1,721,254 research outputs found
Tunnelling in urban areas by EPB machines: technical evaluation of the system
Full text linkThe paper refers to the methods adopted for building a high-speed railway tunnel system between Bologna and Firenze (Italy), focusing attention on the Bologna node which represents the heart of the system, connecting the high speed network's main lines. The project includes 9 tunnels, accounting for 73 km of the 78 km route crossing below the Apennines. The paper pays attention to the main aspects to be taken into consideration for correctly choosing the tunnel boring machinery (TBM) tobe used in urban areas. Thefundamental point in analysing technical aspects regarding an earth pressure balance (<br />EPB) machine concerned storing the main excavation parameter values; having collected and organised such data, statistical methods were used for processing it, the instantaneous velocities attained were empirically estimated and idle times were evaluated. The evaluation was made by calculating excavation specific energies (during different<br />excavation phases) to find a satisfactory correlation with the type of ground crossed. Interesting results have been found by comparison with other excavation parameters; in particular, a better understanding of an earth pressure balance shield's working phases has been reached thanks to an experimental study conducted during the construction of tunnels for a high-speed railway system in Italy. The paper contains details collected regarding the operation of two different EPB machines
Analysis of the Excavation Techniques to Optimize the productivity in an Italian Dimension Stone Basin
No full textThe Ossola basin is an important dimension stone producing district in the North-Western Italian Alps, from which different kinds of stones are extracted, mainly pertaining to the granite and gneiss families. After a general information on the geological features of the basin, the exploitation methods and the current blasting practices, comprising also cases of mixed methods (explosive plus mechanical cutting), are described and typical examples are provided. Then, a historical quarry is examined. The main objective of the research aims to assess the excavation technique adopted and, in light of the input data and results obtained from on-site experiments, to verify the possibility of introducing any changes in order to increase the productivity. The main exploitation techniques used for the extraction of hard and abrasive stones are investigated, with particular regard to those currently employed, which are the dynamic splitting and diamond wire cutting, and is qualitatively compared the applicability of alternative techniques. Many data were collected on site, related to the drilling time and to the implement of the dynamic splitting; specific consumption of explosives was evaluated and other parameters that led to the formulation of new proposals for optimizing the production cycle. The most appropriate seems to be the combined use of explosive and diamond-wire cutting, to combine the advantages of both techniques and to increase productivity, also thanks to the possibility of a partial overlapping of the operations that compete one and the other techniqu
Un criterio per la previsione del danno arrecato a strutture in roccia da brillamenti sotterranei-Parte II
No full textIl metodo della miccia detonante per il taglio del granito: analisi di procedure correnti4
No full textCriteri di previsione del danneggiamento di opere sotterranee da lavori di scavo con esplosivo- Parte I
No full textProve meccaniche su rocce a piccolissima scala - Parte terza - Indagine sperimentale sulla prova NCB Cone Indenter
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Factors Affecting Blasting Accuracy and Influence of Rock Type on the Difficulty of Tunnels Excavation by Drilling and Blasting
No full textDrilling and Blasting is a common technique of tunnel driving, either for mining or civil purposes, at least for lengths shorter than 3 - 4 km. The technology is surely "mature", hence it offers a huge variety of cases to be analyzed. The report deals with the subject of the compliance of the actual blasting results with the design requirements (contour and pull). Three factors are obviously involved: explosive, rock and drilling; the main objective of the report is to asses in some simple cases the relative importance of each of them, and to describe a simple methodology to do that. A number of rounds in mine drifting operations, covering a variety of rock-drilling system-explosive assortments have been carefully surveyed; rock shows important differences from one site to another with respect to the quality class; drilling is performed with manually steered jumbo in some drifts, with computerized jumbo in other drifts; the general blasting pattern is not different from one site to another, but at places pipe charges are used in contour holes, at places fully coupled charges. The evaluation of the influence of the rock on the excavation difficulty is another objective of the study. Difficulty can be inferred from specific drilling work consumption, specific explosive consumption or from both. Drilling consumption, which means the relative fineness of explosive distribution in the rock-mass required in order to obtain a satisfactory blast, has been assumed to be a reliable criterion on the basis of the narrower dispersion of the data, with respect to explosive consumption. Being the study aimed to classify by relative difficulty the rock types, rather than the operations, the effect of the cross section (whose influence on specific consumption by far exceeds the one of rock type) has to be accounted for by normalizing consumptions, i.e. by defining a normal cross section v/ specific consumption correlation, to be used as a reference line. Rock classes are related to difficulty classes; a wide dispersion is still observable, which indicates that the rock designation criterion based on lithological type should be improved by adding at least a second descriptive element. Anyhow, the simple lithological designation provides a first approximation ranking of the rocks to the intended purpose. The sensitivity of the pattern performances to drilling precision is analyzed in the same way. Tolerance standards for drilling machinery related to drilling pattern features are proposed. Data collected to establish the quality of the results of the blasts are: the overbreak value, the efficiency (actual pull/design pull ratio), the half cast factor of the contour holes. The relationships linking these indicators of quality to the features of the rock, of the drilling system and of the charging are analyzed and discussed. The statistical basis of the study is provided by data collected from a large number of cases, obtained from technical literature and from on site inspections. Analysis has been carried out on rounds of variable cross sections (from few to 160 m3), with either parallel or inclined hole cuts, blasted using a wide range of explosives and ignition systems. A general methodology to establish the main reasons of observed inaccuracies and to foresee the consequences of changes in the drilling and blasting practice is presented in the conclusion
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