ISSN 1062-7391, Journal of Mining Science, 2016, Vol. 52, No. 4, pp. 647–661. © Pleiades Publishing, Ltd., 2016. 647 _________________________________ GEOMECHANICS _______________________________ ____________________________________________________________________________________________________________________________________ ___________________________________________________________________________________________________________________________ Effect of Tensile Strength of Rock on Tensile Fracture Toughness Using Experimental Test and PFC2D Simulation 1 H. Haeri a* , V. Sarfarazi b , A. Hedayat c , and A. Tabaroei d a Young Researchers and Elite Club, Bafgh Branch, Islamic Azad University, Bafgh, Iran *e-mail: h.haeri@bafgh-iau.ac.ir; haerihadi@gmail.com b Hamedan University of Technology, Hamedan c Department of Civil and Environmental Engineering, Colorado School of Mines, Golden, CO 80401 USA d Department of Civil, Science and Research Branch, Islamic Azad University, Tehran, Iran University, Tehran, Iran Received December 8, 2016 Abstract—The effect of tensile strength on the tensile fracture toughness of rock like specimen was studied in this paper. Brazilian test was done to determine tensile strength of material. A compression to tensile load transforming (CTT) device was developed for determination of mode I fracture toughness of concrete. Also particle flow code (PFC) was used for validation of the experimental outputs. Three concrete slabs with different tensile strength were prepared for investigation of the effects of tensile strength on the fracture toughness. The samples were made from a mixture of water, fine sand and cement with different ratio. These samples were installed in CTT device. A 30-tons hydraulic load cell applied compressive loading to CTT end plates with a constant pressure of 0.02 MPa per second. Compressive loading was converted to tensile stress on the sample because of the overall test design. The results show Fracture toughness has a close relationship with tensile strength of concrete so it increases with increasing the tensile strength. In constant join length, the angle of crack growth related to normal load was decreased with increasing the grain size. Numerical simulation shows that failure pattern and fracture toughness was nearly similar to experimental results. Finally, it can be concluded that CTT device was capable for determination of fracture toughness of concrete. Keywords: PFC2D, mode I fracture toughness, compression to tensile load transforming device. DOI: 10.1134/S1062739116041046 INTRODUCTION Linear elastic fracture mechanics has been developed to describe crack growth and fracture within a material under essentially linear elastic conditions. It is based on the assumption that the influence of applied loads upon crack extension can be represented in terms of certain parameters that characterize the stress – strain intensity near the crack tip. The introduction of the fracture mechanics approach to engineering geology and rock engineering has led to the development of rock fracture mechanics, which mainly refers to the discrete initiation and propagation of an individual crack or cracks in geological materials subjected to a particular stress field [1]. The explosion in rock fracture mechanics research has touched many diverse areas including blasting , hydraulic fracturing and in situ stress determination, mechanical fragmentation, rock slope analysis, earthquake mechanics, earthquake prediction, plate tectonics, magmatic intrusions, hot dry rock geo-thermal energy extraction, fluid trans port proper ties of fracturing rock masses, propagating oceanic rifts, crevasse penetration and other glaciological problems, the development of steeply dipping extension fractures that are nearly ubiquitous at the earth’s surface and are formed through folding, up warping and rifting and the modeling of time-dependent rock failure [2, 3]. A fundamental fundamental feature of rock fracture mechanics lies in its ability to establish the relations hip between rock fracture strength to the geometry of a crack or cracks and the fracture toughness, the most fundamental parameter in fracture mechanics describing resistance of a material 1 The article is published in the original.