Clay Mass Research Articles

On the thermal consolidation of Boom clay

When a mass of saturated clay is heated, as in the case of host soils surrounding nuclear waste disposal at great depth, the thermal expansion of the constituents generates excess pore pressures. The mass of clay is submitted to gradients of pore pressure and temperature, hydraulic and thermal flows, and changes in its mechanical properties. In this work, some of these aspects were experimentally studied in the case of Boom clay to help predict the response of the soil, in relation to investigations in the Belgian underground laboratory at Mol. Results of slow-heating tests with careful volume change measurements showed that a reasonable prediction of the thermal expansion of the clay-water system was obtained by using the thermal properties of free water. Despite the density of Boom clay, no significant effect of water adsorption was observed. The thermal consolidation of Boom clay was studied through fast-heating tests. A simple analysis shows that the hydraulic and thermal transfers are uncoupled. Experimental results from fast-heating tests showed that the consolidation coefficient does not change significantly with increased temperature, due to the opposite effect of increasing permeability and decreasing porosity. The changes of permeability with temperature were investigated by running constant head measurements at various temperatures. An indirect analysis, based on estimation of the coefficient of volume change mv, showed that the indirect method of estimating the permeability from consolidation tests should be considered carefully. Intrinsic permeability values were derived by considering the change of the viscosity of free water with temperature. A unique relationship between the intrinsic permeability and the porosity was observed, with no dependence on temperature, confirming that the flow involved in the permeability test only concerns free water.Key words: clays, thermal consolidation, adsorbed water, permeability, temperature effects, radioactive waste disposal.

COMPARISON OF GROUNDWATER COLLOIDS IN ADJOINING SOILS OF FLORIDA FLATWOODS1

Colloids in soil water are a constituent of natural geochemical fluxes and have the potential to facilitate contaminant transport, but few data are available on their composition and concentration. This study addresses how the composition and concentration of groundwater solids relate to hydrological and soil morphological variables of the Florida flatwoods landscape. Groundwater from saturated soil horizons was sampled biweekly for 1 year along an Aquod/Udult boundary using piezometers designed specifically to minimize disturbance and to permit the valid assessment of suspended solids. Readily dispersible clay from core samples of soil horizons was collected and quantified. Groundwater and soil colloids were analyzed physically, chemically, and mineralogically. Aquod groundwater had consistently lower pH, higher electrical conductivity, and more total solids (TS) and organic carbon (OC) than did Udult groundwater. Significant decreases in both TS and OC concentrations in groundwater occurred with depth for both soils. In contrast, the mineralogy of groundwater colloids was insensitive to soil and horizon differences. Quartz dominated inorganic colloid fractions in groundwater samples from all horizons, even in argillic horizons where clay fractions contained little or no quartz. No statistical correlations were found between masses of groundwater colloids and soil water-dispersible clay. However, the proportion of organic carbon was higher in groundwater than in soil matrices. Results are consistent with carbon and colloidal quartz movement in shallow groundwater of the soils studied and document that natural colloid and solute fluxes can be highly soil specific.

Thermal Conductivity of Soils at Very Low Moisture Content and Moderate Temperatures

An analysis of soil thermal conductivity data shows that, at very low moisture content, this property first varies insignificantly and then begins to increase from a certain critical moisture content, whose value tends to depend on clay mass fraction. Two simple models evaluating the critical moisture content were developed; the first one is a fraction of the permanent wilting point; the second one is a simple linear function dependent on clay mass fraction. An insignificant variation of soil thermal conductivity is observed at 20°C, within a water pressure head ranging from 1 × 103 to 1 × 103 m, while for higher temperatures (45–50°C) from 5000 to 100000 m. Three extensions of the enhanced thermal conductivity model by Sundberg, namely SUN-1, SUN-2 and SUN-3, were proposed and tested. They produce an average root mean square error of 27%, 24% and 30%, respectively, with respect to experimental data. SUN-1and SUN-2 predictions could be further improved if better estimates of thermal conductivity at the dry state and the permanent wilting point were provided. SUN-3 is a simple model which does not require information about the PWP and critical moisture content. All SUN models have a potential for implementing the latent heat transfer component.

