Swell-compressibility characteristics of lime-blended and cement-blended expansive clays – A comparative study

Chemical stabilisation of expansive soils has been quite efficacious in reducing swelling characteristics, namely, swell potential (S%) and swelling pressure (p_s). When chemicals such as lime and cement are added to an expansive clay, flocculation and cementation take place. Flocculation, which is an immediate reaction, is instrumental in reducing plasticity and swell potential significantly. It also reduces the time required for equilibrium heave. This paper presents experimental data on lime-blended and cement-blended expansive clay specimens. Free swell index (FSI), heave, rate of heave and swelling pressure were studied. FSI, heave and rate of heave decreased with increasing lime content and cement content in the blends. But, during a 3-day inundation (a period, generally allowed for the sample to attain to equilibrium heave), cementitious products developed and resisted the applied compressive loads stiffly, resulting in high swelling pressures in the case of lime-blended specimens. Swelling pressure could not be determined in the case of cement-blended specimens. Hence, short inundation tests (inundating the specimens only for 15 minutes) were performed. But, even from these tests, swelling pressure could not be determined for cement-blended specimens. This indicated the development of strong cementitious products in them. It was interesting to find that, in both long and short duration, the lime- and cement-blended specimens attained to equilibrium heave in the same time period. FSI decreased from 185% to 63.63% when lime content was increased from 0% to 4%, and from 185% to 110% when cement content was increased from 0% to 20%. Swell potential reduced by 42.5% at 4% lime and by 46.4% at 20% cement. Swelling pressure increased from 210 kPa to 320 kPa when lime content was increased from 0% to 4%. Linear shrinkage of the specimens also decreased with increasing additive content.     

Modeling of the swelling–shrinkage behavior of expansive clays during wetting–drying cycles

Acta Geotechnica - This paper presents a constitutive model for simulating the swelling–shrinkage volume change of expansive soils during wetting–drying cycles. Based on the concept of...     

Mineral systems and the thermodynamics of selenites and selenates in the oxidation zone of sulfide ores – a review

Mineralogy and Petrology - Contemporary mineralogy and geochemistry are concerned with understanding and deciphering processes that occur near the surface of the Earth. These processes are...     

A brief review of isotopically light Li – a feature of the enriched mantle?

Lithium isotope geochemistry is increasingly being used to trace deep-earth processes, reflecting the observed large variation of Li isotope ratios in mantle-derived rocks, including peridotite xenoliths associated with ancient continents. We briefly review the Li isotopic compositions of major geochemical reservoirs, the assumed mechanisms of Li isotopic fractionation, and, in particular, the origins of isotopically light Li in mantle-derived rocks based on the latest developments in Li isotope geochemistry. Comparison of Li isotope data with existing Sr-Nd isotope ratios reflects the subduction-recycling of ancient oceanic crust and the reappearance of Li in volcanic rocks. This circulation may play an important role in generating the isotopically light-Li component in the mantle – perhaps the enriched mantle end member defined by the Sr-Nd isotopic compositions of oceanic basalts.     

Interpretation of unsaturated soil behaviour in the stress – Saturation space,I: Volume change and water retention behaviour

Unsaturated soil behaviour, such as volume change, shear strength and yield stress, is usually interpreted and modelled in terms of stress and suction. This approach is consistent with laboratory tests where suction is a controllable variable. However, it also suffers some limitations. This paper (Parts I and II) presents an alternative approach for interpreting unsaturated soil behaviour, which is built in the space of stress versus degree of saturation. In Part I, a new volume change equation is proposed in terms of stress and degree of saturation, to give a better explanation to the non-linear change of soil compressibility under constant suctions. The soil compression index is assumed to be a function of the effective degree of saturation and is interpolated from the known compressibility at the fully saturated state and that at a dry state. An alternative approach to simulate hydraulic hysteresis and hydro-mechanical interaction is then introduced, which enables the calculation of the effective degree of saturation under complex stress and suction paths. The proposed volume change equation and the approach to describe saturation variation, which are two fundamental aspects to establish constitutive laws for unsaturated soils, are validated against a variety of experimental data in literature.     

