Ali Hakan Ören

Settling of Kaolinite in Different Aqueous Environment

Settling characteristics of soils carry great importance for geotechnical engineers since sediments properties are formed during the settling of soil particles in an aqueous environment. In this study, settling characteristics of kaolinite are investigated. Different ionic strengths of NaCl, CaCl2 and AlCl3 were considered as a function of pH in aqueous environment of varying solid concentrations. Factors affecting the settling characteristics and fabric of kaolinitic sediments have been identified. The results of the study reveal that kaolinite settles in either flocculated or dispersed forms depending on pH and ion concentration. Flocculated settling occurs in acidic pH due to formation of flocs in edge-to-face structure with increasing positive charges at the particle edges. Dispersed settling occurs in alkaline pHs when ionic strength is low. When ionic strength is increased in alkaline pHs, kaolinite particles settle in flocculated form. Furthermore, the results show that pH has a significant role on the final sediment thickness or void ratio of kaolinite. Densely packed structures in alkaline and loosely packed structures in acidic aqueous environments are formed depending on pH level. Results also show that as the solid concentration increases, the settling rate decreases due to buoyancy effect. Finally, the zeta potential of kaolinite is correlated with the final sediment thickness or void ratio of kaolinite as a function of pH. This correlation proves that there is a good agreement between zeta potential and the final sediment thickness or void ratio, especially when the soil is settled in a dispersed form.

Some engineering aspects of homoionized mixed clay minerals.

Many studies have been conducted to investigate thephysicochemical behavior of pure clay minerals and predicttheir engineering performance in the field. In this study, thephysicochemical properties of an artificial mixture of differentclay minerals namely, 40-50% montmorillonite, 20-30% illite and 10-15% kaolin were investigated. The mixture was homoionized with sodium, Na+; calcium, Ca2+; andaluminum, Al3+. The engineering properties studied wereconsistency limits, sediment volume, compressibility behavior,and hydraulic conductivity. The results revealed that theliquid, plastic and shrinkage limits of soil increased withincreasing cation valence. The hydraulic conductivity of thesoil also increased with an increase in the valence of thecation at any given void ratio. Aluminum and sodium treatedclays had the highest and the lowest modified compressionindex values, respectively. Furthermore, trivalent cationsaturated clayey soil consolidates three times faster thanthat of monovalent and two times faster than that of divalent.These properties of the soils determined were, in general,similar to those of kaolinite rather than those ofmontmorillonite. The comparison of the results obtained withthe published data in the literature revealed that thephysicochemical behavior of the tested clay soil was, ingeneral, similar to that of kaolinite.

Determination of Cylindrical Soil Specimen Dimensions by Imaging with Application to Volume Change of Bentonite-Sand Mixtures

Volumetric shrinkage of compacted bentonite and sand mixtures has been continuously monitored at small strain levels (i.e., <5 %) using a digital image processing technique. A special digital measurement setup and a computer algorithm have been developed in order to identify volume of the drying specimens. Volume change of three compacted bentonite-sand mixtures at different initial moisture contents were recorded during drying by means of vernier caliper and digital measurements. Continuous monitoring of the volumetric shrinkage of specimens using digital images proved that digital measurement and data reduction methodology developed herein is capable of determining the shrinkage amount with desired accuracy. It is shown in the study that consistent volumetric shrinkage strain readings can be taken using this cost effective, nondestructive, and operator independent measurement setup, which may have become the preferred shrinkage measurement methodology in soil mechanics laboratory practice with some added features.

Geomechanics of Landfills—Innovative Technology for Liners

Cracks in clayey landfill liner, which cannot be closed up upon re-wetting, affect the long-term performance of a landfill. In this paper, the mixture bentonite-zeolite (BEZ) is presented as a potential liner material due to its plastic properties. Also, it may fulfill an existing demand, in developing countries, for liners that are cost-effective, natural and in compliance with environmental regulations. Traditional liners have shortcomings: (i) clayey soil is suitable for liners if the temperature and moisture fluctuations are not high; otherwise, they may form cracks; (ii) geomembranes, considered as the best alternatives for liners, are out of reach of most underdeveloped countries for their high price, and do not last more than 4 years; (iii) the interface of a CGL (clay geosynthetic liner) is susceptible to sliding. In the studies performed, the low volumetric shrinkage of the BEZ indicates that it is not affected by moisture content fluctuations, and its hydraulic conductivity in the order of 10 −10 cm/s meets regulatory agency requirements. Also, its inherent chemical properties (specially clinoptilolite zeolite) and its natural selectivity indicates that it will adsorb heavy metals such as Pb 2+ , Zn 2+ , Cd 2+ , Ni 2+ ,Fe 2+ , and Mn 2+ that may be present in leachate. Therefore, BEZ is a potential innovative material for liners in landfills.

