1. IntroductionFracture toughness is one of the basic parameters infracture mechanics indicating the ability of rock to resistfracturing, i.e., the initiation and propagation of cracks[1]. In other words, it is the fracture energy consumptionrate required to create new surfaces [2]. Some applica-tions of such values for rocks are (i) a parameter forclassification of rock material (ii) an index of fragmenta-tion processes such as tunnel boring [2], (iii) blasting [3],(iv) gas driven fracturing [4], (v) modelling of rockdeformation [5] and (vi) slope stability [6] in cold regions.The above-explained utilities of fracture toughnessvalues have motivated this laboratory study. The studyhelps to quantify the effect of sub-zero temperatureconditions on rock blasting and other similar jobs. Assuch, this paper deals with the testing of eight Indianrock samples at different temperatures, viz. y50, y40,y30, y20, y10 and +308C (room temperature) usingthe lnternational Society for Rock Mechanics (ISRM)Cracked Chevron Notched Brazilian Disc (CCNBD)suggested method.2. Details of samples2.1. Size and location of samplesRock cores of NX-size (54mm diameter) werecollected from various locations for the testing purpose(Table 1).2.2. Petrographic descriptionPetrographical analysis of the tested rocks wascompleted and the respective mineralogical composi-tions are given in Table 2. (The agglomerate could notbe tested for various reasons.)3. Various techniques to prepare specimens for obtainingfracture toughnessThe laboratory study involved preparation of speci-mens and their testing for fracture toughness under sub-zero temperatures in an environmental chamber (acryogenic testing chamber) developed by CMRI. Inthe following paragraphs, the technique of samplepreparation with testing facility is described.To determine the fracture toughness of rocks, thethree following testing methods have been suggested byISRM:(i) Chevron bend specimens method,(ii) Short rod specimens method, and(iii) Cracked chevron notched Brazilian disc (CCNBD)method.The advantages of the CCNBD method are muchhigher failure loads, fewer restrictions on the testingapparatus, larger tolerance on the specimen machiningerror, simpler testing procedure and lower scatter ofresults [7]. Moreover, ISRM [8] suggests that theCCNBD method is more suitable for practical purposes.Hence, the CCNBD method is used for this study.Apart from the above-suggested methods, pastresearchers used the three-point bend test, doubletorsion test, thermal shock test, cone indentation test,and Vickers indentation test methods because of thenon-availability of any standard method at their time.Table 3 compares the fracture toughness of differentrocks determined by other researchers ( K