Abrupt climate changes: from the past to the future – a review

 A review of climatic variability is given with a focus on abrupt changes during the last glacial. Evidence from palaeoclimatic archives suggests that these were most likley due to reorganisations of the atmosphere–ocean system. The mechanisms responsible for these changes are presented. Their implication for future climate changes is discussed in light of recent climate model simulations. Received: 24 June 1998 / Accepted: 27 November 1998     

Degree of weathering in the identification of laterite materials for engineering purposes — a review

Laterite materials include a large succession of reddish, tropically weathered, decomposition products starting with fresh rock and ending with sesquioxide-rich pedogenic rock (cuirasse). Identification of the various grades of such materials for engineering purposes is a problem which repeatedly faces the engineer engaged in the design and construction of structures on or with laterite materials.The author has attempted to assemble available information useful for the identification and evaluation of all grades of laterite materials for engineering purposes. In the first part he summarises information on the significant genetic characteristics which appear to underlie the deviation of engineering behaviour of laterite materials from the expected properties based upon conventional soil mechanics as developed for temperate-zone soils.The second part summarises available information on the identification of significant geotechnical properties of various grades and genetic groups of laterite materials for engineering purposes.The engineering behaviour of laterite materials forms the substance of the third part of the paper.A literature study has revealed that the geotechnical characteristics and engineering behaviour of laterite materials depend mainly on the genesis and degree of weathering (i.e., decomposition, laterisation, dessication and/or hardening). Other significant genetic characteristics include morphological characteristics as well as the type and content of secondary minerals.Progress in the field of identification and evaluation of laterite materials for construction appears to depend on the simultaneous consideration of all the major factors which affect the behaviour of rocks and their derived soils (i.e., rock type, weathering condition, degree of weathering, type of derived materials as well as their chemical and mineralogical composition).Such an approach is desirable to increase the accuracy of predictions and assessments of the engineering behaviour of most laterite materials.     

Swelling behaviour of expansive soil treated with fly ash–GGBS based binder

In this article, the potential of a binder developed by admixing fly ash and ground granulated blast furnace slag (GGBS) to stabilise expansive soils is evaluated. Laboratory tests included determination of free swell index, swell potential and swelling pressure tests of the soil/binder mixtures at different mixing ratio. The test results showed decrease in the swelling behaviour of the soil with increase in binder content. The percent swell–time relationship was observed to fit the hyperbolic curves enabling us to predict the ultimate percent swell from few initial test results. Addition of 1% of lime to the binder showed further improvement in reducing swelling. A good linear relationship is established between percent oedometer swell and modified free swell index (MFSI) for soil/binder mixtures without lime but the same has not been observed in the presence of lime. The compressibility characteristics of the soil/binder mixtures reduced nominally with increase in binder content but in the presence of lime, the compressibility reduced significantly. Binder used in this study has been found to be effective and economic to stabilise expansive soils with lesser amount of chemical additives such as lime.     

The Zaghawa and the Midob of North Darfur – A comparison of migration behaviour

Two ethnic groups of North Darfur, the Zaghawa and the Midob, are being compared as regards their migration behaviour and their identification in their destination areas. Both groups have severely suffered as a result of the drought phase of the last three decades, during which more than half of the Zaghawa and Midob have migrated southwards and to the towns. Despite the similarity of the two ethnic groups, being non-Arab agropastoralists who are socially and politically marginalised both within Darfur and within the Sudan, they show marked differences in their migration behaviour and ethnic solidarity. The Zaghawa migrants are considerably more economically successful than the Midob migrants. The main reasons are: – The Zaghawa started their outmigration earlier than the Midob. Thus, they could establish ethnically-based networks in Libya and the Gulf countries, to which Zaghawa migrants can resort to make a good start in their destination areas. By the time the Midob started their migration in the 1980s, the conditions of employment in the Arab oil countries had worsened. – The Zaghawa show a strong clan solidarity. They readily lend money to young members of their clan to cover the high costs of travelling to the Arab oil countries for work, where many of them have already established themselves. – The Midob, both in the Sudan and abroad, have much less resources available. The only country open for them outside the Sudan is Libya. Lacking capital, the Midob go there on camels, mostly illegally. Having no connections in Libya, except those to other poor Midob there, they usually try to work in herding sheep and goats, which is not a lucrative profession. This revised version was published online in July 2006 with corrections to the Cover Date.     

