Mass rock creep and landsliding on the Huangtupo slope in the reservoir area of the Three Gorges Project, Yangtze River, China

The Huangtupo slope is one of the most noted large-scale slopes with proble ms related to the residential safety of immigrants in the reservoir area of the Three Gorges Project, Yangtze River, China. The gravitational process blended with tectonic deformation, large-scale covering of loose debris, an d long-term surficial mass movement complicate the Huangtupo slope and give rise to a lack of consensus on the slope nature and stability. Characteriz ation of the structural geometry of the slope deformation and reconstructio n of its development history are believed to be pivotal in understanding wh at has happened and what will happen to the slope. Based on a thorough fiel d investigation combined with an electrical resistivity survey, a three-sta ge model involving mass rock creep-primary landsliding-partial reactivation is proposed. The first stage follows the incision of the Yangtze River alo ng the axes of the Guandukou syncline, when Huangtupo experienced long-term gravitational deformation referred to as 'mass rock creep' here. Mass rock creep in the Huangtupo slope can be classified as two basic processes: top pling and deep-seated creep. Toppling mainly occupies the exterior part of the slope and is characterized by inclination, sliding and segmentation of brittle deformation of cleavage rocks, while deep-seated creep occurs domin antly in the interior part of the slope and brittle-ductile flow folding ac companying low-angle shearing is its representative deformation. A primary, large-scale landslide occurred in the second stage as a subsequence of pre vious mass rock creep. The landslide was ca. 4 x 10(7) m(3) in volume with elevations 640 m a.s.l. at the head and 80 m a.s.l. at the foot. Significan t evidence for the landslide is the variation of attitudes of structural fo liation and lineation among outcrops in the slope. The last stage began sub sequent to the original sliding; surfacial and partial reactivation on the Huangtupo landslide plays a leading role in this stage. Two sliding events in this area in 1995 were ascribed to the partial reactivation mainly due t o rainfall, water level fluctuation of the Yangtze River, as well as human activity. It was suggested that analogous failures in 1995 would continue o n the Huangtupo landslide and become even more frequent under the combined effect of human activity and reservoir filling. (C) 2000 Elsevier Science B .V. All rights reserved.