共查询到20条相似文献，搜索用时 31 毫秒
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An experimental study on the thermo-hydro-mechanical behaviour of two heavily overconsolidated clays is presented. Laboratory tests have been conducted on a Spanish bentonite (FEBEX bentonite) and a Belgian kaolinitic/illitic clay (Boom clay), statically compacted at different initial dry densities and water contents. Volume change behaviour of the soils during suction reduction paths at different temperatures and during heating-cooling cycles at constant water content or suction have been investigated through the use of suction and temperature controlled oedometer cells. In addition, the volume change response under unconfined conditions and constant water content has been measured to determine thermal expansion coefficients. The results show similarities and differences between the observed behaviour of the two types of clays that have been interpreted on the basis of their different structures and regarding their proportion of intra-aggregate water. 相似文献
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Utilizing computational neural networks for evaluating the permeability of compacted clay liners 总被引：1，自引：0，他引：1
The design of lined waste-storage facilities is significantly influenced by the permeability of the liner. The permeability of compacted clay liners, in turn, is influenced by factors such as clay type and composition, compaction type and effort, and operating conditions. The complexity of the permeation process makes it difficult to predict analytically the permeability from these factors. As a result, empirical regression models are frequently used to predict permeability. In this paper, permeability prediction models are developed using computational neural networks (CNNS). The developed CNN models are used to predict the permeability of compacted clay for a known set of soil properties and field and laboratory conditions. Moreover, the models are used to determine the relative importance of the various input parameters to the model output. Also, a comparison between regression models and neural networks for predicting permeability is presented and the advantages of utilizing CNN methodology over regression techniques in model development are highlighted. 相似文献
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干湿循环作用下压实黏土力学特性与微观机制研究 总被引：1，自引：0，他引：1
针对干湿循环作用下填埋场封场覆盖系统压实黏土防渗结构损伤等问题,系统开展了干湿循环作用下（室内模拟填埋场气候环境）压实黏土力学特性及微观结构特征试验研究,从微观层次揭示了压实黏土在干湿循环作用下变形特性和强度衰减内在本质。研究结果表明：随着干湿循环次数的增加,压实黏土初始变形段区间割线模量增加,末段区间割线模量大幅度降低,变化幅度随初始压实度的增加而增加;同时,压实黏土剪切强度呈减小趋势,但减小幅度随初始压实度和围压的增加而减小。经过3次干湿循环后,压实黏土发生不可逆的体积收缩,体积收缩比例随压实度的增加而减小,低压实黏土和高压实黏土的体积收缩20.5%和11.5%。同时,低压实黏土和高压实黏土的大孔体积增加25.7%和53.9%,微裂隙体积增加3.1%和41.7%,增加幅度随初始压实度的增加而增加。压实黏土不可逆的体积收缩致使土体更加密实,从而导致压实黏土初始切线模量和强度增加。同时,大孔体积增多和微裂隙的发育,导致压实黏土剪切强度和末端切线模量降低,干湿循环对不同压实度黏土力学特性影响是二者的综合表现。 相似文献
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南阳膨胀土的工程地质特征和填筑适宜性 总被引：5，自引：1，他引：4
施工阶段的工程地质调查发现,宁（南京）西（西安）铁路内乡-镇平段南阳膨胀土成因类型上不仅有第四系冲积洪积粘土,而且发育上第三系湖相沉积粘土。不同成因的膨胀土具有不同的空间分布特征和工程性质,X射线衍射测试表明,南阳膨胀土的主要膨胀性粘土矿物是伊利石/蒙脱石混层矿物。物质组成和物理化学性质差异导致击实土在含水量变化条件下膨胀力和膨胀变形有明显的差别;对同一种膨胀土材料,其击实含水量越小,膨胀性越强,甚至含水量降低1 %～2 %,膨胀力就可以增加到200 %以上;击实膨胀土的直剪强度受到钙质结核含量的影响,对于膨胀势为高或强的膨胀土,结核含量小于15 % 时,经过干湿循环后直剪强度衰减量为40 %～65 %,结核含量为25 %～30 % 的强膨胀土直剪强度衰减量则低于30 %;对膨胀土的地质特征、工程性质、击实土的膨胀性和直剪试验结果进行分析,探讨其用于填筑铁路路基的适宜性,进行了填筑适宜性分级。依据研究成果制定的路基施工工艺取得了比较理想的工程效果 相似文献
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Scaly clays are stiff and highly fissured clays often used as construction materials. This paper presents the results of triaxial compression tests carried out on saturated and unsaturated samples of a compacted scaly clay. Complementary investigation on the microstructural features and their evolution with the amount of water stored into the material are also presented in order to shed light on the evolution of the micro- and macroporosity with suction. The water retention behaviour of the compacted scaly clay is also addressed. The results from the controlled suction triaxial tests are used to discuss the applicability of a single-shear strength criterion to compacted double-structured clays when the effective stress concept for unsaturated soils is used. The choice of the degree of saturation to be included in the effective stress definition for obtaining a satisfactory representation of the shear strength is addressed. It is shown that the best results are obtained when the macropore degree of saturation is considered along with its evolution during the applied stress path. 相似文献
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De la Morena Gema Navarro Vicente Asensio Laura Gallipoli Domenico 《Acta Geotechnica》2021,16(9):2775-2790
