Landslide Slip Zone Research Articles

Shear constitutive model for various shear behaviors of landslide slip zone soil

Shear constitutive model for various shear behaviors of landslide slip zone soil

A thermo-poro-mechanical model for catastrophic landslides under unsaturated conditions

Large landslides are one of the most menacing geological hazards in mountainous regions around the world due to their high-speed, large-scale characteristics. Up to now, the thermo-poro-mechanical coupling mechanism of catastrophic landslides under initial water-saturated conditions has been recognized by many scholars. Nevertheless, most slip zones of landslides are located in both the unsaturated and saturated zones and the unsaturated zone can account for a much larger portion when the groundwater level is relatively low. Typical examples of this situation include many loess landslides which have occurred in northwestern China. In this study, a unified quasi two-dimensional thermo-poro-mechanical model was proposed taking into account both the unsaturated and saturated zones in the slip band of landslides and an attempt was made to describe the complete movement process. Moreover, the Dongfeng loess landslide was chosen as a case study with an assumed triggering condition, and the model was validated by comparison between the simulation results and previous published work. A sensitivity analysis demonstrated that the frictional heating mechanism and the presence of a dry air phase in the slip band have clear impacts on the characteristics of the landslide. In particular, it was found that the soil–water characteristic curve and the initial degree of saturation are of significance.

Effect of Dry-Wet Cycling on the Residual Strength Characteristics of Coal Measure Soil

Coal measure soils are the main component in the slip zones of landslides along the Changli highway in China. Therefore, exploring the residual strength of coal measure soil affected by dry-wet cycling is helpful for evaluating landslides. However, very few researchers have reported on the residual strength behavior of coal measure soil subjected to dry-wet cycling. In this study, we performed three tests (ring shear test, scanning electron microscopy test, and mercury intrusion porosimetry test) to evaluate the residual strength behavior of coal measure soil under different dry-wet cycles. Our results indicated that the peak strength decreased with increasing dry-wet numbers and that dry-wet cycling had no evident effect on the residual strength. Moreover, the residual strength in the slip soil was approximately proportional to the normal stress. Furthermore, the degeneration of peak cohesion exponentially increased, and the porosity and fractal diameter also increased with the dry-wet numbers. The connection between mineral particles changed from a stable layered structure to an unstable chain structure. Consequently, we inferred the failure mechanism of K213-type shallow landslides and formulated appropriate preventive measures. This study is of great significance for understanding the mechanical behavior of the slip zone of coal measure soil and predicting the re-emergence of coal measure soil landslides.

Effect of moisture content and shearing speed on shear zone structure in fine-grained soils at large displacement

Fine-grained soils are the main component of slip zones of landslides in the Three Gorges area, China. Studying the shear zone structure in fine-grained soils is helpful to evaluate landslides. In this study, the effect of moisture content and shearing speed on the shear zone structure in fine-grained soils subjected to large displacement was investigated through a series of drained ring shear tests, grain size analyses, and microscopic observations. The concentration of clay fraction around the shear planes and corresponding variations in the shear zone structure were highlighted. The results indicate that with increasing moisture content and shearing speed, the residual strength of the soil samples gradually decreased. The soil grains within the samples were redistributed during extended shearing. The clays tended to concentrate around the shear planes and decrease in number away from the shear planes, which could be caused by grain crushing and the diffusion of silty water. The most obvious concentration of clay fraction was observed at high moisture content and high shearing speed. Moreover, the effect of moisture content and shearing speed on the shear zone structure depended on the grain size. Increasing moisture content and shearing speed resulted in a smaller median grain size and ratio of the amount of sand fraction after shearing to before shearing, while a larger ratio of clay fraction. The corresponding change in the shear zone structure caused significant deterioration in the shear strength and porosity of shear zone soils, to the detriment of landslide stability.

