دانلود رایگان مقاله انگلیسی توزیع و حالت های شکست رانش زمین درتراس Heita ، چین - الزویر 2018

ABSTRACT

Agricultural irrigation has increased the groundwater level in the Heitai terrace (part of the Heifangtai terrace) by 20 m over nearly five decades, which causes 3–5 landslides each year at the edge of the terrace. The Heitai terrace is of great interest in the study of loess-related landslides; but there is no unanimous agreement on the types of either the landslides in this study site or the loess-related slope failures in general. On the basis of aerial images (res. 5 cm), Digital Elevation Model (res. 10 cm), and field investigations, we analyzed the distribution and failure mode of the landslides in Heitai. The geological structure and characteristics of 69 landslides (vol. 5 × 103 –6 × 106 m3 ) are studied. The preliminary results of groundwater recharge in the terrace and formation of the apparent spring lines on the slope surface are analyzed to better understand the failure modes. We divided the landslides in Heitai into two groups based on the location of the failure surface, i.e. loess landslide and loessbedrock landslide, of which the development is governed by the angle between the principle direction of slope deformation and the dip of bedrock bedding. We further analyzed the failure mode of each type observed in Heitai, defined as follows: loess-bedrock planar slide, loess-bedrock irregular slide, loess flowslide, loess slide, and loess flow. The proposed types of loess-related landslide are to be incorporated in the Varnes classification (Varnes, 1978) in consideration of the engineering properties of loess, and to provide backward compatibility for Heitai and potentially other regions in the Loess Plateau of China.

4. Conclusions In this note, the effects of geological structure and groundwater on the loess-related landslides on Heitai terrace are investigated. Notwithstanding the influence of additional factors, such as chemical concentration variations in the loess matrix due to groundwater (Zhang et al., 2013) and freezing-thawing cycles (Ge et al., 2011), on the temporal distribution of the landslides on the terrace, the spatial distribution can be ascribed to the geological structure and groundwater variations. By analyzing the distribution and failure mode of the landslides in Heitai, we classified the landslide types into: loess-bedrock planar slide, loess-bedrock irregular slide, loess flowslide, loess slide, and loess flow. The landslide types introduced here better characterize the loess-related slope failures into more specific types under the framework of the updated Varnes classification. The main conclusions are as follows:

1. A total of 69 landslides is located in 7 sections in Region A and B of Heitai. We divided the landslides into group of loess-bedrock landslides or loess landslide. The failure surface of the loess-bedrock landslide originates in the overlying loess layer and extends into the bedrock, whereas that of the loess landslide remains entirely within the loess layer. Most of the loess-bedrock landslides are concentrated on the consequent slope in RA with slow movement and large volume, whereas most of the loess landslides developed in RB.

2. The difference between the principal direction of slope deformation and bedrock dip, α of each section governs the landslide groups: 1) for α < 30°, the failure surface is likely to propagate into the bedrock and cause failure along the bedding plane, resulting in loess-bedrock landslides (S1, S3, and S6); 2) for α > 30°, the failure surface develops entirely within the loess layer resulting in loess landslides (S2, S4, S5, and S7).

3. Irrigation triggers landslides in Heitai. With the increasing groundwater level, landslides recur at the edge of the terrace showing an unclear temporal correlation at different sections with possible transformation of landslide types.