1,720,991 research outputs found
Analysis of the techniques for assessing the features of blast-induced fragmentation in an open pit quarry
Full text linkThe paper deals with the study of empirical models for the analysis of blasts-induced fragmentation. To verify the reliability of the method, the results obtained a priori through the application of the models are compared with the analyses of muck piles photos taken from a series of blasts in an open pit quarry, thanks to the Split-desktop software (Split Engineering, LLC, Tucson, USA). The study of the particle size distribution is very important when sizing an excavation site, as the average size of the pile must be compatible with the equipment used for clearing and conveyance, and with the first phase of the processing plant, i.e. primary crushing.
After a description of the excavation technique in use at the quarry site, its main characteristics are outlined. The parameters used to create the empirical models refer to the geomechanical characteristics of the rock, the geometry of the blasts, the characteristics of the explosive and its interaction with the rock mass, paying attention to the correlation between initiation timing and
induced fragmentation. A detailed description of some empirical models together with the Splitdesktop software were therefore provided. Thanks to both data and photos of the muck-piles from the exploitation at the quarry, the particle size curves resulting from each model were compared with those obtained from the software. This allowed to validate the empirical method in a preliminary design phase
Horizontal and inclined tunnels excavated by TBMs: Analysis and comparison of the TBM performances for some cases in Italy
No full textBentonite in two-component grout applications
Full text linkTwo-component grout is a cement-based material, currently the most used technology for backfilling in tunnelling applications. Despite its intensive, knowledge on this material is quite limited, especially as concern the role of ingredients and their effect on the properties of fresh mortar and hardened grout. In this work, an accurate and innovative test campaign focused on the role of the bentonite was performed. Three different bentonites were used. The activation of the bentonite and its effect on both mortar stability and grout strength was investigated with the purpose to recognise the bentonite parameters useful to select, at the design stage, the best bentonite according to the designers’ requirements. Swell index and Atterberg's liquid limit were recognised as useful parameters for predicting results in terms of suitable bleeding and surface compression strength
A review of the benefits of electronic detonators
No full textComputerized drilling and the electronic timing of detonations are two technological breakthroughs which have had an important role in updating drilling and blasting excavation methods, although the electronic timing of detonators is still a comparatively infrequent technical solution to precision blasting problems. On the basis of an extensive collection of published cases, this paper reviews the successes achieved and the main expected advantages from the electronic ignition devices. After describing the primary characteristics of these detonators, some elements will be considered, in order to better understand their applications in different conditions, both in open pit and underground sites: extension of the time delay number, freedom in the choice of time intervals between detonations, timing accuracy, reduction of vibrations, control of back-break and fragmentation. The results are compared to those obtained by pyrotechnical timing devices, and summarized in the concluding remarks
Blasting in densely jointed rock to obtain slabs
No full textThe economic return of rock blasting is not provided by brute volume of broken rock, rather by the amount of marketable product. That i s the case of the porphyry quarries of Trento district, whose output is mainly absorbed by road paving and building facing elements production. Blasting at the quarries evolved from heading blast system to parallel holes blasts. A study for the optimal yield geometry, charging and timing of the blasts is synthetically presented, and the underlying criteria are exposed. A model of how explosive acts separating and breaking the rock slabs, and the use of the model in blast design and quarry face orientation is illustrated with examples
Laboratory characterization aimed at analyzing the performance of diamond wires for marble cutting
No full textOver the years the diamond wire has got many improvements and optimizations, thanks to which one of the greatest revolutions in the stone industry took place. However, its use is still the cause of injuries, sometimes fatal, following the opening of the loop during cutting, with consequent whiplash and high-speed projection of its elements. The present work is focused on the study of some possible causes of diamond wire breakage, from those known, including slipping of the support cable from the junction clamp and cable break near the clamp, to that, observed in quarries of the Carrara Basin during on-site analyzes, of breaking the same junction clamp.
To help improving the safety level in the quarries, tensile tests were carried out at the “Marmotest s.a.s” laboratories of Carrara and DISEG of the Politecnico di Torino on wire elements, in detail junction clamps, pressing devices and support cable, supplied by the ‘Megadiamant Srl’ manufacturer of diamond wires, reproducing configurations and technological choices observed on site and assessing compliance with the European reference standard UNI EN 13236:2016 (“Safety Requirements for superabrasive products”). 100% of pressing devices and more than 90% of junction clamps subjected to slip tests have respected the limit value imposed by the reference standard.
For the latter, three factors mainly contribute to the slip resistance: the type of material, the length of the junction clamps and their thickness. Despite the research carried out, no technical documents are available regarding the chemical composition of the materials with which the joints are made but, in general, the clamps marketed as copper (or, more properly, copper steel) and annealed steel have provided greater extraction resistances than those in steel. Furthermore, the slip resistance is linked to the length of the clamp by direct proportionality, and its thickness by inverse proportionality. The water for cooling the diamond wire during cutting may not be used correctly or be limited byenvironmental problems. For this reason, the study of the slip resistance of copper and steel clamps has been extended, including the variation of their properties to temperature increase. Finally, the deterioration of the mechanical characteristics
of the diamond wire following the cutting was measured by performing tensile tests on used elements
3D slope stability analysis of a limestone quarry expansion in Northern Italy
Full text linkSlope stability is a crucial aspect in case in quarrying, both in term of legal and technical restrictions. The availability of data regarding the rock mass characterization is not sufficient to guarantee a satisfactory stability analysis, which must be assessed by means of more accurate procedures. Limit equilibrium analyses have been used since many decades, as they can give satisfactory results for simple cases, such as planar or wedge blocks. Nevertheless, when dealing with more complex cases, such as opencast quarries and mines, where the slope geometry consists on several benches plunging in different directions, this simplified approach cannot give a satisfactory answer. In this scenario, numerical models can return a much more complete and accurate assessment of the overall stability. The paper describes a possible approach to evaluate the stability of the slopes of a limestone opencast quarry in Northern Italy. The country is experiencing a growing demand of limestone for the production of cement for the construction sector and this determined the need to expand the previous exploitations. Since the quarry experienced several expansion plans throughout the years, several site investigation campaigns have been carried out and the results were not always consistent with each other. Starting from the two most recent rock mass characterizations and by using 3D numerical models, the overall stability has been simulated by means of continuum and discontinuum analyses, to obtain a reproduction of the real episodes of instabilities that occurred in the past. The implementation of models with reliable data is essential to obtain results that are comparable with the reality: this would allow to proceed more effectively and safely with the exploitation of the future slopes
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