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1.
Silt is available in many parts of the world in combination with sands and clays. However, due to lack of clear understanding of its engineering behaviour, most of the time it is interpreted in terms of either sands or clays. Structures that are usually built on silty soils are designed to take into account design procedures developed for sandy or clayey soils. Presence of silts in combination with varying amount of sand and clays produces silt that is either plastic or non-plastic in nature. Silt is available in and around the Delhi region, in a majority mixture along with fine sands, which is non-plastic in nature. On the other hand silty deposits found in offshore Bombay High region are found in abundance along with significant amounts of clays and are termed as plastic silts. In this paper a comparison of the stress-strain behaviour of plastic and non-plastic silts is carried out under triaxial compression loading during both drained and undrained conditions. Two representative samples each from Delhi and Bombay High regions were considered for this comparison and results of stress-strain under four sets of confining pressure are discussed in detail. It is observed from this study that behaviour of silts is mainly dependent on the composition and structure of the resultant soil matrix. It is concluded from the results that shear strength parameters as well as volume change/pore pressure response of silty soils is dominated by the constituent soil present along with the silt. It is seen from the comparative behaviour of non-plastic and plastic silts that the presence of sand and clays has a governing effect on pore pressure development and the resultant friction angle. The study also corroborated that the nature of silt is transitional both in the case of plastic and non-plastic forms. 相似文献
2.
The presence of coarse-grained sediment can potentially reduce the effectiveness of conventional sampling methods in recovering fluvial sediments. A modification to freeze-core technology was used to collect fine to coarse sands, silts, and clays in fluvial deposits that contain significant amounts of gravels, cobbles, and boulders for the purpose of characterizing the extent of heavy metal contamination. This modification uses either a 2.5 or 2.9 cm diameter by 30-cm- long finned mechanical or hand-driven samplers. The sediment is frozen to the outside of the sampler by injecting liquid CO2 into the sampler. The fins protect the sample from coarse material upon removal. Field testing and laboratory testing of the method were completed to establish a methodology and assess possible cross contamination of the sediment layers during the driving of the sampler. The results indicated that this method is effective for recovering non-cohesive sediment samples at depths up to 6 m for the purpose of characterizing the extent of heavy metal contamination. 相似文献
3.
R. I. Acworth W. A. Timms B. F. J. Kelly D. E. Mcgeeney T. J. Ralph Z. T. Larkin 《Australian Journal of Earth Sciences》2013,60(6):657-680
The Liverpool Plains in northern New South Wales contain some of the best agricultural land in Australia and are underlain by extensive smectite clay-dominated soils sourced from weathering the alkali basalts of the Liverpool Ranges. It had been thought that a relatively simple geological model explained the underlying Cenozoic sequence with salt-rich clays of the Narrabri Formation overlying sands and gravel aquifers comprising the Gunnedah Formation. Extensive groundwater modelling based upon this simple conceptualisation has been used in management plans proposed by the mining and agricultural industries. A 31.5 m core has been recovered using minimally disturbed triple-tube coring methods at Cattle Lane (Latitude –31.52° S, Longitude 150.47° E) to resolve uncertainty concerning the aquitard status of the upper layer. Recovered core has been examined and tested to determine grainsize, cation-exchange capacity, X-ray diffraction, X-ray fluorescence and microscopic examination of granular components. These measurements complement surface and borehole geophysical techniques, hydrogeological data and hydrochemical analysis of water samples recovered from a series of specially constructed piezometers adjacent to the cored hole. The sequence overlies a Late Cretaceous channel cut into Permian bedrock at 91 m depth with sands and clays below 31.5 m considered to represent various alluvial fill events mostly occurring since the Early Pliocene. Erosion of Late Eocene alkali basalts on the Liverpool Ranges, with the formation of smectite clays, pedogenic carbonates and with the addition of quartz from both eolian sources and locally derived from adjacent Triassic sandstone hills, provides the great majority of the sediment recovered from the cores. Late Pleistocene (114 ka) to Holocene ages were determined for the core from three optically stimulated luminescence (OSL) measurements on fine sands (13, 23 and 29 m BG). Detailed examination has failed to detect any evidence of a boundary between Narrabri and Gunnedah formations revealing rather a gradual change in dominance of clays and silts over sands and gravels embedded in a clay-rich matrix. This result challenges the conceptualisation used to conduct groundwater modelling on the Liverpool Plains. 相似文献
4.
