1,720,985 research outputs found
Laboratory test for EPB tunnelling assessment:results of test campaign on two different granular soils
Get PDFEarth Pressure Balanced shields are currently the most utilized tunnelling machines throughout around the world. The possibility of using conditioning agents that change the mechanical and hydraulic behaviour of a soil, changing it into a plastic paste and thus permitting soil pressure applications at the tunnel face, is the key point to explain the increasing utilization of this technology. Despite its great importance, not much laboratory researches can be registered on soil conditioning, particularly for cohesionless soils. The conditioning criterion is usually defined on the basis of a trial-and-error procedure developed directly at the job sites. A test that is able to simulate the extraction of soil from the bulk chamber with the screw conveyor inclined upwards, as in real machines, can offer a quantitative indication of the conditioned soil behavior for EPB use. The characteristics of the device and the results obtained on many different types of soil are discussed in order to point out the great importance and quality of results that can be achieved using the proposed test devic
How tunnel boundary irregularities can influence the stresses in a shotcrete lining
Get PDFThe shape of a tunnel boundary excavated by drill & blast in fractured rock masses is influenced by geological conditions and blasting operations. The overbreaks, apart from influencing the construction times and costs, also have an important influence on the stresses acting in the shotcrete lining, particularly when it is used as the final lining. These effects have been analyzed, on the basis of a parametric numerical analysis, and the results have shown that if the boundary shape is more irregular there are traction stresses. These tractions are not evident if a regular shape of the boundary is considered in the numerical mode
Influence of granulometry, time and temperature on soil conditioning for EPBS applications
No full textEarth Pressure Balanced full face tunnelling machines have got experience thanks to a remarkable increase in the number of applications throughout the world due to both mechanical developments and a more effective use of additives to condition the ground. Soil conditioning modifies the mechanical and hydraulic properties of a soil by making it suitable for the pressure control in the bulk chamber and extraction with the screw conveyor. The results of a laboratory test campaign using slump test on granular soils, turned to understand the influence of the amount of conditioning agents, of time and temperature are presented and discussed. The obtained results put in evidence that exist a conditioning optimum range, taking into account the soil water content and the amount of injected foam (FIR) and that the properties of the conditioned mix decay after one or two hours of the production. Finally the preliminary research on temperature influence, highlights the great importance of this facto
The behaviour of a two-component backfilling grout used in a Tunnel-Boring Machine
Get PDFThe instantaneous filling of the annulus that is created behind the segment lining at the end of the tail during the TBM advance is an operation of paramount importance. Its main goal is to minimize the surface settlements due to any over-excavation generated by the passage of the TBM. To correctly achieve the goals, a simultaneous backfilling system and the injected material should satisfy the technical, operational and performance characteristics. A two-component system injection for the back-filling is progressively substituting the use of traditional mortars. In this paper different systems of back-filling grout and in particular the two-component system are analyzed and the results of laboratory tests are presented and discusse
Analisi mediante modellazione numerica e modelli analitici di un presostegno con infilaggi in gallerie superficiali
No full textIl lavoro presenta i risultati del confronto tra un modello numerico tridimensionale sviluppato mediante il codice di calcolo FLAC 3D ed un modello
analitico che si basa sull’approccio della trave su appoggi cedevoli, in termini di sollecitazioni e spostamenti che si generano negli elementi resistenti
(tubi) di un presostegno con infi laggi per una galleria superfi ciale con copertura pari a tre volte il diametro della stessa, per due diversi tipi di terreno.
I risultati consentono di valutare quale carico agente nel modello analitico meglio permetta di riprodurre i risultati del modello numerico e quindi fornire
indicazioni utilizzabili in sede di progettazione.
Analysis of a pre-reinforcement umbrella-arch in shallow tunnels through numerical modelling and analytical approaches. This paper shows the results
of a comparison between a three-dimensional numerical model developed with the code FLAC 3D and an analytical model based on the approach
of a beam on yielding supports, in terms of stresses and displacements induced within the resistant elements (tubes) of a pre-reinforcement structure
for a shallow tunnel, with a coverage equal to three times its diameter, for two different types of soil.
The results permit to defi ne which is the load applied in the analytical model that reproduces the results of the numerical model and then provide
suggestions for the design phase
Study of the Permeability of Foam Conditioned Soils with Laboratory Tests
Get PDFEPB tunneling requires that the excavated soil has a plastic and pulpy behavior to be able to apply a stabilizing pressure to the face, but it should also be impervious to counteract filtration forces that could develop ahead of the face. The evaluation of this parameter in granular soil, before and after conditioning, is therefore of key importance for a correct conditioning agents choice. Approach: A new laboratory procedure for testing the permeability of conditioned soil with foam has been proposed. The tests have been carried out at different hydraulic loads, chosen to be 0.1 bars and 1 bar. Results: The proposed procedure has been applied to determine the behavior of differently conditioned granular soils: a fluvial sand and a pozzolanic soil and has shown that an increasing of the FIR induces a relative increase in the time required by water to pass through a standard sample, emphasizing, in this way, the effectiveness of the conditioning on impermeability of the soil. Conclusion: The tests have shown the laboratory procedure adequately captures the behavior of the conditioned soil. Further, the proposed test may also be used as an index for the preliminary definition of the quality of the soil conditioning and suitability for EPB tunnelin
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