The need for low�]cost spur roads with a simple structure is rapidly increasing. Cracks and collapse are caused by the insufficient compaction of embankments on spur roads. A simple method is required for inspecting embankments on low�]cost spur roads. Therefore, an inexpensive portable dynamic penetrometer known as the Tottori FK�]type penetrometer was developed. Penetration tests were carried out at the center and shoulder of eight spur roads geologically characterized by granite. The results are summarized as follows. 1) When a weight is dropped five times, the penetration depth exceeds 25 cm at the site where a crack has already occurred. 2) The cracks most likely occur when the penetration depth at the shoulder is more than three times greater than that at the center. 3) In the case of 2), the crack occurs at a position near the shoulder. 4) When the penetration depth exceeds 25 cm at both the center and the shoulder, the crack occurs at a position near the center. On the basis of the results stated above, we proposed an inspection method that divides the compaction condition of embankments into four categories. The collapse of the shoulder actually occurred in the part of the shoulder that was categorized as weak according to the proposed inspection method. We confirmed that the proposed method can be adopted to evaluate the structural strength of embankments on spur roads.

Key words�Finspection method of embankment, portable dynamic penetrometer, spur road