共查询到20条相似文献,搜索用时 15 毫秒
1.
V. A. I. Huvenne D. G. Masson A. J. Wheeler 《International Journal of Earth Sciences》2009,98(4):865-884
Grainsize, mineralogy and current-meter data from the Northern Rockall Trough are presented in order to characterise the sandy
contourite that forms the sedimentary environment of the Darwin cold-water coral mounds, and to investigate the impact of
this environment on the mound build-up. Large clusters of small cold-water coral mounds, 75 m across and 5 m high, have been
found southwest of the Wyville Thomson Ridge, at 900–1,100 m water depth. Their present-day sedimentary environment consists
of a subtly sorted sandy contourite, elongated NE–SW, roughly parallel to the contours. Critical erosional and depositional
current speeds were calculated, and trends in both the quartz/feldspar and foraminifera fractions of the sands show a bi-directional
fining from bedload/erosion-dominated sands in the NE to suspension/deposition-dominated sediments in the SW and towards the
S (downslope). This is caused by a gradual reduction in governing current speed, linked to a reduction in slope gradient,
and by the increasing distance from the current core in the downslope direction. No specific characteristics were found distinguishing
the mound sediments from the surrounding sands: they fit in the overall spatial pattern. Some mound cores show hints of a
fining-upward trend. Overall the mound build-up process is interpreted as a result of sediment baffling. 相似文献
2.
Aerial photographs taken in the 1963 and 2001 and bathymetric charts, in conjunction with coastal processes are analyzed to assess changes in rate of shoreline position, seabed level, and seabed grain sizes along the Tabarka–Berkoukech beach at the north-western Tunisian coastline. The littoral cell of this beach, 12-km-long, is bounded by pronounced embayments and rocky headlands separated by sandy stretches. Although not yet very much undeveloped, this littoral is still experienced degradation and modification, especially along its shoreline, with significant coastal erosion at some places. Results obtained from analysis of shoreline position indicate that El Morjene Beach is experienced a landward retreat of more than −62 m, at a maximum rate of −1.64 m/year, whereas the El corniche beach is advanced about 16–144 m, at an average rate of 0.42 m–3.78 m/year. This beach accretion has been formed on the updrift side of the Tabarka port constructed between 1966 and 1970. Comparison of bottom contours deduced from bathymetric charts surveyed in 1881 and 1996 off the coastline between Tabarka Port and El Morjene Beach identifies erosional areas (sediment source) and accretionary zones (sediment sink). Erosion (0.87–4.35 cm/year) occurs between El kebir River Mouth and El Morjene beach, whereas accretion exists in the zone down wind of the port ranges between 0.87 and 5.21 cm/year. Morphological analyses of the shoreline and the seabed of the study nearshore area indicate that shoreline retreat corresponds to areas of seabed scour (sediment source) while shoreline accretion is associated with areas of seabed deposition (sediment sink). Furthermore, simulation of wave propagation using STWAVE model combined with grain size distributions of the seabed shows that fine sands are much dominated in depositional areas with low wave energy, whereas coarser sands in erosive zones with high wave energy. The results obtained suggest that the change of seabed morphology, wave height pattern and grain size sediment have a great influence on the modification of shoreline morphology and dynamics. 相似文献
3.
Trace metals (Cd,Pb, Cu,Zn and Ni) in sediment of the submarine pit Dragon ear (Soline Bay,Rogoznica, Croatia) 总被引:1,自引:0,他引:1
Vertical profiles of trace metal (Cd, Pb, Zn, Cu, Ni) concentrations, organic matter content, carbonate content and granulometric
composition were determined in two sediment cores from the submarine pit Dragon Ear (Middle Adriatic). Concentrations of the
analyzed metals (Cd: 0.06–0.12 mg kg−1, Pb: 28.5–67.3 mg kg−1, Zn: 17.0-65.4 mg kg−1, Cu: 21.1–51.9 mg kg−1, Ni: 27.8–40.2 mg kg−1) were in usual range for Adriatic carbonate marine sediments. Nevertheless, concentrations of Cu, Zn, and especially Pb in
the upper layer of sediments (top 12 cm) were higher than in bottom layer, while Cd and Ni concentration profiles were uniform.
