Date

2020-12-22

Author

Uragan, Semkan

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Geomembrane – soil interface is a critical consideration in geotechnical engineering applications such as liners and covers in landfills, canals or mine tailing dams. In some cases, lack of sufficient shear strength in these interfaces leads to poor performance, uneconomical design (such as requiring a longer geomembrane in an anchor trench), or may even lead to failure. To eliminate such problems, geometrical features known as asperities (or protrusions) are used on the geomembrane's interfacing faces. These asperities improve the interface shear strength by providing a surface that rakes through the soil rather than slipping. Research involving the optimization of these asperities requires rapid manufacturing of variety of these prototype geomembranes used as samples for interface shear tests. In this study, commercially available HDPE geomembrane samples are compared to 3D printed geomembrane samples in terms of their tensile strength and interface shear characteristics. Firstly, Polypropylene (PP) is selected among other thermoplastics namely PLA, ABS and re-PETG to replicate High Density Poly Ethylene (HDPE) using the data obtained from tensile strength tests. Three soil samples are prepared (containing 0%, 12% and 40% fines content) using Çine sand and non-plastic silt and the index properties for these soil samples are determined. Finally, using the selected prototyping material PP, 3D printed geomembrane samples are compared to HDPE geomembrane samples in interface with these soil samples under 20, 100, and 200 kPa vertical pressures using 60 x 60 mm direct shear tests. Seventy-two direct shear tests are conducted for geomembrane-soil interface shear strength using three different soil mixtures, where each soil sample is prepared at two different densities (loose and dense condition). To simplify the comparison of the similarity between HDPE and FDM-manufactures PP specimens, three comparison indexes are calculated, namely, Asperity Similarity (AS), Smooth Similarity (SS), and Improvement Similarity (IS). As a result of these tests, while FDM-manufactures PP showed promising and comparable results in replication of HDPE samples for all soil mixtures interfaced with geomembranes with asperities, some amount of deviation is observed in soil mixture A, which consists only of sub-angular Çine sand, interfaced with smooth PP geomembrane especially under higher normal loads. This deviation is attributed to the elevated effect of the raking mechanism provided by sub-angular sand coupled with the rougher surface profile that is a known characteristic defect of FDM manufactured parts. Finally, the use of FDM technique in optimization of geomembrane interfaces was recommended and discussed.

Subject Keywords

Geomembrane, 3D Printing, Interface Shear Strength, Direct Shear, Asperity Optimization, Fused Deposition Modelling

URI

https://hdl.handle.net/11511/89565

Collections

Graduate School of Natural and Applied Sciences, Thesis