Identification of groundwater exfiltration,interflow discharge,and hyporheic exchange flows by fibre optic distributed temperature sensing supported by electromagnetic induction geophysics     

Jaime Gaona  Karin Meinikmann  Jrg Lewandowski 《水文研究》2019,33(10):1390-1402

Water exchange across the sediment–water interface of streams impresses a characteristic thermal pattern at the interface. The use of fibre optic distributed temperature sensing at the sediment–water interface in a small sand‐bed stream identifies such temperature patterns. Groundwater and interflow can be differentiated based on the temporal evolution of temperature patterns. Additionally, sudden temperature changes at the sediment–water interface observed during the transit of floods enable spatial identification of local up and downwelling. Electromagnetic induction geophysics can detect subsurface texture structures that support groundwater–surface water exchange. Our results show that areas of permanent temperature anomalies observed with fibre optic distributed temperature sensing match areas of comparatively homogeneous electrical conductivity. This indicates groundwater discharge and enables differentiating groundwater discharge from interflow and local downwelling.  相似文献   

Shear strength behaviour of polypropylene fibre reinforced cohesive soils     

Costas A. Anagnostopoulos  Dimitrios Tzetzis  Kiriakos Berketis 《Geomechanics and Geoengineering》2014,9(3):241-251

Soil reinforcement through the inclusion of oriented or randomly distributed discrete elements such as fibres has recently attracted increasing attention in geotechnical engineering. Therefore, the purpose of this paper is to investigate the influence of certain parameters (the strength properties of the fibre, the relative size of the fibres and grains, and the rate of shear) on the shear strength of polypropylene fibre reinforced cohesive soils. A series of consolidated drained or undrained direct shear tests were conducted on unreinforced and reinforced sandy silt and silty clay specimens. Two types of polypropylene fibres with different mechanical indices were used. The fibre content was varied between 0.3% and 1.1% by weight of dry soil. The test results revealed that the inclusion of fibres in soil significantly increases the shear strength. The attainment of the high shear strength is attributed to the micromechanisms involved in the fibre/soil interactions as studied through scanning electron micrographs. The results also showed that the reinforcement effect was more pronounced under undrained shearing conditions. An important outcome from the current work is that, from the data obtained, the strength of the reinforced soil composites is not practically affected by the fibre mechanical indices.  相似文献   

后压浆提高钻孔灌注桩承载力的试验研究   总被引：1，自引：0，他引：1  

肖坚  赵刚 《岩土工程技术》2011,25(1):10-12,16

后压浆技术能改善桩端沉渣和桩周泥皮。通过某工程压浆试验,表明后压浆工艺能大幅度提高基桩承载能力,减小沉降量,并结合分布式光纤检测得到了桩身侧摩阻分布图,对压浆效果及作用机理进行了直观地分析。  相似文献   

Localized failure of fibre‐reinforced elastic–plastic materials subjected to plane strain loading     

Dunja Perić  Hayder A. Rasheed 《国际地质力学数值与分析法杂志》2007,31(7):893-916

We consider discontinuous bifurcations as the indicator of a localized failure for a class of composites that are characterized by elastic fibres reinforcing an elastic–plastic matrix. A macroscopic tangent stiffness tensor for the fibre‐reinforced composite is developed by consistently homogenizing the contribution of fibres in a spherical representative volume element. Analytical solutions are derived for the critical hardening modulus and corresponding bifurcation directions for the case of plane strain loading. Properties of the solutions are further illustrated on the example of the non‐associated Drucker–Prager model at onset of yielding. Results show that presence of fibres decreases the critical hardening modulus, thus inhibiting the onset of strain localization. The rate of decrease in the critical hardening modulus is the highest for pure shear, followed by uniaxial tension, uniaxial compression, biaxial tension and biaxial compression. The main fibre parameters that control the onset of strain localization are their volumetric content and their stiffness modulus whereby very stiff fibres can produce the most significant decrease in the critical hardening modulus, especially for the state of biaxial tension. The critical hardening modulus for the non‐associated Drucker–Prager model exhibits a full range of localization modes including compaction bands, dilation bands, and transition in the form of shear bands regardless of the presence of fibres. Presence of fibres affects bifurcation directions, except in the case when Poisson's ratio of the matrix is equal to 0.25. The results demonstrate stabilizing effects of fibres by which they provide the control against the onset of strain localization. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Tip-tilt requirements for coupling starlight into single-mode photonic crystal fibres using a lenslet: A first analysis     

Jason C.W. Corbett  Tim J. Morris  Jeremy R. Allington-Smith 《New Astronomy Reviews》2006,49(10-12):675

Single-mode fibres do not suffer from modal noise and are available in polarisation maintaining form. Single-mode photonic crystal fibres (smPCF) have a wavelength insensitive mode field allowing coupling of the telescope exit pupil into the fibre using a lenslet with a flat spectral response. This may allow single-mode Integral Field Spectroscopy (IFS) and fibre fed integral field spectro-polarimetry. Initial results from a theoretical analysis of telescope/smPCF coupling using a lenslet are presented. Coherent imaging theory is used to determine the coupling efficiency into the fibre and thence the fibre numerical aperture is defined and used to compute the sample size on the sky. A higher degree of tip-tilt correction is shown to be required for coupling into single-mode fibres with a lenslet than the multimode fibre alternative, for sparse sampling integral field and multi-object spectroscopy and interferometry, but the magnitude of which is within the scope of current NIR and planned (extreme) VIS AO systems. Extension of the model to contiguous integral field spectroscopy is also considered.  相似文献   

The sequence of geological events and the dynamics of the Milky Way galaxy     

Johann Steiner 《Australian Journal of Earth Sciences》2013,60(1):99-131

Present‐day galactic data permit the construction of a galactic model in which the galactic gravitational field is described by a gravitational function rather than the Newtonian gravitational “constant” G. The concept of this empirical gravitational function, which is based on galactic orbital velocity data, envisages G as a function of time and space. In this model the interaction of this gravitational function, which has rotational symmetry in the galactic plane, and the slightly elliptical galactic orbit of the solar system results in a systematic variation of G. This interaction specifies a simple galactic time‐scale which can be conveniently compared with events of the geological time‐scale. For reasons of galactic evolution and modifying effects due to suspected changes of mass distributions in the universe with the passage of time, which are classed here under the Dirac‐Jordan Effect, such a comparison is initially restricted to the past 1#fr1/4> cosmic years, or 350 million years. The problems in extending such a comparison to 8 cosmic years are discussed, and such an extension seems promising, but it is hampered by the paucity of geological and geophysical data from the lower Palaeozoic and the Precambrian and the present uncertainties in regard to galactic evolution.

“Worldwide” statistical maxima and minima of the following geological criteria disclose an episodic correlation with the variation of G and the rates of change of G during the past 350 million years, as specified by this galactic model. It is possible to interpret this correlation in terms of accepted geological principles and concepts in most cases. The following geological phenomena are considered in this comparison of the galactic and geological time‐scales for the past 350 million years.