Regression analysis and principal component analysis were used to interpret distribution of trace metals, organic matter and
carbonate content in sediment cores. Results of both analysis showed that concentrations of all trace metals in the core below
the entrance to the pit were significantly positively correlated with organic matter and negatively correlated with carbonate,
while in the core more distant from the entrance only Pb showed significant positive correlation with organic matter. Obtained
results indicated that, except for lead which was enriched in surface sediment, in the time of sampling (before the building
of the nautical marina) investigated area belonged to unpolluted areas. 相似文献
4.
Batch experiments were performed to investigate cephapirin (a widely used veterinary antibiotic) adsorption on various size
sands of low total organic carbon content (0.08–0.36 wt%). In the aqueous concentration range investigated (11–112 μmol/L
cephapirin), adsorption to nearly pure quartz filter sands (0.50–3.35 mm diameter) is low. Isotherms are S-shaped and most
display a region of minimum adsorption, where decreased adsorption occurs with increasing solution concentration, followed
by increased adsorption at higher concentrations. Cephapirin adsorption to quartz-rich, feldspar-bearing dune sands (0.06–0.35 mm
diameter), and the smallest quartz filter sand investigated (0.43–0.50 mm), can be described by linear sorption isotherms
over the range of concentrations investigated. Distribution coefficients (K
d) range from 0.94 to 3.45 L/kg. No systematic relationship exists between grain size and amount of adsorption for any of the
sands investigated. Cephapirin adsorption is positively correlated to the feldspar ratio (K-feldspar/(albite + Ca-plagioclase).
Feldspar-ratio normalization of distribution coefficients was more effective than organic carbon normalization at reducing
variability of K
d values in the dune sands investigated. 相似文献
5.
Fathe Bouteldja Pierre Breul Daniel Boissier 《Geotechnical and Geological Engineering》2011,29(6):1009-1021
Domestic wastewater-treatment system is today a widely held technique. In order to evaluate the efficiency of these systems,
it is necessary to determinate the in situ hydraulic conductivity of the water-treatment granular materials constituting them.
The in situ measurement of the hydraulic conductivity of soils has proven to be imprecise, take a long time. Empirical equations
based on the physical properties of soil have been proposed to overcome these difficulties. In this context, the originality
of this paper is to propose an in situ method to obtain reliable input parameters for the predictive equations of Chapuis
(Can Geotech J 41(5): 787–795, 2004) and Carrier (J Geotech Geoenviron Eng 129(11): 1054–1056, 2003) by using both a penetrometer and a geoendoscope. This method is described in the first part of this paper. Then, the validation
of the method based on laboratory tests performed under controlled conditions for three kinds of soils is presented. Hydraulic
conductivity obtained when applying the method is compared to that measured by a Darcy permeameter. The difference between
these two hydraulic conductivities is less than 25%. Finally, the precision of the results is discussed. 相似文献
6.
Le-ping Yue Li-rong Yang Zhi-pei Li Min Wang Wei-ji Zhang Hao-gang Nie 《Environmental Geology》2007,51(7):1197-1201
In this paper, nine sediment sequences in the inner desert, desert-loess transitional zone (agro-pastoral transitional zone)
and the northern margin of the Loess Plateau were investigated to study the sediments of Mu Us (Maowusu) and Otindaq (Hunshandake)
sandy land in northern China since the last glaciation. All of these sequences consisted of the upper Holocene dark paleosol
and the lower aeolian sand formed during the last glacial stage. The Mu Us and Otindaq sandy land became the active desert
since the last glaciation and covered a larger sandy area than at present. Mu Us sandy land began to show a landform of sandy
desert and expanded southward towards the northern boundaries of the Loess Plateau. The Holocene was characterized by the
advent of warmer and wetter climatic conditions in northern China, resulting in the rapid growth of surface vegetation and
Mu Us and Otindaq sandy land became a steppe. The thickness of surface soil reached up to as much as 50–80 cm. Thick paleosol
covered the drift sands, and served as a protective layer for the steppe and farmland. Although the last glacial cycle is
far away, paleo-aeolian sands formed during that period are still the material sources of regional desertification. Unreasonable
cultivation destroying the Holocene paleosol, combined with dry climate and strong wind would result in activation of paleo-
aeolian sand leading to the desertification of the study areas. 相似文献
7.