Investigation of a landslide in Maskinongé, Québec

Several first-time landslides occurred in the Maskinongé area, Quebec, during the summer, which is rather unusual. They have been studied in detail, including a site investigation. The results show the following: (i) piezocone tests indicate that the clay mass close to the slopes of precarious stability is softened; (ii) the failure surface develops within the softened zone; and (iii) three of the four landslides occurred during the summer period when pore pressures are low, indicating that failure could be due to fatigue phenomena.

Mechanical interaction between swelling compacted clay and fractured rock, and the leaching of clay colloids

We consider the interaction between a saturated clay buffer layer and a fractured crystalline rock engineered disturbed zone. Once saturated, the clay extrudes into the available rock fractures, behaving as a compressible non-Newtonian fluid. We discuss the modelling implications of published experiments carried out in Sweden and more recently in Japan. Extrusion is halted either when the advancing clay front reaches a narrow enough aperture along the fracture (relative to the yield stress of the gel-like front), or when enough of the clay mass has extruded so as to reduce the density back in the buffer, and hence the swelling pressure (which is exponentially dependent upon density). In the latter case a relatively small reduction in density may be sufficient. As the clay extrudes, the gel-like front may be a source of clay colloids, being sufficiently hydrated so as to allow clay platelets to escape the matrix and diffuse away. We show that such mass loss is limited as a mechanism for leaching away the emplaced barrier, yet may still be significant in mobilising otherwise highly sorbing radionuclides within the buffer.

Investigation of a landslide in Maskinongé, Québec

Several first-time landslides occurred in the Maskinongé area, Quebec, during the summer, which is rather unusual. They have been studied in detail, including a site investigation. The results show the following: (i) piezocone tests indicate that the clay mass close to the slopes of precarious stability is softened; (ii) the failure surface develops within the softened zone; and (iii) three of the four landslides occurred during the summer period when pore pressures are low, indicating that failure could be due to fatigue phenomena.

CHARACTERISTICS OF SOILS ON DEBRIS APRONS IN THE SOUTHERN BLUE RIDGE, NORTH CAROLINA

Aprons of bouldery diamicton frequently have been observed in concave landscape positions in the Southern Blue Ridge. Because of their relatively flat topography, large aprons often are the focus of local economic activity. An environmentally sound development of these landforms can benefit from systematic pedological studies. The present research provides characterization data, and examines spatio-geomorphic variability, for some pedons that have developed on these debris aprons under a warm to temperate humid climate. This study also compares the pedons to those derived from nearby saprolite. Thirteen pedons, located variously on the foot slopes and the apices of the aprons, were studied in three sequences of multiple deposits. The pedons typically contain high amounts of rock fragments and have clay contents that are related to age. Most pedons have lithologic discontinuities. Some of these discontinuities result from the stacking of different deposits, whereas others represent internal variations within one deposit. Because of the heterogeneity in parent material, many soil characteristics do not possess systematic trends with depth. Depth to maximum clay mass and free-iron mass accumulation, however, systematically increase from foot to apex positions, and from topographically low to high deposits. deposits. [Key words: debris flows, soils, lithologic discontinuities, Blue Ridge.]

Making building products by extrusion and cement stabilization: limits of the process with montmorillonite clay

The addition of cement to a montmorillonite clay does not result in an adequate stabilization of end products which are extruded. This can be explained as follows: firstly, Ca 2+ ions of the binder are adsorbed by montmorillonite preventing the hydration of the binder and secondly, montmorillonite is very susceptible in contact with water because of its expansive property. Other mixtures have been tested by substituting progressively montmorillonite by kaolinite which has been successfully used in some previous research works. A `stabilization threshold'—corresponding to the minimum amount of montmorillonite and defined by a water resistance criterion—allows to determine under which conditions extrusion is possible. It appears that clay masses containing more than 5% montmorillonite cannot be stabilized with economically justified amounts of cement. Silico–aluminous fly ash has been used in such cases in order to benefit from the filler and possibly pozzolanic effects of this additive. The use of fly ash allows also to contribute to the problems of waste elimination. The results show that the products containing fly ash have a good dimensional stability, water resistance and mechanical properties. A small quantity of montmorillonite (5%) acts in such a case as a plasticizer.

