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1.
Physical modeling tests were conducted on pile foundations to measure the seismic performance of a new ground improvement technology, called passive site stabilization, for use on sites susceptible to liquefaction and liquefaction-induced lateral spreading. The method involves the slow injection of a low-viscosity stabilizer in conjunction with the natural groundwater flow. The effectiveness of the treatment using dilute colloidal silica as the stabilizer was tested by two centrifuge models that simulated soil–pile interaction of a 2×2 end-bearing pile group embedded in a multilayer soil deposit of 10-m thickness. The models utilized a laminar box and involved gently inclined soil profiles with and without the applied soil improvement. Response of the pile groups and the lateral spreading behaviors of the treated and untreated soil under a simulated base shaking were investigated and compared. The results showed that treatment with dilute colloidal silica stabilizer minimized permanent lateral deformations and reduced the liquefaction potential of the soil. Significant reductions occurred in the measured pile bending moments and axial forces because the layer treated with dilute colloidal silica did not liquefy. Thus, the technique can be an alternative to traditional methods of ground improvement.  相似文献   

2.
Runoff components of the Zastler catchment (18\4 km2, southern Black Forest, Germany) were analysed with hydrograph separations using stable oxygen isotopes and dissolved silica. It was shown that event water and components with low silica contributed only small amounts to total runoff. In addition, comparison of the two‐component hydrograph separations showed that the low‐silica components are generated by both event water and pre‐event water fractions, depending on the state of the system. A modified three‐component hydrograph separation method was introduced using dissolved silica and 18O. During storm events an interaction of three runoff components having distinct silica concentrations could be shown. Based on the geological and geomorphological genesis of the study site, it was appropriate to assign (i) the low silica component to the riparian zones and impermeable areas, (ii) the medium silica component to the periglacial debris cover and (iii) the high silica component to the crystalline detritus and crystalline hard rock. Exact quantification of the runoff components remained difficult. However, runoff components with medium silica concentrations reacted very sensitively and intensely. The contribution of this component to total runoff is comparatively large. This shows the important role of the periglacial debris to runoff generation of the study site and emphasizes the importance of runoff generation processes occurring in this reservoir. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

3.
Total concentrations of formate, acetate, and isobutyrate varied from less than 5 to greater than 9,000 μmol/l over distances of < 3 m in ground water from a shallow hydrocarbon contaminated aquifer. Laboratory incubations of aquifer material indicate that organic acid concentrations were dependent on the amount of hydrocarbon loading in the sediment and the relative rates of microbial organic acid production and consumption. In heavily contaminated sediments, production greatly exceeded consumption and organic acid concentrations increased. In lightly contaminated sediments rates were essentially equal and organic acid concentrations remained low. Concentrations of dissolved calcium, magnesium, and iron generally were one to two orders of magnitude higher in organic acid-rich ground water than in ground water having low organic acid concentrations. Carbonate and Fe(III)-oxyhydroxide minerals were the likely sources of these elements. Similarly, concentrations of dissolved silica, derived from quartz and k-feldspar, were higher in organic acid-rich ground water than in other waters. The positive relation (r = 0.60, p < .05, n = 16) between concentrations of silica and organic acids suggests that the microbially mediated buildup of organic acids in ground water enhanced quartz/k-feldspar dissolution in the aquifer, although it was not the only factor influencing their dissolution. A model that included organic acid microequivalents normalized by cation microequivalents significantly strengthened the correlation (r = 0.79, p < .001, n = 16) between dissolved silica and organic acid concentrations, indicating that competition between silica and cations for complexation sites on organic acids also influenced quartz/k-feldspar dissolution. Physical evidence for enhanced mineral dissolution in organic acid-rich waters included scanning electron microscopy images of highly corroded quartz and k-feldspar grains from portions of the aquifer containing organic acid-rich ground water. Microporosity generated in hydrocarbon contaminated sediments may adversely affect remediation efforts that depend on the efficient injection of electron acceptors into an aquifer or on the recovery of solutes from an aquifer.  相似文献   