Physical and hydraulic properties of sediment from two karst aquifers were measured to determine (1) the similarity of sediment
between karst aquifer systems and (2) the importance of sediment in modeling flow through karst aquifers. The sediment from
the two systems was similar in size and composition. Within both aquifers, the silt-sized sediment was composed primarily
of quartz, with minor amounts of plagioclase and clays. Hydraulic conductivity of the sediment measured directly (falling-head
test) ranged from 1.61×10−7 to 1.33×10−6 m s–1 and estimated using the Campbell equation ranged from 8.30×10−8 to 8.98×10−7 m s–1. These values of hydraulic conductivity fall within the span of hydraulic conductivities for carbonate rocks, indicating
that the sediment and carbonate matrix could be represented as one mathematical unit in modeling flow through karst aquifers.
Statistical agreement in the hydraulic conductivity values generated by the two methods indicates that the estimation technique
could be used to calculate hydraulic conductivities; thus allowing karst scientist to collect bulk sediment samples instead
of having to collect cores from within karst aquifers.
Electronic Publication 相似文献
8.
Behavior of heavy metals in sulfide mine tailings and bottom sediment (Salair,Kemerovo region,Russia) 总被引:2,自引:1,他引:1
The given work focused on solving the problem of environmental geochemistry related to investigation of element speciation,
their mobility, and migration in polluted areas. The purpose was to describe quantitatively migration, distribution, and redistribution
of heavy metals by the example of the old tailings (Talmovaya sands) of the Lead Zinc Concentration Plant (Salair, Kemerovo
region, Russia) and technogenic bottom sediments of the Malaya Talmovaya river. Contents of elements in the sulfide tailings
range in the following limits: Zn: 1,100–27,000 ppm, Cd: 1.3–240 ppm, Pb: 0.01–0.81 ppm, Cu: 220–960 ppm, As: 15–970 ppm,
Fe: 19,000–76,000 ppm, and Ba: 80,000–1,00,000 ppm. Element concentrations in the river sediment are proportional to the element
contents in the sulfide tailings. Element speciations in the sulfide tailings and technogenic bottom sediments were investigated
by the modified sequential extraction procedure. Chemical forms of heavy metals in pore water and surface water were calculated
by WATEQ4F software. Principles of heavy metal migration in the sulfide tailings and technogenic bottom deposits were established.
The obtained results about element species in the sulfide tailings and sediment explain the main principles of element migration
and redeposition. In the mine waste and technogenic bottom deposits, there is vertical substance transformation with formation
of geochemical barriers. 相似文献
9.
