ORIGINAL PAPER Experimental Study of Dry Granular Flow and Impact Behavior Against a Rigid Retaining Wall Yuan-Jun Jiang • Ikuo Towhata Received: 1 December 2011 / Accepted: 17 July 2012 Ó Springer-Verlag 2012 Abstract Shallow slope failure in mountainous regions is a common and emergent hazard in terms of its damage to important traffic routes and local communities. The impact of dry granular flows consisting of rock fragments and other particles resulting from shallow slope failures on retaining structures has yet to be systematically researched and is not covered by current design codes. As a pre- liminary study of the impact caused by dry granular flows, a series of dry granular impact experiments were carried out for one model of a retaining wall. It was indirectly verified that the total normal force exerted on a retaining wall consists of a drag force (F d ), a gravitational and frictional force (F gf ), and a passive earth force (F p ), and that the calculation of F d can be based on the empirical formula defined in NF EN Eurocode 1990 (Eurocode structuraux. Base de calcul des structures, AFNOR La plaine Saint Denis, 2003). It was also indirectly verified that, for flow with Froude number from 6 to 11, the drag coefficient (C d ) can be estimated using the previously proposed empirical parameters. Keywords Granular flow  Retaining wall  Impact  Drag force 1 Introduction In recent years, with the expansion of human activities in mountainous areas, such as road construction, tourism and recreational activities, etc., more and more shallow slope failures have occurred. Earthquakes, rainfall, and other geological and meteorological events also accelerate the occurrence of shallow slope failures. A great number of slopes in the earthquake-affected zone were found to be potentially unstable after the M8.0 Wenchuan earthquake in China on May 12, 2008. Figure 1 shows severe shallow slope failures along a key road in Yingxiu County, the epicenter of the Wenchuan earthquake in 2008. Dry granular flows pro- duced by these shallow slope failures, which contained large amounts of gravel and rock fragments, were able to travel downward to the foot of mountains, destroying and blocking important roads. Generally, dry granular flows are forms of rock avalanche (Gerber 2001), but are smaller in volume than conventional rock avalanches, which have volumes of more than 10,000 m 3 (Hungr et al. 2001). To guarantee the safety of roads and the smooth flow of traffic in landslide-prone areas, protective structures are needed, especially retaining walls. However, prior to the design of such a retaining structure, the impact force likely to be exerted on it has to be determined. Therefore, this paper studies the impact of dry granular flow on a retaining wall, and investigates the impact force generated by the dry gran- ular flow. As introduced by Hungr (1995), several approaches can be applied to the analysis of granular flows, being expected to shed light on the calculation of the impact force generated by a dry granular flow. Furthermore, the methods used in existing impact studies could be useful for reference. In geotechnical engineering, there are several studies related to the impact of rocks and soils against barriers, such as: Y.-J. Jiang (&) Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, 9#, Section 4, RenMinNanLu Avenue, Chengdu 610041, Sichuan, China e-mail: yuanjun.jiang.civil@gmail.com I. Towhata Laboratory of Geotechnical Engineering, Department of Civil Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan 123 Rock Mech Rock Eng DOI 10.1007/s00603-012-0293-3