Evaluation of the effects of shaking history on liquefaction and cone penetration resistance using shake table tests

This paper presents a study of the effects of shaking history on liquefaction and cone penetration resistance of a clean sand by using 1-g shake table and piezo-cone penetration test (CPTu). A uniform liquefiable clean sand specimen was air-pluviated and saturated in a large laminar shear box. The sand specimen was subjected to four shaking events. Piezometers were embedded at different depths to measure the excess pore pressures during and after each event. A series of CPTu tests were conducted on the sand specimen across different shaking events to investigate the effect of shaking history on cone penetration resistance. The main findings of the paper are: 1) the relative density (D_r) increased as a result of prior shaking events; increase of liquefaction resistance was observed from Event #1 to Event #4-1, as a result of densification; 2) input motion with an acceleration amplitude of 0.4 g and 25 cycles induced dilatancy of very dense sand specimen and reduced the liquefaction resistance in subsequent shaking events; a mild shaking event with an acceleration amplitude of 0.1 g and 14 cycles was able to erase the disturbance caused by strong shaking, recompact the sand and increase the liquefaction resistance; 3) the post-shaking pore pressures increased with time after shaking had ended; the magnitude of increase was related to D_r and pore pressure ratio at the end of shaking; 4) liquefaction significantly disturbed the existing soil structure and thus reduced the cone resistance immediately after the shaking; both shaking disturbance and sand densification affected the cone resistance variation before and after shaking.