This paper presents a constitutive model that predicts the water retention behaviour of compacted clays with evolving bimodal pore size distributions. In line with previous research, the model differentiates between the water present inside the saturated pores of the clay aggregates (the microstructure) and the water present inside the pores between clay aggregates (the macrostructure). A new formulation is then introduced to account for the effect of the macrostructural porosity changes on the retention behaviour of the soil, which results in a consistent evolution of the air-entry value of suction with volumetric deformations. Data from wetting tests on three different active clays (i.e. MX-80 bentonite, FEBEX bentonite, and Boom clay), subjected to distinct mechanical restraints, were used to formulate, calibrate, and validate the proposed model. Results from free swelling tests were also modelled by using both the proposed double porosity model and a published single porosity model, which confirmed the improvement in the predictions of degree of saturation by the present approach. The proposed retention model might be applied, for example, to the simulation of the hydromechanical behaviour of engineered bentonite barriers in underground nuclear waste repositories, where compacted active clays are subjected to changes of both suction and porosity structure under restrained volume conditions.
相似文献9.
饱和膨润土及其与砂混合物的压缩变形特性 总被引：1，自引：0，他引：1
对用不同制样方法得到的饱和膨润土及其与砂混合物进行了压缩试验。试验结果表明,饱和膨润土的压缩曲线呈双线性,不同于普通黏土的压缩曲线。压缩试验中量测了侧向应力,由此得到的饱和膨润土的静止侧向压力系数值较一般黏土的数值要大。对膨润土与砂混合物的击实样进行了由非饱和到饱和状态的浸水试验,并得出试验过程中侧向应力的变化规律。由于浸水饱和的试样和抽真空饱和的试样在较高压力时压缩曲线趋于一致,可采用快速抽真空饱和的方法进行试验研究,以缩短非饱和混合物击实样浸水饱和所需时间。引入骨架孔隙比的概念,用来判断膨润土与砂混合物中砂骨架是否形成,得出影响混合物压缩特性的决定因素。 相似文献
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Free-Swell and Swelling Pressure of Unsaturated Compacted Clays; Experiments and Neural Networks Modeling 总被引：1，自引：0，他引：1
Expansive soils have received attentions of several investigators in the past half of century in the problematic soils context.
Volume change behavior of unsaturated compacted soils in presence of water and change of degree of saturation was observed
in two form of heave or collapse. Low water content and low density compacted soils in presence of enough surcharge pressure
lose stability and collapse, because of their metastable and susceptible structure to change of degree of saturation. Free-swell
and swelling pressure of five compacted clays, covering low to high plastic clays have been investigated in respect to compaction
states and swelling pressure was compared with collapse pressure threshold. The results of experiments were utilized in two
Artificial Neural Networks to predict free-swell percent and swelling pressure of a soil sample based on index properties
and compaction state. 相似文献
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本文对原状软土和重塑软土进行渗透特性试验,考察了饱和软土的渗透特性。原状样加载初期,渗透系数变化较小,当固结应力大于结构屈服应力时,渗透系数急剧下降,而结构屈服应力前后阶段的孔隙比与渗透系数对数坐标的直线关系没有发生变化,说明胶结对渗透性的影响较小。重塑土的渗透系数在加载过程中变化相对较小。试验结果表明,相同孔隙比时原状土渗透系数要明显大于重塑土。这是由于两者的组构不一样,即原状样的大颗粒和凝聚体间的大孔隙以及历史上形成的土颗粒的排列使其渗流通道要比重塑土通畅。用相同重塑方式制样得到的不同含水量土样,其渗透系数值相近;而用不同重塑方式制样得到的相近含水量土样,其渗透系数相差相对较大。确定饱和软粘土渗透性时要考虑孔隙比和组构的影响。 相似文献
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The generation of municipal solid waste incinerator fly ash (MSWIF) has been increasing significantly over the recent past, and its disposal is problematic and costly due to high concentration of leachable heavy metals present in the material. This study explored a potential stabilization of MSWIF by blending with a natural sorbent material with low permeability, clay, and assessed the potential release of heavy metals from the stabilized mixtures under various simulated subsurface environments. The leachability of heavy metals such as Pb, Cd, Cr, Zn and Cu in the MSWIF-clay mixtures cured for 1 to 360 days was investigated by performing leaching tests and sequential chemical extractions (SCE). Leaching tests were performed at acidic, neutral and alkaline pH values. The leaching test results suggested that the natural clay could turn the MSWIF into non-hazardous material. All the MSWIF-clay mixtures demonstrated leaching behavior different from that of the original MSWIF. SCE results revealed that the acidic and reducing conditions were the most unfavorable to the immobilization of the heavy metals in the stabilized MSWIF-clay matrix. Conversely, the oxidizing and alkaline conditions were not critical to the stabilized MSWIF-clay mixtures. Apparently, clay in the mixtures could function as an adsorptive micro-barrier to retain the heavy metals within the MSWIF-clay matrices. 相似文献
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C. Kayadelen 《Environmental Geology》2008,54(2):325-334
The compacted soils are extensively employed as mineral liners or a sealing system, constructed under municipal solid waste
and other containment hazardous materials to prevent or minimize the leakage of pollutant liquids and gases into ground water
and sublayers. This article presents a detailed experimental study on settlement characteristics, which are required for the
