421 research outputs found
The Interaction Between Shield, Ground and Tunnel Support in TBM Tunnelling Through Squeezing Ground
When planning a TBM drive in squeezing ground, the tunnelling engineer faces a complex problem involving a number of conflicting factors. In this respect, numerical analyses represent a helpful decision aid as they provide a quantitative assessment of the effects of key parameters. The present paper investigates the interaction between the shield, ground and tunnel support by means of computational analysis. Emphasis is placed on the boundary condition, which is applied to model the interface between the ground and the shield or tunnel support. The paper also discusses two cases, which illustrate different methodical approaches applied to the assessment of a TBM drive in squeezing ground. The first case history—the Uluabat Tunnel (Turkey)—mainly involves the investigation of TBM design measures aimed at reducing the risk of shield jamming. The second case history—the Faido Section of the Gotthard Base Tunnel (Switzerland)—deals with different types of tunnel support installed behind a gripper TB
The Effect of Consolidation on TBM Shield Loading in Water-Bearing Squeezing Ground
Jamming or overstressing of the shield due to ground pressure are potential problems for tunnel boring machine (TBM) tunnelling in squeezing ground. The risk of shield jamming depends essentially on the deformation rate of the ground in the vicinity of the working face. The time-dependency of the ground response to the excavation is associated with its rheological properties as well as with the transient consolidation process that takes place around the opening in the case of a low-permeability saturated ground. The present paper focuses on the second mechanism and investigates the interaction between the advancing shield, tunnel lining and consolidating ground by means of transient numerical analyses. For a given set of geotechnical conditions and a given TBM configuration, the load exerted by the ground upon the shield during TBM operation decreases with increasing gross advance rate. During a long break in operations, the ground pressure may increase significantly, thereby necessitating a higher thrust force to overcome shield skin friction and restart the TBM. It is interesting to note that a high advance rate reduces the risk of shield jamming not only during TBM advance, but is also favourable with respect to any subsequent long standstill
Robust Inference of Trees
This paper is concerned with the reliable inference of optimal
tree-approximations to the dependency structure of an unknown distribution
generating data. The traditional approach to the problem measures the
dependency strength between random variables by the index called mutual
information. In this paper reliability is achieved by Walley's imprecise
Dirichlet model, which generalizes Bayesian learning with Dirichlet priors.
Adopting the imprecise Dirichlet model results in posterior interval
expectation for mutual information, and in a set of plausible trees consistent
with the data. Reliable inference about the actual tree is achieved by focusing
on the substructure common to all the plausible trees. We develop an exact
algorithm that infers the substructure in time O(m^4), m being the number of
random variables. The new algorithm is applied to a set of data sampled from a
known distribution. The method is shown to reliably infer edges of the actual
tree even when the data are very scarce, unlike the traditional approach.
Finally, we provide lower and upper credibility limits for mutual information
under the imprecise Dirichlet model. These enable the previous developments to
be extended to a full inferential method for trees.Comment: 26 pages, 7 figure
Clinical Effects of the Extract of the Seeds of the Indian Celery-Apium Graveolens-In Horses Affected by Chronic Osteoarthritis.
The extract of the seeds from Indian celery, Apium greaveolens (CSE), tested in experimental
animals (rodents), and in humans aected by chronic osteoarthritic diseases, exhibits anti-inflammatory
eects that can be compared, to some degree, to those of non-steroid anti-inflammatory drugs (NSAID).
In view of a potential use of CSE in the equine species, it was tested on horses aected by chronic
articular pathologies. The trial was performed on 20 horses divided into three dierent groups, orally
treated with 0 (controls), 7.0 or 30 g of CSE BID. Basic orthopedic examinations were conducted, vital
signs were observed, and blood samples collected. Improvement was observed at the highest dosage
tested (30 g of CSE BID), as reflected in the score values of three clinical parameters, (i) amplitude and
(ii) sensitivity to passive flexion and (iii) flexion test. Since the improvement of these parameters can
be correlated with a lower perception of the pain, the present data suggest that the CSE treatment can
have an analgesic eect in horses aected by chronic osteoarthritic diseases
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