Calibration of the parameters for a hardening–softening constitutive model using genetic algorithms

The present paper introduces a genetic algorithm-based optimization technique to calibrate a nonlinear strain hardening–softening constitutive model for soils using five material parameters. The efficiency of the proposed technique is analyzed through the use of different GA techniques. The effects of elitism, crossover, and mutation, as well as population size, on the performance of the conventional GAs for this problem are investigated. Micro-genetic algorithms (mGAs) are chosen and tested for different population sizes. The mGAs with a population size of five yields the optimal parameter values after fewer function evaluations and capture the overall simulated or experimental behavior at every point in stress–strain and strain paths in triaxial compression. The proposed calibration technique is validated through comparison with the traditional calibration technique.     

Tectonic controls of the onset of aeolian deposits in Chinese Loess Plateau – a preliminary hypothesis

Previous studies show that the thick aeolian dust deposits in the Chinese Loess Plateau (CLP) have accumulated since the early Miocene or even late Oligocene. They are considered to provide the best terrestrial record for the onset of Asian interior aridification and the evolutionary history of the Asian Monsoon. However, large variability in the basal ages of aeolian deposits makes the aeolian dust depositional history and the controlling dynamics controversial. Here, we present a preliminary hypothesis for the tectonic controls of aeolian dust deposition in the CLP by connecting the two main uplift events of the Tibetan Plateau and the regional tectonic events with the aeolian dust accumulation history. Regional tectonic events in the Ordos Block (the basement of the CLP) during the late Cenozoic are less recognized as controlling aeolian dust accumulation by sculpting the surface landscape. The stable tectonic environment of the Ordos Block since the late Miocene might have been the main controlling factor that enabled the widespread deposition of the aeolian red clay after ~8 Ma. Here, we hypothesize that because the large-scale monsoon system and central Asian aridity had existed since at least the early Miocene, the accumulation and preservation of aeolian deposits within the CLP are actually largely controlled by the regional tectonic environment and less by climatic factors.     

The Characteristics of Fluorine in the Groundwater of North China and the Significance of Fluorite-Water Interaction to Fluorine Transportation

This paper approaches the transportation of fluorine in the groundwater ofepigene Quarternary aquifer by calculation and laboratory studies.The conclusionthat the enrichment and saturation abilities of fluorite are related to the transpor-tation of fluorine in groundwater is reached.They would be conducive to findingthe cause of regional fluorine distribution in the groundwater of North China.     

The Environment Significance of Aerinite——First Discovered in the UBC Cliffs

To analyze the composition and structure of the pale blue outcrop from the UBC Cliffs and research the environmental significance of aerinite recorded in the sediments, mineral composition, bulk chemical composition and structural analyses were carried out by means of X-ray diffraction(XRD), field emission scanning electron microscope(FESEM), transmission electron microscope(TEM), electron microprobe analysis(EMPA) and X-ray fluorescence spectra(XRF). Quartz, feldspar, mica, chlorite and aerinit...     

Determination and Significance of the Bluemull Blastomylonite Zone in the Northeast——East of Yell,Shetland

There is a zone of blastomylonites containing hornblende gneisses of Lewisian Inliertype in the northeast-east of Yell,Shetland.This zone with a north—northwesterlytrend consists of blastomylonised hornblende-banded gneiss,hornblende-feldspar gneissand mica-felsie-gneiss with lenses of hornblende gneiss.It is indicated that theblastomylonite zone is actually a ductile shear zone and the sense of shear is dextral.This contributes to understanding the details of tectonic evolution in this area,and thiszone is probably a part of tectonic system of the British Caledonides.     

