Physical Model Test Study Of Failure Mechanisms In A Reservoir Landslide-Pile System

The scientific evaluation and effective prevention of reservoir landslides are of great significance to ensure the lives and properties of residents and the safety of reservoir operation.The stabilizing pile is one of the most widely used structures for landslide control in reservoir areas.A reservoir landslide-pile system is formed after piles are implanted into a reservoir landslide,whose stability is affected by internal and external factors.In this thesis,the physical model tests of the reservoir landslide-pile system are carried out to achieve a more targeted long-term effective prevention for reservoir landslides.The design and analysis methods of physical model tests are proposed.Based on the comprehensive analysis of multi-field information,the evolution characteristics and failure type of the reservoir landslide-pile system are analyzed and its intrinsic failure mechanisms are revealed,which helps to provide the optimized pile design of reservoir landslides.The detailed conclusions are as followed:(1)The design method of physical model test of the reservoir landslide-pile system is improved.The general process of selecting basic quantities,similarity constants and similarity indicators in the physical model of the reservoir landslide-pile system is given;the distortion chain in a 1-g physical model test is derived;the similarity of seepage field in physical model tests of reservoir landslides is re-examined from a theoretical perspective,and a quantitative control strategy to reduce the distortion of seepage field is proposed;verification is carried out through ideal physical model tests of reservoir landslides.The results show that based on the distortion control strategy proposed,a seepage field highly similar to the prototype can be simulated in the distortion model,and the proposed quantitative distortion control strategy is a supplement and improvement to the general selection of similarity parameters;the special design principles and the general design steps of the physical model test of reservoir landslidepile system are proposed,which include physical model generalization,similar material selection,and boundary condition design.(2)Two new methods are proposed for analyzing the temperature and displacement fields of a physical model.A workflow of landslide displacement field reconstruction is proposed.An automatic batch point cloud processing procedure is provided to reduce research costs and human intervention but improve data processing efficiency;based on error analysis and validation tests,the magnitude and distribution of errors involved in this method are quantified,and the test results indicate that the method has good noise immunity and can provide high accuracy displacement analysis;the reconstruction of the landslide displacement field and the visualization are realized,which comprehensively describes the landslide displacement information,including displacement scalars and vectors for different times,directions and profiles.Based on the assumption of infrared radiation on the model surface,an index more applicable to soil temperature analysis is proposed.By comparing the applications in remote sensing rock mechanics,the thermal infrared temperature of the soil is found to be weaker,but the regularity of the temperature index is found to be greater than the randomness by long-range correlation analysis,and the index is considered to provide the possibility of studying the landslide-pile system from the energy perspective.(3)The characteristics of multi-field information evolution of the reservoir landslide-pile system and their mutual responses are analyzed.The physical model tests of the reservoir landslide-pile system under static and long-term fluctuated water level are studied,and the evolution characteristics of deformation,stress,seepage,and temperature are analyzed.In addition,the comprehensive analysis results of various types of data show that there is a good mutual response relationship between multi-field information.The failure modes of the reservoir landslide-pile system under static and fluctuating water level are proposed based on the deformation and failure characteristics of the tests.Verifications based on numerical simulation and comparison with the failure mode of the reservoir landslide are conducted.The results show that the effective pile design can change the evolution mode of reservoir landslide under fluctuating water level and thrust,in which the uplift upstream of piles,slip downstream of piles,and collapse at slope toe only occur within a limited range,preventing a critical sliding surface and landslide occurrence and improving the stability of the reservoir landslide.(4)The failure mechanisms of the reservoir landslide-pile system are revealed.The long-term water level fluctuation causes two different progressive failure mechanisms,i.e.,retrogressive failure at the slope toe and composite failure downstream of piles;the former can be attributed to seepage failure and long-term loading-unloading cycles,while the latter is influenced by the coupling of pile-soil interaction and water-soil interaction.The soil arch effect and its long-term evolution characteristics are quantitatively described,and the mechanisms of soil arch evolution and failure are revealed.The results show that the soil arch first undergoes a general development process,and then show a significant dynamic response relationship with the excess pore water pressure in the soil.The generation of excess pore pressure and its accumulation accelerate the failure of soil arch on the macroscopic level,and the failure form is the unbalanced arch foot.The evolutionary characteristics of effective stress in the sliding mass are quantitatively analyzed.It is found that when,and only when the effective stress in the soil around the pile decreases sharply,the thrust remains unchanged but the landslide displacement increases continuously as well as the system becomes unstable.This result strongly proves that the most fundamental failure mechanism of the reservoir landslide-pile system is controlled by the soil arch or piles.Based on the failure mechanism of this system,three soil arch evolution models in the reservoir landslidepile system are summarized,and then failure identification of the system is realized.(5)Optimization schemes of pile design for reservoir landslides are proposed.The deformation characteristics of the sliding mass downstream of piles in the reservoir landslide-pile system are analyzed.Three mechanical models are proposed,their physical significances are analyzed,and the selection of the soil resistance and the calibration of its ultimate resistance under the current code are discussed.The analyses show that if the lateral load of piles is within the allowable value of the bearing capacity,the system will be not failed and the ultimate resistance can be considered as a constant after considering the possible failure in the reservoir landslide.The soil resistance under short-term mechanical effects and long-term physical and chemical effects as well as bank collapse is determined.Furthermore,the upper limit of the pile location,force transfer ratio,and spacing are determined.In addition,the theoretical analysis of the soil arch effect in discrete rowed piles is carried out,its validity is verified based on the existing literature,shortcomings of the existing mechanical models of soil arching and the corresponding problems of the existing spacing optimization are presented,and the rationality of the proposed optimization scheme of pile spacing is demonstrated.In summary,the research on the failure mechanism of reservoir landslide-pile system based on the physical model test carried out in this thesis is of great theoretical significance and application value.