Visual and Quantitative Investigation of the Settlement Behavior of an Embankment Using Aerial Images Under Large-Size Field Loading

In this study, the settlement behavior of the embankment due to the surcharge loading have been visually and quantitatively investigated. The spatial variation of settlements of an oversized embankment have been monitored using aerial images taken at intervals. In order to achieve the deformations due to the surcharge loading in the field, two topographical three-dimensional models (before and after surcharge loading), derived from aerial images and ground control points, have been generated and compared. The aerial images were acquired by an unmanned aerial vehicle with autonomous flight capabilities. The topographies were compared by generating two cloud point models. The deformations, determined from the comparison of two cloud points, were visualized by assigning an intensity value, which was calculated based on the three-dimensional variations of each data point. The surficial settlement profiles nearby the surcharge load have been computed. It has been concluded that centimeter level accuracy on surficial settlement has been achieved by low altitude aerial images, although the illumination condition of the area has an influence on the measurements.

Discussion of “Swelling characteristics of bentonite in artificial seawater”Appears in Canadian Geotechnical Journal, 46(2): 177–189.

The authors have to be congratulated for presenting such interesting research. The results are important not only in terms of buffer material to fill disposal facilities, but also in terms of understanding the effect of rising seawater level and regression of seawater inland due to excessive fresh water withdrawal at coastal areas (Yukselen et al. 2008). Thus, the discussers are very interested in the results presented in this paper, and would like to offer the following comments on the authors’ interpretations. The experimental results reveal that the maximum swelling pressures of bentonites B–E are affected by artificial seawater to varying degrees. However, results are obscure for several reasons. For example, it is known that calciumtype bentonite has lower swelling potential than sodiumtype bentonite under the same testing conditions (Azam et al. 2000). However, the comparison of maximum swelling pressures shown in Fig. 6 indicates that the maximum swelling potential of calcium-type bentonite yields a larger swelling pressure than sodium-type bentonite. Furthermore, even though the other sodium-type bentonites (B, D, E) are affected by artificial seawater, bentonite A is not affected. These results from Fig. 6 are also in apparent contradiction with Figs. 9 and 12. For example, the maximum swelling strain difference between distilled water and artificial seawater is negligible for bentonite C. On the other hand, there are appreciable strain differences in bentonite A. We wonder if the presented maximum swelling pressures of the bentonites are merely a function of the water content of the samples. To this end, we plotted the maximum swelling pressure of bentonites as a function of their average water content (Fig. D1). We also plotted the maximum swelling pressure as a function of the montmorillonite content of bentonites (Fig. D2). As seen from Fig. D1, the swelling pressure of bentonites increases linearly with average water content, implying that the reported maximum swelling pressures are also a function of moisture content. In conclusion, the results show that the maximum swelling pressure of bentonites appears to increase concomitant with montmorillonite and water contents (Fig. D2). This should be expected as the listed average water content is a function of the montmorillonite content (Fig. D3). We believe that the reported swelling pressures of bentonites are a coupled function of their water and the montmorillonite content. Thus, from the presented data it is hard to reach the conclusion that the ‘‘influence of artificial seawater on the swelling characteristics of sodium-type and artificial sodium-type bentonites is low’’ and ‘‘the influence of artificial seawater on swelling characteristics of calcium-type bentonite is more slight than sodium-type and artificial sodium-type bentonites.’’ Further evidence of the above statements is the variation of maximum swelling pressures with liquid limit. As seen from Fig. D4, the swelling pressure decreases with an increase in the liquid limit of bentonites. This appears to contradict previous research that documents swelling pressures that increase (not decrease) with an increase in liquid limit of soils (Vijayvergiya and Ghazzaly 1973; Chen 1988; Issa 1997). Additional evidence of the above stated statement comes from the authors’ own data. For example, if we take the maximum swelling strain differences between distilled water and artificial seawater at 1.4 Mg/m3 of initial density under 10 kPa vertical pressure and plot them as a function of the liquid limit of bentonites, the maximum swelling differences increase with an increase in liquid limit (Fig. D5). We chose the initial dry density of 1.4 Mg/m3 as this density is the only initial density in all tested samples. We validate our observations by plotting the observed maximum swelling strains presented in Fig. 9 as a function of the liquid limit of samples at 1.65 Mg/m3. As seen from Fig. D6, the observed maximum swelling strain is a function of liquid limit. We would appreciate the authors’ comments on our interpretation of the reported results.