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991.
《Norsk geografisk tidsskrift. Norwegian journal of geography》2012,66(2):129-138
Based on grain-size analysis of sediment samples from a delta at Altermarka, it has previously been suggested that two tills were deposited on the delta surface as a glacier planed off the delta topsets and created its adverse surface slope. In this reinvestigation of the delta, there was no evidence that a glacier overrode the surface: the topset beds remain intact and no appreciable till was found. Sediments resembling the ‘till’ samples were located, but soil processes and other sedimentary processes easily account for the wide grain-size distributions of these sediments. As a result, this study cautions against using grain-size analysis, on its own, to interpret the genesis of sediments. Other processes potentially responsible for the adverse surface slope include differential isostatic rebound, recent differential slip along ancient thrust faults, and failure of the delta surface to reach sea level. Based on the sedimentology of the topset beds and the local relative sea level history (indicating the delta (9495±70 14C yr BP) formed about the time of the local marine limit (9560–9375 14C yr BP) 17 m higher than the delta surface), the feature is determined to have built up below sea level with an adverse surface slope. 相似文献
992.
993.
Unconfined and triaxial compression tests were carried out to examine the behavior of light-weighted soils (LWS) consisting of expanded polystyrene (EPS), dredged soils, and cement with respect to initial water content. The stress-strain behavior of LWS are analyzed with varying initial water content and silt contents of dredged soils, cement ratio, and confined stress. As initial water contents increase, the compressibility index increases and the preconsolidation pressure was vice versa. As initial water contents increase, the slope of stress-strain curve in elastic zone increases and strain rate at failure decreases and the strain rate at failure was not changed by the being of foams. As initial water contents increase, a compressive strength of LWS decreases. The decrement ratio of compressive strength of LWS with foams increases as cement content increases and initial water contents decreases. The compressive strength increases as silt contents increases. 相似文献
994.
Wei-Yun Chen Guo-Xing Chen Chen-Cong Liao Hong-Mei Gao 《Marine Georesources & Geotechnology》2013,31(8):924-935
AbstractIn this paper, a 2D poro-elastoplastic model for wave-induced dynamic response in an anisotropic seabed is derived analytically. The seabed is treated as a porous medium and characterized by Biot’s consolidation equations. The soil plasticity and wave non-linearity are included in the model and both the pore fluid and the soil skeleton are assumed to be compressible. The nonlinear ocean waves are respectively considered as progressive and standing waves. The previous experimental data is used to validate the proposed model. Numerical results demonstrate that the influence of nonlinear wave components should not be ignored without committing substantial error. A significant difference between progressive and standing waves is also observed for the development of residual pore pressure, as well as the distribution of liquefied zone. A detailed parametric investigation reveals that the nonlinear wave-induced seabed response is also affected significantly by cross-anisotropic soil parameters. 相似文献
995.
Hamid Gadouri Khelifa Harichane Mohamed Ghrici 《Marine Georesources & Geotechnology》2013,31(9):1130-1148
AbstractAn experimental investigation was undertaken in order to assess the effect of sodium (Na2SO4) and calcium (CaSO4·2H2O) sulphates and curing period on stress–strain curves and failure modes of grey (GS) and red (RS) clayey soils stabilised by lime (L), natural pozzolana (NP) and their combinations (L–NP). Several soil–L–NP mixtures were studied to be used as subgrade soils for road pavements. Stress–strain curves were obtained from unconfined compressive strength (UCS) test made on several soil–L–NP specimens after curing for 7 and 120 days. Tests results showed that the use of L or L–NP without sulphates produced a significant increase in peaks stress of both clayey soils and then modified their stress–strain curves from nonlinear to linear behaviour almost up to 70% of peak stress after a longer curing period. However, the presence of 2% Na2SO4 or any CaSO4·2H2O content provided beneficial effects on peaks stress and stress–strain curves of both stabilised clayey soils and then improved their linearity almost up to 95% of peak stress after curing for 120 days. In contrast, the presence of 6% Na2SO4 caused undesirable effects. In addition, both sulphates greatly affected the failure modes of soil–L–NP specimens, particularly at a later stage. 相似文献
996.
