1,721,183 research outputs found
The determination of the tunnel structure loads through the analysis of the interaction between the void and the support using the convergence-confinement method
No full textThe evaluation of the load acting on a tunnel support is of fundamental importance for the correct dimensioning of the structure when analytical calculation methods are used. The load acting on the support depends on various factors and for this reason its evaluation can appear somewhat complex. One way of evaluating the load acting on a support is to use the convergence-confinement method. This process involves intersecting the convergence-confinement curve with the support reaction line. However, in order to be able to adopt this technique, it is necessary to know the radial displacement of the tunnel wall at the point in which the support is to be installed. A technique for the evaluation of the load acting on a support is presented in this study. This technique is based on the convergence-confinement method and on the Vlachopoulos and Diederichs formulation for the estimation of the radial displacement of the tunnel wall at the point in which the support is to be installed. An iterative procedure has been introduced in order to obtain a final evaluation of the load acting on the support. Application of the procedure to over 1700 representative cases of the typical conditions that can be encountered during excavation of a tunnel in rock masses has made it possible to obtain graphs that illustrate the load acting on the support for variations of the in situ lithostatic stress. An analysis of the results has led to considerations on the factors that influence the load acting on the support and has made it possible to identify which factors are of greatest influence and those that can be considered negligibl
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
Back-analysis techniques for the improvement of the understanding of rock in underground constructions
No full textIn many cases, it is necessary to realize design and begin the construction of underground works with only an approximate
understanding of the geomechanical parameters of the rock mass that are necessary for a correct definition of the construction
technique and of the support structures. The purpose of back-analysing the measured displacements of the tunnel perimeter and the
loads on the support structures during the construction of the work is to calibrate the initial estimations of the geomechanical
parameters of the ground.
Today the use of the back-analysis procedure is not so common and, when it is used, it does not follow a scientific scheme. Full
advantage is not taken of the monitoring data, with the consequence of a waste of money.
Computers are nowadays able to quickly perform many numerical analyses and therefore the time is ripe to set up a correct backanalysis
procedure to use together with a calculation model of the problem, when monitoring data are available.
The principles on which the treatment of information derived from the monitoring of underground works during their construction
is based are shown in this paper. The paper proposes new efficient mathematical back-analysis techniques for the problem
under consideration and some interesting examples.
Finally, a real case is presented to which back-analysis was applied
Simplified analysis of the lining behavior during earthquakes in deep rock tunnels
No full textThe sizing of the lining of a tunnel requires to consider not only the static loads transmitted from the surrounding rock, but also the effects of earthquakes on the stresses and strains of the lining. The detailed evaluation of the interaction earthquake-lining using numerical methods typically requires very long calculation time and can be limited to the verification of the project final configuration. In this study a simplified procedure for the assessment of the effects of an earthquake on the tunnel lining is presented. This procedure is based on the calculation method Einstein and Schwartz and quickly allows the estimation of maximum moments induced by the earthquake in the lining. Through this procedure it was possible to develop a parametric analysis that allowed to evaluate the pseudo-static loads that is necessary to consider on the rock around the tunnel, according to the earthquake characteristics and to the geomechanic quality of the rock mass. A final calculation example illustrates the modalities for the analysis of a tunnel lining in the presence of a defined earthquake, using the charts developed in the present pape
Analysis of the tunnel-support interaction through a probabilistic approach
No full textThe analysis of the behavior of a tunnel requires the evaluation of numerous parameters, relative to the ground and the support structure and which are generally only known with a certain degree of approximation. The uncertainty of these parameters is reflected on the results of the calculation, that is, on the state of stress in the support structure. In order to be able to manage this uncertainty on the representative ground and support structure parameters in a rational way, it is useful to resort to a probabilistic type analysis, making use of the Monte- Carlo method and to simple analytical methods for an analysis of the tunnel-support structure interaction. A calculation procedure of probabilistic type that is able to establish representative values of the maximum moment and of the associated normal force in the support structure is presented in this study. This procedure can be used to verify the suitability of the support structure to sustain the induced load
Il Dimensionamento della Bullonatura Radiale Passiva in Galleria attraverso Analisi Tensionali e Deformative nella Barra e nella Roccia
No full textDistinct analysis of fully grouted bolts around a circular tunnel considering the congruence of displacements between the bar and the rock
No full textThis paper presents a new calculation procedure for the analysis and dimensioning of fully grouted radial bolts in tunnels. This procedure is based on the principle of congruency of the displacements, imposing the conditon that the lengthening of the bolt, added to the displacements due to the shear strains in the bolt-rock interface, is equal to the expansion in the radial direction of the reinforced rock annulus. A comparison of the results obtained using this procedure with those obtained using the traditional numerical modelling method, which is more costly in computational terms, has led to satisfactory results. The application of the procedure to a real case has given results that are comparable with the in situ measurements. The proposed instrument is able to analyse the stress and strain state in rock in detail, in the presence of a bolting intervention, and to proceed with its correct dimensioning with the objective of improving the degree of stability of the rock around the tunne
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