Haidi J. L. Hancock Gerald R. Dickens Ellen Thomas Kevin L. Blake 《International Journal of Earth Sciences》2007,96(5):925-946
Bulk carbonate content, planktic and benthic foraminiferal assemblages, stable isotope compositions of bulk carbonate and
Nuttallides truempyi (benthic foraminifera), and non-carbonate mineralogy were examined across ∼30 m of carbonate-rich Paleogene sediment at Deep
Sea Drilling Project (DSDP) Site 259, on Perth Abyssal Plain off Western Australia. Carbonate content, mostly reflecting nannofossil
abundance, ranges from 3 to 80% and generally exceeds 50% between 35 and 57 mbsf. A clay-rich horizon with a carbonate content
of about 37% occurs between 55.17 and 55.37 mbsf. The carbonate-rich interval spans planktic foraminiferal zones P4c to P6b
(∼57–52 Ma), with the clay-rich horizon near the base of our Zone P5 (upper)—P6b. Throughout the studied interval, benthic
species dominate foraminiferal assemblages, with scarce planktic foraminifera usually of poor preservation and limited species
diversity. A prominent Benthic Foraminiferal Extinction Event (BFEE) occurs across the clay-rich horizon, with an influx of
large Acarinina immediately above. The δ13C records of bulk carbonate and N. truempyi exhibit trends similar to those observed in upper Paleocene–lower Eocene (∼57–52 Ma) sediment from other locations. Two successive
decreases in bulk carbonate and N. truempyi δ13C of 0.5 and 1.0‰ characterize the interval at and immediately above the BFEE. Despite major changes in carbonate content,
foraminiferal assemblages and carbon isotopes, the mineralogy of the non-carbonate fraction consistently comprises expanding
clay, heulandite (zeolite), quartz, feldspar (sodic or calcic), minor mica, and pyrolusite (MnO2). The uniformity of this mineral assemblage suggests that Site 259 received similar non-carbonate sediment before, during
and after pelagic carbonate deposition. The carbonate plug at Site 259 probably represents a drop in the CCD from ∼57 to 52–51 Ma,
as also recognized at other locations. 相似文献
10.
The reflectance of sediments (gray level) were measured on 11 sediment cores from the Norwegian–Greenland–Iceland Sea (Nordic
seas). The analyzed time interval covers the past five glacial–interglacial cycles. Although the results demonstrate that
the gray-level method has a potential for stratigraphic purposes, it is indicated that gray-level changes in the Nordic seas
are not necessarily driven by variations in the content of biogenic calcite. A detailed comparison of gray-level values with
contents of total CaCO3 (carbonate) and total organic carbon (TOC) reveals no overall causal link between these proxies. However, specific glacial
core sections with layers containing organic-rich sediment clasts as a consequence of iceberg-rafting seem to correlate well
with law gray-level values. Of those cores which show relatively high and comparable carbonate values in the last three main
interglacial intervals (stages 11, 5.5, and 1), stage 11 is always marked by the highest gray-level values. A close inspection
of the surface structure of the foraminiferal tests as well as the conduction of reflectance measurements on these tests leads
to the conclusion that enhanced carbonate corrosion occurred during stage 11. The test corrosion not only affected the reflectance
of the tests by making them appear whiter, it also seems responsible for the comparatively high gray-level values of the total
sediment in stage 11. In contrast, the relatively low gray-level values found in stages 5.5, and 1 are not associated with
enhanced test corrosion. This observation implies that variable degrees of carbonate corrosion can have a profound effect
on total sediment reflectance.
Received: 6 September 1998 / Accepted: 4 April 1999 相似文献
11.
The Brandberg West region of NW Namibia is dominated by poly-deformed turbidites and carbonate rocks of the Neoproterozoic Damara Supergoup, which have been regionally metamorphosed to greenschist facies and thermally metamorphosed up to mid-amphibolite facies by Neoproterozoic granite plutons. The meta-sedimentary rocks host Damaran-age hydrothermal quartz vein-hosted Sn–W mineralization at Brandberg West and numerous nearby smaller deposits. Fluid inclusion microthermometric studies of the vein quartz suggests that the ore-forming fluids at the Brandberg West mine were CO2-bearing aqueous fluids represented by the NaCl–CaCl2–H2O–CO2 system with moderate salinity (mean=8.6 wt% NaClequivalent).Temperatures determined using oxygen isotope thermometry are 415–521°C (quartz–muscovite), 392–447°C (quartz–cassiterite), and 444–490°C (quartz–hematite). At Brandberg West, the oxygen isotope ratios of quartz veins and siliciclastic host rocks in the mineralized area are lower than those in the rocks and veins of the surrounding areas suggesting that pervasive fluid–rock interaction occurred during mineralization. The O- and H-isotope data of quartz–muscovite veins and fluid inclusions indicate that the ore fluids were dominantly of magmatic origin, implying that mineralization occurred above a shallow granite pluton. Simple mass balance calculations suggest water/rock ratios of 1.88 (closed system) and 1.01 (open system). The CO2 component of the fluid inclusions had similar δ
13C to the carbonate rocks intercalated with the turbidites. It is most likely that mineralization at Brandberg West was caused by a combination of an impermeable marble barrier and interaction of the fluids with the marble. The minor deposits in the area have quartz veins with higher δ
18O values, which is consistent with these deposits being similar geological environments exposed at higher erosion levels. 相似文献
12.
