dc.description.abstract | The Daguangbao landslide which triggered by the 2008 Wenchuan earthquake is one of the largest earthquake-triggered landslides in the world over the past century. Therefore, it is important to well document this landslide, such as the geometry of the sliding mass, the dominating structures, and the failure mechanisms. In this study, remote sensing images analysis, field investigation, laboratory experiment and slope stability analysis were adopted to characterize this Daguangbao landslide. Based on the remote sensing images and pre- and post- DTMs, as well the field works, the dominating structures of this landslide are folded bedding plane and a steeped-out joint system, which outcropped at the south and north of the landslide site respectively. Accordingly, this landslide is a gigantic, atypical wedge failure. With the inferred slip planes, the intersection line is curved and counterclockwise rotated, which fit the trajectory of mining tent well. Meanwhile, the intersection line will be daylighted. That is, rock mass shear-off on the toe of this landslide, as assumed by most of the researchers, is no more required with adopting the inferred sliding surfaces. According to the proposed wedge shape, pre- and post- DTMs, the volume of moving mass is about 10.51 × 108 m3 with a travel distance of 1.9 km. The characteristics of the sliding surface on the south part of the landslide site were carefully investigated. The identified slip zone was composed of breccia and gouge layers of several centimeters thick. The intact dolomite rocks adjacent to the slip zone and the thin gouges were sampled to conduct X-ray diffraction analysis. The results show that the mineral of the gouges is nearly identical to the dolomite country rocks. The friction coefficients of the dolomite discontinuity and gouges near the sliding surface were measured utilizing a rotary shear apparatus under a normal stresses of 11.47 MPa (dolomite discontinuity) and 1~3 MPa (gouges) with slip rates of 0.0009~1.3 m/s. A threshold velocity of 0.001 m/s was identified that the slip strengthening behavior under slowly shearing turned into slip weakening. The peak friction coefficient of the tested dry dolomite discontinuities and wet gouges are 0.52~0.96 and 0.75~0.92 and the steady-state friction coefficient of the two samples are 0.1~0.57 and 0.13~0.74, respectively. The wedge analysis shows that the slope is quite stable (F.S. = 2.45) without the seismic force. However, the gigantic wedge can be triggered by the Wenchuan earthquake based on the pseudo-static slope stability analysis. Moreover, the friction coefficient of the gouges under large shear displacement will drop below 0.25 (~tan(14°); the intersection line plunged 14°) when the shear velocity exceeds 1.3 m/s. That is, the gigantic wedge can be speeded up by the inertial force generated by the earthquake and keep moving rapidly with long run-out. | en_US |