Quaternary desert loess and sandstone-loessite relationships in the geological record raise questions regarding causes and mechanisms of silt formation and accretion. In the northern Sinai-Negev desert carbonate terrain, only sand abrasion in active erg could have produced the large quantities of quartzo-feldspathic silts constituting the late Quaternary northwestern Negev loess. In the continuum of source (medium to fine sand of dunes) to sink (silts in loess) the very fine sand is unaccounted for in the record. This weakens the sand abrasion model of silt formation as a global process. Here, we demonstrate that, as predicted by experiments, abrasion by advancing dunes generated large quantities of very fine sand (60-110 μm) deposited within the dune field and in close proximity downwind. This very fine sand was generated 13-11 ka, possibly synchronous with the Younger Dryas under gusty sand/dust storms in the southeastern Mediterranean and specifically in the northern Sinai-Negev erg. These very fine sands were washed down slope and filled small basins blocked by the advancing dunes; outside these sampling basins it is difficult to identify these sands as a distinct product. We conclude that ergs are mega-grinders of sand into very fine sand and silt under windy Quaternary and ancient aeolian desert environments. 相似文献
5.
This paper describes recent proglacial lacustrine sediments exposed by the drainage of a small (probably never more than 0·03 km2) ice-dammed lake basin at Leirbreen, central Jotunheimen, Norway. The dominant facies include ripple-laminated, massive and horizontally-stratified sands, massive and horizontally-laminated silts, and irregularly-laminated fine sands and silts. The major control on lake circulation and the nature and distribution of these facies was an underflow driven by a subglacial meltwater stream which formed the major lake input. Although much of the sedimentary sequence indicates a pulsatory input, the proximal character of this small lake prevented the development of classic varved silts. Compressional deformation of shoreline sediments was due to winter lake ice push. Other deformational processes included the grounding of icebergs, water escape and syn-sedimentary downslope collapse. Observations from an adjacent small ice-marginal lake at Leirbreen provide support for several of the inferences drawn from the sediments of the former ice-dammed lake. 相似文献
6.
Liquefaction characteristics of silts 总被引：1，自引：0，他引：1
S. Singh 《Geotechnical and Geological Engineering》1996,14(1):1-19
Summary The paper presents a summary of the results of cyclical triaxial load testing of samples of silt and silty sands. The paper emphasizes differences in behaviour observed between reconstituted triaxial samples of clean sand, of sand containing 10, 20, 30 and 60% silt, pure silt, and undisturbed samples of silt and silty sand. An important observation is that the mechanisms of deformation for sit are different for reconstituted and undisturbed samples, the undisturbed sample having a specific geological structure which seems to slow down the excess pore water pressure accumulation, but which still results in cyclic deformations regularly increasing from the very beginning of the test and rapidly reaching high levels. The other important observation is that fine-grained noncohesive soils such as silts and silty sands can be as, or even more, susceptible to liquefaction as clean sands. Test results on samples of sand containing 10, 20 or 30% of silt indicate lesser resistance to liquefaction than pure sand samples. The paper shows the difficulty in identifying a representative parameter to compare the behaviour of silts and silty sands with pure sand, and it seems that more research will be needed in this area. 相似文献
7.
