A new versatile constitutive law for modelling the monotonic response of soft rocks and structured fine-grained soils

This paper deals with a new critical state–based constitutive model for soft rocks and fine-grained soils. The model, formulated in the single-surface plasticity framework, is characterised by the following main features: (i) a generalised three-invariant yield surface capable of reproducing a wide set of well-known criteria, (ii) the dependency of the elastic stiffness on the current stress state by means of a hyperelastic formulation, (iii) the ability of simulating the plastic strain–driven structure degradation processes by a set of appropriate isotropic hardening laws, and (iv) a nonassociate flow rule in the meridian plane. The adopted formulation is hierarchical, such that the various features of the model can be activated or excluded depending on the specific kind of geomaterial to be modelled and on the quality and quantity of the related available experimental results. The constitutive model was implemented in a commercial finite element code by means of an explicit modified Euler scheme with automatic substepping and error control. The procedure does not require any form of stress correction to prevent drift from the yield surface. The performance of the model is first analysed by means of a wide set of parametric analyses, in order to highlight the main features and to evaluate the sensitivity of the formulation with reference to the input parameters. The model is then adopted to simulate the experimental response observed on three different geomaterials, ranging from soft clays to soft rocks.     

Numerical simulation of the undrained stability of slopes in anisotropic fine-grained soils

The undrained stability of slopes in anisotropic fine-grained soils is studied in this paper using the finite element method (FEM). A constitutive model is presented, able to account for the observed variation of undrained strength with loading direction. The model is able to encompass the different strength distributions observed in normally, slightly overconsolidated and heavily overconsolidated soils. A series of stability analyses have been performed to explore the effect of the type of undrained strength anisotropy on the stability and failure mechanisms of slopes of different inclinations. In addition, a real case study of the failure of an underwater slope is analysed with the numerical approach presented. It suggests that, by considering undrained strength anisotropy, the failure can be satisfactorily explained.     

基于混合物理论的水力-化学-力学污染物输运模型研究

由于废弃物的堆积以及填埋场上覆盖层的重量,衬垫因此承受一定的压力,发生力学固结;由于黏土本身的结构特性,当污染物通过黏土垫层时可能会发生化学固结,而固结作用可直接对污染物的对流输运产生影响,也会引起土层体积和结构的变化,从而改变其固有的输运性质。从混合物理论出发,建立了水力-化学-力学作用下的溶质输运理论框架,统一地描述了水力-化学-力学作用下变形、水的吸附或解吸附、对流和扩散现象。将输运系数考虑为有效孔隙率的函数,由此反映固结对输运参数的影响。对所建立的数学模型进行无量纲化处理,并使用有限元软件COMSOL Multiphysics进行求解,最后进行了参数分析。研究结果表明,垫层土体中吸附水和自由水之间的化学势差异越大,层间吸附水的解吸附量越大;当土体的软硬性质不同时,当层间吸附水解吸附后,土体固结程度不同,从而对污染物输运过程的影响不同。而当垫层上覆荷载增大时,土体宏观孔隙的扩张的限制作用增强,从而对土体产生一种修复作用,抑制污染物在土体中的输运。     

Some investigations to quantify hysteresis associated with water retention behaviour of fine-grained soils

The soil water retention characteristics curve (SWRC) has been reported to be quite useful for estimation of unsaturated soil properties. However, the uniqueness of SWRC is questionable due to hysteresis associated with the drying- and wetting-path SWRCs and this poses great challenge in utilising the SWRC for reliable estimation of unsaturated soil properties. Although hysteresis associated with SWRCs has been extensively studied for coarse-grained soils, due to limited studies on wetting-path SWRC for fine-grained soils, the hysteresis for fine-grained soils is not well understood. The present work attempts to address this gap, by studying the drying- and wetting-path SWRCs for eight different fine-grained soils by employing Dew point Potentiameter (WP4C®), Environmental Chamber and Controlled Water Sprinkling method. The study employs the concept of ‘Suction Hysteresis’, ψ_h, for quantification of hysteresis. Further, the influence of various soil-specific properties on the variation of ψ_h-water content relationship (viz., slope of variation of suction hysteresis, S_ψh) has also been studied and demonstrated. The findings of the study are quite encouraging and it has been realised that extensive studies on soils of different characteristics would be quite useful in quantifying the variation of SWRC during drying and wetting cycles.     

