Calculation of Lijiawan Landslide Stability under the Drawdown and Rainfall Conditions
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To solve the phreatic line location of soil slope in the combined effects of drawdown and rainfall,based on the Boussinesq's differential equation of unsteady-seepage,this paper takes Lijiawan landslide for example to simulate the phreatic line location in the different conditions of drawdown velocity,rainfall intensity and rainfall duration.Then the paper discusses the landslide stability in every condition using transfer coefficient method.The results show that when it dose not rain,the stability of landslide becomes worse with the increasing acceleration of the decline of reservoir level;when it is in the state of rainfall,the stability of landslide gets equally worse with the strengthening of intensity and the rainfall duration.The landslide will probably get failure especially when it suffers from heavy rain weather or the rain lasts for 3 days or more.Keywords:
Phreatic
Drawdown (hydrology)
Intensity
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Through numerical simulation research,a landslide in two kinds of rainfall intensity in the change of the matric suction,and the landside stability were analyzed.The results show that the rainfall intensity with constant rain continued,landslide soil safety coefficient reduced,but after rain stopping,the landslide gradually restored to the original statement;when the rainfall intensity is different,the greater rainfall intensity,the more significant effect of stability of landslide soil by the time.
Intensity
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This paper takes Pengkeng landslide as a case study on the basis of the theory of unsaturated soil mechanics. The finite element method is used to calculate and analyze the slope seepage, deformation properties and stability under rainfall infiltration. The calculation results are utilized to study dynamic response mechanism of landslide due to rainfall and the relationship between safety factor and displacement under different real working conditions. Results show that the loose structure of the slip mass has provided a convenient condition for rainwater infiltrated. Thus it changes the spatial distribution of matrix suction and weakens the rock-soil mass parameters. The ground water level is risen under sustained rainfall. Deformation instability occurs in the zone of slope toe, then pulls the slope rear edge and causes the tensile fissures, which forms partial landslide in unsaturated area during rainfall period. In the initial stage of the heavy rainfall, the safety factor of the slope drops rapidly, which easily causes the landslide. The safety coefficient reduces further due to the continued infiltration of rainwater. Landslide occurrence after rainfall should be paid more attention. Safety factor is affected and vibrated with water in different parts of the slope. Finally, the concept of risk factor is proposed to reflect the harmful degree of slope under groundwater level and rainfall condition variation. The relationship between the risk factor and incremental displacement is established to describe the changes of surface displacement of slope measure point at different time periods. The above research and method will be useful and meaningful as reference for the management and early warning of the similar projects.
Infiltration (HVAC)
Rainwater Harvesting
Factor of safety
Safety factor
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Rainfall early warning criterion is a useful tool for rainfall-induced landslide mitigation.Unfortunately,it is hard to be used effectively in practice owing to the complexity between rainfall infiltration effects and slope stability.Hencet,he landslide model test for soil slope and previous research results are used to study the influence of rainfall characteristics on soil slope failure.The results show that fluidized landslide and soil erosion will be triggered by high intensity rainfall easily;and the pore water pressure in the deep soil of slope will increase easily under the long duration rainfall with low intensity;and the landslide magnitude which is triggered by the long duration rainfall with low intensity will be larger than that triggered by high intensity rainfall.Besides,the threshold accumulative rainfall is an important factor of rainfall-induced landslide.Moreover,it is suggested that the rainfall intensity and accumulative rainfall are effective parameters in rainfall early warning criterion.The rainfall intensity can be represented by the rainfall amount per hour,which can predict fluidized landslide and debris flow.The accumulative rainfall is helpful to predict sliding landslide.
Debris flow
Slope failure
Intensity
Landslide mitigation
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Under influence of heavy rainfall, the Zheng-gang landslide in Gu-Shui hydropower station of China started to have serious deformation. Based on the geological field investigations, the mechanism of rainfall infiltration was qualitatively analyzed previously. The rainfall infiltration reduces shear strength on the slip surface by increasing pore water pressure and the hydrodynamic pressure is generated which increased with the hydraulic gradient and water level, thus resulting in the instability of landslide and increased landslide movement. Secondly, combined with the seepage theory of saturated-unsaturated, quantitative study was carried out on the seepage properties of landslide under rainfall condition. Not only the dynamic sliding mechanism of landslide is revealed, but also the seepage stability was evaluated. The worst stability condition came out 4 days after the rain stopped, and the maximal thickness of perched water up to 6m. The results of stability analysis have agreement with the field observations. Finally, the effective drainage measures were proposed.
Infiltration (HVAC)
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In relation to the changes in the seepage and stability characteristics of Xiabi Landslide,Fujian under heavy rainfall condition,the seepage field was simulated and the stability calculated with SEEP and SLOPE software. The results show that,during rainfall,the rain water infiltrated along the slope surface almost vertically,the impact is minor in the deep,and major on the colluvial soil layer which will have more significant seepage performance than residual soil layer; as a result,perched water arises at the interface between the colluvial and residual soil layers after long-time continuous rainfall,that is why Xiabi Landslide is in creep state. The stability of landslide is very poor on the first day after rainfall,then is going to increase gradually. The result reflects the status quo and rules of the landslide stability actually. At last,the related control measures were proposed.