In this paper, an experimental investigation of cement treated sand is performed under triaxial tests in order to quantify
the effects of cementation on the stress–strain behavior, stiffness and shear strength. Samples were cured up to 180 days.
The results show that the stress–strain behavior of cemented sands is nonlinear with contractive–dilative stages. The stress–strain
response is strongly influenced by effective confining pressure and cement content. Stiffness and strength are greatly improved
by an increase in binder content. An increase of the angle of shearing resistance and cohesion intercept with increasing cement
content is observed consistently. Brittle behavior is observed at low confining pressure and high cement content. After yielding,
the increase in the dilatancy accelerates. Two competing related processes determine the peak strength: Bond breakages cause
a strength reduction but the associated dilatancy leads to a strength increase. This finding and the experimental observation
that the dilatancy at the peak state increases with increasing cement content explain why the measured peak-state strength
parameters, c′ and φp′, are relevant to the binder content. 相似文献
13.
黄土在应力作用下迂水时力学强度迅速下降 ,产生大范围的快速沉陷。这就是黄土的湿陷性 ,是黄土的诸多特性之一。鉴于对黄土湿陷性以往用各种实验室试验指标进行评价 ,这里提出运用动力触探和静载荷试验进行黄土湿陷性原位评价的一种简便的新方法。该方法的试验程序是 ,先用轻便可变动能触探仪在天然状态和饱水状态下进行触探试验 ,而后在触探孔完成静载荷压缩性试验。运用中国黄土高原黄土原位动力触探和静载荷试验测得的资料 ,详细分析了天然状态的黄土对探头阻力 qdnat,饱水状态的黄土对探头阻力 qdsat,实验室测得的湿陷性指数s压缩曲线参数 (即触探极限压力 ppf,触探蠕变压力ppl 和触探载荷模量Epn)的关系。结果证明所提出的方法适用于原位判定黄土的湿陷性。 相似文献
14.
Dominique Ngan-Tillard Johan Haan David Laughton Arno Mulder Art Nooy van der Kolff 《Engineering Geology》2009,108(1-2):54-64
Carbonate sands undergo degradation when transported hydraulically from a dredging vessel to the reclamation site. Risks involved in the production of fines during hydraulic transport are a deterioration of the mechanical properties of the fill in certain areas of the reclamation area where these fines concentrate. In order to assess sand degradation in the concrete and road construction industry, the Micro-Deval test for fine aggregates was developed in France and Canada. During Micro-Deval testing, aggregates degrade when tumbled in a rotating steel drum with water and steel balls. In the Canadian standard, the steel charge is lower than in the French standard and balls have the diameter of the smallest balls used in the French test. During testing, the quantity of fines produced is measured. This makes the Micro-Deval test an option for assessing the degradation of sand during hydraulic transportation of slurries in the dredging industry. Three sands are tested: two shelly carbonate sands and one quartzic river sand for comparison. The carbonate sands were sampled on reclaimed land and had been subjected to hydraulic transportation in pipeline before artificial deposition. Due to differences in particle shape, the carbonate sands and the quartz sand have a different number of contacts with the steel charge in the drum of the Micro-Deval and are not exposed to the same degradation forces during testing. It was found that the quartzic sand suffers relatively much degradation as compared to the carbonate sands, despite its greater hardness and resistance to crushability. The French test appears to create turbulence that promotes floatation of the curved shells of the carbonate sands instead of shell grinding at the bottom of the drum by contact with the steel balls. Microscopic observations of sand samples before and after testing showed that the French Micro-Deval test is too destructive. The test leads to the fragmentation by impact of the quartz sands and the destruction of certain particle types that had survived hydraulic transportation. With respect to the Canadian test, microscopic examination of sand grains before and after testing shows there is still much fragmentation of quartz grains. A lower rotational speed combined with a limited steel charge made of uniform balls of a smaller diameter, reduces turbulence, shell floatability and last but not the least, impact forces. It produces the desired result: a high Micro-Deval loss for the carbonate sands in comparison to that for the quartz sands and a very limited fragmentation of the quartz grains. Once the slurry reaches its destination, the grain size distribution of the fines fraction will influence the mechanical behaviour of mixed sands. A procedure is proposed to measure the particle size distribution of the fines fraction produced during Micro-Deval testing.Field validation is needed to validate preliminary laboratory results. 相似文献
15.
