The hydraulic performance and durability of geosynthetic clay liner containing various amounts of sodium polyacrylate polymer are experimentally studied. Sodium polyacrylate, generally known as a super-absorbent polymer, is a polymeric material with a potential of high water absorbance due to its chemical structure. In this study, sodium polyacrylate powder is used as a partial replacement of bentonite as much as 3%, 5% and 7% by the weight of bentonite. For comparison, the hydraulic performance of geosynthetic clay liner without super-absorbent polymer is also experimented. Atterberg limits, free swell index, hydraulic conductivity, self-healing capacity and wet/dry cycle tests are conducted in order to assess how super-absorbent polymer can affect the performance of geosynthetic clay liners as landfill liners and covers. The results show that the hydraulic conductivity and self-healing capacity of geosynthetic clay liner are relatively enhanced by super-absorbent polymer inclusion. The results of wet/dry cycle test show that using super-absorbent polymer as a partial replacement of bentonite considerably improves the durability of geosynthetic clay liner against wet/dry cycles. Geosynthetic clay liner containing super-absorbent polymer shows a negligible increase in hydraulic conductivity while there is a noticeable increase in hydraulic conductivity of specimen without super-absorbent polymer after 10 cycles of wetting and drying.

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The van Genuchten Model (1980) is widely-used for the description of the Soil-Water Characteristic Curve (SWCC) of a variety of soils. This study uses the Genetic Programming (GP) for the presentation of equations estimating the van Genuchten (vG) Model fitting parameters for unsaturated clean sand soils. Moreover, this study uses the data derived from the valid dataset of Benson et al. (2014), including 95 measured SWCCs in both drying and wetting phases. The data on the particle size distributions includes the fine-grain percentage (Fines %), d60, d10, besides the residual and saturated volumetric water content (θ and θ ), as the GP model inputs of set of terminal. As for the model outputs of set of terminal, the fitting parameters for the vG model include a and n. The functions used in the GP training were 'plus', 'minus', 'times', taken from the MATLAB default functions, 'mydivide' proposed by Silva (2007), and some other new power functions included by this study. Accordingly, new equations were presented for the estimation of vG Model fitting parameters for both forms of wetting and drying. Finally, to evaluate the accuracy of the proposed estimation equations, the GP results were evaluated and verified in different procedures.Keywords: SWCC, van Genuchten Model, Unsaturated Soils, Genetic Programming, Fitting Parameters *Corresponding author. Tel: +98-912-568-3767 Fax: +98-6633243999 E-mail addresses: am.taban@gmail.com (A. Taban); msadeghi@ieht.ac.ir (M. Mirmohammad Sadeghi); mohamali@cc.iut.ac.ir (M.A. Rowshanzamir); Postal Address: Department of Civil Engineering Isfahan (Khorasgan) Branch, Islamic Azad University, Jey Street, Arqavanieh, University Blvd. PO Box: 158-81595, Isfahan, Iran 2 1.IntroductionSoil-Water Characteristic Curve (SWCC) is one of the widely-used concepts in the earth-related sciences, and particularly, in the mechanics of unsaturated soils. It describes the relationship between the amounts of water in the soil structure and the matric suction in the soil. Many analyses and numerical studies of unsaturated soils depend on the SWCC. Such expressions as the volumetric water content, the degree of saturation, and the normalized water content are used for the amount of water within the soil [1].There are various methods for the measurement of SWCC, many of which are costly and time-consuming. However, they are different from each other in terms of their capabilities of measuring different ranges of the suction. What follows is a list of measurement methods that directly measure the SWCC: The Hanging Column, the Pressure Plate Extractor (PPT), the Chilled Mirror Hygrometer, and the Centrifuge, which directly measure SWCC and the procedure has been explained in ASTM D6836 [2]. In contrast, there is another group of experiments which measure the values indirectly, for example: Filter Paper, Heat Dissipation, Thermal Conductivity Sensor Technique, Chilled-Mirror, Hygrometer Technique, and so forth [3]. These methods of suction measurement will measure different ranges of suct...

This paper aims to investigate the likely e ects of geogrid reinforcement con guration on the bearing capacity of footings. Using geogrid reinforcement layers with certain total areas in various uniform and non-uniform arrangements, the bearing capacities of footing models on reinforced sand beds were determined and compared. The rst arrangement was the conventional uniform layout in which three geogrid layers of equal dimensions were considered. In the second group, the same amount of geogrids was used in a trapezoidal pro le in which smaller sized geogrids were placed at upper layers and the geogrid dimensions increased with embedment depth. The third group consisted of arrangements in which the same amount of geogrids was used in an inverse trapezoidal layout, i.e. the layer sizes decreased with embedment depth. The e ect of soil density on the footing performance was also investigated. The tests results indicated that in all soil densities, the greatest bearing capacities were obtained for the sand beds reinforced with inverse trapezoidal reinforcement layouts, while the least bearing capacities were determined for trapezoidal arrangements. The improvement ratio of bearing capacity due to geogrid reinforcement varied from 1.8 to 5.35 depending on the reinforcement layout and the sand bed density.