Xiangjun Pei

Historical Co-seismic Landslides Inventory and Analysis Using Google Earth: A Case Study of 1920 M8.5 Haiyuan Earthquake, China

1000 landslides triggered by the 1920 Ms 8.5 Haiyuan Earthquake were mapped as polygons with remote sensing images provided by Google Earth. Although it was more than 90 years ago, the boundary of medium and large scale landslide triggered by the earthquake is still clear on the images. The landslides were mainly distributed in the west part of Xiji County and the southeast of Haiyuan County, which could be attributed to the difference of loess thickness. The statistical analysis results indicated that the landslide distribution was not mainly controlled by the earthquake parameters (the distance to the epicenter, the seismic intensity and the distance to the seismogenic fault rupture), but by the topographical parameters (elevation, slope height, slope gradient and slope aspect). The field surveys found that most of the landslides occurring on concave slopes of gentler than 20° with long run-out and high speed may be due to the loess liquefaction.

Centrifuge model test of an irrigation-induced loess landslide in the Heifangtai loess platform, Northwest China

The Heifangtai platform in Northwest China is famous for irrigation-induced loess landslides. This study conducted a centrifuge model test with reference to an irrigation-induced loess landslide that occurred in Heifangtai in 2011. The loess slope model was constructed by whittling a cubic loess block obtaining from the landslide site. The irrigation water was simulated by applying continuous infiltration from back of the slope. The deformation, earth pressure, and pore pressure were investigated during test by a series of transducers. For this particular study, the results showed that the failure processes were characterized by retrogressive landslides and cracks. The time dependent reductions of cohesion and internal friction angle at basal layer with increasing pore-water pressure were responsible for these failures. The foot part of slope is very important for slope instability and hazard prevention in the study area, where concentration of earth pressure and generation of high pore-water pressures would form before failures. The measurements of earth pressure and pore-water pressure might be effective for early warning in the study area.

A new rock creep model based on variable-order fractional derivatives and continuum damage mechanics

The creep model is the main form of rock model used to describe the rheological behavior of rocks. A large number of creep models have been proposed, but many are complicated and/or are not able to fully simulate the three stages of rock creep. Hence, an important focus of research on rock creep has been to develop a model with few parameters and better simulation performance. To achieve this, in this study, we propose a new four-element creep model, based on variable-order fractional derivatives and continuum damage mechanics. The newly proposed creep model agrees well with experimental data for Changshan rock salt. The results show that the segmentation treatment is an effective approach for simulating the creep behavior of rocks.

On the initiation, movement and deposition of a large landslide in Maoxian County, China

At 5 am 24th June 2017, a catastrophic landslide hit Xinmo Village, Maoxian County, Sichuan Province, China. The slide mass rushed down from an altitude of 3400m and traveled 2700 m in a high velocity. The 13 million m3 deposition buried the whole village and caused about 100 deaths. The source area of the landslide is located in a high steep slope, average slope angle is 40º and maximal angle is 65º. The strata are interbedded Triassic Zagunao Formation metamorphic sandstone and slate with the dip slope angle of 45°. Based on high-resolution satellite remote sensing image, UAV image, DEM data, and field investigation, failure mechanism, travel features, and deposit characteristics were analyzed. The results showed that this landslide was influenced by Songpinggou Fault zone. According to the topography before the failure, the landslide is located in the back scarp of an antecedent landslide induced by Diexi Earthquake in 1933. The bedding slope provided potential rupture surface. Historical seismic activities and long-term gravitational deformation caused rock mass accumulated damages. Weathering and precipitation weakened the rock mass and finally induced shearing and tension failure. A huge block detached from the top rock slope, pushed the past landslide deposits in the middle part, rushed out of the slope bottom in a high velocity and buried the Xinmo Village. The rapid movement entrained and brought the soil into the Songping Gully which recoiled with and bounced back from the opposite mountain.

Rolling motion behavior of rockfall on gentle slope: an experimental approach

The effects of slope surface material, slope gradient, block shape, and block mass conditions on rockfall rolling velocity were estimated with orthogonal test approach. Visual analysis shows that the importance of the factors is slope surface material > slope gradient > block shape > block mass. All the factors except block mass have the F value greater than the critical value, suggesting that these three factors are the key factors affecting the rockfall rolling velocity. Factor interaction analysis shows that the effect of the slope gradient relies largely on the slope surface conditions, and the block shape has little influence if the slope gradient is larger than a critical value. An empirical model considering the three key factors is proposed to estimate the rolling velocity, of which the error is limited to 5% of the testing value. This model is validated by 73 field tests, and the prediction shows excellent correlation with the site test. Thus, this analysis can be used as a tool in the rockfall behavior analysis.