PURPOSE: To precisely determine the liquefaction of the ground by using a constitution in which reaction forces produced by vibration of a vibrator and a vibrating plate is received by the reaction floor and reaction wall of a tank, and the vibration output of the vibrator is transmitted as it is to a test soil layer.

CONSTITUTION: A concrete floor and four concrete side walls are integrally formed, and a tank 1 consisting of the floor as a reaction floor 2 and a side wall as reaction wall 3a is constructed. In the tank 1, two vibrating plates 4a and 4b facing each other at a given interval are erectly set between both side walls adjacent to the reaction wall 3a, and their lower ends are connected to the reaction floor 2 in a pivotally movable manner. When a vibrator 15 is operated to apply repeated horizontal vibrations to the plates 4a and 4b, the plates 4a and 4b are displaced in a rocking manner and the shearing deformation is received by a test soil layer (a) in the soil tank 5. The occurrence and degree of liquefaction are judged from measured values of a void water pressure gauge 23 and a seismometer, etc.