The role of lime migration in lime pile stabilization of slopes

Abstract Lime piles, which essentially consist of holes in the ground filled with lime, have been successfully used worldwide for the in situ treatment of failing clay slopes. The literature on the technique does not, however, permit a full explanation as to why lime piles work or how to design them. It is widely reported that migration of the lime from the piles into the surrounding clay provides the major stabilizing mechanism. This paper aims to review the literature on lime migration from piles and to report the results of recent research at Loughborough University to determine migration mechanisms from compacted quicklime piles. Potential applications are then discussed in the light of the findings. Hydroxyl (OH - ) ion migration by diffusion processes in intact clay is shown to be limited by high reactivity to approximately 20-30 mm. Nevertheless hydraulic transport via dehydration cracking or other discontinuities in the clay mass could result in migration extending for far greater distances. Calcium (Ca 2+ ) ion migration, would be expected to occur over distances greater than 1 m in ten years. Thus while full clay stabilization might only occur to a limited degree, modification of the clay is likely to be widespread. Mineralogical changes indicate a strength gain equivalent to that of lime mixed with clay at the initial lime consumption (Eades & Grim 1966) value plus 2% and cured for 28 days.

Occurrence and mineralogy of a deposit of shampoo-clay in southern Iran

The mineralogy and occurrence of an Iranian clay size deposit, locally called ‘Gel-E-Sarshour'’ or shampoo-clay, was studied. The material is mined from shallow subsurface channels of 25 to 50 m in length which occur on hilly landforms of limestone outcrops associated with the Cretaceous Jahrom Formation in S-Iran. Clay masses (1 to 2 m thick) inside caves are wet and plastic with dominantly gray colors and sandwiched between two layers, of dense dolomitic limestone. The clay is extremely hard with a soapy feeling upon dehydration. After wetting and mixing with some rose water for the purpose of fragrance, the substance is mainly used as a shampoo (to combat dandruff and excessive greasiness) because of its swelling property, high specific surface and absorption capacity (especially Mg). The powdered form is used for treatment of burns, rashes, and also as a deodorant, poison absorbent and soil conditioner. Upon hydration, it forms gel-like masses and swells in excess of its original volume. The mineralogy of the Zarrin-Mine bentonite, which is mined in Iran and used by oil companies, was also studied as a reference. The study carried out by XRD, IR and chemical analysis has shown that the main component of the Gel-E-Sarshour clay is a dioctahedral smectite of high layer charge, with minor amounts of mica, vermiculite and quartz.

Hydrological triggering conditions of landslides in varved clays in the French Alps

In this paper the meteorological and hydrological conditions are analyzed which trigger shallow and deeper landslides in glacio-lacustrine deposits (varved or laminated clays) in the French Alps. The hydrological system of these landslides consists of a colluvial cover which supplies water into the fissures of the underlying varved clays. From these fissures water can infiltrate more or less horizontally into the silt layers of the varved clays. A combined reservoirs model was used to simulate the water fluctuations in the colluvial cover and the fissures. Both the water level in the fissures and the residence time of water in the fissures are mainly controlled by the amount of water storage in the colluvial cover. Simulations over the last 25 years show that almost each year the fissures are completely filled with water for several months a year. Infiltration experiments in the field show that infiltration into the varved clays occurs mainly by horizontal infiltration into the silt laminae. Calculated infiltration rates from these fissures into the silt layers show that the mean yearly residence time of water in the fissures is not sufficient to fully saturate the clay mass each year. It is therefore concluded that the triggering of the landslide movements is mainly controlled by the development of positive pore water pressures in the fissure system and that the rise of pore water pressures induced by the matrix system of the varved clays only plays a minor role. The calculations also show that drainage of the colluvial cover is a very efficient measure to stabilize the deeper landslides.

Leaching of salt from a heavy clay subsoil under simulated rainfall conditions

A considerable proportion of the water from low and high intensity applications (2 and 108 mm day t-1 falling on an unsaturated saline and sodic clay subsoil moved rapidly down through the soil profile via the macropores, and was capable of efficiently leaching salts from the unsaturated clay mass. The high efficiency of leaching indicates that saline sodic clay soils in temperate climates, such as those in the Hoo Marshes, might be more safely and more cost effectively drained by means of surface drainage systems rather than buried pipe drainage systems.

