Loess Stratigraphy and Loess Landslides in the Chinese Loess Plateau
02 Nov 2020-pp 269-288
TL;DR: Based on the Sassa motion simulation model, the modified models for simulating the catastrophic long run-out loess landslides are proposed which consider the effects of curved moving path, frontal plowing, bed entrainment on the running distance and coverage area of the sliding materials as mentioned in this paper.
Abstract: Chinese Loess is a dust deposit brought by wind from North-West desert. In the past four decades, the age and the strata of the loess stratigraphy were well defined by dating and correlating with deep sea core isotopic curves. A standard loess stratigraphic profile and the correlation among the different areas are introduced, and typical river terrace with loess deposit is also illustrated. Loess has a loose texture and is sensitive to water, which makes it susceptible to failure during rain or engineering activities. Landslides on the Chinese Loess Plateau are the most common and widespread geological hazard, which results in human deaths and severe injuries. Moreover, it damages infrastructures such as road, tunnels, bridges, railway tracks and engulfs agricultural land every year. Based on the failure modes and motion characters, the loess slope failure can be classified into two main types, shallow slide, and deep-seated landslide. The shallow failure can be further divided into two types of small collapse and shallow flow slide; while the deep-seated failure can be divided into the four types of rapid long run-out slide, rapid flow slide, slow creep slide and quick slump slide. The mechanism of the landslide movement is controlled by the moisture state on the failure surface and the moving path. Based on the Sassa’s motion simulation model, the modified models for simulating the catastrophic long run-out loess landslides are proposed which consider the effects of curved moving path, frontal plowing, bed entrainment on the running distance and coverage area of the sliding materials.
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TL;DR: In this article, three groups of full-scale field experiments with different rainfall intensities were conducted in Jingyang County, Northwest China to reveal the surface infiltration process and deformation characteristics of unsaturated loess slopes.
16 citations
TL;DR: In this article, two groups of irrigation-erosional experiments were conducted to study the hydrologic characteristics and failure processes of unsaturated loess slopes, and the results indicated that smaller slope gradients are associated with higher average infiltration rates, greater sliding surface depths, and farther sliding distances.
Abstract: Irrigation-induced shallow loess landslides on south bank of the Jing River, Shaanxi Province, usually occur on slopes where loess flowslides had previously occurred. Two groups of irrigation-erosional experiments were conducted to study the hydrologic characteristics and failure processes of unsaturated loess slopes. In addition, SEEP/W and SLOPE/W in Geo-Studio were selected to quantify the effects of soil suction, slope gradients and soil properties on the stability of the unsaturated loess slope. Results indicated that smaller slope gradients are associated with higher average infiltration rates, greater sliding surface depths, and farther sliding distances. However, the smaller the gradients of the slope, the longer irrigation times and more water are required for slope failure. There are four stages in the evolution of the loess slope during artificial irrigation: the erosion of slope surface - the generation of tension cracks at the slope shoulder - partial failure occurrence and generation of potential sliding surface - retrogressive slope failure. The suction strength is a dominant component of shear strength in maintaining stable conditions in small-scale loess slopes. The irrigation caused dissipation of soil suction in the near-surface soil, thereby reducing shear resistance and triggering shallow loess slide. However, the finiteness of the suction strength determines that its attenuation will not determine the stability of large-scale landslide. Our results have implications for the understanding of surface erosion and shallow sliding of small-scale loess slopes at South Jingyang Plateau.
13 citations
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TL;DR: In this article , the role of preferential flow and piston flow in moisture transfer in the thick loess vadose zone remain controversial, and the authors used a 100m-thick loess shaft to monitor soil moisture content and soil temperature over 5 years, whereas climate indices were monitored on Earth surface.
