Effects of Applying Nano Clay Particles and Polypropylene Fibers on Geotechnical Properties of Clayey Soil for using in Pavement Layers

If the geometric design of a road is in a way that it has to pass through areas with weak and problematic soil layers or borrow materials are located far away from project sites, stabilization of pavement improvement operations should be performed to construct pavement layers, especially its subgrade level. Generally, stabilization method of soils is divided into chemical and mechanical procedures, and simultaneous geosynthetic materials can be used. Nowadays, nano materials are proposed in order to improve geotechnical properties of soils in terms of bearing capacity. The present study was aimed to investigate the capability of nanoclay particles and the application of polypropylene fibers in the clayey soil of Eslami Island near Lake Urmia to construct layers in pavement. In the first step, nanoclay particles with 5 and 10 percentages were mixed with soil, and then the curing process was carried out in 7, 14, and 28 days. In the second step, polypropylene fibers were added to the clayey soil in 0.4, 0.8, and 1.6 percentages. Finally, the optimal values of polypropylene fibers and nanoclay particles simultaneously mixed with soil specimens and, similar to the first step, curing operations were carried out. To this end, laboratory tests containing compaction, uniaxial strength, direct shear, and California Bearing Ratio (CBR) in dry and saturate conditions were executed according to ASTM standards. Furthermore, swelling values in the improved specimens at saturate positions were estimated. The findings revealed that optimum combination was obtained at 5% of nanoclay blended with 0.8% of polypropylene fibers in specimens undergoing a 28-day curing process since this condition was found to upgrade the stabilization of soil specimens in terms of compressibility, bearing capacity, strength, and reduction of swelling potential.