Colluvium
Typhoon
Landslide mitigation
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Abstract Rainfall is one of the primary factors that induce landslides. Rainfall infiltration forms a transient seepage field in slopes, thereby leading to an increase in water content, a decrease in matric suction, and an increase in the volume weight of slopes. The increase in water content in rock and soil leads to the degradation of the mechanical properties of the slope medium and reduces the shear strength, thus causing slope instability. In this study, a large-scale accumulation landslide is taken as the research object. The front edge of the landslide is high and is not eroded by river water. Hence, rainfall is regarded as the main external factor that changes the groundwater and seepage field of the landslide. According to the landslide’s topography, geological data, local rainfall, and hydrological monitoring results, the saturated–unsaturated seepage theory of rock and soil and the finite difference method are used to analyze the impact of rainfall on the landslide’s seepage field and groundwater. The evolution law of the transient seepage field of the landslide under the condition of rainfall duration is studied. The results provide a basis for the analysis of landslide deformation and stability.
Infiltration (HVAC)
Landslide mitigation
Cite
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Research purposes: Taking the K290 landslide of Yingtan-Xiamen Railway as an example,with the finite element method for saturated-unsaturated seepage,the variations of transient seepage field of saturated-unsaturated slope were simulated under the condition of change of rainfall and underground water level,the discussion is made on the variable laws of pore water pressure and matrix suction in the landslide under the conditions of different rainfall infiltration,the analyses are made for the influence of rainfall intensity and rainfall duration on the stability of slope of the unsaturated slope,and the evaluation is made on the results of prevention and treatment of landslide in the fields of micros and matrix suction. Research conclusions:The changes of rainfall infiltration and groundwater level change make the rapid change of pore water pressure with the different change laws in different areas.At the initial stage of rainfall,there is a most notable variation of pore water pressure.Matrix suction of landslide changes with the change of rainfall.On later stage of rainfall,the most matrix suction vanishes,which is very harmful to the stability of slope.The water level change,rainfall intensity and rainfall have much influences on the stability of landslide,among them the comprehensive influences of rainfall intensity and water level change are the most prominent.In the circumstances of strong rainfall and underground water level going up and down,the stability coefficient of slope is reduced sharply.
Infiltration (HVAC)
Intensity
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GEO-SLOPE finite element software was adopted in numerical simulation calculation on variation and stability of groundwater seepage field under the effect of reservoir water level rise,rainfall,and the combination of reservoir water level rise and rainfall for Muzhuping landslide.The results show that there is a big difference in underground water level under different working conditions.Nevertheless,the slip surface ranges in different working conditions are almost the same.With the lowest safety factor,the combination of reservoir water level rise and rainfall poses the greatest threat to the stability of Muzhuping landslide.
Safety factor
Factor of safety
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In accordance with theories of unsaturated flow and shear strength,limit equilibrium method was employed to analyze the stability of landslide in different conditions: different raising and falling rates of water level,different rainfall intensities,and combined action of water level fluctuation and rainfall infiltration. Fujiapingzi landslide on the Jinsha river was taken as an example. The calculation results show that: when the water level raises faster,the growth rate of landslide's safety factor increases; the effect of water level drawdown velocity is generally parabolic,which means that the safety factor reduces firstly and then increases. There is a critical water level at each drawdown velocity. When rainfall intensity increases,the stability of landslide worsens. With the raise of water level,the effect of rainfall on safety factor decreases. By analyzing the most unfavorable combination of reservoir water lever drawdown and rainfall infiltration in terms of time,we found that the rainfall acting in the last period is more beneficial than that acting in the initial period. The variation of safety factor of this high and steep landslide is small in all the above conditions.
Drawdown (hydrology)
Safety factor
Infiltration (HVAC)
Factor of safety
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The large-scale landslides,widely distributed in southwest mountains and canyons,are prone to produce instability due to rainfall.In Gushui hydropower station,not only is the extremely large volume of Zhenggang large landslide accumulation body up to more than 4 750×104 m3,but also the thicknesses of many ultra-deep landslide are over 50 m.Under the influences of the heavy rainfall in 2008,the landslide started to deform again and even more seriously.According to the results of field engineering geological investigation and analysis of geologic structure characteristics and hydrogeology conditions,the mechanism of rainfall infiltration and stability in the current situation was qualitatively analyzed first.Then the whole landslide was transfixed slipping surface in the state of creep deformation;so it should be treated such as excavating and reinforcing.Combined with the analysis result,quantitative study of the seepage properties of landslide showed the dynamic sliding mechanism that water infiltration caused deformation,evaluated the stability and treatment,thus proposed effective drainage measures before and after the treatment under the rainfall.The results also showed that the saturation line and backwater was formed due to saturated soil by infiltration.Before the treatment,the backwater was seriously persisted in local landslide and slip surface;and the worst stability came out 4 days later after the rain stopped;and the maximum thickness of backwater increased up to 6 m.However,with backwater reduced obviously,the stability was significantly increased by the treatment.The results truly reflected the situations and laws of the stability of landslide,which were consistent with the results of field exploration.The results were significantly improved by the treatment.Drainage measures proposed would keep the landslide’s stability efficiently.The research results will be useful and meaningful in the same projects as reference.
Landslide mitigation
Infiltration (HVAC)
Slipping
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Citations (5)