1,721,007 research outputs found
Analisi geomeccanoiche per la stabilità degli scavi in sotterraneo della Pietra del Cardoso
Full text linkL'articolo decsrive sperimentazione, caratterizzazione e modellazione relative alla pietra del Cardoso, nella quale sono impostate cave sia a giorno sia in ostterraneo. In particolare lo studio è stato rivolto proprio al passaggio in sotterraneo della coltivazione
SOIL CONDITIONING OF SAND FOR EPB APPLICATIONS: A LABORATORY RESEARCH
No full textEPB tunnelling requires the application of soil conditioning to increase its field of applicability particularly for cohesionless soils. Choosing the most suitable conditioning set for the various soils requires the use of a feasible laboratory test which can permit to define the characteristics of the conditioned soils and provide measurable data. A series of tests has been carried out using a laboratory screw conveyor device which was designed for this purpose and which simulates the extraction of the spoil from a pressure chamber in a similar way as in EPB tunnelling. The tested soils were medium-grain sands with varying amounts of silt and the tested conditioned mixtures were obtained with different water contents and amounts of foam. A simple slump test was also used to analyze the global characteristics of the conditioned soils. The test has shown that the proposed laboratory procedure permits a quantitative comparison to be made between different conditioning amounts and agents on the basis of measurable parameter
Ricerca applicata e prospettive di sviluppo tecnologico nel settore delle opere in sotterraneo
No full textScrew Conveyor Device for Laboratory Tests on Conditioned Soil for EPB Tunneling Operations
No full textEarth pressure balanced _EPB_ full face tunneling machines have experienced 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. 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 extraction system plays a fundamental role during the EPB operations particularly for a correct application of the face pressure. Despite the extensive use of the EPB technique, little knowledge exists concerning the understanding of the behavior of conditioned soil, particularly for noncohesive ground _sand and gravel_. This paper presents and describes a prototype laboratory device, which simulates the extraction of the ground from a pressurized tank with a screw conveyor. The results of a preliminary test program carried out on a medium sized sand show that the prototype device is efficient in verifying the effects of foam for an optimal use in EPB conditionin
Muck classification: raw material or waste in tunnelling operation.
Full text linkTunnel construction, structural diaphragms, debris from quarry exploitation require careful consideration of the spoil management, as this involves environmental, economic and legal requirements. In this paper a classification that considers the interaction between technical and geological factors in determining the features of the resulting muck is proposed. This gives indications about the required treatments as well as laboratory and field characterisation tests to be performed to assess muck recovery alternatives. While this reuse is an opportunity for excavations in good quality homogeneous grounds (e.g. granitic mass), it is critical for complex formation. It is therefore necessary to define a procedure that enables to assess the properties of
natural ground and of the relative spoil or waste arising from the excavation or exploitation phases. This approach is presented in this paper for usual tunnelling cases, where the materials are resulting from the tunnel excavation carried out by drill and blasting and mechanised tunnelling.
Physical parameters and technological features of the materials have to be assessed, according to their valorisation potential, for defining re-utilisation patterns. The methodology has proved to be effective in some cases tested by the Authors and the laboratory tests carried out on the materials
allowed the suitability and treatment effectiveness for each muck recovery strategy to be defined
Experimental and Numerical Studies on Rock Breaking with TBM Tools under High Stress Confinement
No full textThe understanding of rock breaking and chipping due to the TBM cutter disks mechanism in deep tunnels is considered in this paper. The interest stems from the use of TBMs for the excavation of long Trans-Alpine tunnels. Some tests that simulate the disk cutter action at the tunnel face by means of an indenter, acting on a rock specimen are proposed. The rock specimen is confined through a flat-jack and a confinement-free area on one side of the specimen simulates the formation of a groove near the indenter, like it occurs in TBM excavation conditions. Results show a limited influence of the confinement stress versus the thrust increment required for breaking the rock between the indenter and the free side of the specimen. Numerical modelling of the cutter disk action on confined material has also been carried out in order to investigate further aspects of the fracture initiation. Also in this case the importance of the relative position between disk cutter and groove is pointed ou
Effects of Fly Ash Inclusion and Alkali Activation on Physical, Mechanical, and Chemical Properties of Clay
No full text: This study investigated the improvement in the behaviour of a clay soil due to the addition of alkali-activated fly ash as a stabilising agent, and the effects of different activation factors such as alkali dosages and silica moduli. The alkali activator solution used was a mixture of sodium silicate and sodium hydroxide. Class F fly ash was used as the precursor material for the geopolymerisation process. Soil samples stabilised with non-activated class F fly ash were prepared and tested to compare the results with samples stabilised with alkali-activated fly ash. Compaction tests, unconfined compressive strength tests, X-ray diffraction analysis, and scanning electron microscopy analysis were carried out on samples cured 1, 7, and 28 days at room conditions. The results showed that the compressive strength of stabilised soil significantly increased when the fly ash was activated. The optimal activation parameters to stabilise the soil were found to be alkali dosages in the range of 12% to 16% and a silica modulus of 1.25. The highest compressive strength recorded was at 1293 kPa with an alkali dosage of 16% and a silica modulus of 1.25, while for the non-stabilised soil, it was at 204 kPa at 28 days of curing. Mineralogical analysis showed a decrease in the peak intensities of kaolinite and illite, while microstructural analysis indicated an alteration in soil texture with the addition of the alkali-activated fly ash
Condizionamento con schiuma dei terreni per applicazioni EPB: sperimentazione mediante un nuovo apparato di laboratorio
No full textL’uso di macchine di scavo a piena sezione tipo Earth Pressure Balance per la realizzazione di gallerie in terreni alluvionali si sta sempre più diffondendo nel mondo.
L’impiego di agenti di condizionamento come le schiume è sempre più frequente per consentire di estendere il campo di utilizzo delle macchine a contropressione di terra verso terreni con granulometrie differenti dai campi originari di impiego della tecnologia EPB. Non sono tuttavia ancora disponibili studi approfonditi riguardo il comportamento del terreno quando additivato, così come sono assenti precise indicazioni riguardo all’idoneità sia dei dosaggi degli additivi sia delle proprietà finali dell’impasto.
Il Centro per le Gallerie e lo Spazio Sotterraneo del Politecnico di Torino, nell’ambito di una più ampia ricerca sul tema del condizionamento, ha sviluppato una procedura di prova che si basa sull’utilizzo di un apparato sperimentale di grandi dimensioni in grado di simulare le condizioni di scavo che si presentano negli EPB.
Nel articolo viene descritto l’apparato di prova e sono presentati e discussi i risultati di una prima campagna sperimentale eseguite su una sabbia uniforme a grana media
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