共查询到20条相似文献，搜索用时 296 毫秒
1.
Liu Zhang-Rong Ye Wei-Min Cui Yu-Jun Zhu He-Hua Wang Qiong Chen Yong-Gui 《Acta Geotechnica》2021,16(10):3145-3160
Bentonite pellets are recognized as good buffer/backfill materials for sealing technological voids in high-level radioactive waste (HLW) repository. Compared to that of a traditional compacted bentonite block, one of the most important particularities of this material is the initially discrete pellets and the inevitable heterogeneous porosity formed, leading to a distinctive water retention behaviour. In this paper, water retention and mercury intrusion porosimetry (MIP) tests were conducted on pellet mixture (constant volume), single pellet (free swelling) and compacted block (constant volume) of GMZ bentonite, water retention properties and pore structure evolutions of the specimens were comparatively investigated. Results show that the water retention properties of the three specimens are almost similar to each other in the high suction range (>?10 MPa), while the water retention capacity of pellet mixture is lower than those of the compacted block and single pellet in the low suction range (<?10 MPa). Based on the capillary water retention theory (the Young–Laplace equation), a new concept ‘saturated void ratio’ that was positively related to water content and dependent on pore size distribution of the specimen was defined. Then, according to the product of saturated void ratio and water density in saturated void, differences of water retention properties for the three specimens at low suctions were explained. Meanwhile, MIP tests indicate that as suction decreases, the micro- and macrovoid ratios of pellet mixture and compacted block decrease as the mesovoid ratio increases, while all the void ratios of single pellets increase. This could be explained that upon wetting, water is successively adsorbed into the inter-layer, inter-particle and inter-pellet voids, leading to the subdivision of particles and swelling of aggregates and pellets. Under constant volume condition, aggregates and pellets tend to swell and fill into the inter-aggregates or inter-pellets voids. While under free swelling condition, the particles and aggregates in a single pellet tend to swell outward rather than squeezing into the inter-aggregate voids, leading to the expansion of the pores and even formation of cracks. Results including the effects of initial conditions (initial dry density and fabric) and constraint conditions (constant volume or free swelling) on the water retention capacity and pore structure evolution reached in this work are of great importance in designing of engineering barrier systems for the HLW repository.
相似文献2.
The paper presents the results of an experimental study on the effects of the initial water content and dry density on the
soil–water retention curve and the shrinkage behavior of a compacted Lias-clay. The initial conditions after compaction (initial
water content and initial dry density) have been chosen on the basis of three Proctor tests of different compaction efforts.
According to the eight chosen initial conditions clay samples have been compacted statically. The relation between total suction
and water content was determined for the drying path starting from the initial conditions without previous saturation of the
specimens. A chilled-mirror dew-point hygrometer was used for the suction measurements. For the investigation of the shrinkage
behavior cylindrical specimens were dried to desired water contents step-by-step without previous saturation. The volume of
the specimens was measured by means of a caliper. Based on the test results the influence of different initial conditions
on the soil suction and the shrinkage behavior is analyzed. The soil–water retention curves obtained in terms of the gravimetric
water content are independent of the initial dry density. At water contents above approximately 11–12.5% a strong influence
of the compaction water content is observed. At smaller water contents, the soil–water retention curve is independent of the
compaction water content. The results of the shrinkage tests show that the influence of the compaction dry density on the
shrinkage behavior is negligible. Similar to the drying behavior of saturated samples a primary and a residual drying process
could be distinguished. The primary drying process is strongly influenced by the initial water content. In contrast, the rate
of the volume change of the residual drying process is unaffected by the initial water content. 相似文献
3.
Richard Wan Mehdi Pouragha Mahdad Eghbalian Jérôme Duriez Tai Wong 《国际地质力学数值与分析法杂志》2019,43(5):956-973
The paper offers an analytical determination of the hydraulic properties of an unsaturated soil with reference to its retention curve, which describes the relationship between the volumetric water content and capillarity through matric suction. The analysis combines a particulate approach focused on the physics at the pore scale, including microstructural aspects, with a probabilistic approach where the void space and grain size are considered as random variables. In the end, the soil water characteristic curve of an unsaturated granular medium along a drying path can be derived analytically based on the sole information of particle size distribution. The analysis hinges on the tessellation of a wet granular system into an assemblage of tetrahedral unit cells revealing a pore network upon which capillary physics are computed with respect to pore throat invasion by a non-wetting fluid with evolving pendular capillary bridges. The crux of the paper is to pass from particle size probability distribution to a matching void space distribution to eventually reveal key information such as void cell and solid volume statistics. Making reasonable statistically based assumptions to render calculations tractable, the water retention curve can be readily constructed. Model predictions compare quite favourably with experimental data available for actual soils, especially in the high saturation range. Having a sound scientific basis, the model can be made amenable to address a variety of soils with a wider range of particle sizes. 相似文献
4.