Landslide Developmental Characteristics and Response to Climate Change since the Last Glacial in the Upper Reaches of the Yellow River, NE Tibetan Plateau

Abstract:The upper reaches of the Yellow River in northeastern Tibetan Plateau are geohazards areas. The evolution of the Yellow River, chronology of some landslides, and spatiotemporal distribution characteristics of super large scale and giant landslides within the region are summarized using paleoclimate evidence, and the relationship between the intensive landslide period and climatic changes since the Last Glacial period is analyzed. It is concluded that (1) Super large scale and giant landslides are distributed widely within the region, particularly in the Qunke‐Jianzha basin. (2) The chronological sequence of landslides is established by dating the slip zones of landslides and analyzing the relations between landslides and their overlying or underlying loess formations. Five landslide development periods are determined: 53–49 ka BP, 33–24 ka BP, 10–8 ka BP, 5–3.5 ka BP, and the present. (3) These correspond closely to warm and wet periods during the last 100,000 years, i.e., two weak paleosol development stages of Malan loess deposited during the last Glacial period in the Chinese loess Plateau, L1–4 and L1–2 that belong to the marine oxygen isotope stage 3, the last deglacial period, the Holocene Optimum, and the modern global warming period. (4) Landslide triggers may be closely linked to warm and wet periods related to rapid climatic transitions.

Pyrite in sliding mud: A potential indicator of landslide development

A new principle of geochemical conditions within a landslide slip zone is presented based on the concept of a self-sealing closed system for which newly formed pyrite should be considered as a potential indicator. Once slip zones occur, a series of water-rock interactions may take place, particularly, a change in redox conditions simultaneously with progression of the landslide. This change induces weathering of the debris and bed rocks, and leads to accumulation of newly formed sliding mud within the slip zone. Pyrite formation along with clay mineral accumulation occurs under a weak alkaline-strong reducing environment along with landslide development. Thus, formation of neogenetic pyrite, iron speciation, and clay mineralization are all important factors for a better understanding of landslide progression.

Mineral Compositions and Elements Concentrations as Indicators for the Role of Groundwater in the Development of Landslide Slip Zones: a Case Study of Large-scale Landslides in the Three Gorges Area in China

Reduction of shear strength in landslide slip zone is one of the fundamental mechanisms for landsliding. The causes of decrease in shear strength in landslide slip zones are keys to the understanding of landslide mechanism and to the prediction of landsliding events. Groundwater within slope is known to play an important role in reducing shear strength in landslide slip zones during the development of landsliding physical and chemical interactions with solid phases in the slip zones. In this paper, we report the results of a case study that shows the role of groundwater during the development of landsliding. The physical and chemical effects of groundwater in reducing shear strength in these slip zones may be evaluated by examining the variations of mineral compositions and major elements within the slip zones and surrounding areas. The characteristics of mineralogy and geochemistry of two large-scale landslides in the Three Gorges area, China, the No. 1 Linjiang landslide at Huangtupo and the Xietan landslide, reveal that these slip zones developed along pre-existing weak zones within the slopes. Particularly, minerals and elements that are reactive with groundwater within the landslides indicated that groundwater within the slip zone of the No. 1 landslide at Huangtupo is recharged by rainfall, which caused oxidation within the slip zone. The shear strength reduction in the slip zone could have resulted from physical and chemical processes involving hydrolyses, argillation of marls fragments, dissolution of calcite, and transformation of illite to interlayered illite and smectite. In contrast, groundwater in the slip zone of Xietan landslide has little rainfall component. Consequently, reduction is overwhelming, and shear strength decrease in the slip zone during its development was largely caused by chemical weathering of feldspar and transformation of illite to interlayered illite and smectite.

Residual strength of slip zones of large landslides in the Three Gorges area, China

Slip zones of the large landslides in the Three Gorges area are commonly composed of fine-grained soils with substantial amount of coarse-grained particles, particularly gravel-sized particles. In this study, residual strength of the soils from slip zones of these landslides were examined in relation to their index properties based on a survey of 170 landslides. It was found that laboratory-determined residual friction angle using gravel-free fraction of the disturbed soils from the slip zones was closely related to clay content, liquid limit and plasticity index. On the other hand, in-situ residual friction angle of these soils (i.e. including gravel fraction) showed very weak correlations with clay content and Atterberg limits, but was largely dependent on gravel and fines (clays + silts) contents, increasing with gravels and decreasing with fines, and displayed strong linear correlation with the ratio of gravel to fines contents. These observations indicate that among the index properties, clay content and Atterberg limits can be used to estimate residual strength of the soils finer than 2 mm, but they are not appropriate evaluate the residual strength of the soils containing considerable amount of gravel-sized particles. For the latter, particle size distribution (particularly the ratio of gravel to fines contents) appears to be a useful index. Additionally, it was found that there was no identifiable correlation between relative abundance of individual major clay minerals and residual friction angles of both gravel-free fraction of disturbed and in-situ soils, suggesting that influence of clay minerals on residual strength of these soils can not be simply evaluated based on their abundance.

