SKS03: Centrifuge Test of Liquefaction-Induced Downdrag in Interbedded Soil Deposits

The SKS03 centrifuge model test examined liquefaction-induced downdrag in a layered liquefiable soil deposit with a surface clay crust. The soil profile consisted of 1 m of coarse sand, 2 m of clay crust, and 4.7 m of loose sandy soil (prototype scale). Below the loose sand was about 1.3 m of a clayey silt layer underlain by 5 m of medium dense sand and dense sand beneath it. The test included three medium 635 mm diameter (D) piles, with their tips embedded to a depth of 3D in the dense sand layer. The loads applied on the piles were 500 kN, 1500 kN, and 2400 kN, respectively. The model was shaken with a suite of scaled Santa Cruz earthquake motions with peak horizontal accelerations ranging from 0.08g to 0.61g. A pile load test was performed at a constant penetration rate to obtain the pile capacity (including the shaft and tip resistance). Similar to SKS02, drag loads were observed to increase along the piles with multiple shakings. Most of the pile settlement occurred during shaking with very minimal settlement (< 10 mm) post shaking. Among all piles, the heavily loaded ones suffered the most settlement. Higher drag loads were observed on lightly loaded piles as compared to the heavily loaded piles. The neutral plane was deeper for the lightly loaded pile and correspondingly much shallower for the heavily loaded pile.