Changes in the HOAr isotope composition of clays during retrograde alteration

K-Ar ages of illite alteration associated with Middle Proterozoic Athabasca unconformity-type U deposits in Saskatchewan range from 414 to 1493 Ma. The K-Ar ages correlate with water contents and δD values such that illites with young K-Ar ages have δD values as low as −169 and water contents as high as 7.7 wt.% whereas illites with older ages have δD values near −70 and water contents near 4 wt.%. Water extracted at 400°C from illites with low δD values and high water contents has low δD and δ¹⁸O values similar to those of modern meteoric water suggesting that some of the illites associated with the original deposition of the ore underwent varying degrees of retrograde alteration. The alteration is initiated by hydration of sites in the interlayer region of the illite which results in the partial resetting of the K-Ar ages and introduction of excess structural water in the form of interlamellar water. The interlamellar water is enriched in ¹⁸O by about 7 per mil relative to the water that physically surrounded the clay particle. Further alteration decreases the δD value and increases the δ¹⁸O value of the illite by isotopic exchange between the mineral and the interlamellar water. Although the chemical compositions and XRD patterns of the altered illites indicate that no detectable smectite component is present in the samples, the isotopic results suggest that the altered illites may be an early precursor in the formation of mixed-layer illite/smectite by retrograde alteration of pure illite. The wide variation of δD values of chlorite and kaolinite from these U deposits is analogous to that of the illite suggesting that retrograde alteration of clays by meteoric water can be substantial. The general association of altered clays with areas containing the highest concentrations of U is probably related to localized permeability within the ore zone.     

Discovery of a Huge Early Permian Reef Zone and Its Significance in theTethyan Evolution

AhugeEarlyPermianorganicreefzonehasbeendiscoveredrecentlyintheEastKunlunMts.ofsouthernXinjiang,duringajointgeologicalsurveyofChina--France.Thereefzonecropsoutonbothlimbsofacompoundsynclinewhichisabout25-50kmwideinSNdirection,andextendsabout300kminEWdirection,fromtheBuhadabanPeaktothewesternAqikekuleLake,whichformsthemainridgeoftheEastKunlunMts.Thestrataofthereefzoneare3000-4000minthickness,whichfarexceedsthatofPermianreefspreviouslyreportedinChina,e.g.ca.100mthickinthenorthwesternHunan…     

A laboratory study of the self sealing behaviour of a compacted sand–bentonite mixture

Bricks made of compacted sand–bentonite mixture are considered as a possible engineered barrier to isolate high-level radioactive waste at great depth. This work is aimed at investigating some specific effects related to the presence of discontinuities at the contact between the bricks and the excavation wall. In order to do this, an experimental device was developed in the laboratory. The model is made up of a specially designed infiltration cylinder which allows the precise definition of a planar discontinuity between the compacted specimen (a sand–bentonite mixture made up of sand and Kunigel clay from Japan) and a metal wall. During hydration and subsequent specimen swelling, the planar wall is filled, resulting in a healing process. Three total pressure gauges placed along the wall allow a detailed observation of the increase in total stress against the wall. After different periods of swelling, the maximum resistance of the specimen–wall interface to pressure was tested by imposing a pressure increase through a porous stone placed at one end of the cylinder. It was found that the maximum pressure supported by the interface is a function of the initial thickness of the discontinuity and the initial density of the specimen. It was also found that the maximum sustainable pressure depends linearly on the elapsed time. These results are of interest for optimizing water infiltration procedures in either mock-up tests or real disposal systems. If the maximum sustainable pressure at the interface is known, it is possible either to ensure homogeneous hydration of a mass of bricks by respecting the maximum injection pressure limit or to accelerate hydration by forcing water paths along the discontinuities.     

Andean oblique folds in the Cordillera Oriental – Northwestern Argentina: Insights from analogue models

The dominant Cenozoic structural grain in northwestern Argentina trends north–south. However, several oblique folds have been mapped, mainly in the Cordillera Oriental and the Sistema de Santa Bárbara. Two oblique NE–SW-trending anticlines are well exposed in the Luracatao Valley-Salta, along the western border of the Cordillera Oriental. These oblique anticlines are defined by the Palaeogene Santa Bárbara Subgroup and are cut by the reverse faults bounding the Luracatao Valley. We constructed analogue models to simulate the generation of oblique NE–SW anticlines inside the narrow, trough-like Luracatao Valley. Orthogonal compression and basement oblique heterogeneities, oblique compression and basement oblique heterogeneities, and oblique compression configurations were tested in the models. The first two configurations simulate the anticline formation well. In addition, we analyse dextral rotation and the influence of Neoproterozoic basement/Cretaceous rift structures as the cause of the oblique orientation. The analogue models suggest pre-Andean oblique structures controlling the oblique orientation of these Andean folds despite being a second-order planes of weakness.