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31.
Piping/tunnelling erosion is a widely spread process in the Plio-Pleistocene marine clays of the Basilicata region in southern Italy. The pipes are often closely concentrated along the surface drainage networks at different depths with a tunnel (length) and a diameter varying from just a few centimetres to some metres. The formation and evolution of pipes in the badlands can be explained through: (1) geo-structural characteristics of the clay, (2) material properties such as a high exchangeable sodium percentage, (3) favourable climatic conditions, and (4) hydraulic gradient along the path controlled by the gully or ravine bottom that is acting as a local drain. The exposure and the extension of joints at the surface and in the bedrock along the slope are the main factors required for development of the pipes. The absence of the piping erosion on the slopes, where a reasonably thick layer of the soil material covers the open joints, shows that although certain material properties and climatic conditions play an important role, they are not sufficient to develop extensive piping erosion in the area. 相似文献
32.
Summary This paper is a contribution to the study of tunnelling in difficult conditions, with attention paid to large time-dependent
deformations, which may develop either during construction, causing instabilities of the tunnel heading and of the face, or
during the service life of the tunnel. Under these circumstances the construction costs may rise due to the delays in excavation
time, the stabilisation and heavy support measures that need be adopted. Following a review of characterisation and modelling
of time-dependent behaviour in rock, the mechanical behaviour of Clay Shales (CS), a structurally complex formation of the
Apennines (Italy), is described. Then, the key factors involved in the selection of the constitutive model for CS are identified.
Two constitutive models are selected and discussed and their specific material parameters determined. A case study of a large
size tunnel is presented where numerical modelling by the finite difference method is carried out. The results of modelling
are compared with the monitoring data in terms of radial convergence of the tunnel and extrusion of the tunnel face. 相似文献
33.
Three-dimensional (3D) finite element analyses have been performed to study the behaviour of a single pile and 3 × 3 and 5 × 5 pile groups during open face tunnelling in stiff clay. Several governing factors, such as tunnelling-induced ground and pile settlement, axial pile force changes and shear transfer mechanism at the pile–soil interface, have been studied in detail. Tunnelling resulted in the development of pile head settlement larger than the free-field soil surface settlement. In addition, axial force distributions along the pile change substantially due to changes in the shear transfer between the pile and the soil next to the pile, which triggers tunnelling-induced tensile forces in the piles with tunnel advancement. It was found that the relative displacements and the normal stresses at the pile–soil interface drastically affected shear transfer. The extent of slip length along a pile increased as the tunnelling proceeded. The apparent allowable pile capacity was reduced by up to approximately 42% due to the development of tunnelling-induced pile head settlement. Shear stress on the pile was increased for most of the pile depth with tunnel advancement, which was associated with changes in soil stresses and ground deformation, and hence, the axial pile force was gradually reduced with tunnel advancement, indicating the development of tunnelling-induced tensile pile force. The maximum tunnelling-induced tensile force on the pile was approximately 0.33Pa, where Pa is the allowable pile capacity applied to the pile head prior to tunnel excavation. The range affected by tunnelling in the longitudinal direction may be identified as approximately −2D ∼ +(1.5–2.0D), where D is the tunnel diameter, from the pile centre (behind and ahead of the pile axis), in terms of pile settlement and axial pile force changes based on the analysis conditions assumed in the current study. Larger pile head settlements and smaller changes in axial pile forces were computed for piles that were part of groups. It has been found that the serviceability of piles experiencing adjacent tunnelling is more affected by pile settlement than by axial pile force changes, in particular for piles inside groups. The magnitude of the tunnelling-induced excess pore pressure was small and may not substantially affect pile behaviour. 相似文献
34.
