Foundation piles of piers are always surrounded by rubble mounds. Although the rubble must restrict lateral movement of piles, its mechanism is not clear, and the restriction is not taken into consideration in the design of the piles. In order to evaluate the restriction, a series of model tests have been carried out, where a lateral load is applied to model piles with various bending stiffness, breadth and shape (plate and cylinder) in model grounds various in density consisted of rubble with various maximum grain size.
　Main conclusions can be summarized as follows:
1) PHRI method of analyzing lateral resistance of a pile is valid for a pile in rubble.
2) The influence of bending stiffness of a pile and of repeated loading on lateral resistance characteristics of a pile in rubble is similar to that in sandy grounds.
3) The results of a field tests shows that the lateral resistance of a pile in rubble mounds is small and can be evaluated as C-type ground of PHRI method.