Modelling the poroelastoplastic behaviour of soils subjected to internal erosion by suffusion

Granular soils subjected to seepage flow may suffer suffusion, ie, a selective internal erosion. Extending the classical approach of poromechanics, we deduce a new form of the Clausius-Duhem inequality accounting for dissipation due to suffusion, and we deduce restrictions on the constitutive laws of the soil. We suggest (a) a possible coupling between the seepage forces and the suffusion kinetics and (b) an extension of an existing elastoplastic model for the skeleton mechanical behaviour. Numerical integrations of the elastoplastic model are carried out under drained axisymmetric triaxial and oedometric conditions. As a result, we prove that the extended model is able to qualitatively reproduce the suffusion induced strains and the strength reduction experimentally observed. Predictions on the oedometric behaviour of suffusive soils are also provided.     

Integrating isolated and riparian wetland modules in the PHYSITEL/HYDROTEL modelling platform: model performance and diagnosis

Mathematical modelling is a well‐accepted framework to evaluate the effects of wetlands on stream flow and watershed hydrology in general. Although the integration of wetland modules into a distributed hydrological model represents a cost‐effective way to make this assessment, the added value brought by landscape‐specific modules to a model's ability to replicate basic hydrograph characteristics remains unclear. The objectives of this paper were the following: (i) to present the adaptation of PHYSITEL (a geographic information system) to parameterize isolated and riparian wetlands; (ii) to describe the integration of specific isolated wetland and riparian wetland modules into HYDROTEL, a distributed hydrological model; and (iii) to evaluate the performance of the updated modelling platform with respect to the capacity of replicating various hydrograph characteristics. To achieve this, two sets of simulations were performed (with and without wetland modules), and the added value was assessed at three river segments of the Becancour River watershed, Quebec, Canada, using six general goodness‐of‐fit indicators and 14 water flow criteria. A sensitivity analysis of the wetland module parameters was performed to characterize their impact on stream flows of the modelled watershed. Results of this study indicate the following: (i) integration of specific wetland modules can slightly increase the capacity of HYDROTEL to replicate basic hydrograph characteristics; and (ii) the updated modelling platform allows for the explicit assessment of the impact of wetlands (e.g. typology and location) on watershed hydrology. Copyright © 2015 John Wiley & Sons, Ltd.     

Contained density currents with high volume of release

Contained density currents with high volume of release reflect against the boundaries of the reception environment commonly leading to oscillatory flow. These flows exist in sediment clarifiers, compromising their operations, and deposited signatures of contained turbidity currents are found as part of the infill of sedimentary basins; for operation of the former and interpretation of the latter it is essential to understand the dynamic processes of these flows. Six lock‐exchange experiments with different initial densities were made in a horizontal flume, where the volume of the saline mixture in the lock was equivalent to the volume of the ambient fluid. A further two tests, with a repeated initial density, were made: one with high volume of release and very long duration; and another with low volume of release. Firstly, the movement of the current is discussed, including the oscillations within the experimental tank involving the density current and an upper layer counter‐current. It is shown that the cyclic behaviour is self‐similar with the reduced gravity of the initial density in the lock. Secondly, entrainment and water mixing processes are characterized. The time evolution of mixing is characterized qualitatively by analysing the background potential energy of the density distributions to show that mixing occurs even in the earlier stages of the current, and mainly within the first cycle of the oscillation. Quantified analysis reveals that, in currents with high volume of release, entrainment discharge is one order of magnitude higher, mainly due to the larger interface between the ambient fluid and the current. A model for the evolution of the mixing process is proposed for density currents with high volume of release. Finally, the dynamics of the head of the current is analysed. The entrainment in the head, when compared to the entrainment in the remainder body of the flows, is less important for the configuration with a larger lock.     

