Effect of Water and Leachate on Hydraulic Behavior of Compacted Bentonite, Calcareous Sand and Tuff Mixtures for Use as Landfill Liners

Compacted soil–bentonite liners, consisting of a sandy soil mixed with bentonite as backfill, are used extensively as engineered barriers for contaminant containment. This paper studies the valorization of local materials containing calcareous sand, tuff obtained from Laghouat region (in the South Algeria), to associate with bentonite in order to improve their hydraulic characteristics for use as landfill liner material. Firstly, a geotechnical characterization of mixtures chooses from a fixed percentage to 10% bentonite and different percentages of calcareous sand and tuff so that they are complementary to 90% by not 10%. Thereafter, the determination of saturated hydraulic conductivity at falling-head permeability (K_v) and oedometer (K_id, indirect Measure) tests of all compacted mixtures at Optimum Normal Proctor have been carried out using both permeates by tap water and a landfill leachate in order to simulate long-term conditions. The results showed that the saturated hydraulic conductivity of tap water is relatively lower than the one saturated by leachate in the falling-head test, unlike the oedometer test. The B₁₀CS₂₀T₇₀ mixture has satisfied the hydraulic conductivity criterion of bottom barriers (i.e. water permeated: k_v20° = 1.97 × 10⁻⁹ and k_id from 7 × 10⁻⁹ to 1.83 × 10⁻¹⁰ < 10⁻⁹m/s; leachate permeated: k_v20° = 2.91 × 10⁻⁹ and k_id from 7 × 10⁻⁹ at 1.44 × 10⁻¹⁰ < 10⁻⁹ m/s). Finally, a comparison between direct measurements of the saturated hydraulic conductivity by triaxial (K_d) test and oedometer test (K_id) in the range of effective stress applied 100–800 kPa led to propose equations of correlations between these two methods. In conclusion, adopted formulation B₁₀CS₂₀T₇₀ perfectly meets the regulatory requirements in force and constitutes an economic product based on available local materials for engineers barriers.