Modelling of the effect of scale on the compressibility parameters of fine-grained soils

ABSTRACT

The effect of sample scale represents a challenge when obtaining engineering parameters in the laboratory compared to those obtained in the field. This study aimed at contributing to existing knowledge numerically using the finite element software PLAXIS 2D. The investigations were analysed in terms of height scale (HS) and diameter scale (DS) through a series of laboratory tests. Its effect on compressibility parameters such as coefficient of consolidation (c_v) was noted experimentally and showed that the sample scale greatly influences soil parameters most particularly at DS. The soil behaviour was found to be dependent on both DS and HS with a correlation factor of 0.650 and 0.062, respectively. The experimental data were validated in PLAXIS and a new proposed model was developed in PLAXIS 2D under the DS. The new proposed model developed was found to show no significant difference with the laboratory data.     

Continuous determination of drying-path SWRC of fine-grained soils

Establishing the soil water retention curve, SWRC or the soil water characteristic curve, SWCC, is very useful for determination of unsaturated properties of soils. However, it has been observed that SWRC of a soil is not unique and depends on various factors such as the initial moisture content, density of soil, method of compaction, soil fabric and the path (drying or wetting) adopted for establishing it. In this context, many techniques and instruments have been employed by earlier researchers for determination of the SWRC of soils. However, these techniques entail weighing of the samples during prolonged testing, manually, and hence yield discrete data points. In this situation, AquaSorp® Isotherm Generator (manufactured by Decagon Devices Inc., USA) has been found to be quite useful for continuous determination of the drying-path SWRC of fine-grained soils. This device has been primarily employed for food products, powders and amorphous materials. Hence, demonstration of the utility and limitations of this device for SWRC determination of fine-grained soils becomes essential. With this in mind, extensive studies were conducted on commercially available soils (Kaolinite and Bentonite) by employing this device. In order to understand the influence of specimen specific parameters on the obtained SWRCs, the molding water content and thickness of the specimens were varied and the results have been evaluated critically. Details of the methodology adopted for these investigations, and the findings of the study are presented in this technical note. Based on a critical comparison of the results obtained from this device with those obtained from the dewpoint potentiameter, WP4®, the utility of this device for continuous determination of drying-path SWRC of the soils has also been demonstrated.     

Factors influencing undrained strength of fine-grained soils at high water contents

Understanding the undrained strength of fine-grained soils has been of interest to geotechnical researchers from many practical considerations. In several civil engineering applications, water content of soil is quite high being near or above the liquid limit of soils, and understanding the factors responsible for imparting the strength of soil at high water contents is of great significance. Recently, it has been reported in the literature that the shear strength of soils at these limiting water contents has significant variation. However, the reasons and the factors that probably influence for this variation have not been reported in the literature. This experimental investigation is an attempt in the direction of understanding the reasons for the variation in the undrained strength at higher limiting water content, namely liquid limit considering the various influencing factors like clay mineralogy and fine-sand content present in soil used for determining liquid limit. The results from this study are quite revealing and have been explained based on the mechanisms controlling the undrained strength at liquid limit.     

土壤中可挥发性污染物清除的离心试验研究

土工离心模拟试验技术是研究环境岩土工程问题的有效手段。本文研究了非水相流体污染物在非饱和土中的迁移以及随后的抽气清除过程。 当离心机运行到要求的加速度时,汽油污染物从地下油罐中释放并在非饱和土中迁移一年,之后采用土壤通气法对污染土壤进行修复。对土壤取样分析,得到污染物在土体中的迁移规律和分布特征。试验结果表明,土壤通气法可以清除非饱和土体中的挥发性有机污染物,是一种有效的原位土壤修复技术。     

Use of lateritic fine-grained soils in road pavement base courses

Summary Lateritic fine-grained soils are, in large areas of Brazil and other tropical countries, the most frequent local materials found along road routes. However the use of these soils in pavements has been difficult, because they do not conform to the traditional specifications for base courses. This paper presents successful uses of many of these soils in pavement base courses, particularly sandy soils, following specially developed geotechnical test methods and construction procedures, thus sensibly reducing the cost of pavements, mainly for low to medium traffic levels.     

