Recommendations for extension and re-calibration of an existing sand constitutive model taking into account varying non-plastic fines content

• The mechanical behavior of silty sands is extensively reviewed.
• An intergranular void ratio as an index of the density of load carrying structure of silty sands is introduced.
• An existing constitutive model for clean sands is modified to cover both clean and silty sands.

Experimental findings have revealed that up to a certain transitional threshold, adding non-plastic silt to coarse soils like sands leads to the increase in susceptibility of liquefaction. In silty sands, silt grains fill voids between the coarse constituent, but do not actively participate in stress transmitting microstructure. To consider the partial participation of fines in load bearing structure, an equivalent intergranular void ratio is suggested. The proposed empirical relationship, takes into account the combined influence of fines content, soil gradation, and the average shape of coarse and fine constituents. An equivalent intergranular state parameter is employed in the model formulation to define soil state uniquely. Moreover, recent experimental studies indicate that the consequences of initial anisotropy on the mechanical behavior of silty sands are mitigated with the increase in fines content. To consider this phenomenon, vector magnitude, a measurable index of anisotropy, is related to fines content. Then, proper constitutive equations are introduced to modify plastic hardening modulus and critical state line in loading paths involving rotation of principal stress axes. The simulative capability of the model is evaluated by direct comparison of its predictions with experimental data of triaxial and hollow cylindrical cells reported by four research teams.