Ramiro Daniel Verástegui Flores

Advances in geosynthetic clay liners: polymer enhanced clays

Bentonite clay is widely used in Geosynthetic Clay Liners (GCLs), because of its elevated sealing capacity in presence of water. However, exposure to high concentrated inorganic solutions can change the clay fabric increasing its hydraulic conductivity. To improve the hydraulic performance of GCLs, a chemical-resistant clay (HYPER clay) was developed through treatment of a natural bentonite with an anionic polymer, Sodium Carboxymethyl Cellulose (Na-CMC). The swelling ability, water adsorption capacity and hydraulic conductivity of the HYPER clay were evaluated. Test results showed the beneficial effect of the anionic-polymer treatment on the swelling, water adsorption and hydraulic performance of the clay.

Analyzing Settling of Fine-Grained Soil by Electrical Resistance Measurements

The industry and construction sector face an increasing problem of how to dispose of its voluminous residues. Much of these residues are constituted of large amounts of liquid phase and fine-grained solids in suspension, for example mine tailings and dredged materials. Therefore, there is a need to develop technologies that aim at reducing the volume of these residues for economical disposal or treatment. Depending on the type of solid and liquid phase, a number of additives are currently used to speed up the sedimentation and reduce the volume of these suspensions. In order to investigate the impact of different additives, a laboratory setup was designed to monitor the sedimentation process. This setup consists of a transparent plastic tube provided with electrodes. This paper focuses on the evaluation and performance of electrical resistance measurement as a means to monitor the sedimentation of a fine-grained soil. Experimental work was carried out on suspensions of kaolin clay in deionized water and electrolyte solutions. The results showed that electrical resistance measurements can provide valuable information related to densification and fabric of the soft sediment.

Hydraulic and mechanical behaviour of cement-bentonite mixtures containing HYPER clay: impact of sulfate attack

Cemented clays are regularly employed as cut-off walls to isolate polluted soils or in ground improvement technologies. The objective of this research was to evaluate the performance of a polymer-treated bentonite (HYPER clay) and its impact on hydraulic and mechanical properties of cement-bentonite (CB) mixtures in contact with sulfates. In this research, bender elements were installed in a hydraulic conductivity cell, to simultaneously monitor the small-strain shear modulus (G(0)) and the hydraulic conductivity (k) of cement-bentonite mixtures. Initially, during permeation with deionized water, an increase of G0 with time was observed, due to cement hydration (hardening). Conversely, after prolonged permeation with sulfates, a decrease of G0 and a gradual increase of k are expected due to degradation of the cemented material. Preliminary results show that k of mixtures containing untreated bentonite increases due to contact with sulfates; conversely, k of mixtures containing HYPER clay remains unaffected. The stiffness modulus G0 was not significantly affected after a sulfate contact period of about 100 days in none of the cement-bentonite mixtures. More extensive monitoring is required for evaluating long-term mechanical degradation. These observations suggest that the use of polymer-treated bentonites could improve the resistance of cement-bentonite mixtures to sulfate attack maintaining a low hydraulic conductivity.

Crushability on granular materials by strain controlled oedometer testing at high stress levels

The crushability of artificial and natural granular materials has been analyzed using one-dimensional strain-controlled compression tests and standard oedometer tests at high stress levels to study the effect on the breakage of a number of parameters such as: grain mineralogy, grain size, uniformity coefficient, strain rate and loading time. Measuring the breakage factor at different stages of compression, it was demonstrated that the crushing started before reaching the point of maximum curvature (yield point) in the compressibility curve. Beyond yielding the crushing increased abruptly. Among the natural materials analyzed, the lowest yield stress value occurs in the carbonate sand, and the highest in the silica sand. We found that the breakage increases with increasing size of the grains. Coarse uniform samples showed higher breakage than uniform fine samples and well-graded samples. The breakage increased with decreasing strain rate or increasing load application time. For natural soils it is difficult to study separately the influence of isolated parameters on the breakage. The study of homogeneous artificial materials facilitated this analysis.