Models of compacted fine-grained soils used as mineral liner for solid waste

To prevent the leakage of pollutant liquids into groundwater and sublayers, the compacted fine-grained soils are commonly utilized as mineral liners or a sealing system constructed under municipal solid waste and other containment hazardous materials. This study presents the correlation equations of the compaction parameters required for construction of a mineral liner system. The determination of the characteristic compaction parameters, maximum dry unit weight (γ _dmax) and optimum water content (w _opt) requires considerable time and great effort. In this study, empirical models are described and examined to find which of the index properties correlate well with the compaction characteristics for estimating γ _dmax and w _opt of fine-grained soils at the standard compactive effort. The compaction data are correlated with different combinations of gravel content (G), sand content (S), fine-grained content (FC = clay + silt), plasticity index (I _p), liquid limit (w _L) and plastic limit (w _P) by performing multilinear regression (MLR) analyses. The obtained correlations with statistical parameters are presented and compared with the previous studies. It is found that the maximum dry unit weight and optimum water content have a considerably good correlation with plastic limit in comparison with liquid limit and plasticity index.     

太湖疏浚底泥堆场黏土防渗层阻隔污染物的试验研究

底泥疏浚是治理太湖污染的必要途径之一。限于目前国内的经济与技术条件以及疏浚底泥的数量巨大,太湖雪浪底泥堆场只能直接采用下部的天然黏性土层作为防渗层而不加任何处理。为了确保疏浚污染底泥在堆放期间不对周围环境和地下水造成污染,采用渗透与阻隔、静态吸附、动态土柱等试验测定和分析了黏土层对底泥中主要污染物（总氮、氨氮、硝氮、亚硝氮、总磷、化学耗氧量（COD））渗透和运移的阻隔能力,同时得到了可用于分析污染物在土层中运移和转化规律的一些重要参数。试验结果表明,雪浪堆场下部的黏土层对疏浚底泥中的主要污染物具有较强的吸附和阻隔能力。     

Sequestration of organic contaminants in soil/sediment and its impact on contaminant fate

Adsorption and desorption are critical processes controlling the fate and transport of organic contaminants in natural environment. Numerous studies have shown that only a fraction of contaminants in soil or sediment can readily be desorbed to the aqueous phase, while desorption of the remaining fraction is very difficult and does not follow the conventional desorption models-a phenomenon typically referred to as ＂resistant desorption＂ or ＂sequestration＂ and is argued by many as the cause of reduced availability of contaminants in soil and sediment. While this reduced availability often reduces the effectiveness of soil and sediment remediation, the same effect can also greatly reduce risk of contaminated soil and sediment. The authors have conducted extensive lab and field studies to characterize the unique properties of sequestration of organic contaminants and to understand the mechanism（s） controlling sequestration. Thus far, over 50 different contaminant-soil/sediment combinations have been evaluated, using contaminants of varied physical-chemical properties （e.g., chlorinated benzenes, PAHs, PCBs, DDT, atrazine, hexachlorocyclohexane isomers, etc.）. Several unique characteristics of sequestration have been observed, and the most striking one is that despite the significant differences in chemical and soil properties, desorption of sequestered contaminants for all the contaminant-soil/sediment combinations exhibited very similar KOC （organic-carbon normalized partition coefficient） and very similar desorption kinetics.     

