Expansive clays

A DUAL POROSITY MODEL FOR CONTAMINANT TRANSPORT IN EXPANSIVE CLAYS... 

In this article we propose a homogenized form of the modified convection-diffusion equations to describe contaminant transport in expansive clays char-acaterized by three disparate length scales and two levels of porosity. The microscale consists of macromolecular structures saturated by an electrolye... 

A Dual Porosity Model for Contaminant Transport in Expansive Clays 175... 

Slickensides are easily observable shiny planes of weakness along which movement occurs in shrink-swell medium-to-heavy clay soils. These are shearing faults, which exist permanently in wet or dry expansive clays. They take the form of cracked, polished, or grooved surfaces, ranging from 10 mm to 200 mm across. Slickensides often run through the soil mass in many directions and may break the structure up into bowl-shaped blocks. They can move up to 25 mm per year. Hence, the frequency and size of slickensides present can quantify the potential capacity of the soil to shrink and swell (i.e., develop cracks when dry). Soils or soil layers with slickensides are highly impermeable to water movement, especially when they are moist and root growth is restricted. 

Figure 2. Effect of water on specimens containing 25% expansive clay by volume. Disintegration time depends on volume of clay present as little as 1/2% by volume of clay will cause failure.

The loosely anchored indigenous particles can be categorized into two major groups expansive authigenic clay minerals and nonexpansive clay minerals. A simple kinetic expression is set up for the generation of these indigenous fines. The variable r represents the fraction of expansive clay minerals with respect to the total releasable fines, ap. ... 

Villar, M.V., and Lloret, A., Variation of the intrinsic permeability of expansive clays upon saturation measurement with gas and water. Clay Science for Engng. Balkema 259-266, 2001. 

In relation to radioactive waste disposal, during last years a number of laboratory results referring to thermal effects on saturated soils have been presented (Baldi et al. 1988, Towhata et al. 1993, Tanaka et al. 1997, Sultan et al. 2002, Burghignoli et al. 2000). However, results focused on the thermal influence on volume change behaviour of unsaturated soils are still limited (Wiebe et al. 1998, Romero et al. 2003). In particular, information concerning the temperature effects on the mechanical behaviour of highly expansive clays in unsaturated conditions is still scarce (Lingnau et al. 1996, Romero et al. 2001). 

The results of swelling tests are shown in Figure 7, in which the dispersion of data can be mostly attributed to the variations in dry density caused by the small displacement allowed by the equipment. A clear decrease of swelling pressure as a function of temperature is observed. This behaviour is well-matched with the observed increase in the compressibility of the bentonite in the compression tests and the reduction of swelling strains in the soaking tests. Lingnau et al. (1996) and Romero et al. (2003) found also a reduction in swelling pressure with temperature for a sand/bentonite mixture and for a moderately expansive clay, respectively. 

Alonso, E.E., Vaunat, J. Gens, A. 1999. Modelling the mechanical behaviour of expansive clays. Eng. Geol. 54 pp. 173-183. Baldi, G., Hueckel, T., Pellegrini, R. 1988. Thermal volume changes of mineral-water system in low-porosity clay soils. Can. Geotech. J. 25(4) pp. 807-825. 

Alonso, E, J Vaunat A Gens (1999) Modelling the mechanical behaviour of expansive clays. Engineering Geology. 54 173-183. 

Kessler D, Marsh CP, McCormick JJ, Cropek DM, Deguzman AR, Robles R, Gent D. (2004). Investigation of Cyclodextrin-Enhanced Electrokinetic Soil Remediation Fate and Transport of Nitroaromatic Contaminants and Cyclodextrin Amendments in Expansive Clays. ERDC-CERL TR-04-3. 

Coating systems that are susceptible to disruption by backfill settlement and expansive clays will also be prone to failure under the action of soil creep on unstable slopes. 

Intraparticle swelling (i.e. swelling due to the take up of water - not only between particles of clay minerals but also within them - into the weakly bonded layers between molecular units) of clay minerals on saturation can cause mudrocks to break down where the proportion of such minerals constitutes more than 50% of the rock. The expansive clay minerals such as montmorillonite can expand many times their original volume. 

The maximum movement due to swelling beneath a building founded on expansive clay can be obtained from the following expression ... 

Desiccation cracks may extend to depths of 2 m in expansive clays and gape up to 150 mm. The suction pressure associated with the onset of cracking is approximately pF 4.6. The presence of... 

Bell, F.G. and Maud, R.R. 1995. Expansive clays and construction, especially of low-rise strucfures a viewpoint from Natal, South Africa. Environmental and Engineering Geoscience, 1, 41-59. 

The aim of this work is to study basalt quarries located in the NE of Argentina to identify deleterious species, mainly fresh and devitrified volcanic glass, expansive clays and residual cryptocrystalline silica. 

Figure 5. Diffractograms of the natural, glicolated and calcined (at 500 °C) samples. The black arrow indicates the shift of 001 reflection of the expansive clay. S Smectite, Sa Sanidine, Aug Augite, PI Plagioclase.

Considering the petrographic characteristics of the studied rocks, the main source of soluble silica is volcanic glass and cryptocrystalline silica (tri-dymite) caused by glass alteration. The presence of expansive clays can contribute to increase the expansion values in the accelerated mortar bar test method. 

The presence of expansive clays may contribute with the concrete expansion. 

Moyne C, Murad MA (2006) A two-scale model for coupled electro-chemo-mechanical phenomena and Onsager s reciprocity relations in expansive clays I homogenization analysis. Transp Porous Media 62 333-380... 

Expansive clays that alternately expand and contract when saturated with water, then become dried out, can cause enormous damage to structures, making the construction of basements virtually impossible in some areas. Sinkholes occur in areas where rock formations are dissolved by... 

Some types of soils, particularly so-called expansive clays, expand and shrink markedly as they become saturated with water and dry out. Although essentially never life-threatening, Ihe movement of structures and the damage caused to them by expansive clays can be very high. Aside from years when catastrophic floods and earthquakes occur, the monetary damage done by the action of expansive soil exceeds that of earthquakes, landslides, floods, and coastal erosion combined. 

Hydrothermal field experiment simulating steel canister embedded in expansive clay -physical behaviour of the clay. Scientific Basis for Nuclear Waste Management, XV, 547-556. 

On the other hand, accumulation of potassium in the upper part of the soil has been suggested as a possible reason for authigenic mica formation in Hawaian soils (Juang and Uehara [1968]). Evidence of an aeolian origin of this mica has been presented by Jackson et al. [1971]. St. Arnaud and Mortland [1963] postulated the formation of mica by fixation by expansible clays of potassium brought to the surface soil by plants. 

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