construction of a sealing system. For the experimental study where a compacted unsaturated soil taken from Adana in Turkey
has been used, a special equipped consolidation cell has been designed and constructed. The matric suction adopted as independent
stress-state variables has been controlled by using the axis translation technique. The consolidation tests have been performed
under constant matric suction. Furthermore, the pressure plate tests for various net vertical stresses have been conducted.
The test results have indicated that the settlement characteristics of a compacted soil as mineral liners and covers are highly
affected by matric suction. The water retention capacity of mineral liners, an important factor for hydraulic conductivity,
also changes with the vertical load. The compressibility decreases as the matric suction increases. It has been observed that
there exists an exponential relationship between the compressive indexes (C
t, D
t) and matric suction. 相似文献
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Bentonite clays are regarded a promising material for engineered barrier systems for the encapsulation of hazardous wastes because of their low hydraulic permeability, swelling potential, ability to self-seal cracks in contact with water and their high sorption potential. SKB (Svensk Kärnbränslehantering) has been conducting long term field scale experiments on potential buffer materials at the Äspö Hard Rock Laboratory for radioactive waste disposal in Sweden.The Alternative Buffer Material (ABM) test examined buffer properties of eleven different clay materials under the influence of groundwater and at temperatures reaching up to 135 °C, replicating the heat pulse after waste emplacement. Clay materials were emplaced into holes drilled in fractured granite as compacted rings around a central heater element and subsequently brought into contact with groundwater for 880 days. After test termination, and against expectations, all clay materials were found to have undergone large scale alterations in the cation exchange population. A reactive-diffusive transport model was developed to aid the interpretation of the observed large-scale porewater chemistry changes. It was found, that the interaction between Äspö groundwater and the clay blocks, together with the geochemical nature of the clays (Na vs Ca-dominated clays) exerted the strongest control on the porewater chemistry. A pronounced exchange of Na by Ca was observed and simulated, driven by large Ca concentrations in the contacting groundwater. The model was able to link the porewater alterations to the fracture network in the deposition hole. The speed of alterations was in turn linked to high diffusion coefficients under the applied temperatures, which facilitated the propagation of hydrochemical changes into the clays. With diffusion coefficients increased by up to one order of magnitude at the maximum temperatures, the study was able to demonstrate the importance of considering temperature-dependant diffusion in understanding and predicting geochemical alterations of engineered barriers systems after relatively short exposure times following waste emplacement. 相似文献
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T. Hueckel 《国际地质力学数值与分析法杂志》1997,21(1):43-72
Isothermal chemo-elasto-plasticity of clays is discussed, to describe strains induced in clay by permeation of it with a low dielectric constant organic contaminant, in the presence of stress. The strain is crucial in controlling permeability changes in chemically affected clay barriers of landfills and impoundments. The theory encompasses chemical softening or yield surface reduction, coefficient of chemical reversible expansion or contraction due to mass concentration increase, as well as chemical sensitivity of bulk plastic modulus. The experiments on chemistry and stress dependent permeability of Sarnia clay performed by Fernandez and Quigley (1985, 1991) are interpreted using this model. The numerical representations of the chemo-plastic softening function and the chemo-elastic strain function, as well as plastic bulk modulus sensitivity to concentration are evaluated for dioxane and ethanol. Specific requirements for the tests for chemo-plastic behavior of clays are discussed. © 1997 by John Wiley & Sons, Ltd. 相似文献
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Post-Cyclic Undrained Behavior of Compacted Composite Clay Subjected to Various Cyclic Loading Paths
H. R. Tavakoli A. Shafiee M. K. Jafari 《Geotechnical and Geological Engineering》2011,29(6):1085-1097
Using a sequential procedure of undrained cyclic and post cyclic tests, the strength and stiffness degradation characteristics
of compacted composite clays are studied immediately after various cyclic loading paths by triaxial and hollow cylinder tests.
