1、翻译部分英文原文The performance of pressure cells for sprayed concrete tunnel liningsC . R . I . C L AY TO N,J. P. VA N D E R B E R G , G . H E Y M A N N, A . V. D. B I C A a n d V. S . H O P EAbstract:The paper examines the factors that affect the performance of tangential cells embedded in shotcrete tunne
2、l linings. New data, derived from field monitoring, numerical modelling,and calibration tests carried out to simulate the embedment and crimping processes, are presented. These suggest that although well-designed embedded total pressure cells will have cell action factors close to unity, they cannot
3、 be assumed to provide reasonable estimates of the stresses within sprayed concrete linings, unless the influences of installation effects, temperature changes, shrinkage and subsequent crimping can be taken into account.Keywords: field instrumentation; tunnels.IntroductionThe pressure cells used fo
4、r measuring the compressive stresses in shotcrete tunnel linings generally consist of two stainless steel plates with a thin fluid- filled cavity between them. The cavity is connected either to a membrane-type bypass valve or to a vibrating-wire pressure transducer. The use of other direct-stress in
5、struments has been reported in the literature, although infrequently. Pressure cells are typically installed in one of two orientations: radial, to record the stress between the sprayed concrete and the ground surrounding the tunnel; and tangential, to record the hoop stress within the tunnel lining
6、 itself. This paper considers only tangential cells.Despite their widespread use in practice, there has been very little research reported in the literature on the use and behaviour of shotcrete pressure cells. Many practitioners remain doubtful of the ability of embedded pressure cells to measure t
7、he actual stresses in concrete tunnel linings. In a previous paper reviewing instrumentation for sprayed concrete lined tunnels the present authors noted some of the potential difficulties, stating that it was extremely unlikely that embedded cells be used for monitoring the actual stress in a tunne
8、l lining. Yet, potentially, pressure cells are a valuable source of information that might be used to assess whether tunnel design assumptions are justified, and this paper therefore reports the findings of our further research into this important topic.Factors affecting the pressures recorded by ta
9、ngential pressure cells in tunnel liningsDirect stress measurement within any medium is made difficult by the many factors that can affect the results. In the case of tangential pressure cells embedded in shotcrete our recent experiences during tunnel monitoring suggest that these are as follows.Cel
10、l propertiesThe cell should be constructed so that the stresses in the shotcrete are not significantly modified by its presence. Since the compressibility of the fluid in the cell is less than the surrounding materials it will under-read, but this can largely be compensated for by making the cell wi
11、de and thin. The use of cell fluids such as mercury or oil will affect not only the compressibility of cells but also their temperature sensitivity. Changes in temperature will expand the fluid against the surrounding, relatively rigid cell metal and surrounding concrete, and will produce a change i
12、n measured stress.Installation effectsThe inadvertent formation of cavities around the cell during shotcreting will lead to a soft measurement system, which will subsequently under-read. Incorrect positioning of the cell within the lining, rotating it towards the radial direction, can also cause it
13、to under-read somewhat, because radial stresses are typically less than 10% of tangential. Indeed the actual thickness of the lining at the point of installation will also affect the interpretation of the stress measurements.Post-installation factorsAs noted above, temperature changes can be expecte
14、d to lead to changes in measured stresses. Shrinkage during the early life of the shotcrete will result in changes in the recorded stress that are not due to external stress changes. Crimping, which is often undertaken to ensure that pressure cells are properly bedded within the shotcrete , can prov
15、ide a significant offset to the measured pressures.Numerical and physical experiments, and results from monitoringNumerical modelling and physical simulation have been carried out to assess the actual performance of some stress cells used in practice, and to place their performance in the context of
16、 other cell designs.Numerical modelling to assess the effects of cell fluidTo examine the effect of cell fluid on cell performance two idealised circular cells embedded in a block of concrete were modelled under axisymmetric conditions using the finite element package LUSAS. The geometry of the cells and the material properties modelled are shown in Fig. 1. The 160 mm diameter cell is somewhat larger than many of the cells currently in