5.
测量了在宽广吸力范围内原状样和压实样的脱湿持水曲线,对比分析了单双峰结构持水性能的差异;并利用压汞试验测试两种土样在脱湿过程的孔隙分布,分析了两者的差异并探讨了脱湿过程孔隙的演化规律;在考虑收缩变形的基础上,基于孔隙分布曲线确定了土?水特征曲线的基本参数。试验结果表明：原状样在宽广吸力范围内基本上呈单峰孔隙结构;饱和压实样具有单峰孔隙结构,随着吸力的增加,双峰结构越来越明显,当吸力达到很大时,演化成完全双峰孔隙结构。原状样的持水曲线为经典的S形,而压实样的持水曲线在过渡段出现了水平台阶状;低吸力段,压实样的持水曲线低于原状样,而高吸力段,两者的持水曲线基本重合。基于孔隙分布曲线确定了控制持水曲线进气值和残余值的孔径,并计算出对应的吸力值,其值更符合实际物理意义。 相似文献
6.
This paper presents a three‐dimensional elastoplastic constitutive model for predicting the hydraulic and mechanical behaviour of unsaturated soils. It is based on experimental results obtained from a series of controlled‐suction triaxial tests on unsaturated compacted clay with different initial densities. Hydraulic hysteresis in the water‐retention behaviour is modelled as an elastoplastic process, with the elastic part modelled by a series of scanning curves and the elastoplastic part modelled by the main drying and wetting curves. The effect of void ratio on the water‐retention behaviour is studied using data obtained from controlled‐suction wetting–drying cyclic tests on unsaturated compacted clay with different initial densities. The effect of the degree of saturation on the stress–strain‐strength behaviour and the effect of void ratio on the water‐retention behaviour are considered in the model, as is the effect of suction on the hydraulic and mechanical behaviour. The initial density dependency of the compacted soil behaviour is modelled by experimental relationships between the initial density and the corresponding yield stress and, thereby, between the initial density and the normal compression line. The model is generalized to three‐dimensional stress states by assuming that the shapes of the failure and yield surfaces in the deviatoric stress plane are given by the Matsuoka–Nakai criterion. Model predictions of the stress–strain and water‐retention behaviour are compared with those obtained from triaxial tests with different initial densities under isotropic compression, triaxial compression and triaxial extension, with or without variation in suction. The comparisons indicate that the model accurately predicts the hydraulic and mechanical behaviour of unsaturated compacted soils with different initial densities using the same material constant. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
7.
对京九线路基粉土用GDS三轴仪进行固结不排水剪试验,研究不同围压、含水量、压实度下压实粉土样的应力-应变关系。结果表明:压实粉土在低围压下为应变软化,高围压下为应变硬化,存在一个屈服应力;含水量和压实度对粉土强度和应力-应变关系影响显著,随着含水量的减小、压实度的增大,压实粉土样强度增大,应力-应变曲线上升。对围压小于屈服应力的应变软化曲线,用常规的土的软化关系式进行拟和;对围压大于屈服应力的应变硬化曲线,用邓肯-张模型进行拟和;这二者的结合能描述压实粉土的应力-应变关系曲线,效果良好。 相似文献
8.
9.
在我国西北干旱半干旱地区,处于高吸力范围内的非饱和土广泛存在于各种岩土工程中。非饱和土土水特性的研究是非饱和土渗流、强度与变形研究的基础。为研究高吸力下不同初始孔隙比非饱和土的土水特性,以一种粉土试样作为研究对象,采用饱和盐溶液蒸汽平衡法控制土试样的吸力,利用阿基米德原理量测不规则土试样的体积,通过修正的Van-Gen... 相似文献
10.
