Experimental Evaluation of Marly Soil’s Mechanical and Dynamical Behavior

Marls are among the problematic soils that threaten developmental projects. As moisture increases, the resistance of these types of soil decreases and their deformability increases. During an earthquake, its parameters and properties are likely to alter. The effect of moist Marl quality is considerable on both static behavior and dynamic properties of soil. These parameters include shear and pressure wave velocity, natural frequency, shear modulus, and damping ratio. The mechanical properties of soil might be specified through both laboratory experiments and field experiments. This research study was carried out on Marls of the north of Shiraz city to identify their dynamic behavior. To achieve this, in addition to field and laboratory static tests, cyclic triaxial test was also done on the samples. The obtained results revealed that in these Marly Soils, as the confined pressure increased (increase in soil depth), the shear modulus also increased. It was also understood that the damping ratio behaved slightly different for less than 1% and more than 1% strains. However, in general, for strains more than 1%, increasing confined pressure led to reduction of damping ratio. The study also showed that as the percentage of moisture increased, the shear and compression resistance decreased which, in turn, led to an increase of soil consolidation. Comparing the static and dynamic behavior of soil indicates that the cyclic shear modulus in 100 kPa stresses and 1% strain is roughly 60%; and in 10% strain, it is less than static modulus by almost 48%. This difference reduces as the enclosing pressure increases.