The effects of cyclic loading paths, sand contents, cyclic loading amplitude and confining pressure on the post-cyclic mechanical
behavior of the composite clays are evaluated. The results point out different peculiarities which can be of interest in assessing
the mechanical behavior of the composite clays under post seismic shaking. The results show that effect of cyclic loading
on post cyclic pore water pressure build-up is significant when pore water pressure build-up is considerably lower than the
associated value in monotonic loading. The effect of sand content and cyclic loading path on degradation of stiffness is more
remarkable than shear strength. Test results also reveal that the effect of sand content on the post cyclic pore water pressure
build-up is minor. However, when the aggregate content increases the shear strength increases. 相似文献
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为研究上海浅部黏土的渗透系数及其各向异性,沿水平及竖直方向对上海浅部主要黏土层进行了不同压力下的固结试验,联合使用时间平方根法和时间对数法获取了试样的渗透系数,探讨了渗透系数与孔隙比及渗流方向之间的关系,并通过电镜扫描,从微观角度分析了水平和竖直方向渗透系数存在差异的原因。研究结果表明：上海浅部主要黏土层的渗透系数均随着孔隙比的增加而增大。对于单组试验来说,渗透系数k与孔隙比e在e lgk坐标系中呈现很好的线性关系,且渗透变化指数Ck大致呈现Ck = 0.5e0的规律;但对于整体试验而言,渗透系数与孔隙比在e lgk坐标系中大致呈现出曲线关系。通过扫描电镜观察,揭示了沉积形成的絮状微观结构是竖直和水平渗透系数差异较小的主要原因。 相似文献
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天然沉积结构性土的次固结变形预测方法 总被引：1，自引：0，他引：1
结构性土存在着其特有的变形和强度特性,次固结特性也表现出明显区别于与重塑土。通过对连云港天然沉积原状土和重塑土进行一维压缩次固结试验,研究了典型结构性土的次固结特性。试验结果表明,土体由于受结构性影响,结构破坏前后其次固结特性发生明显变化;结构屈服前（固结压力小于固结屈服压力）不发生次固结变形或次固结变形甚微;当土体处于屈服状态时,土体次固结变形突然增大,次固结系数Cα出现峰值;结构屈服后（固结压力大于固结屈服压力）,Cα随固结压力的增大而减小,表现为与当前的应力水平和时间密切相关的特性,应力水平对Cα的影响会随着次固结时间的增长而削弱。基于以上机制,建立了考虑结构性影响的次固结变形计算模型,该模型中Cα不仅与压缩指数Cc有关,且也与时间有关,基于该模型计算得到的Cα值和次固结变形均与试验值吻合较好。 相似文献
20.
The conditions of the bentonite in an engineered barrier for high-level radioactive waste disposal have been simulated in a series of tests. Cylindrical cells with an inner length of 60 cm and a diameter of 7 cm have been constructed. Inside the cells, six blocks of FEBEX bentonite have been piled-up, giving rise to a total length similar to the thickness of the clay barrier in a repository according to the Spanish concept. To obtain the blocks, the clay with its hygroscopic water content has been uniaxially compacted at a dry density of 1.65 g/cm3. The bottom surface of the material was heated at 100 °C and the top surface was injected with granitic water. The duration of the tests was 6, 12 and 24 months. The temperatures inside the clay and the water intake were measured during the tests and, at the end, the cells were dismounted and the dry density, water content and some hydro-mechanical properties of the clay (permeability, swelling pressure and swelling under load) were measured at different positions. The values obtained are compared to those of the untreated FEBEX bentonite. The injection of water provokes in the vicinity of the hydration surface an increase of the water content and a decrease of the dry density due to the swelling of the clay, while heating gives rise to an increase of the dry density and a reduction of the water content in the 18 cm closest to the heater, even after 2 years of thermo-hydraulic (TH) treatment. The swelling capacity and the hydraulic conductivity after TH treatment are mainly related to the dry density and water content attained during it. No major irreversible modifications of these properties with respect to those of the untreated clay have been detected. 相似文献