4.
Bank erosion is the main source of suspended sediment (SS) and diffuse total phosphorus (TP) in many lowland catchments. This study compared a physically based sediment routing method (Physical method), which distinguishes between stream bed and bank erosion, with the original sediment routing method (Original method) within the Soil and Water Assessment Tool (SWAT) version 2009, for simulating SS and TP losses from a lowland catchment. A SWAT model was set up for the lowland River Odense catchment in Denmark and calibrated against observed stream flow and phosphate (PO4) loads. On the basis of an initial calibration of hydrological and PO4 parameters, the SWAT model with the Original method (Original model) and the SWAT model with the Physical method (Physical model) were calibrated separately against observed SS and TP loads. The SWAT model simulated daily stream flow well but underestimated PO4 loads. The Physical model simulated daily SS and TP better than the Original model. The simulated contribution of bank erosion to SS in the Physical model (99%) was close to the estimated contribution from in situ erosion measurements (90–94%). Compared with the Original method, the Physical method is not only more conceptually correct but also improves model performance. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

5.
典型枯水年长江干流硅的分布、输送与滞留   总被引：1，自引：0，他引：1  
于特枯水情年对三峡水库溶解硅和长江干流自涪陵至河口段悬浮颗粒物、溶解硅、生物硅和叶绿素a浓度等进行调查.研究表明,在平水期和汛期末,长江干流水体溶解硅和生物硅浓度和通量在其上游受大坝"滞留"效应的影响呈现沿程降低的趋势,中、下游受"两湖"和汉江等的补充作用有明显升高.在枯水年,长江干流水体生物硅浓度占活性硅(溶解硅和生物硅之和)浓度的2%~5%,显著低于平水年的比例(13%),同时也低于世界河流的平均水平(16%).三峡水库在4-12月份减少溶解硅向下游的输送通量,而在1-3月份增加溶解硅的输送通量;水库在枯水年滞留了大约3%~6%的溶解硅.三峡水库内低的初级生产水平和高的生物硅再生速率是其难以对溶解硅形成有效滞留的主要因素.大坝下游会因清水下泄产生潜在的滞留效应,不过还需要更多的数据去量化.  相似文献   

6.
Previous studies have shown how biogenic silica particles undergo conversion to aluminosilicate phases in large tropical deltaic systems, thus affecting the world ocean budget of major seawater cations. This study tackles the important question of the silica budget in the coastal zone of the Mississippi River Delta, providing evidence for the role of biogenic silica diagenesis in this subtropical system from direct examination of individual diatom particles, sediment leachates and pore-water composition. The estimated reactive silica stored in the study area (5990 km2) is based on operational leaches that account for altered biogenic silica particles and other authigenic aluminosilicate phases in addition to fresh biogenic silica. Early diagenesis of silica in the delta front occurs mainly where more siliceous material is deposited. An inner-shelf area, where hypoxic conditions are found, significantly contributes to the formation of authigenic products of Si alteration. Data suggest that the limiting factor of silica alteration processes is the availability of detrital phases such as Al and Fe. The estimated total reactive silica accumulation in the study area is 1.45×1010 mol Si year−1, representing ∼2.2% of the long-term bulk sediment accumulation. On the basis of a conservative appraisal, the authigenic mineral components account for ∼40% of the long-term reactive silica storage. This study shows that non-tropical deltaic systems are significantly more important sinks of silica than previously thought and that, where conditions are favourable, a consistent portion of reactive silica not leaving the shelf is stored within the delta in the form of authigenic components.  相似文献   

7.
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8.
Chemicals, especially silica, have been suspected to cause genetic alterations in pottery industry workers. The present study aims to analyze the frequency of chromosomal aberrations (CA), micronucleus (MN) and DNA damage (comet assay) in the peripheral blood lymphocytes and the immunological alterations workers chronically exposed to silica and in control subjects. In our study, 50 silica exposed workers and 35 control subjects were recruited and silica level was measured by respirable dust and respirable quartz concentrations of badge dosimeter. The serum immunoglobulins (IgM, IgG, and IgA) of all the subjects were measured by using ELISA method. The individuals exposed to silica have a significant increase in the frequency of CA, MN and the total DNA damage (p < 0.05). Immunoglobulin elevation on silica exposed workers was statistically significant (p < 0.05) on comparison with their respective controls. Investigation of the smoking and alcohol habitats coupled with silica exposure in exposed and control subjects represents alcohol consumption and smoking as additional risk factors and must be avoided. Multiple linear regression analysis obtained for CA, MN and comet assay confirm these tests as biomarkers for silica exposed pottery workers. Some confounding factors also showed significant influence on exposed subjects. These results indicate the mutagenic risk in the working environment has a high probability of association with the silica dust exposure in pottery industries. Nevertheless, the present study will create awareness and public concern not only among the silica exposed workers but also to the welfare of their progeny.  相似文献   

