In this paper the method for estimating the statistical parameters of the medium from traveltime measurements of refracted
waves is applied to study the statistical characteristics of crystalline rocks at the Multifunctional Station Faido (Gotthard
Base Tunnel, Switzerland). The method is based on the geometrical optics (GO) approximation. A covariance function for traveltime
fluctuations has been obtained by considering quasihomogeneous fluctuations of sound velocity in a plain-stratified medium.
Strongly anisometric (having unequal dimensions in different directions) random inhomogeneities were embedded in this medium.
To estimate the statistical parameters around the tunnel, the traveltime fluctuations are calculated. It is assumed that each
observation of traveltime-distance relation for a given shot-receiver group corresponds to a particular realization of a medium
statistical ensemble. By calculating the variance and the zero cross intervals of the first derivative of traveltime fluctuations,
the standard deviation of the velocity fluctuations and the characteristic horizontal scale of the inhomogeneities are estimated.
Although the method allows to obtain the characteristic lengths of the inhomogeneities in vertical as well as in horizontal
direction, the limited offset of the field data made it only possible to measure the latter. The estimated horizontal characteristic
scale is about 13 m, which is reasonably close to the direct geological measurements in the studied region, where quartz lenses
are dominant among the inhomogeneities. The standard deviation of the velocity is estimated as 4.5%, which might be caused
by the fractured structure around the tunnel and also by the fault zone near the study area. 相似文献
A design method for the prediction of lining loads should include the decrease of lining loads due to the stress release before lining installation and the increase of lining loads due to development of ground yielding. Schwartz and Einstein included both factors in their original closed form solutions in the form of a support delay factor λd and a yield factor λy respectively. The validity of the design method is reviewed by comparing the loads calculated using the methods with the field measurements obtained from several tunnels. The possible causes of the load discrepancy between measurements and predictions are presented.
Schwartz and Einstein's proposed method gives reasonable results for tunnels with short delay lengths. However, the method could not be used reliably for tunnels either with long delay lengths or with voids between the soil and TBM due to the difficulties finding the pre-support ground movements and therefore λd. 相似文献
The paper presents the results of electromagnetic radiation (EMR) measurements in the Feuerberg tunnel in southwest Germany. EMR is associated with small scale fracturing processes. The measured numbers of EMR impulses are shown to be proportional to shear stresses. From the correlation of EMR and shear stresses along the long axis of the tunnel, orientations and magnitudes of the horizontal principal stresses are determined. The major horizontal principal stress is 3.6±0.3 MPa and has an azimuth of 143±6°. The minor principal horizontal stress is 2.1±0.3 MPa. Zones in the tunnel are located where low shear stresses occur because vertical overburden and horizontal stresses are equal. In these zones also minimum radiation was detected. A possible stress accumulation close to a fault is suggested by higher EMR values in a part of the tunnel. Orientations and magnitudes of the horizontal principal stresses, which are derived from the measurements of EMR, correlate well with conventional stress measurements. It is suggested that the cross-section measuring method described in the study is used to determine regional stress fields as well as to investigate endangered zones with high stresses in underground facilities, which may be critical with regard to stability. 相似文献
A simple analytical formula is developed to calculate transient discharge inflow rates into a tunnel or a well under constant drawdown. The agreement with the classical, but cumbersome diffusion-equation-based solution of Jacob and Lohman is excellent throughout the range of dimensionless times. By using only a straightforward logarithmic function, this explicit solution may therefore be used with great computational benefits in practice, and also when further mathematical manipulations such as differentiation or integration are required.
Resumen Una fórmula analítica sencilla fue desarrollada para calcular el grado de descarga transitoria hacia un túnel, o un pozo, bajo condición de un abatimiento constante. Existe una concordancia excelente, desde el comienzo hasta el final, en el rango de los tiempos adimensionales, con la solución clásica pero complicada, de Jacob y Lohman, basada esta última en la ecuación de difusión. Solamente mediante el uso de una función logarítmica simple, esta solución explícita puede por tanto ser usada en la práctica con grandes ventajas computacionales, y también cuando se necesitan manipulaciones matemáticas adicionales, tales como diferenciación o integración.