A small isolated outlier of Lower Oligocene chalk, which grades upwards into what was originally a sandy marl, has been truncated by a paleokarst surface, which is overlain by cross-bedded, well-sorted glauconitic sands. A sandy clay horizon (probably originally tuffaceous) and a basaltic lava flow of probable Miocene age cap the local sequence. Below the paleokarst surface and roughly parallel to it, the original sediment has been intensely altered to an average depth of 1.5 m. The alteration front is sharply defined, even where it extends along the walls of glauconitic sand-filled fissures in the chalk.In the alteration zone, the chalk has been entirely replaced by silica (opal-CT, largely in the form of lepispheres). The calcareous fraction of the marl has been replaced by montmorillonite and clinoptilolite. Rounded gravel clasts (largely basaltic) in the base of the overlying glauconitic sands also have been replaced (by montmorillonite), which suggests that all alteration followed deposition of the sands. However, neither the glauconite nor any other mineral in the sands appears highly altered. Similarly, the quartz grains show no evidence of dissolution or silica precipitation. Preservation of most silica sponge spicules, the only siliceous microfossils in the chalk, indicates that the source of the silica was extraneous to the carbonate sediments.Migrating interstitial liquid, largely confined to the sands between the impervious cap of sandy clay plus basalt and the porous but less permeable chalk, is inferred to have been the causal agent for the replacement. Silica, and any other components necessary for the formation of opal-CT, montmorillonite and clinoptilolite, were probably derived by chemical alteration of the capping volcanics in a groundwater regimen. Replacement reactions in the chalk and marl presumably were dependent on the original presence of calcium carbonate, and apart from montmorillonitization of volcanic material, occurred only where this compound was present. 相似文献
16.
V. Palchik 《Rock Mechanics and Rock Engineering》2006,39(3):215-232
Summary. This paper presents a model created by the author to predict stress–strain relationships for weak to strong carbonate rocks
(σc < 100 MPa) exhibiting axial strains up to 1%. The stress–strain model based on Haldane’s distribution function (Haldane,
1919) relates the axial stress (or normalized axial stress) to the square of an exponential function where the exponent is
axial strain. To obtain accurate stress–strain relationship over the whole pre-failure strain with the proposed stress–strain
model, it is necessary to have only one datum point (peak axial stress and maximum axial strain at this peak stress). It is
shown that the stress–strain relationships observed in laboratory compression tests on samples collected from six carbonate
rock formations (chalk, dolomites and limestones) from different parts of Israel, agree well with the stress–strain prediction
model proposed by the author. 相似文献
17.
