(4)

In this paper, an extensive series of direct shear box tests (99 tests) were conducted to explore and compare the effects of raw and treated natural fibers, specifically Doum fibers on the mechanical behavior of three categories of sandy soils with distinct mean particle sizes (D50 = 0.63, 1, and 2 mm). Specimens from every soil category, containing 0 to 0.8% raw Doum fibers and 0 to 1% treated Doum fibers in incremental step of 0.2%, were reconstituted at an initial relative density of (Dr = 87 +/- 3%) and subjected to three different initial normal stresses (100, 200, and 400 kPa). The obtained results indicate that incorporating raw or treated Doum fibers improve the mechanical and rheological properties (internal friction angle, ductility, and maximum dilatancy angle) of the tested mixtures up to specific thresholds Doum fiber content (FD = 0.6% and FTD = 0.8% for raw and treated Doum fibers respectively). Beyond these limiting values, the mechanical and rheological properties decreased with further increases in Doum fiber content. Additionally, specimens reinforced with treated Doum fibers exhibit higher shear strength than that of the raw Doum fibers for all tested parameters. Based on the experimental results, it has been found to suggest a reliable correlation between Particle Size Distribution (PSD) characteristics and mechanical properties for all reconstituted specimens. The recorded soil trend is especially pronounced for the mean grain size (D50) ranging between 1 and 2 mm, where a notable increase in shear resistance is noticed. The analysis of the obtained outcome suggests the introduction of new enhancement factors (EF tau peak and EF phi degrees) as useful parameters for predicting the mechanical behavior of sand-fibers mixtures. Furthermore, new relationships have been developed to forecast changes in mechanical properties (peak shear strength, internal friction angle, and maximum dilatancy angle) of the tested mixtures under the impact of the selected parameters (FD/TD, D50, and sigma n).

来源平台：INTERNATIONAL JOURNAL OF CIVIL ENGINEERING