Temporary industrial binders for molding of industrial ceramics (Review)

The basic stages of the evolution of the technology for ceramic and refractory materials are directly related to refinement of the temporary industrial binders (TIB) used. This constituent of the molding mass and semifinished product determines the properties of the finished product to a significant degree. The information on TIB formulations is primarily concentrated in the patent literature. The number of studies and reviews of the main problems in making up molding masses, the reaction of the TIB with the ceramic solid phase, and planning of the industrial binder with consideration of the requirements for the finished products is limited [1-3]. This is partially due to the lack of unambiguous criteria for evaluating the quality of the masses and selecting binders and the complexities of using the experimental apparatus for methods of physical and colloid chemistry, mechanisms of disperse systems, and the physical chemistry of polymers. This is because dilute solutions, and not the concentrated solutions typical of ceramics technology, solutions of macromolecular compounds (MMC), and highly disperse fillers are the traditional objects. Due to the necessity of molding semiproducts of complex shape with elevated requirements for surface quality, geometric dimensions, and homogeneity, the urgency of developing new binder compositions has now increased significantly. The analysis of the assortment and trends in the development of TIB formulations can also be useful to some degree in creating new technological solutions. The requirement of increasing the level of the electrophysical properties of sparkplugs for internal combustion aircraft engines has led to the exclusion of clay plastic components from the composition of steatite masses and made it necessary to add molding powder to the composition to give the solution of polyvinyl alcohol (PVA) the required technological properties. The first publications on this problem date back to the mid-1940s [4, 5]. The tendency to reduce or eliminate some of the plastic components in the formulations for ceramic and refractory masses and to use temporary binders in ceramics technology has been tracked since the end of the 1930s. In the 1940sbeginning of the 1950s, a wide range of TIB based on aqueous solutions of natural and partially artificial macromolecular substances and products were used in production: flour, starch, gelatin, cellulose derivatives, alginates, and resins [6-8]. Generalization of the studies published in this period led to the formulation of principles for classification of TIB for molding of semiproducts of the basic kinds of industrial ceramics based on the origin and chemical nature of the polymer [9, 10]. Hypotheses were advanced in the same period concerning the complex physicochemical reactions in the ceramic material-MMC solution system [8], and the role of the viscosity of the dispersion medium in molding was emphasized [11]. Two limiting cases of the reaction in the ceramic material-TIB system and formation of the molding mass were formulated in 1961 [12]: due to the high viscosity of the dispersion medium (resin, petrolatum, etc.) in the almost total absence of any reaction between disperse phase and dispersion medium; with a strong reaction between TIB and solid phase and formation of cross-linked layers on the phase boundary with properties different from the properties of the dispersion medium in bulk. For the first time, a hypothesis was thus advanced concerning the possibility of formation of a plastic molding mass due to forming of interfacial boundary structures with anomalous properties. In the same period, an analogy was drawn in [13] for the structure of plastic hydrate-gel shells in clay masses and the boundary layers in dispersions of the oxide material- MMC

Lois d'écoulement des laves torrentielles boueuses

Debris flows are large masses of water, clay, silt, sand, pebbles and boulders which sometimes flow in mountain streams after long or intense rains and can cause much damages to inhabited areas. Muddy debris flows which are the most common in France exhibit a Herschel-Bulkley behaviour. Here we present theoretical tools for predicting steady free surface debris flows. We first show the fundamental feature of channelized debris flows : an unsheared zone (called plug) within the material. For flow on an infinitely wide plane one can easily compute flox characteristics. From these formulae we deduce an expression for the wall shear stress. We also propose other expressions, established empirically, which may be used for flow in rectangular or trapezoidal channels. We then show that global steady flow characteristics are similar to water flows (supercritical and subcritical regimes, hydraulic jump, rol waves). Nevertheless flow through singularities are somewhat different (dead zones formation).

Rhéologie des laves torrentielles

Click to increase image sizeClick to decrease image sizeDebris flows are large masses of water, clay, silt, sand, pebbles and boulders which sometimes flow in mountain streams after long or intense rains and can cause much damages to inhabited areas. We assume that these materials can be considered as homogeneous fluids. Usual hydraulic methods do not allow to predict natural flows of these non-Newtonian fluids. To make progress in this way the basic tool is the constitutive equation of the material. In this paper we review our present knowledge in the field of rheological properties of the various possible water-debris mixtures. Thus we demonstrate that it is possible to distinguish two main debris flow types : muddy debris flows, which contain at least a moderate clay fraction (> 10 %) and exhibit simple shear behaviour which may be fitted by a Herschel-Bulkley model ; granular debris flows, which contain a very low clay fraction (< 1 %)and exhibit a simple shear flow curve with a minimum. All these materials exhibit a yield stress (flow threshold) which is a key rheological parameter. We review the main practical techniques to estimate this yield stress.

