Influence of structure on the compression and shear behaviour of a saturated lateritic clay

Lateritic clay is well recognized to contain significant amount of iron and aluminium oxides (sesquioxide). These oxides enhance the formation of soil aggregates which would greatly affect soil structure. So far, no study has been carried out purposely to investigate the influence of aggregate-dependent structure on the mechanical behaviour of the lateritic clay. In this study, structure effects on the compression and shear behaviour of a saturated lateritic clay were studied. Intact, recompacted and reconstituted specimens were studied through oedometer, isotropic compression and consolidated undrained shear tests. Microstructure of these specimens was determined using the mercury intrusion porosimetry and scanning electron microscopy (SEM) techniques and then used to explain the observed behaviour. It was found that the compressibility of recompacted/reconstituted specimens was about 90% larger than intact specimen. Different from soft clay, the influence of microstructure does not show an obvious reduction in compressibility after yielding. The peak shear strength of intact specimen was about 100% higher than those of reconstituted/recompacted specimens. The significant difference in compression and shear behaviour is mainly because the aggregates of intact specimen were about 90% larger than those of reconstituted/recompacted specimens, as revealed by the SEM results. As a result, particle contacts forming the force chain were therefore larger in the intact specimen. The intact specimen therefore became less compressible and more dilative.

     

Assessment of three interface elements and modification of the interface element in CRISP90

To model the interaction between a buried pipeline and the surrounding soil either special interface elements or thin conventional elements may be used. In this study the CRISP90 interface element, the DRCRISP interface element and a conventional 8-noded quadrilateral element have been examined and their behaviour compared for a variety of loading conditions. Initial studies reveal that all these elements have limitations and are only suitable for monotonic loading and situations where tensile conditions do not occur across the interface. In the light of these findings the CRISP90 interface element has been modified by introducing a limiting adhesive strength in the normal direction; a flag system has also been introduced to track the various conditions of separation and closure for any gap that is formed. The results of single element and other benchmark tests show that the modified element can satisfactorily model the different modes of deformation relevant to soil–structure interface problems.     

Estuarine phytoplankton dynamics and shift of limiting factors: A study in the Changjiang (Yangtze River) Estuary and adjacent area

Environmental factors in estuaries are highly variable in terms of both spatial and temporal dimensions and hence phytoplankton biomass, as well as community structure, is dynamic. Two cruises were carried out in the Changjiang (Yangtze River) Estuary and adjacent area in spring and summer. The result of CHEMTAX calculation suggests that in spring diatoms and chlorophytes contribute equally to phytoplankton biomass, while phytoplankton community structure is mainly composed of diatoms in summer. We encountered blooms in summer with chlorophyll a (CHLa) over 10 μg l⁻¹ off the Changjiang Estuary and they were mainly caused by diatoms (>90%). Based on the HPLC analysis of samples collected, phytoplankton pigments mainly concentrated beyond the front between 122.5°E and 123°E where nutrients and turbidity were best balanced. Euphotic depth (Z_eu, calculated from Secchi disk depth) to surface mixed layer depth (Z_mix) ratio (i.e. Z_eu/Z_mix) were comparable in spring (average value 1.2) and the ratio increased to 5.2 in summer. Variation of the ratio indicates an apparent shift of light and physical conditions from spring to summer. Correspondingly, CHLa was positively related to Z_eu/Z_mix ratio (r² = 0.83) in spring, indicating the light limitation over the whole investigation area. On the other hand, the relationship of CHLa and Z_eu/Z_mix ratio became unclear when Z_eu/Z_mix ratio >3 in summer. This is probably due to the combination of both light limitation before the front and nutrient limitation beyond the front. In addition, evidence was found that light condition can impact the diagnostic pigments in the Changjiang Estuary.     

A general algorithm for the solution of Kepler's equation for elliptic orbits

An efficient algorithm is presented for the solution of Kepler's equationf(E)=E–M–e sinE=0, wheree is the eccentricity,M the mean anomaly andE the eccentric anomaly. This algorithm is based on simple initial approximations that are cubics inM, and an iterative scheme that is a slight generalization of the Newton-Raphson method. Extensive testing of this algorithm has been performed on the UNIVAC 1108 computer. Solutions for 20 000 pairs of values ofe andM show that for single precision (10^–8) 42.0% of the cases require one iteration, 57.8% two and 0.2% three. For double precision (10^–18) one additional iteration is required. Single- and double-precision FORTRAN subroutines are available from the author.     

Initial Fe/O Enhancements in Large, Gradual, Solar Energetic Particle Events: Observations from Wind and Ulysses

Shocks driven by fast coronal mass ejections (CMEs) are the dominant particle accelerators in large, “gradual” solar energetic particle (SEP) events. In these events, the event-integrated value of the iron-to-oxygen ratio (Fe/O) is typically ～?0.1, at least at energies of a few MeV/nucleon. However, at the start of some gradual events, when intensities are low and growing, initially Fe/O is ～?1. This value is also characteristic of small, “impulsive” SEP events, in which particle acceleration is due to magnetic reconnection. These observations suggested that SEPs in gradual events also include a direct contribution from the flare that accompanied the CME launch. If correct, this interpretation is of critical importance: it indicates a clear path to interplanetary space for particles from the reconnection region beneath the CME. A key issue for the flare origin is “magnetic connectedness”, i.e., proximity of the flare site to the solar footpoint of the observer’s magnetic field line. We present two large gradual events observed in 2001 by Wind at L1 and by Ulysses, when it was located at >?60^° heliolatitude and beyond 1.6 AU. In these events, transient Fe/O enhancements at 5?–?10 MeV/nucleon were seen at both spacecraft, even though one or both is not “well-connected” to the flare. These observations demonstrate that an initial Fe/O enhancement cannot be cited as evidence for a direct flare component. Instead, initial Fe/O enhancements are better understood as a transport effect, driven by the different mass-to-charge ratios of Fe and O. We further demonstrate that the time-constant of the roughly exponential decay of the Fe/O ratio scales as R ², where R is the observer’s radial distance from the Sun. This behavior is consistent with radial diffusion. These observations thus also provide a potential constraint on models in which SEPs reach high heliolatitudes by cross-field diffusion.     