干湿变化是自然界中土体必然经历的过程,对土体工程性质有重要影响。系统掌握干/湿过程中土结构演化特征,对深入认识土体宏观力学性质有重要意义。基于国内外大量文献资料,着重总结了黏性土在干燥过程、湿化过程和干湿循环过程中微观结构的演化特征,得到了以下几点主要认识:（1）含水率是影响土体微观结构的关键因素之一,在最优含水率干侧制备的土样呈典型的团聚体结构,孔隙分布曲线具有双峰特征,而在湿侧则呈相对均匀的基质结构,孔隙分布曲线呈现单峰特征;（2）在干燥过程中（吸力增加）,到达缩限之前,土体积的减小主要由大的宏观孔隙收缩所致。在不同的吸力区间内,主要受影响的孔隙尺寸是不同的;（3）在湿化过程中（吸力减小）,团聚体内的小孔隙和团聚体间的大孔隙都逐渐增大,且以团聚体内的孔隙增大为主,孔隙结构的演化特征与侧限条件密切相关;（4）在干湿循环过程中,土结构变化并不是完全可逆的,土体产生的累积收缩/膨胀形变量主要来自于宏观孔隙,随着干湿循环次数的增加,土体的体变特性会达到一个平衡状态,可用弹性孔隙比进行描述。除此以外,还总结了土结构观测的常规技术方法,包括SEM、ESEM、MIP和CT技术等。最后针对土结构研究现状,提出了今后的研究重点和方向,主要包括制样新方法、观测新技术、湿化过程的微观结构以及微观结构参数与宏观力学模型相结合等。 相似文献
11.
煤矸石作为煤层开采和洗选过程中产生的废弃料,常用于路基填筑。压实的路基煤矸石填料存在双孔隙群结构,其土-水特征曲线（SWCC）具有双台阶现象。而SWCC与土体非饱和渗透系数密切相关,对路基内部水分运移以及路基长期累积变形有重要影响。为了探究压实度、粉粒含量、最大颗粒粒径对双台阶SWCC的影响,对路基煤矸石填料进行了一系列压力板试验,并采用描述双台阶SWCC的Bi-V-G公式拟合实测SWCC,分析了模型参数变化规律。试验结果表明,粉粒含量为5%时,不同压实度试样SWCC均存在双台阶现象;粉粒含量为50%时,随着压实度增大,试样SWCC由双台阶形过渡为单台阶形,在0.90和0.95压实度之间存在一个界限值,双台阶现象消失;增大压实度、提高粉粒含量或减小最大颗粒粒径,均会使SWCC台阶高差减小。随着压实度增大或粉粒含量提高,模型参数 、 （与进气值有关的参数）和 、 （与排水程度有关的参数）值均逐渐减小,试样大、小孔隙部分均进气值增大,持水能力提高。 相似文献
12.
Assia Benchouk Mounir Derfouf Nabil Abou-Bekr Said Taibi 《Arabian Journal of Geosciences》2013,6(12):4565-4573
This paper presents an experimental study carried out on some clayey soils of Tlemcen region situated in the North West of Algeria. The characterization of the volumetric behavior under the effect of suction is studied on drying–wetting paths which highlight the correspondence between void ratio, degree of saturation, and water content versus suction. The initial conditions of studied material are in slurry form and compacted at different initial water contents. For the slurry form, correlations are derived to predict parameters characterizing the drying path. 相似文献
13.
Shengyang Yuan Xianfeng Liu Scott William Sloan Olivier Pierre Buzzi 《Acta Geotechnica》2016,11(4):789-804
This paper presents a comprehensive experimental investigation on time-dependent swelling behaviour at both macroscale and microscale of a natural Australian expansive soil in compacted state. A number of one-dimensional swelling tests under different vertical pressures, different initial void ratios and initial water contents were performed. The characterization at macroscale was complemented by extensive microstructural investigations through mercury intrusion porosimetry and scanning electron microscope observation on both as-compacted and swollen specimens. The results were discussed at two different scales within a framework of double-porosity, which was finalized by linking the macrostructural–microstructural strains ratio with secondary swelling/compression coefficients. The multi-scale correlation appears to be largely independent of the specimen initial conditions. The study showed that the secondary swelling and primary swelling are governed by the same factors and that secondary swelling takes place mainly in macropores, of which the change magnitude depends on the level of confinement applied. The microstructural investigations show that swelling is accompanied by significant microfabric changes. 相似文献
14.
15.
