The geotechnical characteristics and behavior of gravel formations are significantly different from those of alluvial and sedimentary deposits or other rock formations. Due to the facts of complex material properties and orientations of particle arrangement, the results obtained from the laboratory tests and field measurements are quite different and diverse. Up to the present time, the basic data of the gravel formations in Taiwan are still limited. Hence, the reliable relationship between the mechanical properties and index properties for the gravel formations is still under developing. In the authors' opinion, the main reason of the difference may be due to the method of exploration, classification sysytem, testing and analyses used by the engineers are quite different from one another. In other words, there is still lack of standard criteria that can be followed. Therefore, the geotechnical engineers often encounter some problems when dealing with gravel formations. This paper aims to present a rational approach of exploration and testing method for the gravel formation s. Furthermore, through the existing data collected by the authors and others, it is hoped that the paper will stimulate the understanding of the field geotechnical engineering properties of the gravel formations.