Loose saturated cohesionless soils are most susceptible to liquefaction, however there are strong historical evidence suggesting that soils containing fines such as silty sands are also prone to liquefaction during earthquakes. The liquefaction of silty sands has been observed in a number of recent case studies. This paper presents the effects of fine silts on liquefaction potential of sandy soil. Tests have been conducted on the vibration table at different accelerations and pore water pressure is measured. During the lab investigation, locally (Roorkee, India) available Solani Sand and Dhanauri Silt have been used. The soil samples have been prepared by varying silt content and the initial relative density. The results of the study performed are used to clarify the effects of non-plastic fines content on the Solani sand. As the silt content increases, the number of cycles required to produce maximum pore water pressure increases. For a particular level of excitation, rate of pore water pressure generation is maximum at critical silt content. It is observed that critical silt content to generate maximum pore water pressure is different for different accelerations. Further, effect of silt content is very much dependent on relative density. 相似文献
8.
Garg's approximate analytical solutions of Biot's equations for wave propagation in a fluid-saturated elastic porous solid of infinite extent subjected to a velocity boundary condition of a Heaviside function at one end are examined for small and large drag. Garg's approximations were apparently introduced to facilitate exact inversion of Laplace transforms of certain quantities. The approximate solutions are compared with carefully evaluated numerical inverses of the Laplace transform solutions for different soils with widely varying properties. It is seen that for most soils (clays, silts and, sands) the error in Garg's approximate solutions in insignificant, and the solutions can be used as benchmarks for verifying numerical analysis procedures such as finite element codes. 相似文献
9.
10.
Several infilled glacial meltwater channels of Anglian age are described from SE Suffolk, U.K. These channels are up to 4km long, 150m wide and 8m deep. They possess a consistent pattern of infill comprising glacifluvial sands and gravels overlain by subglacial water-lain fine sands and silts; these pass conformably upwards through thinly interstratified tills and sands into basal tills. The channels were formed at the ice-margin. Their sedimentary infill indicates overriding by the ice-sheet and subsequent subglacial deposition. 相似文献
11.
针对部分细粒土进行了室内落锥法确定液限和塑限的试验研究,试验结果表明：对于一些细粒土在双对数坐标上圆锥下沉深度与含水率之间的关系并非线性关系,无法依据线性关系确定液、塑限;采用规程建议的3个含水率范围有时根本无法获得有效试验数据,采用规程建议的3个含水率范围确定得到粉土的液、塑限试验结果的可靠性有待商榷;采用直线段试验数据确定的液、塑限进行分类可能出现相互矛盾甚至错误的结果。进一步试验结果表明：对于黏粒含量高于13 %的粉土,由于其抗剪强度以凝聚分量为主,落锥法适用,所测塑性指数能够反映其可塑性;对于部分黏粒含量低于13 %的粉土及外观接近粉土的粉砂,由于其抗剪强度以颗粒间摩擦分量为主,落锥法不再适用,所测塑性指数不能反映其可塑性。 相似文献
12.
13.
Guidance is provided for geotechnical engineers designing civil engineering works in silty soils based on a detailed characterisation of a glaciomarine silt from Os in western Norway. It was found that these soils are susceptible to disturbance by good quality fixed piston tube sampling and care needs to be taken when using laboratory derived design parameters, particularly for consolidation and shear strength properties. A technique for assessing sample disturbance using shear wave velocity and suction measurements proved promising. Conventional techniques for determining soil strength from triaxial tests in silt are inappropriate due to the dilational nature of the material and more reliable and logical strength estimates can be made from a limiting strain criterion. Field vane data should be used with caution as measured strength, particularly remoulded values, may be high and it seems more reliable parameters can be derived from CPTU tests. One dimensional consolidation and creep of these silts can be modelled successfully by the well-known Janbu formulation. The behaviour of the Os silts does not fit easily into classical soil mechanics and published frameworks for soft soils. It seems the material is of “transitional” type and this work adds to the database of such soils which includes other natural silts and gap graded soils. For future work it is recommended that larger sample tubes (say 75 mm) with a very sharp cutting edge should be used in parallel with in situ CPTU testing. 相似文献
14.
