| Dynamic water pressure type mound landslide has been a hot topic in reservoir-induced landslide research.Since the reservoir storage in the Three Gorges reservoir area,more and more mound landslides have been deformed,and the significant deformation is mainly concentrated in the period of reservoir water decline,such as the famous Shuping landslide,Baishui River landslide,and Bazhimen landslide.With the passage of time,the deformation of such dynamic water pressure landslides grows year by year under the combined influence of rainfall and reservoir water level fluctuations,and even urgent management measures are needed to prevent their further damage.Especially since the flood season in 2022,the water level drop in the Three Gorges reservoir area during the subsidence period has increased from 0.6m/d to 1.0m/d.The increase in the daily drop means that there is a possibility that the surrounding mounding landslides affected by the reservoir water level scheduling,especially the dynamic water pressure landslides,will intensify their deformation activities.Therefore,the study of such dynamic water pressure mounding landslides should not only focus on their activity status and deformation patterns,but also study the response of their deformation to the main influencing factors,further clarify the triggering factors of deformation and the inner correlation mechanism of reservoir water fluctuation,so as to analyze the change trend of their stability.This thesis takes the dynamic water pressure type mounding landslide with high concern in the Three Gorges reservoir area as the research object,and summarizes the geological structure and deformation characteristics of this type of landslide on the basis of field investigation and data analysis;based on data statistical methods and theories,analyzes the dynamic monitoring data of typical landslides,focuses on the correlation between landslide displacement,rainfall and reservoir water level,and analyzes the landslide deformation under the effect of reservoir water level change and rainfall Considering the hysteresis effect of landslide deformation on rainfall and reservoir water level,a VAR model is constructed to quantify the dynamic relationship between landslide displacement and deformation and the inducing factors;in addition,the orthogonal design method is used to analyze the sensitivity of landslide deformation factors under different slip surface forms;for the main influencing factor of landslide permeability coefficient of the mounded layer,a combination of field and indoor tests is used to combine the monitoring data and experimental results to derive the The spatial distribution anisotropy of landslide permeability was obtained by combining monitoring data and experimental results,and the response of landslides under different permeability to different water level drop rates was analyzed by seepage simulation.The main research contents and results are as follows:（1）The geological structure and deformation characteristics of dynamic water pressure type mounded landslides are summarized.Through the statistics of 18 typical dynamic water pressure type accumulation layer landslide data,the analysis concluded that:（1）topographic features:the landslide is mainly large-medium landslide,the form of the slide surface is mostly circular,the structure type is mainly oblique oblique and reverse slope;（2）material composition:the slide body soil is loose,mainly powder clay with gravel,the slide belt soil is mostly muddy weak interlayer,the slide bed is mainly Jurassic and Triassic soft and hard rock interlayer structure.Mostly sandstone,mudstone,shale composition;（3）degree of water involvement:the average inundation ratio of the landslide body is 31%,belongs to the central（forward）water involvement;（4）deformation characteristics:the landslide surface displacement shows a more regular"step type"change,and step acceleration section mostly occurs during the reservoir water level decline,the central front of the landslide by the reservoir water level fluctuations（2）The analysis of the cumulative displacement of different reservoirs was carried out.（2）The deformation response law of typical dynamic water pressure landslide to reservoir water change and rainfall in different reservoir operation stages is analyzed.For different water level fluctuations under reservoir operation and scheduling,it is subdivided into six stages:low water level decline period,medium water level operation period,rapid water level decline period,low water level fluctuation period,water level rise period,and high water level operation period.Through refined data analysis and theoretical quantitative calculation of monitoring points of landslide parts,it is found that:（1）rapid water level decline period plays a dominant role in landslide deformation,and in the low water level fluctuation period,the（2）compared with the reservoir level change,the impact of rainfall on landslide deformation is mostly local deformation,usually concentrated in the middle and rear parts.（3）Using the correlation coefficient,the lag days of landslide deformation initiation in the period of rapid decline of reservoir water are calculated.Taking the monitoring data of Shuping landslide in the period of rapid water level decline in 2013 as an example,the correlation coefficient between the displacement of different parts of the landslide and the reservoir water level is used to determine the lag time of landslide deformation initiation,and it is calculated that the lag time of the front part of the landslide is 4 days,and the lag time of the middle and rear parts is 5-6 days.It is inferred that the displacement response sequence of dynamic water pressure type mounding landslide is from front to back,i.e.,the leading edge drives the trailing edge deformation,which shows a typical landslide traction damage mode.（4）The dynamic relationship between multiple inducing factors and displacement of landslide deformation is quantified.The VAR model in economics is used to analyze the dynamic relationship between water level elevation,daily variation of water level,daily rainfall and typical landslide displacements.The study shows that:（i）for the full time period（complete reservoir operation cycle）,the contribution of water level height variation difference,reservoir water level variation rate and daily rainfall to the cumulative displacement scale are 7.4%,3.6%and 0.6%,respectively;（ii）for the sub-period（different water level operation stages）,the daily displacement VAR variance is ranked from high to low as rapid decline period>low water level fluctuation period>low speed decline period>water level The VAR model makes up for the shortcomings of conventional correlation analysis by considering the lag of displacement-initiated deformation,reflecting the importance of the difference in water level height change on landslide deformation,and further verifying the correlation of landslide deformation response to different water level operation stages.（5）Consider the sensitivity analysis of landslide deformation influence factors under different slip surface forms.The sensitivity of six influencing factors（internal friction angleφof the slip zone,cohesion c,permeability coefficient K of the slip body,inundation ratio p,water level drop rate V,rainfall T）is calculated by using the orthogonal design method.The results show that:（1）For the final stability of the landslide,the primary influencing factor of the two types of slip surface forms is the internal friction angleφof the slip zone material,and for the circular-shaped slip surface The second influencing factor is the infiltration coefficient K,while the second influencing factor for the chair-shaped slide is the inundation ratio p.（2）For the rate of change of landslide stability,the first two influencing factors for the two types of slide forms are the infiltration coefficient K and the inundation ratio p.In addition,the sensitivity of rainfall T to the chair-shaped slide is much higher than that of the circular slide,which is more susceptible to the rate of water level drop V.（3）In addition to the strength parameters of landslide materials,the influence of slide permeability coefficient and inundation ratio on landslide stability should not be neglected.（6）Based on the experimental results of landslide permeability within the range of the water level subsidence zone of the landslide reservoir,the landslide seepage field response and stability change law are simulated.Using a combination of field and indoor tests,the slide permeability coefficients of typical landslides are measured,and numerical simulations are used to analyze the landslide seepage field and stability change laws,and to give recommendations on the selection of the groundwater table line infiltration lineβangle under specific conditions.The study shows that:（1）the slide permeability coefficient within the water level subsidence zone of Three Gorges reservoir area is 10-4～10-6cm/s,which is an important condition for the generation of dynamic water pressure landslide;（2）for the same soil body,the permeability coefficient measured by the indoor permeability test is smaller than that of the in-situ borehole permeability test in the field;（3）when the reservoir water level fluctuates,the size of the slide permeability coefficient will affect the rapidity of groundwater response,thus affecting the landslide body from within stability,and different rates of reservoir water level decline will affect the minimum value of stability in the process of landslide deformation. |