9.
Crushed recycled glass was evaluated as an alternative to silica sand in dual‐media filters. Pilot scale inline filtration experiments were carried out using raw waters from three different water sources with turbidities between 6.0 and 14.0 NTU. Two physically identical filter columns were operated in parallel in the experiments. One filter consisted of 62.5 cm silica sand and 41.5 cm anthracite coal, whereas the other filter contained 62.5 cm crushed recycled glass plus 41.5 cm anthracite coal. The total bed depth was 104 cm for both filters. The properties of the media were as follows: Glass effective size = 0.77 mm, uniformity coefficient = 1.41. Sand effective size = 0.79 mm, uniformity coefficient = 1.33. Coal effective size = 1.45 mm, uniformity coefficient = 1.39. Experiments were repeated five times as follows: (i) Without the use of a coagulant, (ii–iii) with 5 and 10 mg/L of alum, and (iv–v) with 5 and 10 mg/L of ferric chloride. The filtration rate used was 11.5 m/h. Turbidity, particle counts, and head losses were measured and compared as functions of time. The following were observed: (i) Effluent turbidities and particle counts of the two filters were very close, i.e., essentially the same effluent quality was obtained when crushed glass was used instead of silica sand. (ii) In the majority of the tests, the filter with crushed glass generated both a smaller clean‐bed head loss and smaller clogging head losses than those of the filter containing sand. It is concluded that crushed glass may be a good alternative to silica sand in dual‐media filtration.  相似文献   

10.
Two natural dunites were annealed at pressure P=300 MPa, temperature T=1373, 1473 and 1573 K, and fO2 within the stability field of olivine. The starting materials contained small amounts of hydroxyls in the form of minor phases of hydrated minerals, which released an aqueous phase during the experiments. A detailed analytical transmission electron microscopy (ATEM) investigation of these materials revealed that small quantities of two types of silica-rich glass formed during heat treatment. The first type of glass, found at triple junctions as rare partially crystallized glass pockets, results from melting dehydration reactions involving the hydrous phases. The second type of glass is found as pure silica precipitates (0.1–0.5 μm in size, for a total of a few 0.1 vol%) within the olivine grains of specimens heated to ≥1473 K. From considerations of the kinetics of the precipitation at 1473 K, we interpret this silica precipitation as resulting from the condensation of olivine metallic vacancies promoted by increasing fluid fugacities during the runs. Our observations, thus, demonstrate that metastable silica can precipitate in olivine from dunites experiencing rapid changes in their thermodynamical environment.  相似文献   

11.
Hydrochemical data collected in field studies in the near-mouth area and delta of the Don R. (Aksay T.—the mouths of Don delta branches) in 2006–2015 are analyzed. The seasonal dynamics is demonstrated, and the average annual concentrations were evaluated for mineral, total dissolved, and total forms of nitrogen, phosphorus, silica; dissolved and particulate organic carbon; and total suspended solids in river water. The export of dissolved and particulate organic carbon and nutrients by the Don River into the Sea of Azov in the low-water period of 2007–2015 is evaluated. Retrospective analysis of nutrient export into the Sea of Azov with river runoff in the XX–early XXI century is given.  相似文献   

12.
Physical sedimentology experiments have shown that sulfuric acid solutions may have formed some surface features seen on Mars. Recent data returned from Mars show the presence of jarosite, sulfate salts, hematite, phyllosilicates, and opaline silica, all of which precipitate from some terrestrial sulfuric acid solutions. There is a plethora of geochemical, mineralogical, and sedimentological data indicative of past sulfuric acid systems on Mars, but there has never been a comprehensive study published regarding sulfuric acid as a physical sedimentological agent. In the laboratory, we ran liquids of various compositions over sediments in order to test how these liquids entrain, transport, and deposit sediments. Pure water and concentrated sulfuric acid solutions produced the same general features, such as channels, gullies, and alluvial fans. However, sulfuric acid solutions yielded some distinct sedimentary features not produced by pure water runs. These features, narrow, deeply incised channels of consistent widths, rounded discrete fans, and air bubble “craters”, are similar to some Martian landscape features. These experimental results indicate that acid solutions should be considered a possible sedimentological agent on Mars.  相似文献   