在南京市浦口和大厂的五大主要功能区(工业区、交通干线、居民区、蔬菜生产基地和风景区)分别布置采样点,共采集了75个菜地耕层土壤样品,以Cd、Cu、Pb和Zn等典型污染重金属元素的全量数据为基础,运用经典统计分析、综合污染指数和地统计分析相结合的方法对土壤重金属污染进行评价。结果表明,Cd、Cu和Zn分别超出其南京地区土壤背景值的5.42、1.84和1.14倍,Pb未超出。不同功能区菜地土壤的重金属全量水平存在明显差异,其中工业区菜地土壤的重金属污染较为严重。对于Cd和Cu,单因子污染指数大于1的样点数达100%,Zn为52%,Pb为2.67%。研究区内菜地土壤重金属的综合污染指数为4.12,属于中度污染。Cu的空间相关性很弱,Cd、Pb和Zn具有中等的空间结构性;四种重金属的空间相关尺度较为接近。Cd、Cu和Zn的单因子污染指数具有相似的空间分布,总体呈现出南高北低的带状递减趋势,且高峰值具有空间分布的趋同性,而Pb的单因子污染指数分布呈现西北和东南两端高,中间较低的趋势。综合污染指数的空间分布显示,研究区大部分菜地土壤处于中度重金属污染水平,钢铁生产厂周边的斑块状区域重金属污染更加严重。 相似文献
997.
C. J. Loupasakis B. G. Christaras G. Ch. Dimopoulos T. N. Hatzigogos 《Geotechnical and Geological Engineering》2009,27(1):71-80
The selection of the constitutive laws reproducing the response of geomaterials usually becomes a very complicated procedure;
especially during the analysis of geostructures containing coarse grained materials. The objective of this study, is the evaluation
of models based on the perfect and hardening plasticity theory, regarding their ability to analyze the behaviour of soil materials,
used for the construction of earth dams. The evaluated constitutive laws are the elastic–perfect plastic model based on the
Mohr–Coulomb failure criterion and the isotropic hardening CAP model based on the same criterion. The data used for the evaluation
of the models, originate from the body of the Sfikia earth dam. This dam is considered suitable, because of the specialized
laboratory tests’ available data, regarding the materials of every zone. The availability of those data, as well as the variety
of the construction geomaterials, allows the deduction of generalized conclusions, concerning the ability of the specific
models to simulate a variety of similar earth constructions. 相似文献
998.
P. Kallioglou Th. Tika G. Koninis St. Papadopoulos K. Pitilakis 《Geotechnical and Geological Engineering》2009,27(2):217-235
The paper presents results from a laboratory investigation into the dynamic properties of natural intact and model organic
soils by means of resonant-column tests. The natural intact organic soils were sands, cohesive soils and peats with varying
content of calcium carbonate. The model organic soils were formed in laboratory by mixing kaolinite and paper pulp. The influence
of various soil parameters, such as strain level, confining stress, void ratio, plasticity index, organic content and secondary
consolidation time on shear modulus, G, and damping ratio, DT, is presented and discussed. The test results on natural organic
soils show that only high organic contents (OC ≥ 25%) have significant influence on G and DT at both small and high shear
strains. For the model organic soils, however, a significant influence of even lower values of organic content (5% ≤ OC ≤ 20%)
on G at small strains and DT at both small and high strains is observed. 相似文献
999.
A multiphase model is proposed to describe the mechanical behaviour of geomaterials reinforced by linear inclusions. This macroscopic approach considers the reinforced soil or rock mass as the superposition of continuous media. Equations of motion and constitutive laws of the model are first derived. Its implementation in a finite element computer code is then detailed. A modified implicit algorithm for elastoplastic problems is proposed. The model and its implementation are fully validated for rock‐bolted tunnels (comparison with scale model experiments) and piled raft foundations (comparison with the classical ‘hybrid method’). The Messeturm case history is finally presented to assess the handiness of the approach for real structures. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
1000.
Rico, Colorado is a small mountain community that was developed before the turn of the century around and near underground
lead-zinc-silver mines. Today, US regulatory concerns in such communities focus on the metal content, particularly of lead,
in community soils. This study integrates bedrock geology, surficial geology, mineralogy and geochemistry in order to define
the controls on metal distribution in Rico community soils. The principal constituents of concern are As, Pb, and Mn. The
results show that mining-related sources are discrete and localized whereas natural sources, including bedrock (mean Pb content
of 3 500 ppm), colluvium (mean Pb content of 1 410 ppm), and older alluvium (mean Pb content of 744 ppm) are wider spread
and are the principal sources of metals in Rico community soils. Historical mining sites like Rico should be expected to have
significant surficial expressions of mineralized bedrock. In these communities, it is important to accurately define the role
of all metal sources as a foundation for determining environmental liabilities, cleanup guidelines, and health risk assessments.
The application of geology and mineralogy in support of geochemical characterization is necessary to accurately define the
origin and distribution of both anthropogenic and natural metal sources at such sites.
Received: 27 December 1996 · Accepted: 21 February 1997 相似文献