最近20年地震中场地液化现象的回顾与土体液化可能性的评价准则

回顾了1994年美国Northridge地震、1995年日本阪神地震、1999年土耳其Kocaeli地震、1999年台湾集集地震、2008年中国汶川地震、2010年智利Maule地震、2010～2011新西兰Darfield地震及余震、2011年东日本地震中大量的、不同类型的液化实例调查与研究,发现这些地震的液化具有以下特点：（1）罕见的特大地震（Mw9.0）使远离震中300～400 km的新近人工填土发生严重的大规模液化;（2）特大地震（Ms8.0、Mw8.8）使远离震中的低烈度Ⅴ～Ⅵ度地区发生严重液化;（3）海岸、河岸附近地区的新近沉积冲积、湖积土,填筑时间不到50年的含细粒、砂砾人工填土,容易发生严重液化;（4）天然的砂砾土层液化发生严重液化;（5）发生了深达20 m的土层液化现象;（6）松散土层液化后可以恢复到震前状态并再次发生液化;（7）高细粒（粒径≤75 ?m）含量≥50%或高黏粒（粒径≤5 ?m）含量≥25%的低-中塑性土严重液化,对介于类砂土与类黏土之间的过渡性态土,有时地表未见液化现象;（8）液化土层的深度较深或厚度较小时,容易出现地面裂缝而无喷砂现象;有较厚的上覆非液化土层时,场地液化不一定伴随地表破坏。液化实例证明,第四系晚更新世Q3地层可以发生严重液化;黏粒含量不是评价细粒土液化可能性的一个可靠指标;低液限、高含水率的细粒土易发生液化,采用塑性指数PI、含水率wc与液限LL之比作为细粒土液化可能性评价的指标是适宜的。综合Boulanger和Idriss、Bray和Sincio、Seed和Cetin等的液化实例调查与室内试验研究成果,建议细粒土液化可能性的评价准则如下：PI ＜12且wc/LL＞0.85的土为易液化土,12＜PI≤20和/wc/LL≥0.80的土为可液化土;PI ＞20或wc/LL＜0.80的土为不液化土。     

A methodology to determine thermal conductivity of soils from flux measurement

Determination of thermal properties of soils (viz., thermal resistivity, thermal conductivity, thermal diffusivity and heat capacity), which primarily influence heat migration through the soil mass, is essential in situations where geomaterials are relentlessly subjected to higher temperatures and temperature variations. These properties of the soil mainly depend upon its type, mineralogy, particle size and gradational characteristics, density and water content. In this context, earlier researchers have determined thermal conductivity of soils by employing a thermal probe (a line heat source), which works on the principle of transient method (TM) of heat conduction. However, this methodology cannot be employed for establishing the heat flow (read thermal regime) through the soil. Hence, development of an alternate technique, which facilitates quantification of temporal and spatial variation of the heat flux and temperature in the soil mass, becomes essential. With this in mind, a methodology to determine thermal conductivity of soils by employing the concept of thermal flux measurement (TFM) has been developed and its details are presented in this paper. Results obtained from the TM and TFM have also been critically evaluated for the sake of validation and generating more confidence in the proposed methodology.     

渤海湾盆地东营凹陷古近系细粒沉积岩特征及沉积环境

随着泥页岩油气勘探的深入,详细解剖细粒沉积岩的岩石类型和组成,对后续储集层研究中优势岩石组合的确立有重要意义。通过岩心观察、全岩X射线衍射等分析手段,以矿物含量和沉积构造作为主要依据,将渤海湾盆地东营凹陷古近系沙三下沙四上亚段细粒沉积岩划分为9种岩石类型,其以纹层状混合细粒沉积岩、块状混合细粒沉积岩、纹层状灰岩、纹层状粉砂质灰岩、纹层状黏土质粉砂岩为主。由特征元素比值Ca/Mg、Na/Al、Fe/Mn、Sr/Ba、V/(V+Ni)值及Ti、Al含量的垂向变化,可知东营凹陷细粒沉积岩在古气候、古水深、古盐度及水体氧化还原性、陆源输入程度等方面的演化具有明显阶段性,其气候在沙四上亚段沉积时期表现为由干冷变暖湿,在沙三下亚段沉积时期呈现暖湿相对湿冷暖湿相对湿热的演化;且在不同的演化阶段,岩石组合及特征均有差异。因此,温暖湿润的气候和陆源输入量的增加有助于纹层状混合细粒沉积岩大量沉积,而较为寒冷干燥的气候和相对低的陆源输入易于沉积纹层状粉砂质灰岩。这一结论有利于深化断陷湖盆细粒沉积岩岩石学的基础研究,可为后续油气勘探开发奠定坚实的基础。     

