PURPOSE: To automatically estimate the geological feature of a pile hole with high precision by storing a number of boring data in correspondence with each depth and the excavation electric current, taking out the necessary data and comparing the data with the excavation electric current value for each pile hole.
CONSTITUTION: A number of data which represent the geological feature 1 at each depth by the use of a motor-driven type boring machine and the boring electric current value 2 corresponding to the geological feature 1 is stored. Then, the electric current value 3 in the excavating a pile hole at a site is displayed in correspondence with the depth of the pit. Then, the data necessary for a computer 5 is taken out from a data base 4 in which a number of data are stored and displayed on a display device 6. The data of the data base 4 and the electric current value 3 corresponding to the depth in the pile hole excavation are compared, and the geological feature of the pile hole is estimated. Accordingly, the geological feature of the pile hole at each excavation position can be known automatically, and the geological feature in the direction of the depth of the pile hole can be estimated with high precision.