Effect of silt fines on the undrained monotonic behavior of compacted tuff soil

The present study explores the influence of silt content on the undrained monotonic behavior of compacted tuff. All undrained triaxial tests were performed at both Relative Densities D_r = 50 and 90% and compacted with the optimum water content on tuff-soil mixed with silt in the range of 0% to 50%. Experimental results show that adding Fines Content (FC) up to 20% increases the resistance of dense compacted tuff (D_r=90%) by about 35% for 100 kPa of confining pressure, and the addition of 10% silt fines results in a maximum increase of 15.71% in the medium-dense state specimen (D_r=50%). The deviator stress reveals a decrease by adding more than 20% of silt. Moreover, the soil cohesion was found to attain maximum values with the optimum silt percentage of FC = 10% for medium-density samples (D_r = 50%) and FC = 20% for dense samples (D_r = 90%), respectively. Finally, the study showed a direct correlation between the cohesion of the soil prepared in a dense state (D_r = 90%) and the soil's Maximum Dry Density (MDD). In particular, the maximum dry density corresponds to a higher cohesion.