Kannan K. R. Iyer Jeevan Joseph Bruna C. F. L. Lopes D. N. Singh Alessandro Tarantino 《Geomechanics and Geoengineering》2018,13(2):88-103
The soil–water retention (SWR) characteristics of the clays play an important role in controlling their engineering behaviour, particularly, in the unsaturated state. Although, researchers have attempted to understand the water retention characteristics of the clays in their reconstituted or remoulded state, such studies are rare for the clays in their intact state. In this context, it becomes important to understand the influence of initial state of compaction, which would create different pore and fabric structure (viz., microstructure), on the water retention characteristics of the clays. With this in view, SWR behaviour was experimentally determined for the swelling clays (dried from different compaction states, viz., intact, reconstituted and remoulded) by employing Dewpoint PotentiaMeter (WP4C®). The changes in the pore size distribution of the clays at different stages of drying cycle were also studied by employing the Mercury Intrusion Porosimetry. The study reveals that the SWR curves for the intact and reconstituted specimens of the clays converge beyond a certain stage of drying. Also, a critical analysis of changes in the pore structure of the swelling clay specimens, during drying, indicates that the progressively deforming pore structure plays an important role in controlling its water retention characteristics to a great extent. 相似文献
16.
Zhong-Sen Li Assia Benchouk Feth-Ellah Mounir Derfouf Nabil Abou-Bekr Said Taibi Hanène Souli Jean-Marie Fleureau 《Acta Geotechnica》2018,13(1):51-71
The main objective of this paper is to examine how different engineering soils react to environmental variations and to provide correlations to characterize their behaviour under null external mechanical stress. Two French and two Algerian soils with liquid limits ranging from 36 to 112 were prepared under both slurry and Proctor compaction conditions, and then subjected to drying–wetting paths with suction controlled from several kPa to several hundreds of MPa. Experimental results are presented in five diagrams to show globally and simultaneously the shrinkage–swelling, saturation–desaturation and water retention characteristics. A reasonable consistency was observed between the oedometric and drying curves of slurry, confirming the equivalence between hydraulic loading (suction) and mechanical loading (consolidation stress) on the volume change behaviour of different soils. As an intrinsic parameter of soil nature, liquid limit was found to have a significant influence on the shrinkage limit, air-entry suction and compressibility of both slurry and compacted samples. For that reason, correlations between these characteristics and liquid limit were set up, providing a good basis for a first estimation of the drying–wetting curves. At the micro-scale, new experimental results were obtained: either on drying or wetting path, the micro-pores were almost unaffected, whereas, when matrix suction increased from 0.1 to 8 MPa, the volume of macro-pores decreased to quasi-closure. At last, the analogy between the compaction and drying–wetting curves, and the comparison of different methods to determine the water retention curve were addressed. Such analogies and comparisons contribute to a better understanding of the mechanisms of mechanical stress and suction. 相似文献
17.
联合压力板仪和蒸汽平衡法在全吸力范围内对原状与重塑黄土进行持水特性试验,使用非饱和三轴仪对高吸力下的原状与重塑黄土进行剪切试验,同时采用扫描电镜仪(scanning electron microscope,SEM)和压汞仪(mercury injection apparatus,MIP)进行微观试验,探讨了非饱和黄土结构性差异对其水力力学特性的影响。试验结果表明:随着吸力的增大,原状和重塑土的饱和度、含水率均减小,孔隙比稍有减小。由于原状及重塑黄土的初始孔隙比基本一致,因此两者压汞试验总进汞量接近。由扫描电镜和压汞试验得到的原状及重塑黄土的孔隙结构形态及优势孔径范围不一样,结构性有所差异,导致土-水特征曲线在不同吸力范围内呈现不一样的规律。原状和重塑土的应力-应变关系多呈软化现象,吸力为3.29 MPa的重塑土呈硬化现象。且随着吸力的增大,原状和重塑土的黏聚力和峰值强度均明显增加,体变由剪缩趋向剪胀现象。由于原状土具备一定结构性,胶结作用较强,其黏聚力的增幅会大于重塑土,峰值强度也高于重塑土,而两者的内摩擦角基本一致。 相似文献
18.
19.
压实黄土变形特性 总被引：4，自引：0，他引：4
黄土路基填料的变形特性直接关系到路基沉降和路基边坡坡度的选取,是黄土地基工程、边坡工程和洞室工程设计计算的重要参数。基于一维室内固结试验,分析了压实黄土变形特性。引入压缩变形系数,分析了压实黄土的物理指标（含水量、压实度）与变形指标（压缩变形系数、压缩系数）的关系,采用应变法来表达压缩变形曲线结果;引入非线性应力、应变关系的割线模量,研究了压实黄土的加荷本构模型和增（减）湿本构模型。结果表明：压实黄土的物理指标对其变形特性影响较大,压实黄土的应力-应变关系可以用幂函数 的形式来表达,提出了压实黄土的加荷本构模型和增（减）湿本构模型,该模型具有较高的可靠性,为研究黄土路基沉降特性提供了有力依据。 相似文献
20.
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