Mechanism Of Loess Landslides Under The Effects Of Pore Water

As an important part of rock and soil mass,pore water plays a significant role in changing the physical properties and mechanical behavior.The flow of pore water exerts a seepage force on the soil particle skeleton,and besides,it would solute the salt in the soil,which makes them diffuse by leaching and sedimentation.In the process,the interaction between soil minerals and pore water results in a series of dispersion and flocculation and eventually change the size and arrangement of soil particles.In addition,the pore water pressure is also an important factor affecting the effective stress,especially the excess pore water pressure,which strongly facilitates the soil failure and triggers lots of natural hazards,such as landslides,ground liquefaction and so on.From the aspects of chemical and mechanical effects of pore water,this study illustrated the influence of pore water on landslides by utilizing the permeability tests and numerical simulation based on FLAC 3D to investigate the response of landslides to the irrigation on loess plateau.The main conclusions are as below:(1)From the results of permeability tests,with the increase of salt concentration,the hydraulic conductivity decreased below a certain concentration,while an increase occurred afterwards.This is due to the relative less content clay in loess and the special fabric of loess,in which the silt particles were mainly assembled by clay particles.The flocculation of clay particles caused by the increase of salt concentration elevated the interparticle force of silt particles and decreased the pore size.However,when the concentration reached to a critical value,the pore volume among aggregations and clusters were able to change the soil fabric and consequently increased the hydraulic conductivity.(2)The effect of different ions on loess permeability is similar to that obtained from clayey soil tests.The valance and radius of cations positively increased the hydraulic conductivity of loess samples.The influence of anions on loess permeability depends on the ability of neutralizing positive charges and the pH value of solution system.Generally,a higher capacity of neutralizing positive charges and pH value produce and lower hydraulic conductivity.(3)The results of FLAC 3D numerical simulation show that the pore water pressure increases gradually with the increase of irrigation time and the permeability of surface loess.The pore water pressure increases faster both at the interface between silty clay and Malan loess and in the silty clay layer,which is also the main distribution area of the maximum pore water pressure in the slope.When the irrigation was stopped,the groundwater continues to infiltration downward under the action of gravity,which caused the decrease of pore water pressure of the surface soil and the increase in silty clay layer.(4)During the whole seepage process,the displacement of the slope in the X direction increases with the increase of the seepage time and the permeability of the surface loess.The displacement mainly distribute in the Malan loess and silty clay layer,and the maximum displacement occurs at the free face at the top of the slope.Besides,the increment in the vertical direction is greater than the horizontal direction.