The piezocone penetration test (CPTU) is commonly used as a fast and economical tool to identify soil profile and to estimate relevant material properties in soils ranging from fine to coarse-grained. Moreover, in the case of fine-grained soils (clays and silts), the consolidation coefficient and the permeability can be estimated through the dissipation test. Undrained conditions are commonly assumed for the interpretation of CPTU in fine-grained soils, but in soils such as silts, penetration may occur in partially drained conditions. This aspect is often neglected in data interpretation thus leading to an inaccurate estimate of soil properties. This paper investigates numerically the effect of partial drainage during penetration on the measured tip resistance and the subsequent pore pressure dissipation response contributing to a more accurate interpretation of field data. A realistic simulation of the cone penetration is achieved with the two-phase Material Point Method, modelling the soil response with the modified Cam-Clay model. The approach takes into account large soil deformations induced by the advancing cone, soil–water, and soil–structure interactions, as well as nonlinear soil behavior. 相似文献
15.
Martin Thorp Peter Glanville Stephen Stokes Richard Bailey 《Comptes Rendus Geoscience》2002,334(12):903-908
This paper presents the first results of a 14C and optical luminescence dating project on extensive alluvial silt formations in the southern Anti Atlas Mountains in southern Morocco. The silts comprise three members: basal silts, an inter-silt fluvial gravel member and a top silt member and are incised by the rivers. Top silt dates are: 11 340–11 940, 12 670–13 130 cal. yr BP, and 10.6±0.7 ka (OSL). OSL dates for the inter-silt gravels are 29.6±2.0 ka and for the bottom silts is 45.0±3.7 ka. The sediments correlate with Soltanian stratigraphies known elsewhere in Morocco. To cite this article: M. Thorp et al., C. R. Geoscience 334 (2002) 903–908. 相似文献
16.
Peter D. Clift Elizabeth D. Olson Alexandra Lechnowskyj Mary Grace Moran Allison Barbato Juan M. Lorenzo 《Sedimentology》2019,66(2):408-434
Point bars formed by meandering river systems are an important class of sedimentary deposit and are of significant economic interest as hydrocarbon reservoirs. Standard point‐bar models of how the internal sedimentology varies are based on the structure of small‐scale systems with little information about the largest complexes and how these might differ. Here a very large point bar (>25·0 m thick and 7·5 × 13·0 km across) on the Mississippi River (USA) was examined. The lithology and grain‐size characteristics at different parts of the point bar were determined by using a combination of coring and electrical conductivity logging. The data confirm that there is a general fining up‐section along most parts of the point bar, with a well‐defined transition from massive medium‐grained sands below about 9 to 11 m depth up into interbedded silts and fine–medium sand sediment (inclined heterolithic strata). There is also a poorly defined increase in sorting quality at the transition level. Massive medium sands are especially common in the region of the channel bend apex and regions upstream of that point. Downstream of the meander apex, there is much less evidence for fining up‐section. Finer sediment accumulated more readily after the establishment of a compound bar in the later stages of construction, at the terminal apex and in the bar tail. This work implies that the best reservoir sands are likely to be located in the centre of the point bar, deposited in a simple bar system. Reservoir quality decreases towards the bar edge. The early‐stage channel plug is largely composed of coarsening‐upward cycles of silt to clay and is dominated by clay and clayey silt material with poor reservoir characteristics. 相似文献
17.
山西应县护驾岗冲沟阶地地层形成于66.46～33.62 ka,根据该剖面地层的粒度分布特征对该地区冲沟阶地的沉积环境进行了探讨。护驾岗冲沟阶地剖面的粒度分布特征显示:(1)剖面地层总体表现为自下而上由粗到细的正韵律沉积特征,结合野外观察将其分为4段(A—D段);(2)A段粒度分布特征变化不大,均以细砂为主,频率曲线为不对称单峰,概率累积曲线为2段式,以跃移搬运为主,分选相对较好,水动力较强,沉积环境稳定;(3)B—C段粒度分布特征变化较大,以粉砂和细砂为主,频率曲线为不对称双峰,概率累积曲线为2段式,以跃移搬运为主,分选较差,水动力较强,沉积环境不稳定;(4)D段粒度分布特征变化不大,以粉砂为主,频率曲线为不对称单峰,概率累积曲线为2段式,以悬移搬运为主,分选相对较好,水动力较弱,沉积环境稳定。总体来说,冲沟阶地形成于河流沉积环境,顶部为河漫滩沉积环境。粒度分布特征与古里雅冰芯氧同位素变化基本一致,因此护驾岗冲沟阶地粒度特征与沉积环境的变化归因于气候变化。 相似文献
18.
