Shaking table tests were conducted for investigating the relation between the subgrade reaction acting on a pile and the soil response in the non-liquefied and the liquefied soil. The subgrade reaction in the non-liquefied and the liquefied soil is occurred almost simultaneously in proportion to the soil shear stress. Before the occurrence of the liquefaction, the subgrade reaction mainly acts on the piles as the reaction forces, and is correspondent to both the relative displacement of the free ground and the ground among piles. After the occurrence of the liquefaction, the subgrade reaction mainly acts on the piles as the external forces. The subgrade reaction is correspondent to the relative displacement of the ground among piles, and is less-related to that of free ground. Though there is a part of the subgrade reaction in proportion to the relative velocity of the ground among piles, this part is very small.
