| Ma Huanggou No.5 accumulation body is located at the right bank of Mahuang Groove Branch of Qiaoqi Reservoir. As reservoir filling has given rise to changes in hydrodynamic environment of this accumulation body, a series of deformation-failure characteristics have appeared on the surface and they are threats to normal passage of the highway around the lake, life property of residents of the slope body, as well as the long-term service of this reservoir. In this paper, spatial form, material composition, deformation-failure characteristics and bank collapses pattern of this accumulation body are analyzed based on detailed field investigations so that qualitative judgments can be made as a whole for it. Afterwards, software of Geostudio series is adopted to analyze seepage, stress and displacement transformation rules in the accumulation body under a circumstance of reservoir water level variation; moreover, in line with the seepage results, limit equilibrium method is applied to performing stability analysis for this body. Finally, several criteria of forecasting and early warning are presented specifically to this accumulation body. The research contents and the main results are as following:(1) According to particular field geological explorations, engineering geological conditions and deformation-failure characteristics of this accumulation body are figured out. In combination with monitoring data, influencing factors on deformation of the accumulation body are analyzed and summarized together with the bank collapse mechanism of it. It is found that deformation of this accumulation body is intense when reservoir water level drops, which is reflected in the feature of a dynamic water pressure type landslide; the corresponding instability mode is creep-crack. At present, it is in a basically stable to under-stable state.(2) By seepage field analysis of the accumulation body, seepage line and porewater pressure transformation features in it can be figured out provided that the reservoir water level goes up or down. Analysis results indicate that during dropping or rising of the reservoir water level, seepage pressure field within the accumulation body is distributed again together with a change in seepage line which is provided with a lagging time effect. However, after the reservoir water is stabilized for a period, such a seepage line gradually becomes steady.(3) According to a seepage-stress coupled analysis for accumulation body, inner stress and displacement situations of it can be obtained under a circumstance of reservoir water level going up or down. Analysis results show that, for this accumulation body, responses to its horizontal displacement are more prominent than those in the vertical direction in terms of reservoir water level dropping or rising. Meanwhile, accumulation body displacement responses at the time of reservoir water level dropping are more distinct than those when this level rises. Therefore, it is more likely for failure deformation to occur to such an accumulation body when the reservoir water level drops, which is in consistent with the monitoring trend.(4) Qualitative analysis is also carried out on the stability of such an accumulation body so that stability status of it can be acquired at the time of reservoir water level dropping or rising. Analysis results indicate that the stability of it exhibits a tendency of decrease followed by an increase when this level goes up and the body is in a basically stable state. In comparison, when the reservoir water level declines, the accumulation body shows a trend of gradual diminishing followed by a slow increase and it is in an under-stable state.(5) Forecasting and early warning analysis is also performed for the stability of this accumulation body. Main criteria include the drawdown rate of reservoir water level, the contingence angle between displacement and time, as well as the macroscopic deformation of the surface; moreover, these criteria are employed to perform related layered pre-warnings. |
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