Micromechanical approach to swelling behavior of capillary-porous media with coupled physics

A detailed multiscale analysis is presented of the swelling phenomenon in unsaturated clay-rich materials in the linear regime through homogenization. Herein, the structural complexity of the material is formulated as a three-scale, triple porosity medium within which microstructural information is transmitted across the various scales, leading ultimately to an enriched stress-deformation relation at the macroscopic scale. As a side note, such derived relationship leads to a tensorial stress partitioning that is reminiscent of a Terzaghi-like effective stress measure. Otherwise, a major result that stands out from previous works is the explicit expression of swelling stress and capillary stress in terms of micromechanical interactions at the very fine scale down to the clay platelet level, along with capillary stress emerging due to interactions between fluid phases at the different scales, including surface tension, pore size, and morphology. More importantly, the swelling stress is correlated with the disjoining forces due to electrochemical effects of charged ions on clay minerals and van der Waals forces at the nanoscale. The resulting analytical expressions also elucidate the role of the various physics in the deformational behavior of clayey material. Finally, the capability of the proposed formulation in capturing salient behaviors of unsaturated expansive clays is illustrated through some numerical examples.     

煤电阻率与其瓦斯含量关系的实验研究

煤体中的瓦斯含量能显著影响煤的电阻率,本文利用高精度电阻测试实验装置,在连续吸附/解吸与等体积吸附/解吸条件下,对煤样的电阻率随瓦斯含量的变化规律进行测定。研究结果表明:煤样在连续吸附/解吸与等体积吸附/解吸条件下,电阻率随着瓦斯吸附量增大先逐渐减小,后趋于平稳;等体积吸附(静态吸附)时电阻率改变较连续吸附(动态吸附)明显,且等体积解吸结束时,煤体电阻率距离原始值较远;在瓦斯解吸过程中,煤体电阻率随煤中瓦斯含量增大呈线性减小。研究结果为利用煤体电阻率与瓦斯含量的线性关系预测矿井瓦斯含量提供了理论依据,对指导现场的瓦斯含量测量具有重要意义。     

Swelling model study of expansive soil at K-0 and triaxial stress stateEI北大核心CSCD

A series of swelling tests is performed on a typical Nanyang expansive soil with medium swelling capacity compacted at various initial densities and water contents. The swelling tests are separately conducted using the conventional oedometer to confine the lateral swelling of the soil specimens, and using the GDS triaxial apparatus to allow the free volumetric swelling. The multiple nonlinear mathematical method is adopted to obtain the lateral swelling model (i.e. K-0 model), which fully considers the coupled effect of initial degree of compaction, moisture content and overburden pressure on the swelling strain. Also, an empirical model for the relationship between spherical stress and volumetric strain is proposed by triaxial swelling test. Based on the K-0 swelling model, a formula is proposed to quantitatively evaluate the swell potential, and also a theoretical calculation method is derived to determine the processing layer thickness of expansive soil slope. Based on the assumption that volumetric swelling strain only changes with spherical stress and is not affected by the deviatoric stress, the correlations between the K-0 model and triaxial model are analyzed, and a method to calculate the volumetric swelling strain by only employing the K-0 model is given. Experimental results show that the proposed K-0 model with multifactor coupling is reasonable to predict the swelling potential of compacted expansive soil. It is found that the key factor to link the K-0 model and triaxial swelling model is assuming an average static lateral pressure coefficient. The average static lateral pressure coefficient tends to decreases with increasing overburden pressure by inversion method. This tendency of average static lateral pressure coefficient is believed to rely on the fact that lateral swelling pressure decreases with the increase of overburden pressure.     

Sulphate Attack in Lime-Treated Marine Clay

The use of lime to improve the properties of soft clays is not new. Recently the deep lime mixing technique has been extended to coastal regions for improving the behavior of weak marine clays. But lime treatment technique should be approached carefully for clay containing a high percentage of sodium sulphate. The presence of sulphate in lime-treated clays may result in high swelling due to the formation of the expansive mineral, ettringite. A limited study of lime-treated marine clays has shown a need to further explore the formation of ettringite and its stability with time. In this article, a laboratory investigation was carried out to examine the influence of sodium and calcium sulphates on the behavior of lime column treated marine clay. Scanning electron microscopy (SEM) was used to identify the formation of various reaction products, including ettringite. Test results indicate that the formation of ettringite in the lime-sodium sulphate-clay system adversely affects the engineering behavior of the marine clay, whereas the addition of calcium sulphate significantly improves the engineering characteristics of the soil.     

