Improving the Soil Mechanical Properties of Forest Roads by Combinations of Nano-Silica Materials and Horsetail Ash

Aims Fine grained soil shows weak geotechnical properties when they are used in roadbed. The aim of the present study was to assess the efficiency of nano-SiO2 and horsetail ash in improving the mechanical properties of high plastic cohesive soil (CH) and low plastic cohesive soil (CL). Materials & Methods Soil samples were brought from an earthy bed of proposed roads in Bahramnia Forest, Golestan Province, Iran. Then Atterberg limits, maximum dry density (MDD), unconfined compressive strength (UCS) and California bearing ratio (CBR) tests were conducted on the soil samples treated with 0.5% nano-SiO2+1% ash, 1% nano+2% ash, 1.5% nano+3% ash and 2% nano+4% ash. Analysis was done on 7, 14, and 28-day aged samples. Statistical analysis was done using the SAS 9.4 software to compare means among treatments. Findings Results showed that liquid limit and plastic limit increased to 56% and 37% for CH and 50% and 32% for CL with increasing the percentage of nano-SiO2 and ash mixture. These changes reduced the plastic index. With the increase in the percentage of additive materials and curing time, the MDD, UCS, and CBR get increases. Dry density decreased by increasing moisture content at the peak state (1.70g cm-3 for CH and 2.03g cm-3 for CL). The nanoash treated CL soil has a higher density than the nanoash treated CH soil. Conclusion A optimal mixture of 1.5% nano-SiO2+3% horsetail ash and 1% nano-SiO2+2% ash, as well as 28-day curing time, is recommended for the stabilization of CH and CL earthy bed, respectively.