Iron oxide precipitate in seepage of groundwater from a landslide slip zone

Orange precipitate was collected at the mouth of groundwater drainage tubes from the Kumanashi Landslide slip zone in Toyama prefecture, Northwest Japan. Data from XRF, X-ray diffraction, and Mossbauer spectroscopy determined the precipitate as hydrous ferric oxide (HFO) bearing multi-elements such as phosphorous, silica, calcium, etc. The occurrence of HFO may indicate an oxidation of ferrous iron in the percolated groundwater from the slip zone. Moreover, the precipitate iron should be mobilized with groundwater circulation from the slip zone, whose reducing condition was determined by the iron speciation on the same type of landslide profiles within the study area in previous studies. The HFO precipitate may be considered as a secondary reliable indicator to locate the seepage of a slip zone on surface, especially for a landslide newly investigated under wet-warm climate.

Deformation History of a Landslide Slip Zone in Light of Soil Microstructure

Research Article| February 01, 2004 Deformation History of a Landslide Slip Zone in Light of Soil Microstructure BAO-PING WEN; BAO-PING WEN 12Department of Hydraulic and Hydropower Engineering, Tsinghua University, Beijing 100084, China Search for other works by this author on: GSW Google Scholar ADNAN AYDIN ADNAN AYDIN 3Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, China Search for other works by this author on: GSW Google Scholar Author and Article Information BAO-PING WEN 12Department of Hydraulic and Hydropower Engineering, Tsinghua University, Beijing 100084, China ADNAN AYDIN 3Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, China Publisher: Association of Environmental & Engineering Geologists First Online: 02 Mar 2017 Online ISSN: 1558-9161 Print ISSN: 1078-7275 © 2004 Association of Engineering Geologists Environmental & Engineering Geoscience (2004) 10 (2): 123–149. https://doi.org/10.2113/10.2.123 Article history First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation BAO-PING WEN, ADNAN AYDIN; Deformation History of a Landslide Slip Zone in Light of Soil Microstructure. Environmental & Engineering Geoscience 2004;; 10 (2): 123–149. doi: https://doi.org/10.2113/10.2.123 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEnvironmental & Engineering Geoscience Search Advanced Search Abstract The microstructure of a slip zone from a recent landslide was investigated by combined optical microscopy (OPM) and backscattered electron microscopy (BEM) techniques. Along the toe of the slope, the slip zone consisted of two distinct segments, formed a) along a pre-existing slip zone and b) through completely decomposed granite (CDG), both of which comprise composite soils. The microstructural features were systematically captured, quantified, and analyzed using an advanced image-analysis system. It is shown that variations in density, porosity, presence of matching fragments of coarse particles, abundance of tabular aggregates and plates of kaolinite and particle alignment are significant indicators of the deformation history of the slip zone. The results indicate that multiple processes concurred in the course of deformation: compaction and dilation, cataclasis and comminution, and particle rearrangement. Such deformation features of the natural composite soils are fundamentally different from the relatively simple soils commonly used in laboratory studies. The extent of each process depends on the particle-size distribution and stress level that prevailed at time of failure. The particle movement and microstructural evolution of the slip zone could be described as particulate flow through simultaneous bulk simple shear and pure shear. Depending on their relative abundance, fine particles play an important but variable role in the development of the slip zone and the mobilization of its shear resistance to deformation. Reactivation and/or prolonged deformation evidently change the deformation behavior of the pre-existing slip zone. In general, shape-preferred orientation of particles occurs where they are obviously aligned. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Variation of iron species in sliding mud

Results of Mossbauer spectroscopy and ICP-AES measurement revealed a special distribution pattern of iron species in four crossing profiles of the Tertiary Formation Type of Landslides in Japan. In comparison with host rocks, the sliding mud in the landslide slip zone contains the higher ferrous iron content and/or trace pyrite, which indicates that the forming environment was relatively reducing. The total iron content also increased with an increase in ferric iron and pyrite, in contrast, decreased with an increase in ferrous iron content. The deep-gray and black mud layers formed and accumulated in various volumes within landslide slip zones are treated as the basic criteria for the slipping activity, because the soft mud saturated with groundwater is easy to create a plastic deformation.