| The potential reactivation risk of ancient and old landslides under the condition of weak stratum control and strong earthquake activity is one of the main geological safety risks affecting the prevention and control of geological disasters and major engineering construction in the area of Southeast Gansu province.At the same time,the landslide reactivation mechanism and evolution process under different induced conditions are also one of the hot issues.Therefore,this dissertation takes Luobao giant deep-seated mudstone landslide,located in Qin'an,as an example.Through field investigation,aerial survey with UAV,in-situ ground pulsation test,engineering drilling,indoor creep test of rock and soil mass,dynamic test and numerical simulationapproaches,analyzed the region development features and distribution oflarge-scale landslids.The dynamic characteristics,creep characteristics,dynamic stress response characteristics,dynamic deformation,time-dependent deformation and comparative study of deformation characteristics under the two different conditions were analysed.The following preliminary understandings have been obtained:1.The reactivation of old landslides is the main feature that restricts the development of in Qin'an County.The influence of historical strong earthquakes on the maximum intensity of the study area is ? degree.The large and medium landslides are mainly distributed in the erosion-accumulation valley and the transition zone of loess hilly-gully region.The neogene mudstone is the main slip formation in the area.Luobao landslide located in Qin'an Hulu river right bank of loess hilly-gully region.It is a multistage large-scale and deepseated mudstone landslide induced by historical earthquakes.The landslide is controlled by loess/mudstone dual slope structure.The.main sliding zone is located in the yaodian mudstone layer.It developed five slidingmass with a lot of slippage.The landslide is in a relatively stable state under natural conditions.2.Weathered mudstone belongs to low liquid limit silty clay in engineering classification.(1)Static characteristics of weathering mudstone test: The stress-strain relationship of intact weathered mudstone is strain-softening type,and that of disturbed mudstone is strain-hardening type.The residual strength is46%?75% of the peak strength.(2)Dynamic characteristics of weathering mudstone test: Under the same confining pressure and the same dynamic strain amplitude,the dynamic modulus of disturbed sample is68%?88% of that of undisturbed sample,and the damping ratio of disturbed sample is 122%?175% of that of undisturbed sample.(3)Creep characteristics of weathering mudstone test: the axial deformation increases with the increase of confining pressure or stress level,and the growth rate also increases slowly.Burgers creep constitutive model was established on the basis of experimental data.3.Ground motion response and dynamic deformation and failure characteristics of giant mudstone landslide are obviously affected by the properties of slip zone.(1)By comparing the amplification effect of PGA,PGV and PGD,the combined amplification effect of slide band and slidemass,as well as the rhythmic changes of the amplification effect in the surface layer and the main slide band.The amplification coefficient of PGD is 2?3.4 times that of PGA in grade I landslide.(2)Landslides respond differently to simple harmonics of different frequencies.With the increase of seismic wave frequency,the landslide acceleration amplification coefficient increases first and then decreases,and approaches the maximum value at 2.5Hz simple harmonics.(3)Under the earthquake action,with the increase of seismic wave from frequent earthquakes(PGA=0.1g)to rare earthquakes(PGA=0.46g),the horizontal displacement of the landslide increases from 0.15 m to 2.15 m,and the shear strain increases from 0.06% to 0.32%.(4)The dynamic deformation and failure process of Luobao landslide can be divided into four stages: tensile and shear failure of the old slip zone,surface sliding of the slip body,disturbance and expansion of the new slip zone and local shear failure.4.The time-dependent deformation of mudstone landslide can be divided into three stages: initial creep,attenuation creep and steady creep.(1)About 98.6% of the deformation occurs within 60 days and then enters the steady creep stage.The horizontal displacement of sliding body decreases gradually from shallow to deep,and the deformation is mainly concentrated in the sliding mass I,with the maximum displacement of about54.1cm,and the maximum shear strain is about 0.23%.(2)The landslide deformation mode is a push-type.The shear strain appears at the steep-slow turning point of the slide belt at the back edge of the main slide body at each stage of the landslide,but it is not fully connected and generally in a stable state.5.The deformation characteristics of landslide under creep are slightly stronger than that of basic earthquake(PGA=0.2g),but much smaller than that of rare earthquake(PGA=0.2g).(1)In terms of strength and distribution,the displacements of the two kinds of effects are mainly concentrated in the rear edge of the sliding body,and the shear strains mainly occur in the secondary slip zone of the sliding mass ?,?,?.(2)In terms of the deformation model,the landslide shows a push-type under the action of earthquake and creep,but under the rarely earthquake,the landslide forms a trailing edge sliding,leading edge pulling compound deformation and a sliding type deformation respectively. |
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