高温下石灰岩和砂岩膨胀特性的试验研究

利用自行研制的高温岩石膨胀特性试验装置,对石灰岩和砂岩试件300～700 ℃高温过程中的膨胀特性进行试验研究。试验结果表明,升温过程中,石灰岩和砂岩的膨胀应力随温度的增加而增大,且砂岩膨胀速率比石灰岩大,刚到700 ℃时砂岩膨胀应力是石灰岩的2.45倍。升温过程中膨胀应力与温度曲线的拟合函数为2次抛物线,相关系数达0.94以上。恒温过程中,随时间延长2种岩石的膨胀应力缓慢增加,最后逐渐趋于稳定的数值。600 ℃高温后2种岩石膨胀均达到极限,但具体表现不同,700 ℃恒温结束时砂岩稳态膨胀应力是石灰岩的3.14倍。岩石热膨胀应力变化与其岩性、内部矿物分解、孔隙率变化、声速变化等有显著关系。     

Factors influencing determination of shale classification indices and their correlation to mechanical properties

The influence of sample preparation procedure on the measured classification indices such as clay-size fraction, liquid limit, and plastic limit of shales was investigated. Shale samples covering a wide range of composition and plasticity were tested using standard and modified preparation procedures to yield quantitative data required for this investigation. The study specifies the range of shale plasticity in which the measured values of clay-size fraction and liquid limit are sensitive to hydrometer specimen size and rehydration time, respectively. The study also revealed that the degree of shale particle disaggregation has an important influence on the measured clay-size fraction and liquid limit. This influence is maximized for shales with intermediate plasticity and can be interpreted in terms of particle size and shape. Correlations were established between classification indices derived from standard and modified sample preparation procedures. It is recommended to use these correlations to adjust shale classification indices derived from standard sample preparation procedures usually utilized by commercial laboratories. Such correlations help in creating a universally followed procedure for better estimation of shale engineering properties and reliable interpretation of case histories involving shale formations.     

弱膨胀土浸水变形特性及其预测

对取自江苏省淮安市的膨胀土进行了浸水后的膨胀变形和压缩变形试验。在竖向压力25~800 k Pa范围下,研究了不同初始含水率和初始干密度对浸水膨胀变形特性的影响。结果表明:浸水饱和膨胀变形量主要取决于初始干密度,且初始含水率也有一些影响;在相同的含水率下,膨胀变形量随着干密度的增加而增大;在相同干密度条件下,含水率越大,浸水膨胀变形量略微减小。根据各组的固结状态线和浸水饱和膨胀后状态线的交点,得出了介于浸水膨胀和浸水压缩的分界状态线,此线基本上不受初始含水率的影响,进而可以判定不同孔隙比、不同竖向压力下土样处于浸水膨胀还是压缩。最后,基于浸水变形试验结果,提出了一种简便的预测弱膨胀土在不同竖向压力下膨胀变形量的方法。     

Modelling chemo‐hydro‐mechanical behaviour of unsaturated clays: a feasibility study

Effective capabilities of combined chemo‐elasto‐plastic and unsaturated soil models to simulate chemo‐hydro‐mechanical (CHM) behaviour of clays are examined in numerical simulations through selected boundary value problems. The objective is to investigate the feasibility of approaching such complex material behaviour numerically by combining two existing models. The chemo‐mechanical effects are described using the concept of chemical softening consisting of reduction of the pre‐consolidation pressure proposed originally by Hueckel (Can. Geotech. J. 1992; 29 :1071–1086; Int. J. Numer. Anal. Methods Geomech. 1997; 21 :43–72). An additional chemical softening mechanism is considered, consisting in a decrease of cohesion with an increase in contaminant concentration. The influence of partial saturation on the constitutive behaviour is modelled following Barcelona basic model (BBM) formulation (Géotech. 1990; 40 (3):405–430; Can. Geotech. J. 1992; 29 :1013–1032). The equilibrium equations combined with the CHM constitutive relations, and the governing equations for flow of fluids and contaminant transport, are solved numerically using finite element. The emphasis is laid on understanding the role that the individual chemical effects such as chemo‐elastic swelling, or chemo‐plastic consolidation, or finally, chemical loss of cohesion have in the overall response of the soil mass. The numerical problems analysed concern the chemical effects in response to wetting of a clay specimen with an organic liquid in rigid wall consolidometer, during biaxial loading up to failure, and in response to fresh water influx during tunnel excavation in swelling clay. Copyright © 2005 John Wiley & Sons, Ltd.     

模糊数学在当宜高速公路膨胀土判别和分类中的应用

膨胀土胀缩性与指标集之间的关系尚未完全弄清,存在较大的模糊性。应用模糊数学理论对当宜高速公路膨胀土胀缩等级进行分类,该方法通过验证是可行的。     

自由膨胀比测定新方法在胜利油区砂岩储层评价中的应用

粘土矿物的“水敏效应”是引起砂岩储层伤害的最主要原因之一。本文应用自由膨胀比试验的新方法,测定了胜利油区27个砂岩储层岩心样品,并通过X衍射对样品中粘土矿物含量的测定,建立了储层自由膨胀比与蒙脱石含量之间良好的正相关模型。该方法可以更直观、准确地描述出油气储层中粘土矿物的自由膨胀行为,并定量地反映出粘土矿物水敏性导致的储层潜在伤害,也可以用于油田防膨剂的研制,因此在油气田开发中具有较广泛的应用前景。