Cyclic Behaviors of Anisotropically Consolidated Gravelly Soils under Triaxial Condition: Effects of Sand Gradation Part of the Soil

Previous studies have extensively examined the effects of silt contents and gradations on the cyclic behavior of sand and silt mixtures. However, comparable data on the mixture of sand and gravel are limited because of the experimental challenges of getting reliable testing results from gravel-size particles. Furthermore, in several case histories in which liquefaction occurred, the liquefied soils had experienced initial static shear stress because of the sloping ground conditions or the presence of structures and buildings on the site. The effects of initial static shear stress on the cyclic behavior of clean sands have been widely studied, and some recommendations have been suggested for practical engineers. This research aimed to evaluate the effects of the sand gradation part on the cyclic behavior of two gravelly soils, both with 60 % gravel and 40 % sand but different gradations (well-graded vs. uniformly graded). A total of 26 cyclic triaxial tests were carried out on moist-tamped reconstituted specimens of the tested gravelly soils. The specimens were anisotropically consolidated to assess the effects of initial static shear stress combined with sand gradation on cyclic behaviors of the tested gravelly soils. Results of the tests indicated that the gravelly soil with uniform sands had a greater resistance against liquefaction than the one with well-graded sands. The lower cyclic resistance of the gravelly soil with well-graded sands can be attributed to its lower permeability associated with wider gradation and finer particles of the sand part, leading to higher excess pore pressure buildup during cyclic loading. Moreover, a similar increase in the level of initial static shear stress resulted in an increase in the liquefaction resistance of the gravelly soils, whereas the soil with uniform sands experienced a higher increase than the soil with well-graded sands.