13.
In a region along the western margin of the Kalahari in eastern Namibia and western Botswana, many pan basins have mainly calcareous deposits along part of their margins. These are typically lined by low vertical scarps. In Namibia, these pans are mainly located in dry river beds. The petrographical study of these deposits demonstrates that they consist of lacustrine sediments that have to a varying extent been affected by early‐diagenetic processes and by the formation of late‐diagenetic features. The original composition of the deposits ranges from highly calcareous sediments, typically with ostracod, diatom and charophyte remains, to entirely non‐calcareous diatomites. The deposits generally show an upward increase in total carbonate content, which is mainly a synsedimentary feature. The early‐diagenetic processes that affected the deposits include the formation of orthic siliceous nodules. At a later stage, secondary calcite enrichment occurred, leaving only the silica‐impregnated sections unaffected. This enrichment partly accounts for the upward increase in total carbonate content in some profiles and often resulted in the development of a highly calcareous surface horizon. Sepiolite and amorphous silica that are part of the groundmass of the deposits may also partly have formed at this stage. Late‐diagenetic features include various forms of secondary calcite and silica. This study of pan basins in eastern central Namibia indicates that a lacustrine rather than purely pedogenic origin should also be considered for calcareous deposits that commonly occur along pan margins in other parts of southern Africa. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

14.
The investigations were carried out at 6 tidal flats located on the eastern part of the Seto Inland Sea, Japan. This study was focused on physical characteristics of sediments, namely as particle size of sediment and difference in elevation, and generalizes the relationship between sediments and macrobenthos. A total of 192 species were collected at 187 stations at 6 tidal flats. Physical characteristics of sediment were classified into 9 groups by cluster analysis in relation to sediment particle size and difference in elevation. Those groups had also significant difference in physical characteristics of sediments, and were characterized by some specific macrobenthos species. Distribution of macrobenthos can be explained by the classification of physical characteristics of sediment. These findings show the possibility to predict the variety of macrobenthos community using the physical characteristics of sediment.  相似文献   

15.
Simultaneous monitoring of conservative and non-conservative tracers in streamflow offers a valuable means of obtaining information on the age and flow paths of water reaching the basin outlet. Previous studies of stormflow generation in a small forested basin on the Canadian Shield used isotopic (IHS) and geochemical hydrograph separations (GHS) to infer that some event water during snowmelt reaches the stream via subsurface pathways, and that surface water runoff is generated by direct precipitation on to saturated areas (DPSA) in the stream valley. These hypotheses were tested for rainfall inputs using simultaneous IHS (18O) and GHS (dissolved silica) of basin stormflow, supplemented by hydrochemical and hydrometric data from throughflow troughs installed on basin slopes. Comparison of pre-event and subsurface water hydrographs did not provide conclusive evidence for subsurface movement of event water to the stream, owing to the appreciable uncertainty associated with the hydrograph separations. However, IHSs of runoff at the soil–bedrock interface on basin slopes indicated that event water comprised 25–50% of total runoff from areas with deep soil cover, and that these contributions supplied event water flux from the basin in excess of that attributable to DPSA. The surface water component of stormflow estimated from the GHS was also largely the result of DPSA. GHS assumes that dissolved silica is rapidly and uniformly taken up by water infiltrating the soil and that water moving via surface pathways retains the low dissolved silica level of rainfall; however, neither assumption was supported by the hillslope results. Instead, results suggest that the observed depression of silica levels in basin stormflow previously attributed to dilution by DPSA was partly a function of transport of dilute event water to the channel via preferential pathways. Implications of these results for the general use of simultaneous IHS and GHS to infer hydrological processes are discussed. © 1997 by John Wiley & Sons, Ltd.  相似文献   

16.
Cyclic triaxial tests were performed to investigate the influence of colloidal silica grout on the deformation properties of saturated loose sand. Distinctly different deformation properties were observed between grouted and ungrouted samples. Untreated samples developed very little axial strain prior to the onset of liquefaction. However, once liquefaction was triggered, large strains occurred rapidly and the samples collapsed within a few additional loading cycles. In contrast, grouted sand samples experienced very little strain during cyclic loading. Additionally, the strain accumulated uniformly throughout loading rather than rapidly prior to collapse and the samples never collapsed. Cyclic triaxial tests were done on samples stabilized with colloidal silica at concentrations of 5, 10, 15, and 20%. In general, samples stabilized with higher concentrations of colloidal silica experienced very little strain during cyclic loading. Sands stabilized with lower concentrations tolerated cyclic loading well, but experienced slightly more strain. Thus, treatment with colloidal silica grout significantly increased the deformation resistance of loose sand to cyclic loading.  相似文献   