Chennarapu Hariprasad Mekala Rajashekhar Balunaini Umashankar 《Geotechnical and Geological Engineering》2016,34(6):1909-1922
Relative density is an important state parameter that influences the soil behavior. Preparation of sand specimens with uniform density is critical during large-scale laboratory testing in geotechnical engineering. In this study, the details of a stationary air pluviation device used to prepare uniform sand specimens in a large-size test chamber with dimensions equal to 900 mm × 900 mm × 1000 mm (in length, width, and depth) are provided. The proposed device is found to be simple to construct due to presence of only two diffuser sieves with an ability to produce uniform sand beds in a reasonably quick time. Prior to construction of full-scale pluviation device, a scaled-down model of the device with plan dimensions equal to 300 mm × 300 mm is fabricated to perform calibration studies. The range of densities of two gradations of Indian Standard sand (IS Grade II and IS Grade III) obtained using this device for various heights of fall of sand particles and passing through different opening sizes are provided. Relative density in the range of 53–99 % and 74–99 % is achieved for IS Grade II and III sands, respectively. The spatial uniformity in densities is also assessed, and the coefficient of variation (COV) in the density is found to be less than about 7 %. In addition to pluviation method, uniform sand beds are also prepared using pneumatically-operated vibratory method. The target relative density of sand bed is achieved by adjusting the pressure of compressed air inside the vibrator, and the maximum relative density of IS Grade II and Grade III sands from vibratory method is found to be higher than that from pluviation method for the range of pressures chosen in the study. 相似文献
19.
Collapsible soils are problematic by nature. They undergo collapse or sudden settlement or subsidence under a given stress when their water content is increased. Collapse is characterised by collapse potential expressed as ΔH/H x 100, where ΔH is collapse compression. The amount of stress applied and the water content at the time of collapse govern the amount of collapse. In other words, collapse potential depends upon the amount of stress and the water content. Loess and other wind-blown silts are examples of collapsible soils. This paper presents a parametric study on the collapse behaviour of a lateritic soil. Remoulded specimens of a lateritic soil passing through a 425 µm sieve were compacted in 1-D consolidometer or oedometer at a density of 13 kN/m3 for studying collapse under varied initial moisture contents and initial surcharge pressures. Collapse compression of the samples was induced by saturating the specimens with water contents corresponding to 100% degree of saturation. After collapse occurred, the 1-D consolidation tests were continued up to an applied stress of 160 kPa. Collapse behaviour was studied for the applied initial pressures (σi) of 10, 20 and 40 kPa and for the initial water contents (wi) of 5%, 10%, 15% and 20%. Collapse compression and collapse potential decreased with increasing wi for all σi. 相似文献
20.
Peter H. Feldhausen 《Mathematical Geology》1970,2(2):113-129
Ordination is a multivariate technique developed by plant ecologists which has proven effective in the interpretation of paleoenvironments.
It allows gradational relationships among samples to be depicted in contrast to other quantitative techniques which classify
samples into discrete groups. In this study, ordination is used to interpret textural data for 62 bottom samples taken from
the Cape Hatteras, North Carolina, continental margin. The ordination suggests the existence of six sedimentary facies that
are similar to those obtained by cluster analysis using a dendrograph display. The facies represented are: littoral sands
and outer-shelf shelly sands; inner-shelf sands; outer-shelf sands and silts; outer-shelf slope silts; and two highly biogenic,
deep-water silt and clayey silt facies with similar characteristics. The facies are related in a qualitative manner to the
environmental processes operating off Cape Hatteras.
Chicago Bridge Technical Paper No. 5139. 相似文献