Clay Diagenesis and Mass Balance—The Forest and the Trees

Clay Diagenesis and Mass Balance—The Forest and the Trees

Branched-Pore Kinetic Model for Basic Dyestuff Adsorption onto Natural Clay

The adsorption of Basic Blue 69 from aqueous solution onto natural clay has been studied using an agitated batch adsorber. The branched-pore kinetic model (BPKM). based on external mass transfer, macropore diffusion and micropore diffusion, has been used to predict the performance of a batch adsorber. A computer program has been developed to generate theoretical concentration-time curves and these results adjusted to experimental concentration-time curves by a ‘best fit’ approach. A sensitivity analysis has been performed to study the effect of the main mass-transfer parameters, Ks, Ds, Kb and f, on the shape of the concentration decay curves. The variables of initial dye concentration and natural clay mass have been successfully correlated using constant values of the mass-transfer parameters Ks, Ds, Kb and f. The Ks value is (3.7 ± 0.1) × 10−3 cm/s, the Ds value is (2.6 ± 0.1) × 10−8 cm2/s. the Kb value is (1.7 ± 0.1) × 10−7 cm/s and finally the f value is 0.56 ± 0.01. The micropore diffusion terms enable the concentration decay curves to be predicted accurately for a longer period of time than in previous models.

Pore pressure dissipation of highly fissured clays : Federico, F; Musso, A Proc 10th European Conference on Soil Mechanics and Foundation Engineering, Florence, 26–30 May 1991V1, P77–82. Publ Rotterdam: A A Balkema, 1991

One-dimensional consolidation of intensely fissured clay masses accounting for fluid exchange between fissures and pores is investigated. As main results, layer thickness does not seem to play the same paramount effect as in classical theories and the use of consolidation coefficients inferred from settlements of small laboratory samples is questioned. For the analysis of pore pressure dissipation, an analog model, made out of elastic springs and pistons inserted in communicating fluid-filled boxes, has been envisioned; the equalizing effect of the saturated porous disc at the base of the sample in a test cell is considered. The behavior of the analog model, discussed on the basis of experimental data, suggests that measurement of interstitial pressures in intensely fissured clays might be affected by important limitations.

A novel technique of electrical strengthening of soft sensitive clays by dielectrophoresis

A novel technique of electrical strengthening of soil by dielectrophoresis was developed. The process employs an alternating current at high voltage, generating a converging electric field towards the electrode by which a net resultant movement of water in the clay mass is produced towards the direction of stronger electric field intensity. Laboratory tests were developed to investigate the mechanism of this process and to explore the possibility of its application in electrical strengthening of soft sensitive clays. The preliminary results of this study showed that the process is effective, and the shear strength of the treated clay (Wallaceburg clay) increased drastically by several times with a reduction of moisture content of approximately 25% at an applied electric potential of 20 kV for 28 days. When compared with electro-osmosis, similar results are obtained in dielectrophoresis, such as the increase in preconsolidation pressure, decrease in sensitivity, and improvement of stress–strain behaviour. It is also shown that the improvement of soil properties can be greatly enhanced by increasing the applied voltage and electrode depth. Key words : dielectrophoresis, alternating current, converging electric field, high-voltage electrode, dielectric constant, electro-osmosis, soft sensitive clay, shear strength, consolidation.

Pore Diffusion Model for the Adsorption of Basic Dyestuffs onto Natural Clay in Batch Adsorbers

The adsorption of basic dyestuffs (Basic Blue 69 and Basic Red 22) onto natural clay has been studied using a series of batch adsorption runs. The pore diffusion model (PDM) has been developed based on external mass transfer and pore diffusion to predict the performance of a batch adsorber. A computer program has been developed to generate theoretical Sherwood number-time curves and these results were adjusted to experimental Sherwood number-time curves by means of a ‘best fit’ approach. The variables of initial dye concentration and natural clay mass have been successfully correlated using a single external mass-transfer coefficient, Ks, and a single effective pore diffusion coefficient, Deff. The Ks values are 3.3 × 10−5 and 2.6 × 10−5 m/s for Basic Blue 69 and Basic Red 22, respectively. The Deff values are 7.3 × 10−10 and 9.6 × 10−10 m2/s for Basic Blue 69 and Basic Red 22, respectively.