Mahdizadeh Mahdi, Hosseini Navid, Afzal Peyman, Kaveh-Ahangaran Dariush
5th Iranian Rock Mechanics Conference (IRMC5), Tehran, Iran
Publication year: 2014

It is very important to identify and classify rocks based on their strength in order to appropriately establish and support excavations from technical and economical points of view. There are different methods of classifying rocks that each is convenient and applicable for special environment. The current thesis is planning to zone and separate rock classes in sedimentary layers of Gheshlagh coal mine based on their strength using size-number fractal method. For this approach, 75 samples were taken from parts of the underground network of this mine, then these rocks are classified in different groups and smaller pieces are made and point load strength test is done on 300 samples and uniaxial compressive strength is done on the representative of every rock classification. The results of the point load index are compared with the uniaxial compressive strength in each classification. The linear conversion factor of K is separately calculated for each classification and K average is practiced on the two groups which uniaxial compressive test is not done on them. Finally, the amount of uniaxial compression is calculated by the conversion factor of K for all samples. Then fractal analysis is done on the compressive strength data. Three points identified as the limit among strength zone. Eventually, these rocks are divided into four strength zones among these three points. Since the strength of most of the samples taken from this mine mark under 150 MPa, this classification is perfectly adopted in classes with low strength. Holistically, a three dimensional model is compared with real conditions of tunnel and this model demonstrates that the strength zone over 115 MPa does not need any support.