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Tang Y.,Key Laboratory for Geo hazards in Loess Area | Feng W.,Key Laboratory for Geo hazards in Loess Area | Bi Y.,Key Laboratory for Geo hazards in Loess Area | Bi J.,Key Laboratory for Geo hazards in Loess Area
Geological Bulletin of China | Year: 2015

Some researchers have classified the loess landslides in the light of geological conditions, origins, thickness, and failure mechanics. However, no researchers have made the classification according to the risk assessment requirement. This paper introduced the landslide classification methods abroad and summarized the landslide classifications in China's mainland. On such a basis, the authors put forward the classification method for loess landslides based on the view point of risk assessment. The method considers the kinematics characteristics and the magnitude or speed of landslides comprehensively so as to form a two-dimensional classification table. According to the table, loess landslides can be divided into seven kinds, i.e., peel, topple, fall, slump, slide, mudflow, and complex. Each kind of landslides has its own characteristics of deformation and kinematics, and possesses its unique magnitude, velocity, and sliding distance; hence, its features of risk are different from those of others. In the end, the authors analyzed the different risk features of various kinds of loess landslides. © 2015, Science Press. All right reserved.


Zhang C.,Key Laboratory for Geo hazards in Loess Area | Wang J.,Key Laboratory for Geo hazards in Loess Area | Gao B.,Key Laboratory for Geo hazards in Loess Area | Feng W.,Key Laboratory for Geo hazards in Loess Area
Geological Bulletin of China | Year: 2015

Quantitative evaluation of the hazard may play an important role in risk evaluation of a landslide. In order to study the quantitative risk assessment technique for a single landslide, the authors chose Xujia Village landslide as a case study, conducted field investigation, laboratory test, and stability calculation, used previous achievements and reliability methods to quantitatively calculate the probability of Xujia Village landslide under the natural and strong rainfall condition. Using the quantitative analysis method, the authors investigated and analyzed all kinds of hazard- bearing bodies, values, and vulnerability in the Xujia Village landslide intensity by way of estimation under the specific landslide intensity of vulnerability. The overall risk of the potential economic loss and death was estimated by using international single landslide risk calculation formula which led to a quantitative expression. Under the general condition, the annual probability of economic lose is ¥15.4 million, the annual probability of death is 1.3 persons; under the strong rainfall condition, the instability probability of Xujia Village landslide is multiplied, the property risk and life risk are also multiplied, the annual probability of economic lose is ¥95.8 million, the annual probability of death is 8.3 persons. © 2015, Science Press. All right reserved.


Yu G.,Key Laboratory for Geo hazards in Loess Area | Zhang M.,Key Laboratory for Geo hazards in Loess Area | Zhang C.,Key Laboratory for Geo hazards in Loess Area
Geological Bulletin of China | Year: 2015

The study of the starting mechanism is a prerequisite for mitigation of landslides. In this study, three-dimensional continuum model simulation method was applied by using friction model and Voellmy model to solve the runout process and to simulate the start-up process of debris-flow. The results show that, under the condition of both models and the erosion yield rate, whether the slope is a confined slope (channellized type) or an unconfined slope, with the increasing slope, the motion energy supplied by the topography further increases, the moving distance of the material also further increases, and the corresponding average speed, maximum speed (front speed), and the total kinetic energy will be further increased. The kinematic parameters experience the process from slow creep to rapid increase. Based on the start-up movement of landslide, the deposition process and variation of the kinematic parameters during runout under the condition of different slopes, the critical start-up angle of debris-flow is set at 25° -30°. The determination of the critical start-up angle can provide scientific basis for regional disaster prevention and reduction and scientific research. © 2015, Science Press. All right reserved.


Li Z.,Chang'an University | Li Z.,Key Laboratory for Geo hazards in Loess Area | Sui L.,Chang'an University | Zhang M.,Key Laboratory for Geo hazards in Loess Area | Li L.,Key Laboratory for Geo hazards in Loess Area
Geological Bulletin of China | Year: 2015

Based on the spectral and shape features of loess landslide scarp, the authors segmented the high resolution remote sensing image by using regional growing and merging method, and extracted the landslide scarp area from the segmented image. The skeleton of the scarp area was obtained by way of the binary composition to characterize loess landslide. Firstly, The typical semi- circle or round-backed armchair shape characteristics and spectral characteristics became one of the important marks for loess landslide remote sensing interpretation, whereas the initial shape of the scarp was achieved by taking advantage of the regional growing and merging method with the growing parameter being 47.5 and the merging parameter being 49. Then, the holes of initial scarp of the scarp generated by segmentation process were filled. Finally, the main framework of landslide scarp was extracted using binarization skeleton algorithm, which constituted the mark of the loess landslide. This method is an improved and enhanced means for loess landslide expression in the remote sensing interpretation. © 2015, Science Press. All right reserved.


