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    Effects of elevated temperature on mineralogical/microstructural changes and mechanical responses of clay soil
    (Pergamon-Elsevier Science Ltd, 2023) Aryanpour, Marzieh; Falamaki, Amin; Vakili, Amir Hossein
    High temperatures can affect soil performance and alter its engineering behavior. In this study, a series of ex-periments were carried out on various soil samples provided under different heating conditions (i.e., heated sample and heated clay) to evaluate the various temperatures effects (elevated from 20 to 900 degrees C) on physical, chemical, mechanical, and mineralogical/microstructural characteristics of clayey samples. The main objective of this study is to investigate the influence of temperature and heating conditions on permeability, unconfined compressive strength, shear wave velocity, weight, color, pH, EC, XRD, and FESEM. The results indicated that dolomite can be broken down into magnesium oxide and calcite, and alpha quartz can be broken down into beta quartz. Calcite minerals decompose into calcium oxide at 900 degrees C, beta-quartz into alpha-cristobalite, and kaolinite into mullite and gehlenite. The decomposition of water from the hydroxyl structures of minerals in burnt soil is carbonated on the soil's surface up to a temperature of 700 degrees C; thus, the compressive strength of clay in the temperature range of 500-700 degrees C is approximately 97% lower than its maximum. At 900 degrees C, the formation of mullite, gehlenite, and various oxide structures, such as calcium and magnesium oxide, changes the structure of clay to a glassy and amorphous structure. This improves the strength of clay from 0.17 to 3.7 MPa; however, the permeability increases significantly due to the unstable glass structure. The shear wave velocity increased by approximately 2.74 times at 200 degrees C. It decreased from 300 to 700 degrees C, then increased to 416.7 m/s at 900 degrees C.
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    Experimental investigation of the effect of landfill leachate on the mechanical and cracking behavior of polypropylene fiber-reinforced compacted clay liner
    (Springer Heidelberg, 2023) Falamaki, Amin; Salimi, Mahdi; Vakili, Amir Hossein; Homaee, Mehdi; Aryanpour, Marzieh; Sabokbari, Maryam; Dehghani, Reza
    This paper aims to investigate the effect of leachate on the geotechnical parameters and the cracking behavior of compacted clay liners (CCLs) containing different percentages of polypropylene fibers. Accordingly, 200 compacted clay samples were reinforced with different percentages of fiber contents (FC) (i.e., 0, 0.5, 0.75, and 1%) and prepared with water or leachate to conduct different laboratory tests. First, the physical properties of the clay were determined. Then, the shear strength parameters (i.e., cohesion and friction angle), unconfined compressive strength, and the hydraulic permeability were determined subjected to water or leachate. Notably, the cracking behavior was modeled using visual images of the samples. The leachate increased desiccation cracks in the natural soil from 0.425 to nearly 1.111%. However, the addition of 0.5% (in the case of water) and 1% (in the case of leachate) fiber to the soil reduced the surface desiccation cracks in clay liners to about 0.185 and 0.352%, respectively. In both water- or leachate-prepared samples, the addition of fibers significantly increased the cohesion and friction angle. The shear strengths of the unreinforced leachate-prepared samples were lower than those of the water-prepared samples. The shear strength and unconfined compressive strength of all specimens increased with increasing fiber percentage. The presence of fibers in all samples caused more ductile behavior. The required amount of energy to achieve the maximum strength in the samples increased with increasing FC. By increasing the percentage of fibers, the permeability of the natural soil and the leachate-prepared samples increased. However, the highest permeability was observed in the leachate-prepared samples containing 1% fibers of 8.3 x 10(-10) m/s, which is less than 10(-9) m/s (maximum allowable permeability for clay liners). Finally, the obtained results were satisfactorily confirmed by scanning electron microscopy (SEM) analysis.
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    Soil Improvement by Electrokinetic Sodium Silicate Injection into a Sand Formation Containing Fine Grains
    (Springer, 2024) Falamaki, Amin; Noorzad, Ali; Homaee, Mehdi; Vakili, Amir Hossein
    The effect of electrokinetic sodium silicate injection into sand formation containing fine grains was studied in this research. A soil was grouted by Na-silicate in a 160 mm length electrokinetic cell with a 1 V/cm potential gradient for 1 week. Silicate solutions of 5% and 10% concentrations were injected through the reservoir next to the anode electrode, while 10% phosphoric acid or 30 mg/l bicarbonate solutions were used in the cathode chamber. When comparing the results, it was evident that the electrokinetic (EK) process without additives does not significantly enhance soil strength, except in the vicinity of the cathode electrode. Specifically, the most notable increase in strength was observed in the section proximal to the cathode, which demonstrated approximately 3.1 times higher strength than the control sample (i.e., without EK application). The obtained results indicate that injecting 5% and 10% Na-silicate solutions significantly increase the strength of soil all over the sample. Significant improvement in soil strength was observed when Na-Si was injected with bicarbonate as a catholyte during the EK process. Strength at the anode increased by 82% and 107% at 5% and 10% Na-Si concentrations, respectively. Resistance in the middle of the cell samples remained consistent for both concentrations. Immediate application of bicarbonate catholyte and silicate injection notably enhanced soil strength, while efficiency decreased when Na-Si was injected with phosphoric acid catholyte, especially near the cathode. Higher silicate concentrations resulted in reduced penetration length in both acid and bicarbonate catholytes. It can also be concluded that adding silicate to the anode chamber meaningfully reduces the electro-osmotic flow after 2 or 3 days.