PURPOSE: To correctly estimate the enduranc force on a foundation by comparison- displaying the N value and the electric current value or torque value in each depth in a standard penetration test and estimating the soil feature name in a pile pit from the variation of the excavation electric current value, reading the variation tendency of the graph.

CONSTITUTION: Each column for staff 2, depth 3, soil feature mark 4, soil feature name 5, number of times of striking 6, N value 7, and an electric current recording column 8 are formed in the upper part on a recording paper 1, and longitudinal direction is set as depth, and the lateral direction is set as numerical value, etc. The data in the standard penetration test is written into each column, and the electric current recorded value is displayed by the electric current measured value as it is in the pile pit excavation, and a graph is attached on the electric current measured value in correspondence with the specific depth. Then, the comparison graph between the N value and the electric current value is analyzed, and after the electric current value is applied with correction, the soil feature name is estimated through comparison. The used electric current value or torque value for each depth is drawn in each pile pit excavation on one side of the N value graph, and the boring data is displayed to estimate the stratum.