Summary. In the planning and procurement phases of tunnelling projects, numerous decisions have to be made regarding tender price and
budget. Many case studies have shown that, in practice, the predicted costs and time schedules are often exceeded. This paper
describes a study of the various risk factors in machine tunnelling and their differing impacts on cost and time. It has been
concluded from the study that it is important to make a clear distinction between normal cost and time, and the undesirable events that cause exceptional cost and time. Existing decision-aid estimation models consider variation of the risk factors, but do not consider normal
cost or time separately from undesirable events. Usually, estimations of project cost and time are made in a deterministic
manner, but this does not allow one to consider uncertainty in cost and time variables. However, if the variables are treated
probabilistically, the total cost of tunnelling can be expressed as a distribution curve, and a decision can be made on the
tunnelling method by comparing the respective cost and time distributions. Based on such decisions, the budget and tender
price can be determined separately, both by the client and contractor respectively. To meet the demands placed on decision-making
for tender and procurement for currently favoured construction-contracting methods, a new model for estimating tender price
and budget has been developed, and is described in this paper. This estimating technique has been applied to a case study
of the Grauholz Tunnel. The predictions obtained from the estimation model are shown to be realistic, as the total construction
cost and time obtained from the model correspond fairly well to the actual construction cost and time. The separate estimation
of normal cost and time and exceptional cost and time contribute to the clarity of the results. The use of the proposed model
also shows that the tunnelling method most suitable for the actual geological and hydrogeological conditions can be selected
by this method. 相似文献
35.
The paper combines wavelet and entropy analysis of nonstationary drilling-ability data in order to obtain optimum information on the mechanical behavior of different geological formations. Both methods are multiscale in nature, and while entropy analysis provides information on stationary subdomains, wavelet analysis identifies dominant scales or range of scales at which the entropy analysis is most useful. The combination of the techniques yields relatively simple results that can aid the drilling process by providing information on delays to be expected. 相似文献
36.
简述了我国隧道及地下工程的发展,介绍了当前隧道及地下工程的施工方法、辅助工法,并提出了施工中应注意的有关重要问题。 相似文献
37.
Summary Quick, simple, reliable, and inexpensive measurements of overbreak and underbreak are needed for proper evaluation of tunnelling by the drill and blast method. Problems causing rock damage can be identified and remedied while the work is still in progress. The measurements are also useful in identifying causes of overbreak and overbreak, and in helping to settle contractual disputes relating to payment for replacement concrete and secondary blasting of tights (zones of underbreak). A newly developed method to measure underbreak and overbreak is presented here. The light sectioning method (LSM) uses a radial sheet of light to define the tunnel profile. An image of the final tunnel profile is acquired and digitized, using digital image analysis. This profile is superimposed over the design profile, and from this zones of overbreak and underbreak are identified, quantified, and presented graphically. 相似文献
38.
P. S. Moharir 《Journal of Earth System Science》1992,101(1):1-11
Parasnis has observed in a presidential address that geophysics is not a Popperian science in a major way. That is, hypotheses
are not consciously put forth in a falsifiable format and much of the effort goes in seeking supporting evidence for favoured
hypotheses. Parker evolved a parameter extremization strategy, initially to tackle the problem of non-uniqueness in geophysical
inference. Later he based a hypothesis testing proposal on it, which is refreshingly Popperian. It has not been adopted widely,
partly because it requires global extrema, and not local and this has been regarded as a problem with no solution. Attention
is drawn towards tunnelling algorithm, which solves the problem of global optimization successfully, makes Parker’s Popperian
proposal practical and extends the range of Popperian geophysics. 相似文献
39.
Analysis of shield tunnel 总被引：1，自引：0，他引：1
This paper proposes a two‐dimensional finite element model for the analysis of shield tunnels by taking into account the construction process which is divided into four stages. The soil is assumed to behave as an elasto‐plastic medium whereas the shield is simulated by beam–joint discontinuous model in which curved beam elements and joint elements are used to model the segments and joints, respectively. As grout is usually injected to fill the gap between the lining and the soil, the property parameters of the grout are chosen in such a way that they can reflect the state of the grout at each stage. Furthermore, the contact condition between the soil and lining will change with the construction stage, and therefore, different stress‐releasing coefficients are used to account for the changes. To assess the accuracy that can be attained by the method in solving practical problems, the shield tunnelling in the No. 7 Subway Line Project in Osaka, Japan, is used as a case history for our study. The numerical results are compared with those measured in the field. The results presented in the paper show that the proposed numerical procedure can be used to effectively estimate the deformation, stresses and moments experienced by the surrounding soils and the concrete lining segments. The analysis and method presented in this paper can be considered to be useful for other subway construction projects involving shield tunnelling in soft soils. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
40.