The study is concerned with the influence of various factors on vibro compaction in calcareous soils, This include effect
of carbonate content, and influence of pore water pressures in sand, settlements during vibrocompaction, vibroaccelerations
during sand column installation compared to earthquake accelerations and finally the liquefaction design based on average
CPT parameters. Previous experiences with calcareous sands and literature review confirm the necessity to apply a correlation
factor for calcareous material to the raw cone penetration resistance CPT values obtained in the field. Because of the very
fragile grains of the Dubai calcareous sands the penetration resistance will be influenced by crushing and grinding. To accommodate
for effect of calcareous sands on measured CPT values, a best fit correlations formula called here “correlation factor” is
developed. A parametric dynamic triaxial liquefaction testing programme has been executed on representative samples with loose
and dense zones. Representative testing parameters for field conditions and earthquake design accelerations have been applied
indicating that ground improvement is necessary. It was observed during the dynamic triaxial tests that the whole soil mass
consisting of dense columns and looser zones in between behaves jointly, and therefore compaction control using an average-CPT
approach is possible. 相似文献
18.
The Plio-Quaternary conglomeratic sets within the marine environment of the Viranşehir coast (W Mersin, S Turkey) are responsible
for the evolution of sandy and gravely beaches due to their control on various factors such as sea floor irregularity, wave
energy, and organic activity. The conglomeratic sets close to the shoreline (50–150 cm) act as wave breakers, creating hard
substratum and high energy, well-oxygenated environment for organisms like Patella sp., Phoronida worms and Brachidontes pharaonis (Fischer P. 1870). The boring activities of these organisms have disintegrated the sandy matrix of these sets. Finer-grained
matrix sediments have been transported to the interset and open sea, while cobble–pebbles have been carried landwards and
have created imbricated gravely beach deposits without matrix. Sandy beach is evolving where the conglomeratic sets away from
the shoreline (5.0–10.0 m). In this example, sets form a bar; causing fivefold division as backshore, berm, surf zone, bar
and offshore from land to sea. Poorly sorted, cobbles-pebbles cobbles and pebbles are found associated with the high-energy
environments of bars, whilst well-sorted sands are observed in low energetic environments on shore. The sets and recent shell
fragments are the main sources of coastal sediments in Viranşehir. However, the amount of shell fragments decrease towards
the active river mouth. This is due to sediment and fresh water influx from the river causing deteriorated temperature, salinity
and light penetration of the marine environment resulting in less organic diversity.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
19.
The Oramiriukwa River is within the sandy coastal plain strata of the Benin formation (Miocene–Recent). The base flow is very
high ranging from 79.13–98.56%, which is caused by the excellent hydraulic interconnection between the river and the adjacent
unconfined aquifer. Recharge rates are high, estimated to range from 1.8×1012–2.5×1012 m3/year. Coastal sands are medium-to-coarse grained, moderately-to-poorly sorted, angular to subangular, with lenses of clay
and clayey fine-grained sands. The coastal sands and clay lenses form aquifer and aquitard systems, which are unconfined to
semi-confined. Groundwater recharge potential is high. Runoff from precipitation is low. Groundwater and surface water are
fairly acidic; pH ranges from 5.5–6.1 (groundwater) and 5.8–6.5 (surface water), and hardness is generally low. Chemical analysis
and percentage sodium show that groundwater and surface water are somewhat potable after some pH modification of the surface
water. The waters are good for agricultural use, especially for irrigation and poultry water supply. However, pollution from
landfill leachate is serious.
Electronic Publication 相似文献
20.
The paper presents a simple constitutive model for the behavior of sands during monotonic simple shear loading. The model
is developed specifically to account for the effects of principal stress rotation on the simple shear response of sands. The
main feature of the model is the incorporation of two important effects of principal stress on stress–strain response: anisotropy
and non-coaxiality. In particular, an anisotropic failure criterion, cross-anisotropic elasticity, and a plastic flow rule
and a stress–dilatancy relationship that incorporate the effects of non-coaxiality are adopted in the model. Simulations of
published experimental results from direct simple shear and hollow cylindrical torsional simple shear tests on sands show
the satisfactory performance of the model. It is envisioned that the model can be valuable in modeling in situ simple shear
response of sands and in interpreting simple shear test results. 相似文献