barrier 12 is to be formed in situ the tractor 2 draws the plow 10 horizontally during which time heated asphalt in the liquid form contained in the tank 4 is fed continuously into the first chamber 36 of the plow 10 via the conduit 8 the results of an experimental test indicate that the temperature of the heated asphalt affecting the quality of the formed barrier is suitably in the range of about 135 u00b0 170 u00b0 c for the penetration index 80 u02dc 100 and preferably in the range of about 145 u00b0 150 u00b0 c for the penetration index 80 u02dc 100 asphalt pressure within the first chamber 36 of the plow 10 should not exceed 1 0 kg cm 2 and be preferably in the range of 0 3 0 5 kg cm 2 the asphalt which has filled the first chamber 36 then flows into and fills the second chamber 40 through the holes 44 formed at spaced intervals in the partition wall 42 the asphalt in the second chamber 40 then flows out through the outlets 56 in the rear lower wall 54 the pressure of asphalt when flowing out of the plow does not exceed about 0 1 kg cm 2 thus as the plow 10 advances asphalt supplied continuously from the asphalt tank 4 fills the first chamber 36 and the second chamber 40 at all times and cannot be exposed to an atmosphere within or outside the plow 10 as the plow 10 progresses continuously in the soil at the preselected depth the soil is divided into an upper soil portion supported on the plow 10 and a lower exposed soil portion the asphalt.