This paper reports the results of excavating test of clay by water jet. To investigate the effects of excavation by water jet, we measured depths of excavation under constant nozzle moving speed and got the following result.
　Excavating depth　(D)=C・d1.5・P-D0
　　where　　　　　　　d : Dia,of jet nozzle.
　　　　　　　　　　　　　　P : Outlet pressure of water jet.
　　　　　　　　　　　　　　C : Coefficient which varies with characterestics of soil.
　　　　　　　　　　　　　　D : Constant determined by nozzle moving speed and characterestics of soil.
　Dia of nozzle for the experiment were 4.0,6.0,8.0 and 10.0m/mφ, and max outlet pressure and speed of nozzle were 1.3kg/cm2 and 1.84 m/sec respectively.