Abstract This study investigates the relationship between clay minerals (kaolinite and illite) and rock properties of the claystone, including both mechanical (cohesion, friction angle, stress, and strain) and physical properties (natural water content, void ratio, and wet density), belonging to Warukin Formation of Kalimantan, Indonesia. Mineralogical characteristics of these rocks were studied using petrological and X-ray diffraction techniques, whereas the mechanical and physical properties were tested by conducting uniaxial and triaxial tests. Relationship among the variables was determined using correlation coefficients. It was observed that the mineralogy of the rocks pose strong constraints on their engineering properties. The results showed that an increase in illite content decreases cohesion, friction angle, strength, and safety factor; and increases natural moisture content, void ratio, and wet density. Although illite content of these rocks was just about 10.8% of the total minerals, it has significantly contributed to the modification of physical and mechanical properties. In contrast, kaolinite did not have a significant impact; since the correlation between various parameters was significantly low (correlation coefficient was much less, <0.3). Therefore while selecting the materials for geotechnical engineering applications, illite emerges as a safer alternative to kaolinite, especially when its concentration is less than 10.8% of the total rock mass.

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The Influence of Kaolinite - Illite toward mechanical properties of Claystone

The hydraulic conductivity is highly influenced by the state of confinement and effective pressure applied. Hydraulic conductivity evaluated using indirect (i.e., oedometer tests) or direct techniques such as constant or falling head methods induces lateral confinement. The most reliable direct measurement tests are those considering triaxial or flexible wall setup such that field conditions are simulated. The ASTM D5084 and BS1337-6: 1990 are appropriate approaches to give reliable hydraulic conductivity values. Both tests require considerable time due to various stages of saturation, consolidation, and permeation. This study provides a comparison between indirect hydraulic conductivity tests and standard flexible wall tests in order to cut down the time needed to perform the test for different sand-Alqatif clay mixtures. Sand-clay mixtures used as liners for waste containment or water barriers are very sensitive to the hydraulic conductivity and need to be designed for different values of effective pressures. This research presents prediction equations derived from a series of direct and indirect tests carried out for sand-Alqatif clay mixtures. The results indicated that oedometer tests underestimated the hydraulic conductivity by 2 to 3 orders of magnitude at different effective pressures. The hydraulic conductivity was found to vary with effective pressures indicating that near surface material yields higher hydraulic conductivity than deeply seated similar soils.

Effects of confining pressure and effective stress on hydraulic conductivity of sand-clay mixtures

Effect of attapulgite colloids on uranium migration in quartz column

The surface property of attapulgite was investigated by N2-BET surface area and zeta potential analysis in this paper. Solution pH had a remarkable effect on the sorption process, indicated an inner-sphere complexation. Humic acid (HA) in the solution enhanced U(VI) sorption significantly at pH   9.0. The characteristic fluorescence changes of HA indicated that a strong chemical reaction occurred between the functional groups in HA and UO22+. The sorption was a spontaneous and endothermic process with increased entropy, and the increase in temperature would benefit the sorption.

Influence of pH, soil humic acid, ionic strength and temperature on sorption of U(VI) onto attapulgite

Bentonite mixed with varying quantities of sand is currently of widespread interest as engineering liners for water containment and waste disposal. However, the alternative use of pumice, widespread in many volcanic regions, has been less studied and requires further characterization of geotechnical properties and performance prior to its extensive use. The objective of this study was to determine and compare the compaction and swelling characteristics of sand-bentonite and pumice-bentonite mixtures using available geo-materials from Turkey. Standard Proctor compaction tests and constant volume swell tests were carried out using mixtures with four different bentonite contents (15, 20, 25, 30%) and three different sand and pumice grain size ranges (2.00–1.00; 1.00–0.50; 0.50–0.25 mm). The results indicate that pumice-bentonite mixtures have lower maximum dry unit weights, higher optimum moisture contents and greater swelling potentials than equivalent sand-bentonite mixtures. Important differences occur in the swelling potentials of the sand and pumice mixtures with respect to grain size whereby sand-bentonite mixtures show increased swelling with coarsening grain size, in contrast to the pumice–bentonite mixtures which showed a decrease. These differences are attributed to the amount of grain-size-dependent connected pore space that can be filled during bentonite expansion and the presence of dissolvable salts in the pumice. It is concluded that locally available pumice material could be used to replace sand in engineering bentonite seals, despite some differences in their geotechnical properties.

Compaction and swelling characteristics of sand-bentonite and pumice-bentonite mixtures

This paper investigates the potential use of sand–attapulgite (palygorskite) mixtures as a landfill liner. The sand and attapulgite clay used in this study were brought from Wahiba (eastern Oman) and Al-Shuwamiyah (southern Oman), respectively. Initially the basic properties of the sand and clay were determined. Then the attapulgite clay was added to the sand at 5, 10, 20 and 30% by dry weight of the sand. The sand–attapulgite clay mixtures were subjected to mineralogical, chemical, microfabric and geotechnical analyses. The X-ray diffraction (XRD) qualitative analysis showed that attapulgite is the major clay mineral. The chemical compounds, exchangeable cations and cation exchange capacity (CEC) for the␣samples were determined. The CEC for the sand–clay mixtures is low but increases with the increase in clay content. The scanning electron microscope (SEM) examination showed that the addition of clay developed coating between and around the sand grains which results in filling the voids and reducing the hydraulic conductivity of the sand–clay mixtures. The hydraulic conductivity values for the pure clay and sand + 30% clay mixture prepared at 2% above optimum water content are slightly higher than hydraulic conductivity requirements for landfill liners but can be acceptable. The geotechnical study which included grain size distribution, Atterberg limits, specific gravity, compaction, hydraulic conductivity and shear strength tests showed that the sand+30% clay mixture prepared at 2% above optimum water content can be considered to satisfy the requirements for landfill liners. For all sand–clay mixtures no swelling was recorded and the addition of clay to the sand improved the shear strength.

Abdulaziz S. Al-Shabibi

Papers

Sand–Attapulgite Clay Mixtures as a Landfill Liner