细粒浊积岩特征、分布及发育机制:以川北唐家河剖面寒武系郭家坝组为例*

细粒浊积岩是一类较为特殊的浊积岩类型,与可用鲍马序列解释的完整经典浊积岩相比,其颗粒粒径明显偏细,小于63μm的颗粒含量超过50%。通过对四川盆地北部唐家河剖面寒武系第二统郭家坝组上部地层的系统研究发现,Stow细粒浊积岩序列发育广泛。该序列下部(T0-T3)主要为极细砂、粉砂与泥质纹层互层,发育微弱冲刷构造和泄水构造等软沉积物变形构造;中部(T4-T6)为泥质层段夹断续粉砂质纹层;上部(T7-T8)转变为均质泥岩段,生物扰动构造发育,整体序列具有正粒序特征。浊积岩序列中碎屑颗粒主要为石英、岩屑和云母,长石少见,杂基含量高;粒度频率分布曲线(直方图)显示颗粒分选性比传统浊积岩好,且自下而上各砂质纹层内颗粒粒径变细;概率值累计曲线表现为“一段式”和“上凸的折线式”2种,且悬浮组分占据了绝大优势;C-M图以平行于“C=M”基线为特征,但受碎屑颗粒粒级偏小的影响,投点整体沿C=M基线向左下偏移,显示该序列具有浊流递变悬浮沉积的特点。结合筇竹寺阶(第二统)沉积背景,认为靠近研究区西北侧的摩天岭古陆为浊积岩发育的主要物源区,台内地形的遮挡为细粒浊积岩的发育提供了良好的地形条件,悬浮搬运和阵发性环境事件(如风暴、洪水等)搬运为细粒沉积物主要的搬运机制。以唐家河剖面为代表的寒武系郭家坝组细粒浊积岩的广泛发育,对于认识四川盆地北缘古地理格局和非常规油气勘探具有重要意义。     

Determination of undrained strength of fine-grained soils by means of SPT and its application in Turkey

The Standard Penetration Test (SPT) is one of the oldest and the most common in situ test used in soil explorations. In the recent years with the advent of new technology and techniques in determining the drawbacks in SPT, several researchers have attempted to correlate corrected field measured values with several soil properties. In this context, corrections applied to field values have become critical. In this study a questionnaire including the performance of the standard penetration test and equipment used in practice in Turkey is circulated in order to determine the relevant correction factors. Thus the appropriate corrections are used in acquiring corrected SPT-N values. The relationships between SPT-N and the undrained shear strength (S_u) are examined from the statistical point of view by taking the test types and SPT corrections into consideration, and comparison is made with previous studies. It is observed that SPT corrections play an important role on the obtained correlation equations. In addition, the importance of the effects of test types on the correlations is also emphasized. The Standard Penetration Test is found to be sufficient for reliable assessment of S_u.     

The 14-year Performance of a Compacted Clay Liner used as Part of a Composite Liner System for a Leachate Lagoon

The migration of contaminants through a 2.9 m thick compacted clay liner (CCL) for a landfill leachate lagoon is examined 14 years after construction. The clay liner formed the lower portion of the composite liner system but the geomembrane (GM) was found to have defects that had allowed leachate to migrate between the GM and CCL. Chloride, sodium, potassium, calcium and magnesium pore water profiles through the CCL are examined. It is shown that chloride migrated approximately 1.7 m into the CCL during the 14 years of the lagoon operation, sodium approximately 1.2 m, and potassium 0.7 m. Diffusion and sorption data from laboratory diffusion testing are utilized in combination with a finite layer contaminant transport model to predict field contaminant migration profiles through the composite liner system and to establish the time of ‘failure’ of the geomembrane at sometime between 0 and 6 years after installation. Relatively high sorptive uptake of potassium by the CCL soil is observed from batch testing and diffusion testing with field data suggesting an even larger amount of sorption. It is hypothesized that organic sludge matter at the base of the lagoon is responsible for potassium uptake from the leachate. This field case highlights the importance of the compacted clay liner as part of the composite liner system in acting as a diffusion barrier during the lifetime of the lagoon as well as using relatively non-conservative contaminants such as chloride and sodium to estimate geomembrane ‘failure’ times     

