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141.
142.
This paper presents a procedure to compute the values of degradation factors of p-y curves in the pseudo-static analysis of piles in liquefiable soils. Three-dimensional finite-element model was used for the computation of p and y values using OpenSees computer package. The piles were modeled using beam-column elements and elastic section. The soil continuum was modeled using brick elements and a two-surface plasticity model. By comparing the results of models in two cases of liquefiable and non-liquefiable, values of degradation factors were obtained. Validation of the degradation factors computed was conducted through the centrifuge test results. The simulation results showed a similar trend between degradation factor variation in different densities and sands. With increasing depth, the degradation factor increased. By comparing the results of pseudo-static analysis with the centrifuge test results, it was concluded that the use of the p-y curves with computed degradation factors in liquefiable sand gave reasonable results. 相似文献
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146.
Photooxidation degradation of Reactive Brilliant Red K‐2BP (K‐2BP) aqueous solution by ultraviolet irradiation/sodium hypochlorite (UV/NaClO) was investigated. The effects of NaClO dosage, pH, temperature and initial dye concentrations were studied. A possible degradation pathway of K‐2BP was investigated. Acidic or neutral conditions were beneficial to the decolorization of K‐2BP aqueous solution. However, alkaline conditions facilitated chemical oxygen demand (COD) removal. Increasing the solution temperature from 20 to 50°C increased the removal of color and COD. However, at 60°C, the final percentage color and COD removal decreased by approximately 17 and 10%, respectively. Based on the products indentified and theoretical analysis, N=N cleavage and C‐N cleavage were possible initial steps in the degradation of K‐2BP. From the results of this work, we conclude that treatment of UV/NaClO is an efficient method to degrade K‐2BP in aqueous solution. 相似文献
147.
Relationship of environmental geochemistry to soil degradation in Helwan catchment, Egypt 总被引:1,自引:0,他引:1
Ahmed A. Melegy 《Environmental Geology》2005,48(4-5):524-530
Environmental geochemistry plays an important role in understanding the distribution of major cations (Ca2+, Mg2+, Na+, K+) in Helwan catchment, south Cairo, Egypt. Evaluation of soil mechanical erosion rate, depletion rate, exchangeable rates
of base cations and sodium adsorption ratios are essential for understanding soil degradation problems in the representative
Helwan catchment. Soil erosion is a natural process. It often becomes a problem when human activity causes it to occur much
faster than under natural conditions. The results of the mechanical erosion rate of soil and the exchangeable rates of base
cations are 1845 and 80.3 kg ha−1 yr−1, respectively. The high intensity of the mechanical erosion rate is probably attributed to the high specific surface area
of the studied type of Vertisol, intensive application of fertilizer and industrial activities. Mechanical erosion of soil,
exchangeable rate of base cations and the depletion rate of base cations are almost inexhaustible sources of sodium, and all
these increase the problem of sodic soils and may affect plant productivity in Helwan catchment. 相似文献
148.
One of the major goals of geomorphology is to understand the rate of landscape evolution and the constraints that erosion sets on the longevity of land surfaces. The latter has also turned out to be vital in modern applications of cosmogenic exposure dating and interpretation of lichenometric data from unconsolidated landforms. Because the effects of landform degradation have not been well documented, disagreements exist among researchers regarding the importance of degradation processes in the dating techniques applied to exposures. Here, we show that all existing qualitative data and quantitative markers of landform degradation collectively suggest considerable lowering of the surface of unconsolidated landforms over the typical life span of Quaternary moraines or fault scarps. Degradation is ubiquitous and considerable even on short time scales of hundreds of years on steeply sloping landforms. These conservative analyses are based entirely on field observations of decreasing slope angles of landforms over the typical range of ages in western North America and widely accepted modeling of landscape degradation. We found that the maximum depth of erosion on fault scarps and moraines is on average 34% of the initial height of the scarp and 25% of the final height of the moraine. Although our observations are limited to fault scarps and moraines, the results apply to any sloping unconsolidated landform in the western North America. These results invalidate the prevailing assumption of no or little surface lowering on sloping unconsolidated landforms over the Quaternary Period and affirm that accurate interpretations of lichen ages and cosmogenically dated boulder ages require keen understanding of the ever-present erosion. In our view, the most important results are twofold: 1) to show with a large data set that degradation affects universally all sloping unconsolidated landforms, and 2) to unambiguously show that even conservative estimates of the total lowering of the surface operate at time and depth scales that significantly interfere with cosmogenic exposure and lichen dating. 相似文献
149.
This study compares the marker pigment composition in three different lake compartments: the water column; the surface sediment
biofilm (0–0.5 cm), where production and main degradation processes take place; and the deep sediment (15–17 cm), where the
signal is finally stored and marker pigments are used as a proxy in paleolimnological studies. The aim was to evaluate which
marker pigments better record in the sediment the relative contributions of planktonic and benthic production in high mountain
lakes, taking into account the differential preservation existing among pigments. A survey of 82 high mountain lakes distributed
along the major environmental gradients was carried out in the Pyrenees. Comparison of pigments between the three compartments
revealed that both water column and sediment biofilm signals could be distinguished in old sediment layers, despite the observation
that some of the most characteristic carotenoids that appeared frequently and in high concentrations in the water column were
already less common or even absent from the sediment biofilm. In the shallowest lakes, pigment composition in the sediment
biofilm was typical of photosynthetically active communities and their deep sediment samples were characterised by a substitution
of fucoxanthin by diatoxanthin as the dominant diatom marker pigment. However, in the deepest lakes the pigment composition
of the sediment biofilm and deep sediment was similar, characterised by marker pigments of mainly planktonic algal groups
and pheophytins, which are typical pigments of decaying communities. Results are discussed in terms of how pigment source
(planktonic or benthic) and pigment type (lability of molecule) interact to shape pigment composition in the sediment record
of high mountain lakes. 相似文献
150.
A simple, low cost, highly effective, and useful Fenton oxidation treatment of synthetic dye bath waste with pickling liquor as a source of iron (Fe2+ catalyst) is reported. Optimizations of contact time, Fe2+ and H2O2 doses are carried out. Oxidative de‐colorization and degradation of Reactive Blue 4 and Reactive Orange 16 was measured in terms of decrease in absorbance at their wavelength of maximum absorption (RB4, 599 nm; and RO16, 493 nm) and also as reduction in chemical oxygen demand (COD). Approximately, 62% COD was removed in 2 h at optimized doses of Fe2+ (8.95 mM) and H2O2 (61.8 mM) by using pickling waste as a source of Fe2+ catalyst. Similar performance efficiency was observed when neat FeSO4 was used as a source of Fe2+, indicating that pickling liquor can be a low cost source of Fe2+ to treat synthetic dye bath waste by Fenton method. 相似文献