Zeng L.,Chang'an University | Zeng L.,Key Laboratory for Geo hazards in Loess Area | Zhao G.,North China University of Water Conservancy and Electric Power | Hu W.,Key Laboratory for Geo hazards in Loess Area | Huang J.,Chang'an University
Geological Bulletin of China | Year: 2015

The variation of temperature and moisture inside the soil body is obvious when loess slope is freezing and melting in the loess plateau, which is located in the typical seasonal cryolithozone of Northwest China. As a result, there is a corresponding variation of water content and groundwater table inside the soil body, which tends to induce a series of geological environment problems such as landslide and collapse. In this paper, in-situ monitoring of loess temperature and water content was conducted during freezing and melting in Heifangtai loess slope of Yongjin County, Gansu Province. The authors studied variation characteristics and interrelation between temperature and water content of the freezing layer on loess slope under the freezing-thawing condition. It is found that the depth of freezing loess is around 52cm at the monitoring site, and the temperature of loess profile can be divided into three characteristic zones, namely, steady transfer zone, fluctuation zone and significant alternation of temperature. Water content was controlled by temperature during freezing-thawing of loess slope, and hence this changing process can be divided into three phases. First of all, the water content is nonlinearly increased with temperature when it is less than 2℃. Then, water content declines randomly when it is between 2℃ and 6℃. When it is greater than 6℃, water content increases slightly until stableness, and the temperature effect weight decreases. With the fully dissolving of frozen soil body, the freezing moisture melts rapidly and migrates downwards, leading to the sharp increase of water content. It is thus held that, from freezing to thawing, sharp increase of water content is the dominant factor for the slide and collapse of shallow loess. © 2015, Science Press. All right reserved.


Tang Y.,Key Laboratory for Geo Hazards in Loess Area | Zhang M.,Key Laboratory for Geo Hazards in Loess Area | Li Z.,Key Laboratory for Geo Hazards in Loess Area | Fen W.,Key Laboratory for Geo Hazards in Loess Area
Northwestern Geology | Year: 2015

Based on the knowledge of inland and over seas background of geo-hazards management, this paperexplored the methods of geo-hazards risk management from some of the main representative countries or regions in the world, and summarized the research results of geo-hazards risk management in domestic academic circles. It also introduced the actual geo-hazard investigation, assessment and prevention situation in China. On the basis of above, the geo-hazards management methods used overseas and inland were compared. In the end, some suggestions for the geo-hazards risk management in China were put forward.


Yu G.,Key Laboratory for Geo hazards in Loess Area | Zhang M.,Key Laboratory for Geo hazards in Loess Area | Cong K.,Gansu Institute of Geo Environment Monitoring | Pei L.,CAS Beijing Institute of Geographic Sciences and Nature Resources Research
Quarterly Journal of Engineering Geology and Hydrogeology | Year: 2015

Critical rainfall thresholds can be the key to ensuring effective debris-flow forecasting. They are significant for the study of the trigger mechanisms of debris flows, for the forecast of the characteristics of future events, and for the development of engineering guidance for mitigation. Using a hydrological approach, we first calculated the flood peak discharge at different frequencies and then the corresponding rainfall thresholds for the initiation of different scales of debris flows in Zhouqu County, China. This was followed by the establishment of a functional relation between the intensity and duration of rainfall events that trigger debris flows of different warning levels in two initial soil conditions (dry and moist). This, in turn, yielded four warning levels and two preliminary warning levels. For the two early soil conditions (dry and moist) in the Sanyanyu Gully of Zhouqu County, the Level I (red) warning values for rainfall triggering debris flow are 56 and 51 mm h-1, respectively; the Level II (orange) warning values are 41 and 38 mm h-1, respectively; the Level III (yellow) warning values are 32 and 30 mm h-1, respectively; and the Level IV (blue) warning values are 24 and 22 mm h-1, respectively. The Level V preliminary warning values are 17 and 16 mm h-1, respectively; and the Level VI preliminary warning values are 10 and 9.5 mm h-1, respectively. The rainfall intensity and duration were found to exhibit a power function relation, I = aDß, where the values of a and ß vary with the warning levels. Rainfall events capable of triggering debris flows in the new thresholds and intensity-duration relations presented here can be used for forecasting purposes and in operational geohazard warning systems. These research results also provide a scientific basis for regional hazard mitigation and reduction in Zhouqu County. © 2015 The Author(s).


