Scale effect on rock mass strength and stability

Μη διαθέσιμη περίληψηNot available summarizationPresented on

Effectiveness of the swellex rock reinforcement system in the Madem Lakkos and Olympias mines

Μη διαθέσιμη περίληψηNot available summarizationPresented on

Effect of rock discontinuities on certain rock strength and fracture energy parameters under uniaxial compression

Summarization: Five series of test blocks of Pendeli marble with artificially created discontinuities of different crack densities (simulating three mutually orthogonal joint sets) were tested in uniaxial compression in order to study the effect of discontinuities on: (a) the compressive strength and the modulus of elasticity, and (b) certain fracture energy parameters expressed by the ratio W A/W V, where W A is the surface energy and W V the volume elastic strain energy. Mathematical relationships are derived similar to those suggested by other authors relating strength parameters to crack densities. Such relationships clearly show a reduction in strength with increased crack density. The experimental results obtained permit the extension of Persson's relation (which refers to ideal intact rock) to the more realistic case of discontinuous rock mass by introducing the appropriate term that takes into consideration the effect of rock mass discontinuities on the energy ratio W A/W V. A comparison between laboratory results and field observations was subsequently carried out assuming the rock mass to behave as a linearly elastic material, obeying the Hoek and Brown failure criterion. This comparison showed that laboratory results can be extended to larger scale. Furthermore, in order to predict the in situ strength and stability of a rock mass in uniaxial compression (which is of major importance in underground excavations) certain concepts are proposed based on laboratory tests, in situ investigations and first principles of linear elastic fracture mechanics.Presented on: Geotechnical and Geological Engineerin

Pillar failure by axial splitting in brittle rocks

Summarization: An analytical approximate elastic model is presented of the pillar failure mechanism in the case of multiple underground openings in brittle rocks by parallel equidistant vertical splitting cracks forming slabs, which are assumed to buckle. The failure region is considered to be elliptical in shape with the major axis growing as failure proceeds parallel to the minimum applied principal stress. A modified solution for the potential energy loss due to the presence of an elliptical hole in an infinite elastic space was derived in order to account for multiple openings. This solution, which yields the failure initiation stress and the crack spacing, was achieved by inserting configuration correction factors estimated by considering certain limiting conditions. In order to obtain simple approximate formulae and after considering the blast damage effect, equivalent effective circular holes are assumed for the case of square openings and elliptical holes for the case of rectangular openings. Next, the stable mode of pillar failure was formulated based on the observation that the weak inclusion of the axially split rock mass reduces the stresses for some distance inside the pillar. The stable model was obtained first by computing the elastic stresses outside the failure zone using a circular approximation and then applying a stability criterion based on Huber's classical fracture hypothesis. Comparison of the theoretical results with field data concerning a bauxite mine using room and pillar have indicated reasonable agreement. Furthermore, the scale effect exhibited by the strength and the axial splitting crack spacing was predicted sufficiently well by the above model.Παρουσιάστηκε στο: International Journal of Rock Mechanics and Mining Sciences and Geomechanics Abstract

Fragmentation analysis using the photographic method

Summarization: A procedure based on photoanalysis was developed for determining the fragmentation distribution of a muckpile that results from blasting assuming that such distribution follows the two parameter Weibull cumulative distribution function. Eight miniature muckpiles of 100 kg. each were constructed from −2 cm, +2−4 cm. +4−6 cm. +6−8 cm, +8−10 cm, +10−12 and +12 sizes of limestone fragments in order to form in each muckpile a biparametric Weibull fragmentation distribution of known paramenters xc and n. Close-up photographs of different sections through each muckpile were taken and analyzed digitally in reference to a dimensioned frame in order to estimate the fragmentation distribution. Comparison of the known fragmentation distribution of each muckpile to that resulted from the photographic analysis proved that in the latter case the fragmentation distribution follows the three parameter Weibull distribution and that the cumulative curves representing the sieve size distribution to that resulting from photographing and uncorrelated. By introducing a statistical approach through the application of the percentile concept considerable improvement was achieved. Simple mathematical expressions have been determined that convert the photoanalysis percentiles to sieve equivalent values. From them the parameters that describe the Weibull fragmentation distribution and therefore the complete actual distribution curve were obtained. Thus parameters obtained from the analysis of photographs taken from a muckpile can be used to describe succesfully its actual fragmentation distribution.Presented on: International Journal of Surface Mining Reclamation and Environmen

Mine pillar design in brittle rock masses

Μη διαθέσιμη περίληψηNot available summarizationPresented on

Two yachts sailing, New South Wales, ca. 1932 [picture].

Title devised from accompanying information where available.; Part of the: Fairfax archive of glass plate negatives.; Fairfax number: 2829.; Also available online at: http://nla.gov.au/nla.pic-vn6217369; Acquired from Fairfax Media, 2012

Fracture control growth in plexiglas under decoupled conditions

Μη διαθέσιμη περίληψηNot available summarizationΠαρουσιάστηκε στο: Explosives Engineerin

Ποιοτικός χαρακτηρισμός φαινομενικά ισότροπων διακοσμητικών λίθων με την μέθοδο των υπερήχων

Μη διαθέσιμη περίληψηNot available summarizationPresented on: Mineral Wealth -Athens

Study of the rock mass discontinuity system using photoanalysis

Μη διαθέσιμη περίληψηNot available summarizationPresented on