Abstract: Precipitation is the only source of groundwater recharge in the Chinese loess region. However, rainfall has been the main driver of geological disasters and engineering challenges in China, such as landslides, slope collapse and sinking of foundations. The roles of preferential flow and piston flow in moisture transfer in the thick loess vadose zone remain controversial. This study used a 100‐m thick loess shaft to monitor soil moisture content and soil temperature over 5 years, whereas climate indices were monitored on the Earth surface. The soil water characteristic curves and hydraulic conductivity function of the loess and the palaeosol collected in the profile were measured in a laboratory. The soil profile moisture transfer process was simulated based on the climatic boundary conditions and measured hydraulic parameters. The monitored and simulated results suggest that loess moisture transfer is dominated by piston flow. The thick loess vadose zone above the groundwater level could be divided into two sub‐zones, namely the active and steady zones. The active zone has a thickness of ~7 m and shows a direct response to climate change, with soil moisture content regulated by rainfall infiltration, evaporation and transpiration and soil moisture moving as transient flow. Although preferential flow can move in the active zone along joints, fissures and holes when water accumulates in the lower ground during heavy rainfall, piston flow remains the main mode of water movement. The steady zone has a thickness of <7 m and is above the groundwater level. Soil moisture content and soil temperature in the steady zone show temporal stability and soil moisture moves as a steady flow. Piston flow is the only mode of water movement in the steady zone. Since percolation velocity in the steady zone is estimated to be 73.3 mm/year, 1330 years of rainfall infiltration through the 97.5 m thick vadose zone would be required to recharge groundwater.
References
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TL;DR: In this paper, a detailed record of climate changes during the last 2.5 million years in central China has been provided, at least 44 major shifts from glacial to interglacial conditions occurred during this time in China.
787 citations
TL;DR: In this paper, a new basal entrainment model taking advantage of both Coulomb and Voellmy frictional laws is proposed, providing a unified formula to simulate the stop-and-go process of debris flows.
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TL;DR: This paper showed that most of the loess flow-slides in Yan’an were small scale and only occurred at a depth of 2 m. The results from this study showed that the occurrence of loess flows is closely related to infiltration depth, slope angle, slope morphology, rainfall intensity, and loess strength.
Abstract: The Yan’an area, located on the Loess Plateau in Northern Shaanxi Province, China, experienced heavy and prolonged rainfall in July 2013, which induced 8,135 slope failures (loess landslides and loess flow-slides), destroying approximately 10,000 cave dwellings and killing 45 people. Field investigations have indicated that the occurrence of loess flow-slides is closely related to infiltration depth, slope angle, slope morphology, rainfall intensity, and loess strength. The results from this study showed that (a) most of the loess flow-slides in Yan’an were small scale, ranging in volume from tens of cubic meters to hundreds of cubic meters; (b) the loess flow-slides only occurred at a depth of 2 m) and can effectively prevent loess flow-slides.
65 citations
01 Jan 2013
TL;DR: Wang et al. as discussed by the authors proposed an early warning system based on monitoring, which is a practical and economic way to check landslides as much as possible in considering of the present natural environment and national condition.
Abstract: Chinese Loess is a wind origin deposit which records the continuous Quaternary history. In the past 30 years, the loess stratigraphy has achieved a great advantage that the absolute age and the litho-strata were well defined by dating and correlating with deep sea core isotopic curves. That set up a formed basis for further study in the loess properties and geological hazards in view of origin and mechanism. Loess has special characters of typical topographies, vertical joints, loose texture and water sensitivity, which makes it easy to slide. Landslides on the Chinese Loess Plateau are the most severe geological hazards, which deprive people of life, damage gas and oil routes, destroy roads and railways and decrease farmlands. Control of landslides is a long-term strategy. Besides the general used structural methods being applied in the slides related to some engineering, improvement of ecological environment, innovation of irrigation way and availability of drainage systems are more significant. Building of early warning system based on monitoring is a practical and economic way to check landslides as much as possible in considering of the present natural environment and national condition.
26 citations
TL;DR: In this paper, a modified finite difference model is proposed to simulate the propagation of flowslides, which can accurately predict the details of the motion of the landslide, especially behaviors such as turning along the meandering gully and thrusting on the gully slopes due to centrifugal force.
Abstract: In this paper, a modified finite difference model is proposed to simulate the propagation of flowslides. Modifications of the new model are conducted by calculating the lateral pressure coefficient k in the sliding mass and the entrainment and centrifugal effect during the transport process. The strength parameters are modified based on the size of the entrainment to consider the change in the landslide strength due to material mixing. Two dam break problems are simulated to test the accuracy and stability of the numerical scheme, and the results show good agreement with the analytical solutions and the measured data. Then, the model is used to analyze a typical flowslide: the Dagou landslide in Gansu Province, China. The model can accurately predict the details of the motion of the landslide, especially behaviors such as turning along the meandering gully and thrusting on the gully slopes due to centrifugal force.
20 citations