Coefficient of earth pressure at rest for sands subjected to vibration

An oedometer instrumented to measure horizontal pressure was used to examine the behavior of the coefficient of earth pressure at rest, K _o, of clean sands subjected to vertical vibration. Reconstituted specimens of Ottawa, Lake Michigan Beach, and Niigata sands were used in a comprehensive series of tests. The dynamic effort is defined by the ratio of dynamic increase in effective vertical stress to the static effective vertical stress, and frequency and duration of vibration. Dynamic changes in K _o are referenced to a series of lines representing the ratio of the increase in effective horizontal stress to the increase in effective vertical stress corresponding to different void ratios or friction angles through the Jaky equation. An increase in K_o occurs when the combination of the initial sand state and dynamic effort results in periodic disengagement of interparticle contacts, producing a periodic decrease in interparticle shearing resistance and thus a periodic fluidization of the sand. The highest values of [K_o]_max as well as the lowest values of e_min were obtained with dynamic stress ratios equal to or greater than 3-4. Vibration of overconsolidated sands results in an initial K_o drop that increases with previbration density and overconsolidation ratio. Thereafter, the behavior of K_o and void ratio with vibration depend on the potential for fluidization.