潜江凹陷潜江组盐间细粒岩沉积特征及其对页岩含油性的控制

江汉盆地是我国典型的内陆盐湖盆地,位于其中部的潜江凹陷发育盐间细粒沉积,近期油气勘探取得突破。为研究其沉积特征及其对页岩含油性的控制,本文基于岩心和多种测试方法将盐间细粒沉积划分出8种岩相,分别是含灰泥质云岩、云质混合细粒岩、泥质混合细粒岩、灰质混合细粒岩、灰质泥岩/泥岩、云质泥岩、硫酸盐质混合细粒岩和云质/泥质钙芒硝岩。岩相组合有A和B两种:A类岩相组合为含灰泥质云岩、云质混合细粒岩和泥质混合细粒岩,夹少量灰质混合细粒岩、云质泥岩、硫酸盐质混合细粒岩和云质/泥质钙芒硝岩;B类岩相组合为云质泥岩、硫酸盐质混合细粒岩、云质/泥质钙芒硝岩,夹少量灰质泥岩/泥岩和泥质混合细粒岩。A类岩相组合富集碳酸盐质矿物且有机质含量高,岩心上表现为灰黑色泥质岩(泥质混合细粒岩和灰质混合细粒岩)与黄褐色云质岩(含灰泥质云岩和云质混合细粒岩)频繁更替,其中夹有白色硫酸盐质岩,呈透镜体状或层状产出,说明当时环境的盐度较低,镜下纹层大部分呈较为连续的微波状或水平状。其沉积特征反映了A类岩相组合的形成环境为还原性较好、盐度较低的深水区。B类岩相组合硫酸盐矿物含量和有机质含量较低,岩心上表现为白色高硫酸盐质岩夹有黑色泥质层或黄褐色云质层,镜下观察为呈菱形片状钙芒硝,常见穿插双晶,可见明显的粒序变化,云质含量高的薄片镜下为无纹层特征。其沉积特征反映了B类岩相组合形成环境为还原性较弱、盐度较高的较浅水域。本研究将V/(V+Ni)、(S₁+S₂)/TOC、Sr/Ba和Ga/C₃₁H指数等地化参数与岩相特征相结合,进一步佐证了上述观点,并且补充说明了A类岩相组合形成于气候湿润的环境,而B类岩相组合形成环境较为干旱,且将盐间沉积划分为B、A、B三个阶段,对其进行了沉积模式的研究。结果表明:第一、三阶段气候干旱且水深较浅,湖水析出大量盐类,主要发育B类岩相组合,且硫酸盐矿物的增加使硫酸盐还原菌氧化有机质,不利于有机质富集;第二阶段降雨增加,大量淡水注入致使水体淡化且深度变深,这时水体分层性较好,还原性较强,发育A类岩相组合,有机质的保存条件好。由此可见,矿物组分上为灰泥质或云质含量高且岩心具有水平层理、镜下纹层特征明显的岩相,以及湿润气候下的还原性较强、盐度适宜且水体分层性好的深水环境等沉积特征,有助于形成含油性较好的页岩。因此,低TOC含量的B类岩相组合不是油气富集的主要岩相,富集的硫酸盐矿物会稀释有机质浓度,岩相所处的高盐度环境也会减缓微生物活动;而高TOC含量的A类岩相组合为油气富集的主要岩相,频繁的降雨稀释水体盐度,为可以产生有机质的浮游微生物创造了良好的环境,且所含云质纹层矿物间孔隙发育,有利于烃类的存储,所以成为该区内的优质烃源岩,是油气勘探开发的有利岩相。     

矿物中稀土元素扩散作用的理论研究及其扩散参数的预测

矿物中的微量元素在地质环境下能否保持有效封闭,主要取决于其扩散性质,而稀土元素(REE)是探讨地质作用过程及其物理化学条件等重要的示踪剂,查明其在不同矿物中的扩散行为对于地学研究具有重要意义.本文通过分析矿物晶格结构和离子类型对元素扩散行为的制约规律,探讨了REE在不同矿物中的扩散迁移在此基础上,利用多元统计分析方法得出扩散参数与扩散体系不同晶体化学参数之间的关系方程,建立了计算1atm、无水环境下REE在不同矿物中扩散参数的多变量模型,由此模型预测的REE在不同矿物中的扩散参数E和lnD0的值,与实验测定结果在实验误差范围内具有很好的一致性.与以往的预测模型相比,多变量模型能更全面地反映扩散体系晶体化学因素对扩散速率的制约.此外本研究结果显示,REE在矿物晶格中扩散作用的主要影响因素是阳离子,而非当前认为的阴离子.