods to simulate the blasting at tunnel contour holes in joint rock mass [7]. Using regression analysis, Dey and Murthy estab- lished a relationship between the overbreak percentage and rock mass as well as charge and blast design parameters [8]. Lu et al. showed that the in situ stress of surrounding rock mass is one of the main factors controlling the crack propagation in contour blasting, which has a significant effect on overbreak [9]. In order to reduce the overbreak in underground excavations, various parameters such as physico-mechanical properties of rock mass, properties of explosives and geometrical features of blasting patterns should be considered. The conventional methods used for assessing overbreak do not always take into account all parameters that affect the results. Since the excavated area out of the designed periphery of tunnel must be filled with concrete, a prediction of overbreak percentage before performing the blasting patterns can be very helpful in order to minimize the use of costly concrete as well as maximizing the safety of working environment. Fuzzy model can deal with the complexity of the geological problems flexibly. The implementation of this technique in mining engineering has significantly increased in recent decades. Some of the researchers who have worked on this issue are: Chen et al. for road tunnel ventilation system; Sonmez et al. in Geological Strength Index (GSI); Aydin for classification of rock masses; http://dx.doi.org/10.1016/j.ijmst.2015.03.018 2095-2686/Ó 2015 Published by Elsevier B.V. on behalf of China University of Mining & Technology. ⇑ Corresponding author. Tel.: +98 9380232946. E-mail address: Mohammadisalmasi@yahoo.com (M. Mohammadi). International Journal of Mining Science and Technology 25 (2015) 439–445 Contents lists available at ScienceDirect International Journal of Mining Science and Technology journal homepage: www.elsevier.com/locate/ijmst