Effects of Quartzite on the Desiccation Cracks of Clayey Soils Exposed to Wetting-Drying Cycles

The compacted clayey soils crack on drying because of their high swelling potential, and their hydraulic conductivities increase. To solve this problem, it is essential to stabilize the clayey soils using additive materials. The aim of this study is to examine the suitability of quartzite as a stabilization material to reduce the development of desiccation cracks in compacted clayey liner and cover systems. Experimental study was conducted to investigate the effect of wetting-drying cycles on the initiation and evolution of cracks in compacted clayey soils. For experimental studies, seven samples were prepared stabilized by using 0%, 2.5%, 5%, 7,5%, 10%, 12,5% and 15% quartzite and then they were subjected to four subsequent wetting-drying cycles. The results show that quartzite decreases the development of desiccation cracks on the surface of compacted samples. It is concluded that quartzite as a geological material can be successfully used to reduce the development of desiccation cracks in compacted clayey liner and cover systems exposed wetting-drying cycles.

Valorisation of Partially Oxidized Tailings in a Cover System to Reclaim an Old Acid Generating Mine Site

The reclamation of acid-generating mine tailings typically involves building cover systems to limit interactions with water or oxygen. The choice of cover materials is critical to ensure long-term performance, and partly determines the environmental footprint of the reclamation strategy. The objective of this research was to evaluate if tailings pre-oxidized on-site could be used in cover systems. Column experiments were performed to assess the effectiveness of a cover with capillary barrier effects (CCBE), where the moisture retention layer (MRL) was made of pre-oxidized tailings with little to no remaining sulfides (LS tailings). The columns were submitted to regular wetting and drying cycles, and their hydrological and geochemical behaviour was monitored for 510 days. The LS tailings showed satisfying hydrological properties as an MRL and remained saturated throughout the test. The concentrations of Cu in the drainage decreased by more than two orders of magnitude compared to non-covered tailings. In addition, the pH increased by nearly one unit compared to the control column, and Fe and S concentrations decreased by around 50%. Despite these improvements, the leachate water remained acidic and contaminated, indicating that acid drainage continued to be generated despite a hydrologically efficient CCBE.

Test plot study of a tailings stack final cover prototype

Waste storage facilities must be protected against weathering once mining operations come to end, in order to ensure structural integrity and to avoid environmental pollution. Cover systems consisting on earthen materials layers that are placed over the wastes are a widely spread solution to fulfil such requirement. This paper presents an experimental study of a cover system intended to protect a waste storage facility study case located in the arid eastern foothills of the Central Andes range, Argentina. At the study case, filtered tailings and waste rock are stored conjunctly. Both materials are stacked as alternating layers, roughly one-meter thickness each. The cover prototype is comprised of the stack topmost tailings layer, which is expected to act as the store-and-release element of a WB cover. The prototype design also includes a waste rock layer placed on top of the tailings, to avoid wind and runoff erosion. A total of 6 study plots have been setup, each equipped with water content and matric suction sensors. The plots location was decided to tackle cover response under sloping and horizontal ground conditions. The performance of three different waste rock layer thicknesses are being studied under both placement inclinations. Available data shows that the prototype comprising a 10cm thick waste rock layer has served satisfactorily to avoid deep percolation and tailings erosion.

Categorical and algebraic aspects of the intuitionistic modal logic IEL― and its predicate extensions

The system of intuitionistic modal logic $\textbf{IEL}^{-}$ was proposed by S. Artemov and T. Protopopescu as the intuitionistic version of belief logic (S. Artemov and T. Protopopescu. Intuitionistic epistemic logic. The Review of Symbolic Logic, 9, 266–298, 2016). We construct the modal lambda calculus, which is Curry–Howard isomorphic to $\textbf{IEL}^{-}$ as the type-theoretical representation of applicative computation widely known in functional programming.We also provide a categorical interpretation of this modal lambda calculus considering coalgebras associated with a monoidal functor on a Cartesian closed category. Finally, we study Heyting algebras and locales with corresponding operators. Such operators are used in point-free topology as well. We study complete Kripke–Joyal-style semantics for predicate extensions of $\textbf{IEL}^{-}$ and related logics using Dedekind–MacNeille completions and modal cover systems introduced by Goldblatt (R. Goldblatt. Cover semantics for quantified lax logic. Journal of Logic and Computation, 21, 1035–1063, 2011). The paper extends the conference paper published in the LFCS’20 volume (D. Rogozin. Modal type theory based on the intuitionistic modal logic IEL. In International Symposium on Logical Foundations of Computer Science, pp. 236–248. Springer, 2020).