Shear Strength and Pull-Out Response of Tire Shred-Sand Mixture Reinforced with Deformed Steel Bars

The use of scrap tires in various engineering applications has been extensively explored. The present study has the following aim: to evaluate the suitability of tire-sand mixtures as backfill material based on its shear strength. To achieve this objective, modified Proctor compaction tests were performed on tire shred-sand mixture with mixing proportions by weight of tire shreds and sand (0/100, 20/80, 30/70, and 40/60) using different sizes of tire shreds (50 mm, 75 mm, and 100 mm). Based on the results of the modified Proctor compaction test, the two mixing proportions, i.e., tire shred/sand, 20/80 and 30/70, respectively, were selected. Large-scale direct shear test indicated higher internal friction angle and cohesion values for tire shred-sand mixtures (30/70) with 100 mm tire size (38.5° and 19 kPa) as compared with sand-only backfill material (30.9° and 0 kPa). Based on stress-strain behavior plots, it was indicated that the inclusion of tire shreds imparts ductility to backfill mixtures. To achieve the second objective, the pull-out tests were performed with deformed steel bars of two different diameters (12.7 mm and 15.8 mm) embedded in various backfill mixtures prepared with tire shreds of three different sizes (50, 75, and 100 mm). The pull-out test result indicated that the deformed steel bars exhibit higher pull-out resistance in tire shred-sand mixtures (9.9 kN/m) compared with sand-only backfill material (4.1 kN/m).

Assessment of alternative protection layers for a geomembrane – geosynthetic clay liner (GM–GCL) composite liner

A protection layer is required above geomembrane (GM) – geosynthetic clay liner (GCL) landfill liners to limit physical damage (GM strains and GCL thinning) from an overlying granular drainage layer. A 150 mm thick layer of sand has been found to provide excellent protection at a vertical pressure of 250 kPa. However, the use of sand may not be practical in many cases. Experimental results are presented where the effectiveness of alternate protection systems above one particular GM–GCL liner were examined with 50 mm coarse gravel at an applied vertical pressure of 250 kPa. A 150 mm thick layer of compacted clay and a 150 mm thick layer of rubber tire shreds with a nonwoven needle-punched geotextile (570 g/m2) were found to limit the geomembrane strains and GCL extrusion to acceptable levels. Layered geotextiles performed much better than single layers of geotextiles. A layered geocomposite, with a thick nonwoven needle-punched geotextile in the middle to provide cushioning and stiffer woven geotextiles on the top and bottom to carry tensile force, was able to limit the short term strain to less than 3%, but it was not able to prevent local thinning of the GCL because of the deformation required to mobilize force in the geotextiles.