Résumé On a développé une formule analytique simple pour le calcul du flux infiltré en régime transitoire dans un tunnel ou un puits en supposant le rabattement constante. Les résultats sont en accord avec la solution plus compliquée de Jacob-Lohman de léquation de diffusion, sur tout lintervalle de temps adimensionel considéré. En utilisant une fonction logarithmique ce solution explicite peut être utilisée sans un grand effort de calcul dans la pratique courante, ainsi que dans les situations où il est nécessaire à dériver ou intégrer lexpression du rabattement.
Within the last 10 years Slovenia has been constructing its highway network. The Golovec tunnel, as a part of Slovenia's capital ring is thus one of the most important connections of Ljubljana to the east and to the north. It is a double tube three-lane tunnel in soft rock with small to medium overburden. Its construction, following NATM, caused huge problems to all parties involved. The tunnel support was well monitored during its construction, which gave the authors a good opportunity to analyse the results.The Golovec tunnel is constructed through one of few hills surrounding Ljubljana, of Carboniferous age, consisting of clastic rock: siltstone, claystone and sandstone. Golovec hill belongs to the first of two overthrusting zones from this area, so the rock is strongly faulted.Tunnel monitoring consisted of daily 3-D tunnel tube displacement measurements in 97 measuring sections, and of two measuring sections within the tunnel with more complex measuring equipment, to monitor stress changes and rock deformations around both tunnel tubes. Monitoring of the surface 3-D movements gave us the opportunity to study the influence of the tunnel construction on the surface above it. The tunnel, its geology, construction procedure and monitoring results are described in the first part of the paper.The second part consists of the interpretation of monitored results, with an emphasis on results concerning development and evolution of the excavation-damaged zone in the rock around the tunnel. Back-calculations, performed as a basis for the interpretation procedure, are also presented in this part. Calculations of the propagation of the tunnel destressed zone and stress-field around the tunnel, up to the surface, were performed by means of numerical model with the finite difference method. The evolution of tunnel displacements and their prediction was based on the use of Back Propagation Neural Networks, whose principles are presented in one chapter of this paper. Results showed that the most important, for the final settlement at the surface above the tunnel, was the time of installation and rigidity of the primary support. On the basis of the calculated final displacements, this support could easily be strengthened in a short time, when necessary. 相似文献
This paper presents a case study of the instability mechanisms, and the excavation sequence, re-qualification and reinforcement methods adopted to pass through a short segment of a nearly 2-km tunnel built as part of a new 55-km state highway in northern Turkey. The instability problems were encountered during tunnel excavation due to the failure to recognize the fact that alteration in stress field and resulting deformation could cause dilation and increase in the permeability of claystone-shale layers and local fault gouge zones, and in turn significant reduction in shear strength. Change in natural drainage pattern and capillarity exacerbated saturation and the consequent strength reduction. The 92-m3 loose material flowed into the tunnel due to the collapse and caused 2.5 months of delay in completion of the tunnel. Longitudinal and oblique cracks observed in shotcrete were attributed to the reduction in modulus upon saturation, which caused a large cumulative deformation of approximately 110 mm at a section about 30 m behind the collapse face.
It is concluded that early detection or prediction of potentially problematic zones (via probe drilling and monitoring) in tunnelling is of paramount importance, especially through mixed or difficult ground conditions characterized by alternating layers, folding, faulting and localized zones of high water pressure. Because mechanical detection methods cannot be fully relied upon, availability of experienced personnel to predict and deal with such instability problems effectively and promptly is the best insurance for successful completion of tunnelling contracts. 相似文献
The empirical models available for prediction of the tunnel blast results like pull ratio, specific charge, specific drilling and overbreak have some inherent shortcoming in absence of any parametric study at the backdrop. Hence, the models use different constituting parameters and provide values which differ widely. After a thorough review of literature and field investigations in the drivages of mines and tunnels some parameters were identified. Those parameters were subjected to Multiple Linear Regression analyses to filter out the most influencing ones which represent the rockmass properties, the tunnel configurations and the blast designs. A parameter called Tunnel Blasting Index (TBI) was conceptualized and was expressed in terms of those most influencing parameters. All the blast results observed during the filed investigations could be well related to a single index TBI. Some adjustments on account of shape of the tunnel and joint orientations, which were not addressed in the available models, are suggested in the developed models. 相似文献