Study On The Pore Structure And Slope Stability Of Loess In Heifangtai Under Freeze-thaw Action

The study area Heifangtai is a typical landform of loess plateau with wide loess.In the area most edges of the plateau are loess slops.The landslide disasters in the area are frequent and are most concentrated in March every year.The area is a seasonal frozen soil area and its regional freeze-thaw period is from January to March.The freeze-thaw action has a significant impact on the stability of the loess slope.Finding out the influence factors of freeze-thaw action on the stability of loess slope,such as pore structure and mechanical strength,has an important guiding significance for the prevention and control of loess landslide disasters in this area.In this paper,loess samples in the study area were obtained through field sampling,and freeze-thaw action cycle test was conducted on the samples to simulate seasonal freeze-thaw action under natural conditions.CT scans were performed on undisturbed soil samples which have been subjected to freeze-thaw action cycle.After preprocessing and binary image segmentation,the binary image was imported into Avizo software for 3d reconstruction of the sample.Then the software's own algorithm is used to extract the pore equivalent diameter and porosity,and the influence of freeze-thaw action on the pore structure of loess is analyzed.The soil samples under freeze-thaw action were subjected to triaxial test to obtain the shear strength and the Flac3 d simulation software was used to simulate the freezing and stagnant water in the slope,so as to analyze the influence of water level fluctuation caused by freeze-thaw action on the slope stability.Research indicates:1.The 3D reconstruction of the sample based on CT image was realized,and the parameters such as pore equivalent diameter,porosity,large porosity and medium and small porosity of the sample under freeze-thaw action were quantitatively extracted.The effects of freeze-thaw action on the pore structure of loess were expounded: after the freeze-thaw cycle,the equivalent diameter of loess expanded,the porosity and total porosity increased,and the variation of small and medium porosity was not obvious.2.The mechanism of freeze-thaw action on loess landslide is expounded.Based on Flac3 d numerical simulation,a numerical model for evaluating the deformation and stability of loess landslide is established.3.The relationship model between water level evolution and stability coefficient is constructed,and the simulation is carried out near the critical water level to determine the critical water level of slope.