循环温度场作用下PCC能量桩热力学特性模型试验研究

PCC能量桩是河海大学岩土所开发的一种新型能量桩技术。在常规桩基静载荷模型试验基础上,将PCC能量桩放置在南京典型砂土中,并通过导热管内水体的循环对模型桩体施加温度场,以模拟PCC能量桩在实际运行过程中的承载力特性与受力机制,PCC能量桩先加载至工作荷载（极限荷载的一半）,再施加热-冷循环一次,最后加载至极限荷载,测得不同温度下PCC能量桩的荷载-位移关系曲线、桩身应力-应变关系曲线等变化规律。试验结果表明,能量桩换热过程中,热量更容易从桩体传向土体（即夏季模式的热循环）;热循环及制冷循环都明显改变了桩顶位移值,且往复循环作用下产生的塑性变形不能完全恢复,其积累变形可能危害上部结构安全;桩身受温度场作用产生的热应力相对较大,且不同约束条件下其变化值有所差异;在制冷循环下,桩底部甚至可能产生较大拉应力。     

AN INVESTIGATION OF THE ACCURACY OF PARALLAX BAR HEIGHTING BY MEANS OF NUMERICAL SIMULATION

Previous assessments of the accuracy of parallax bar heighting were handicapped by small sample sizes. Numerical simulation was avoided due to the difficulty of obtaining co-ordinates for the conjugate principal points. This problem has been overcome, however, and all required photograph coordinates have been rigorously computed following the generation of fictitious data for ground points and exposure stations. The parallax bar heighting process has additionally been simulated in order to investigate both external factors, such as image errors, tilts and ground relief, and also influences intrinsic in the heighting process, for example estimation of flying height, baselining, control configuration and error surface model.     

Potential Hydrodynamic Performance Enhancement of Hydrokinetic Turbine with Hydrophobic Coatings

China Ocean Engineering - Hydrokinetic energy is a promising technology to harness predictable renewable energy from free-flowing water, tides and ocean currents. Many studies have been conducted...     

Effects of the roots of Cynodon dactylon and Schefflera heptaphylla on water infiltration rate and soil hydraulic conductivity

Water infiltration rate and hydraulic conductivity in vegetated soil are two vital hydrological parameters for agriculturists to determine availability of soil moisture for assessing crop growths and yields, and also for engineers to carry out stability calculations of vegetated slopes. However, any effects of roots on these two parameters are not well‐understood. This study aims to quantify the effects of a grass species, Cynodon dactylon, and a tree species, Schefflera heptaphylla, on infiltration rate and hydraulic conductivity in relation to their root characteristics and suction responses. The two selected species are commonly used for ecological restoration and rehabilitation in many parts of the world and South China, respectively. A series of in‐situ double‐ring infiltration tests was conducted during a wet summer, while the responses of soil suction were monitored by tensiometers. When compared to bare soil, the vegetated soil has lower infiltration rate and hydraulic conductivity. This results in at least 50% higher suction retained in the vegetated soil. It is revealed that the effects of root‐water uptake by the selected species on suction were insignificant because of the small evapotranspiration (<0.2 mm) when the tests were conducted under the wet climate. There appears to have no significant difference (less than 10%) of infiltration rates, hydraulic conductivity and suction retained between the grass‐covered and the tree‐covered soil. However, the grass and tree species having deeper root depth and greater Root Area Index (RAI) retained higher suction. Copyright © 2015 John Wiley & Sons, Ltd.     

Pesticides in Sediments From Queensland Irrigation Channels and Drains

Pesticide concentration in sediment from irrigation areas can provide information required to assess exposure and fate of these chemicals in freshwater ecosystems and their likely impacts to the marine environment. In this study, 103 sediment samples collected from irrigation channels and drains in 11 agricultural areas of Queensland were analysed for a series of past and presently used pesticides including various organochlorines, synthetic pyrethroids, benzoyl ureas, triazines and organophosphates. The most often detected compounds were endosulphans (, β and/or endosulphan sulphate) which were detectable in 78 of the 103 samples and levels ranged from below the limit of quantification (0.1 ng g⁻¹ dw) up to 840 ng g⁻¹ dw. DDT and its metabolites were the second most often detected pesticide investigated (74 of the 103 samples) with concentrations up to 240 ng g⁻¹ dw of ∑DDTs. Mean ∑endosulphan and ∑DDT concentrations were 1–2 orders of magnitude higher in sediments from the irrigation areas which are dominated by cotton cultivation compared to those which are dominated by sugarcane cultivation. In contrast to these insecticides, the herbicides diuron, atrazine and ametryn were the compounds which were most often detected in sediments from irrigation drains in sugarcane areas with maximum concentrations in areas of 120, 70 and 130 ng g⁻¹ dw, respectively. In particular during flood events, when light is limiting, transport of these photosynthesis inhibiting herbicides from the sugarcane cultivation areas to the marine environment may result in additional stress of marine plants.