Tang Y.M.,CAS Institute of Earth Environment | Xue Q.,Key Laboratory for Geo hazards in Loess Area | Li Z.G.,Key Laboratory for Geo hazards in Loess Area | Feng W.,Key Laboratory for Geo hazards in Loess Area
Natural Hazards | Year: 2015

Rainfall infiltration depth in an integrated and homogeneous soil mass is extremely limited. How does rainfall infiltrate into a loess slope developed with various fractures and holes? How do infiltration mechanisms impact slope stability? These are issues this paper researched and discussed. Using the in situ monitoring and field investigation method, it obtained that the infiltration depth of rainfall in integrated loess mass is generally limited to 3.0 m underground and there are often developed various fractures and holes in loess slopes, which usually form the rapid infiltration channels to make the rainwater seep quickly and vastly and to influence the loess slope stability greatly. It put forward that the rainfall infiltration inducing loess landslide can be divided into three modes: (1) superficial infiltration inducing landslide, (2) blockage infiltration inducing landslide, and (3) breakthrough infiltration inducing landslide. The first mode requires a long-time continuous rainfall; the second mode requires a sufficient antecedent accumulative rainfall, meanwhile a certain infiltration time; and the third mode requires certain rainfall intensity. © 2015, Springer Science+Business Media Dordrecht.


Zhang C.-L.,Chang'an University | Li P.,Chang'an University | Li T.-L.,Chang'an University | Zhang M.-S.,Key Laboratory for Geo hazards in Loess Area
Shuili Xuebao/Journal of Hydraulic Engineering | Year: 2014

By many artificial rainfall tests, the depth of rainfall infiltration in loess area was 4 meters at most. So, it is considered that the rainfall is hard to reach groundwater through the normal leaking way, but through vertical fissures, sinkholes or some other water paths to recharge groundwater. However, according to our investigation, these water paths only occur in unloading areas which always in the edge of loess tableland, but rare in the center. In order to make clear surface water recharge groundwater in loess area, a monitoring site was set up in Zhengning county, Gansu Province. By using the soil moisture meters which inserted into the wall of a 10-meter-deep exploratory well, the changes of volumetric moisture content of soil layers with different depth were observed continuously for one year under the condition of natural rainfall, the daily precipitation during the monitoring period was also recorded by rain gauge. The results show that the moisture content of the shallow layers within 2 meters changed in annual cycle, and the trend is consistent with the change of evaporation. When the precipitation is less than 18 mm/d, the circulation of soil moisture occurs mainly in surface layers, and has little effect on the moisture content below 20 centimeters. But when the precipitation is more than 18 mm/d, the moisture content may have a sudden increase. The greater the rainfall, the higher the growth of moisture content and the deeper the affected range will be. With the increasing depth, the growth decreases and the change of moisture content lags behind the depth. The infiltration zone of the loess is about 2 meters. In the unsaturated soil below 2 meters, water moves mainly in the form of unsaturated seepage or vapor form, the motion of vapor is very small but cannot be ignored, the water would gather on the surface as encountering paleosol layer with low permeability, weak zone will be formed after long-term accumulation, inducing loess landslides eventually.


Dong Y.,Key Laboratory for Geo Hazards in Loess Area | Liu J.,Key Laboratory for Geo Hazards in Loess Area | Zhang G.,Key Laboratory for Geo Hazards in Loess Area | Zhang X.,Key Laboratory for Geo Hazards in Loess Area
Global View of Engineering Geology and the Environment - Proceedings of the International Symposium and 9th Asian Regional Conference of IAEG | Year: 2013

The measures of making new land by cutting some hills were employed by the local government to meet the needs of urban development in Yan'an city. It is important to employ engineering treatment to control groundwater level, based on ascertaining the changes of groundwater level induced by the artificially filling of the natural ditches. A case study was conducted in the new urban district of Yan'an city. On the basis of ascertaining the local hydro-geological condition, a comprehensive treatment method is proposed, including enhancing the capacity of surface drainage to reduce rainfall infiltration, enhancing the capacity of subsurface drainage by filling ditches with conductive materials in advance. A groundwater numerical model can be used to predict the changes of groundwater level. The safety of engineering construction can be guaranteed by controlling groundwater level when the appropriate engineering treatment was employed. © 2013 Taylor & Francis Group, London.

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