17.
The silica concentration of 26 Guatemalan geothermal waters were analyzed colorimetrically (spectrophotometrically) and by atomic absorption. Results by the atomic absorption method were less affected by polymerization and precipitation of silica from supersaturated solutions.Shaking the samples prior to analysis improves the accuracy of the atomic absorption results.The advantages of colorimetric analysis over atomic absorption are better sensitivity and precision. However, for accurate colorimetric results, geothermal samples must be sufficiently diluted in the field, which ensures that no further polymerization occurs and that amorphous silica that may be present will redissolve. If the samples are not diluted in the field they should be diluted in the laboratory and left standing for at least a month to allow the silica to redissolve. If analyzed immediately the diluted samples should be made alkaline and heated overnight in a 90° oven.  相似文献   

18.
This paper highlights potential complications that may arise while using in situ produced 10Be to date exposure or burial events using diagenetic silica (chert). The initiation and evolution of large gravitational collapses in sedimentary rocks were constrained using cosmic ray exposure dating. Because these collapses occurred in a stratigraphic level composed of chert (diagenetic silica) concretions interbedded in limestone layers, their development was studied by performing in situ-produced 36Cl and 10Be concentration measurements in both the limestone and coexisting diagenetic silica (chert), respectively. Following the routinely used decontamination and preparation protocols for 10Be produced in diagenetic silica, large discrepancies were observed with exposure ages determined by 36Cl within carbonate for samples originating from the same scarp. While 36Cl exposure ages were clustered as expected for a unique single gravitational event, 10Be exposure ages were scattered along the same studied scarps. To determine the origin of such a bias, petrological investigations were carried out for chert (diagenetic silica). Thin sections highlighted a complex mineralogical texture characterized by remnant silicified ooids showing calcitic cores, calcite inclusions and a dominant amorphous hydrated silica (grain > 20 μm). To decipher and characterize the potential origins of the excess measured 10Be within diagenetic silica, all samples were first reprocessed following the routine decontamination protocol (HCL–H2SiF6 leachings and three partial HF dissolutions) but starting from three different grain size fractions (GS1: 1000–500, GS2: 500–250 and GS3: 250–50 μm). The resulting concentrations clearly showed a decreasing 10Be content as a function of the grain size, but still yielded 10Be exposure ages significantly higher than 36Cl counterparts. Because potential adsorption of 10Be at the surface of amorphous silica grains was suspected, partial dissolution steps following by a leaching step in hydroxylamine were investigated. Finally, it seems that an additional leaching in KOH allowed removal of the amorphous silica phase and the measured 10Be concentrations yielded 10Be exposure ages agreeing within uncertainties with the 36Cl ones. This work suggests that measuring in situ produced 10Be within chert (amongst other types of diagenetic silica, e.g. flint, hornstone, jasper, etc.) containing amorphous silica requires caution.  相似文献   

19.
A method is described for the detection and identification of dissolved organic compounds (DOCs) in various water samples. Acid treated active silica gel sorbent (pH 3) was packed into a micro‐column and used as a solid‐phase extraction medium for adsorption of DOCs. Silica particles‐adsorbed‐organic species were then divided into equal portions followed by suspension into various organic solvents of different polarities such as methanol, acetone, ethyl acetate, and toluene. Suspended silica‐adsorbed‐organic species were shaken for 1 h at room temperature and the organic extracts were subjected to GC–MS analysis under temperature programming conditions for qualitative detection and identification of these species. Blank solvents and silica samples were also subjected to the same extraction procedures and GC–MS analysis for comparison. The mass spectrum of each eluted chromatographic peak was library searched or manually interpreted to identify the compound.  相似文献   

20.
Thermal waters in hydrothermal ponds, bathing pools and the brines of geothermal electric power plants commonly have a characteristic blue color. Although many researchers have assumed that the blue color is due to a colloidal suspension and/or absorption by dissolved ferrous iron or by water itself, there has been no specific effort to identify the physical nature of this phenomenon. We have tested, in synthetic and natural solutions, whether aqueous colloidal silica is responsible for the blue color. Aqueous colloidal silica is formed by silica polymerization in thermal waters of the neutral-chloride type which contain initially monomeric silica in concentrations up to three times above the solubilities of amorphous silica. The hue of the blue thermal waters in the pools tested agrees with that of a synthesized colloidal silica solution. Grain-size analyses of aqueous colloidal silica in the blue-colored thermal waters demonstrate that the color is caused by Rayleigh scattering from aqueous colloidal silica particles with diameters (0.1–0.45 μm) smaller than the wavelengths of visible radiation.  相似文献   

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