Study of centrifuge model testing on a loess landslide induced by groundwater enrichment, Northwest China

中国西北地区地下水富集引发的黄土滑坡离心模型试验研究  

Engineering Geology, In press, accepted manuscript, Available online 6 June 2019, Article 105170  

Zhang Shuo, Pei Xiangjun, Wang Shanyong, Huang Runqiu, Fan Shan  

摘要：Considerable artificial irrigation in the Heifangtai area since 1968 has caused a continued enrichment of groundwater; the groundwater has risen as much as 18 m merely from 1980 to 2010, resulting in dozens of large-scale loess landslides in the loess platform area. Taking the Jiaojia landslide in the Heifangtai area as a geological archetype to study the deformation and failure characteristics and the mechanism of instability of the slope under the condition of continued groundwater enrichment, centrifugal model tests are performed to reproduce the whole process of deformation and failure of a loess landslide induced by the enrichment of groundwater. Additionally, the pore water pressure, earth pressure, deformation and the evolution characteristics of the slope were monitored and recorded in real time during the centrifugal model tests, and isotropically consolidated undrained triaxial testing (ICU) are used to explore the internal mechanism of loess landslides. The results show that a series of parallel, steep tension cracks at the top of the landslide are caused by the softening of the bottom of the saturated loess layer due to groundwater. These cracks, with the development of vertical joint fissures in the loess and the uneven settlement during collapse of the loess slope, cause the rear wall of this kind of landslide to be mostly straight. According to the ICU experiment, the pore water pressure at very small strains (εa < 2%) increases sharply, while the slope vertical compression deformation and local shear deformation are similar to undrained shear processes. As the pore water pressure continues to rise sharply, static liquefaction of the saturated soils occurs, ultimately inducing the sudden destruction of such landslides, showing the failure characteristics of high-speed mudflow. Generally, the failure of a loess landslide induced by the enrichment of groundwater starts at the toe of the local damage and extends during the whole developing process to create a gradual change in the slope failure; the loess landslide exhibits a progressive retreat deformation damage mode.  

Remotely sensed survey of landslide clusters: Case study of Itaoca, Brazil

滑坡群的遥感勘测：巴西Itaoca实例研究  

Journal of South American Earth Sciences, Volume 92, June 2019, Pages 145-150  

José A. N. Batista, Pierre Y. Julien  

摘要：In January 2014, severe rainfall triggered landslides that buried 92 buildings and claimed 27 lives in the City of Itaoca (3000 inhabitants) in Brazil. The investigation of remotely sensed imagery and a ground-based weather radar shows a landslide cluster with 365 landslide scars over a quite uniformly vegetated background. The devastated area covers 33 km2 with hillslopes ranging from 300 m to 1200 m in elevation, where intense rainfall reached 50 mm–170 mm within 2–6 h. The landslide slopes (median value at 26°) are in general steeper for low rainfall intensities and longer rainstorm durations. Landslide clusters behave in response both to rainfall spatial distribution and land slopes. The total scar area of landslide clusters of given median slope exhibits a peak curve with maximum at the overall median slope. The individual scar areas exceedance probability follows a log-gamma distribution and the scar surface area increases with slide slopes.  

A regional-scale landslide early warning methodology applying statistical and physically based approaches in sequence

基于序列统计物理方法的区域滑坡预警系统  

Engineering Geology, In press, accepted manuscript, Available online 13 June 2019, Article 105193  