A collective approach to Pacific islands fisheries management: Moving beyond regional agreements

The sustainable management and profitable development of the Pacific island tuna fisheries is the key ocean governance challenge for the Pacific islands region in the short and medium term. Resolving these challenges is fundamental to the long term future of the region and its ability to implement oceans governance across all resource and conservation concerns.     

Cation disorder in garnets along the Mg3Al2Si3O12-Mg4Si4O12 join: an infrared,Raman and NMR study

We have obtained infrared and Raman spectra for garnets synthesized at high (static) pressures and temperatures along the join Mg₃Al₂Si₃O₁₂ (pyrope) — Mg₄Si₄O₁₂ (magnesium majorite). The vibrational spectra of Mg-majorite show a large number of additional weak peaks compared with the spectra of cubic pyrope garnet, consistent with tetragonal symmetry for the MgSiO₃ garnet phase. The Raman bands for this phase show no evidence for line broadening, suggesting that Mg and Si are ordered on octahedral sites in the garnet. The bands for the intermediate garnet compositions are significantly broadened compared with the end-members pyrope and Mg-majorite, indicating cation disorder in the intermediate phases. Solid state ²⁷Al NMR spectroscopy for pyrope and two intermediate compositions show that Al is present only on octahedral sites, so the cation disorder is most likely confined to Mg-Al-Si mixing on the octahedral sites. We have also obtained a Raman spectrum for a natural, shock-produced (Fe,Mg) majorite garnet. The sharp Raman peaks suggest little or no cation disorder in this sample.     

Infrared vibrational spectra of Beta-Phase Mg2SiO4 and Co2SiO4 to Pressures of 27 GPa

Infrared absorption spectra of the high-pressure polymorphs β-Mg₂SiO₄ and β-Co₂SiO₄ have been measured between 0 and 27 GPa at room temperature. Grüneisen parameters determined for 11 modes of β-Mg₂SiO₄ (frequencies of 300 to 1,050 cm^?1) and 5 modes of β-Co₂SiO₄ (490 to 1,050 cm^?1) range between 0.8 and 1.9. Averaging the mid-infrared spectroscopic data for β-Mg₂SiO₄ yields an average Grüneisen parameter of 1.3 (±0.1), in good agreement with the high-temperature thermodynamic value of 1.35. Similarly, we find a value of 1.05 (±0.2) for the average spectroscopic Grüneisen parameter of β-Co₂SiO₄.     

Densities deduced from perturbations at high altitudes

Atmospheric densities between 1500 and 3000km have been determined from observations of satellites with large surface to mass ratios. The analysis has been made for optimum periods where the satellite is continuously in sunlight and when the effects of Earth albedo are minimum. Twenty six values of density obtained from 1965 to 1970 have been analysed.     

黄土高原秦安中新世黄土-古土壤序列的蜗牛化石初步研究

通过对秦安中新世黄土-古土壤序列蜗牛化石的初步调查研究表明, 在距今22~6.2 Ma期间长达近16 Ma的黄土-古土壤沉积发育过程中, 无论黄土还是古土壤地层中都保存有较丰富的蜗牛化石种类, 目前发现的15种蜗牛化石全部是陆生种类, 化石个体保存完整, 为原地埋藏的种群, 未发现水生的种类, 多数为第四纪黄土-古土壤序列中的常见种类, 可划分为冷干和温湿两个生态类群, 冷干类主要见于黄土地层中, 温湿类主要分布于古土壤地层中. 自中新世至第四纪期间, 蜗牛化石Metodontia(间齿螺)类和Cathaica(华蜗牛)类的属种具有明显的演化趋势, 新的种类的出现和演化与这一时期大的气候环境的改变在时代上有较好的一致性, 反映了蜗牛生态种类对全球/区域性环境格局变化的响应. 初步研究结果表明, 中新世黄土-古土壤序列与第四纪黄土-古土壤序列有着相似的沉积背景. 研究结果为秦安中新世黄土-古土壤序列沉积环境、气候演化等提供了生物化石证据.