Experimental Study On Mechanism Of Fluidized Landslides Induced By Internal Erosion

Fluidized landslides are one of the most dangerous types of landslides as they can run over long distance at high velocity,causing serious loss of life and property,and there are no obvious precursors before the initiation of the landslide.In 2008,a large number of landslides and collapse disasters were triggered by the 2008 Wenchuan earthquake,causing numerous landslide deposits.Those landslide deposits were easily destroyed again under the condition of precipitation and water flow convergence,which would lead to fluidized landslide or destructive debris flow.The raw material of this research is taken from the landslide deposits of Wenjia gully.The mechanism of the fluidized landslides induced by internal erosion is studied mainly through the physical flume simulation test,which will provides some experience for the later research,and can also provide some reference for the prediction and prevention of the fluidized landslides.In this paper,particle analysis was carried out on the material of the Wenjia gully deposits.Permeability tests and triaxial tests were carried out to understand the physical and mechanical properties of the material.Then a series of physical flume tests are carried out.The flume apparatuses were equipped with multiple sensors to evaluate the pore pressures,the internal displacements,surface displacement,vibration signal and acoustic emission.The effect of different density and fine particles inside the material is considered.The mechanism of fluidized landslide induced by internal erosion is further discussed.The main research results are as follows:(1)For the fluidization landslides,as the water seeps into the slope,the soil is gradually saturated.The internal water level of the soil will have a relatively stable phase before the overall flowslide.Through the monitoring of surface and internal displacements,it has been found that large internal displacements and surface subsidence mainly occur in the overall flowslide.In the sliding process,the landslide body experienced two stages of acceleration and deceleration,and the overall sliding front slope body caused settlement due to internal erosion.The sliding process experienced stages of acceleration and deceleration,and the slope had settling before flowslide due to internal erosion.(2)It is found that there are obvious acoustic emission and vibration signals before flowslide.The vibration signals are mainly concentrated in the high frequency section of IMF1,and the time spectrum is obtained through HHT.A series of micro acoustic emission and vibration signals before sliding prove that there is internal erosion in the slope,while the signal generated by flowsliding is the most intense.(3)The deposits of different density has a great influence on the start and movement of the fluidized landslides.From the failure process of the flume test under different density,it can be seen that the different density has an obvious influence on the internal erosion.In the loose state,the internal erosion is very strong,and the slope is more easily destroyed.With the increase of relative density,the effect of internal erosion gradually weakened,and the slope became more and more difficult to destroy.In the medium dense and slightly dense state,a multistage backward sliding mode appeared.In the very dense state,the slope remained stable.(4)With the increase of the relative compactness of the deposits,the peak pore water pressure value gradually decreases,the sliding distance of the landslide gradually decreases,and the sliding failure process and the destruction time increase.(5)Through analysis of particle gradation changes at various locations in the test,it was found that small particles migrated along the direction of water flow infiltration because of internal erosion.With the increase of relative density,the phenomenon of particle migration becomes less and less obvious.(6)The internal erosion is mainly due to the fine particles in the soil being eroded away by the water flow.Through contrast of salt test,fine-particle test,and no fineparticle test,it is found that the strong internal erosion produced fluidized landslide in salt tests.Only a small amount of particles were eroded by the fine-particle test.And there was almost no internal erosion during no fine-particle test.As a result,the slope remains stable.It was confirmed that internal erosion is main factor inducing flowslide.(7)With the water level rising,the flow of water infiltrates into the soil slope,carrying away small particles.The internal pores increase as the fine particles eroded.When the friction stress between the particles is less than the shear stress,the soil will have local shear failure,resulting in micro pores collapsing and the rearrangement of the particles in the soil.With this process continues to circulate,a large area of pore collapse occurs,blocking the seepage channels,resulting in a sharp increase in pore water pressure and a sharp drop in shear strength.Finally,a fluidized landslide occurs.