A COMPARATIVE STUDY FOR STRENGTH CLASSIFICATION
The importance of providing a system for strength classification is emphasized by the diversity of testing methods, number of representative samples needed, and testing equipment required. In the present work three Egyptian types of rocks: Limestone, Sandstone and Granite with different specimen sizes are used to carry out a comparative study concerning the determination of the compressive strength using uniaxial compression, point-load, and Schmidt hammer techniques. Testing results are statistically analyzed and correlated with some physical properties like porosity, density and sound velocity. * Associate Professor, Mining Department, Faculty of Engineering, Cario University TÜRKİYE X I I I . M A D E N C İ L İ K K O N G R E S İ , 1 9 9 3
Influence of blast delay time on rock fragmentation: One-tenth scale tests
ABSTRACT The Bureau of Mines 1s studying blast delay timing influences on rock fragmentation in a series of tests that started in 3-ft concrete blocks and includes reduced-scale and full-scale bench blasts. This paper reports on the reduced-scale tests. In a 45-in high dolomite bench, 18 single-row blasts were fired with 15-in burdens. Spacings were 21 and 30 in. Delay intervals ranged from 0 to 45 ms, equivalent to 0 to 36 ms/ft of burden. Each shot was instrumented for strain and pressure for both in situ dynamics and interactions between blastholes. All fragmented rock was screened. The finest fragmentation occurred at blasthole delay intervals of 1 to 17 ms/ft of burden. In this range, stress-wave-induced strains interacted with longer lasting gas-pressure strains from earlier holes. Coarse fragmentation resulted from short delays ( <1 ms/ft), where breakage approached presplit conditions with a major fracture between blastholes and large blocks in the burden region. Coarse fragmentation also resulted...
Effects of jointing and bedding separation on limestone breakage at a reduced scale
A study was conducted by the Bureau of Mines to provide quarry operators with information regarding the effects of jointing and bedding on rock fragmentation when bench blasting in two small-scale (2.5-ft) limestone benches, and the successful use of inexpensive equipment and field techniques to determine the orientation and spacing of joints and bedding separations within the quarry. Using inexpensive equipment, such as a pocket transit and steel and paper tapes, joint and bedding separations were mapped and their frequencies measured. Results from two small-scale bench blasts are described.