Joon-Young Park, Seung-Rae Lee, Deuk-Hwan Lee, Yun-Tae Kim, Ji-Sung Lee  

摘要：In response to the sharp increase in geological disasters resulting from localized extreme rainfall events in Korea, a landslide early warning methodology is proposed. The method is based on sequential applications of the statistical and physically based hazard evaluation approaches and devised by combining the strengths of these two mutually complementary approaches. Following the decision algorithm for five phases of the warning level, the statistical evaluation was set to be applied first by using two different rainfall thresholds and one fixed geo-property (landslide susceptibility) threshold to determine a preliminary conservative warning level. To assess whether higher warning levels with higher certainties should be assigned, the physically based evaluation was set for application in the precondition of the preliminary warning stage. This was accomplished by using a rainfall threshold related to slope instability based on an advanced analysis using the physical modeling of landslide-triggering mechanisms. Consequently, a landslide early warning model based on the sequential evaluation approach was developed. The model ran through from transforming raw rainfall data to generating a series of geographic information system-based landslide early warning level maps. The spatially-discriminating capability and temporal applicability of the model on the distributed landslide events of 2009 were discussed by comparing the simulated results with landslide historical data while contemplating the adequacy of the durations and lead times of early warning levels. As a result, several advantages were identified for both spatial and temporal landslide early warning performances in the proposed methodology.  

Experimental investigation on the longitudinal evolution of landslide dam breaching and outburst floods

堰塞坝漫顶溃决与溃坝洪水的纵向演化试验研究  

Geomorphology, Volume 334, 1 June 2019, Pages 29-43  

Gordon G. D. Zhou, Mingjun Zhou, Mandira Singh Shrestha, Dongri Song, Huayong Chen  

摘要：Accurate prediction of the evolution of a landslide dam that is breached due to overtopping failure is necessary to estimate the outflow hydrograph and the resulting inundation. In this study, physical flume tests on the breaching of landslide dams were conducted. A wide grain size distribution with unconsolidated dam material was used. Dam breaching was initiated by cutting a notch across the crest of the dam adjacent to the side wall of the flume. This allowed water to escape from the dam while a steady inflow of water was continuously supplied upstream. The effects of upstream inflow on the timescales and magnitudes of the peak discharges and the time to inflection point were also investigated. Experimental results reveal that the whole hydrodynamic process of dam breaching can be divided into three stages defined by clear inflection points and peak discharge. A new longitudinal evolution model is proposed. This model captures the initial increase of the soil erosion rate (of landslide dam) and its subsequent decrease along the longitudinal direction. In addition, a linear relationship between the soil erosion rate and shear stress (of water flow) was observed and this is similar to that observed in large-scale natural landslide dams. Furthermore, soil erosion resistances (of landslide dam) against water flow above are observed to increase with the concentration of entrained sediments along the flow direction.  

Stability analysis of landslide dams under surge action based on large-scale flume experiments

基于大型波浪水槽实验的堰塞坝稳定性分析  

Engineering Geology, In press, accepted manuscript, Available online 11 June 2019, Article 105191  

Ming Peng, Qiu-Lu Jiang, Qing-Zhao Zhang, Yi Hong, Li-Min Zhang  

摘要：In recent years, large magnitude earthquakes have caused the formation of a large number of landslide dams. The rising water level in the landslide lakes may induce a large number of landslides in the lake areas. When landslides rush into a lake area, large-scale surges may be produced and would then strongly impact on the dam stability and cause a breaching process. To understand the erosion failure modes of dam bodies caused by surges and the variation in the pore water pressure in the dam body, large-scale wave flume tests were carried out in this study. Six groups of comparative tests were carried out to study the two main influencing factors, namely, the upstream water level and the wave height. It was found that (1) when subjected to surge waves, the landslide dam stability is determined by the difference (ΔH) between the effective water level (the sum of the water level and the overlapping wave height) and the effective dam height (the dam height after lowering due to local sliding); (2) when ΔH < 0, overtopping does not occur, and the landslide dam remains stable. A stable upstream erosion surface eventually forms, the surface slope angle decreases and the erosion volume increases as the wave height increases; when ΔH > 0, the dam is overtopped and breached by the next waves; (3) During dam breach by overtopping with surge waves, the erosion in the breach initiation phase is much faster than by overtopping without surge waves, but the difference in the breaching development phase is not very significant; and (4) the pore water pressure close to the upstream slope is much more sensitive to the action of the surge waves than deeper inside the dam body.