Predictions of block size distribution for quarrying

Abstract

The in situ block size and shape parameters of a rock mass with discontinuities are of signifcance for determining whether an existing or virgin quarry is suitable for armourstone production and for designing an appropriate blast pattern. A method for predicting these parameters is presented in this paper, which includes a detailed discontinuity survey technique and computer determination of the blocks dissected by the discontinuities. The applications of the method to simulated discontinuity data and natural joint data are discussed.

Rock engineering rating system for assessing the suitability of armourstone sources

“…This is definitely a problem in the USA where large stone is repeatedly sold as a by-product of the aggregate and road metal operations. Latham et al (1994) found that even with blasting methods specifically designed for armourstone production, the V80 size was reduced by a factor of six, but with aggregate-type blasting the I180 size was reduced by a factor of 20 or more. Toksrz et al (1971) found that overblasting appears to activate the development of release fractures.…”

“…From Figs 1 and 2 the following information is required either during the preliminary desk study or during the quarry evaluation: geological age and formation and miscellaneous geological information developed from published information; regional in situ stress conditions (presence of folds, faults, unloading features and their orientation to quarry face, unloading fractures in quarried stone, rockbursts in quarry floor; also see Hudson & Cooling (1988) and Sbar & Sykes (1973); rock mass conditions (lithological classification of rock type or types present, bedding or strata thickness, variability within beds or strata, stratigraphic log of working face); rock quality (block shape, degree of weathering, perme- Priest (1993) or Wang et al (1991); groundwater conditions (position of groundwater table relative to rock strata of interest, conditions of flow, degree of saturation); block integrity (condition of quarried blocks in regards to the presence of flaws, planes of weakness, blasting fractures, microfractures); and production methods (if blasted, information on blasting methods should include number of rows of blastholes, blasthole diameter and inclination, specific charge or powder factor, type of explosive, bench height, burden distance, spacing distance, stemming material and height). From Fig.…”

“…Smith & Collis (1993) provided the information for the weathering grade model. Priest (1993) was the initial source for the guidance on discontinuity analysis, but Wang et al (1991) and CIRIA/CUR (1991) should also be consulted for information on determination of in situ block size distribution. The V8o criteria (I"8o = 80% passing volume) as determined from the in situ block size distribution and the principal mean spacing data are based on a specific gravity of 2.65 and, therefore, the criterion for 'excellent' is assumed to have a mass of 18.5 t or greater.…”

“…The V8o criteria (I"8o = 80% passing volume) as determined from the in situ block size distribution and the principal mean spacing data are based on a specific gravity of 2.65 and, therefore, the criterion for 'excellent' is assumed to have a mass of 18.5 t or greater. The upper limit of 7 m 3 is arbitrary and will actually depend on the project requirements, with the knowledge that even specifically tailored blasting will reduce the in situ V80 by as much as a factor of six (Latham et al 1994).…”

“…tension gashes and unloading fractures associated with stylolites; clay seams which could weather at a more rapid rate than the surrounding rock; micaceous foliated zones), incipient fractures (whether naturally occurring due to stress relaxation or to blasting or quarry processing) or other planes of weakness which may wedge apart on exposure to the elements. To eliminate some judgement variabilities in this standard, Latham (1994) proposed that the fractures or flaws be considered of significant concern only if a feeler gauge 0.5 mm in thickness can be inserted into the fractures or flaws for 1 m of the total length of the total visible fractures and flaws on the rock surface. The number of blocks to be examined will be at the discretion of the individual performing the inspection and will depend on the homogeneity of the source, but the sample size must be representative of the source.…”