Packing Density and Overconsolidation Ratio Effects on the Mechanical Response of Granular Soils

Liquefaction of sandy soils is associated with a sudden loss of the shear strength due to a dramatic increase of the excess pore water pressure in undrained conditions. Its occurrence usually causes significant damages to buildings and infrastructures during earthquakes. Therefore, the proposed laboratory research investigation aims to study the effects of the combined effects of sample depositional methods, initial relative density and overconsolidation ratio on the undrained shear strength of Chlef sand samples under static loading conditions. For this purpose, a series of undrained monotonic triaxial tests were carried out on reconstituted saturated Chlef sand samples and subjected to different overconsolidation ratios (OCR = 1, 2, 4 and 8). The initial confining pressure for all tests was kept constant (σ′₃ = 100 kPa). The samples were prepared using two depositional methods named: dry funnel pluviation (DFP) and wet deposition (WD) at three selected relative densities (D_r = 18%, 52% and 88%). The obtained data confirm the existence of a linear relationship between the undrained peak shear strength of overconsolidated Chlef sand samples (q_peak__OC) and undrained shear strength of normally consolidated Chlef sand (q_peak__NC) for the two sample preparation techniques (DFP and WD) and range of the initial relative density (18% ≤ D_r ≤ 88%) under consideration. The overconsolidation (OCR) and initial relative density (D_r) increase the dilativeness of the normally consolidated and overconsolidated sandy samples for the two sample reconstitution techniques. The dry funnel pluviated sandy samples exhibit higher undrained shear strength (liquefaction resistance) than the wet deposited sandy samples. Moreover, the obtained data reveal that the wet deposited sandy samples were more vulnerable to liquefaction resistance than dry funnel pluviated sandy samples for the range of the initial relative density (18% ≤ D_r ≤ 88%) and lower overconsolidation ratios (1 ≤ OCR ≤ 4).