The Mechanism Of Loess Landslide Induced By Seasonal Freeze-thaw Action

Seasonal freeze-thaw action, one of the main factors of loess landslide, is significant in the construction of new urbanization and the Silk Road Economic Zone as well as the reduction and prevention of the hazards in the Loess Plateau. I had the honor to participate in Mechanism Study on the Loess Slide-collapse Induced by Irrigating Permeation, part of the geological survey and scientific and technological program. According to field survey, dynamic monitoring and experiment in Heifangtai Loess Landslide located in Yongjing, Gansu Province and on the basis of supervisor and program’s results, my paper targeting at the existing problems and shortfalls, develops statistics analysis, freeze-thaw penetration test and analysis stability based on progressive collapse. The results are as following:First, a further analysis of freeze-thaw action. This indicates the mechanism of freeze-thaw action results in loess landslide. The seasonal freezing action causes the spilling of the underground water with freezing leading to output reduction or cutting-off. As a result, the underground water concentrates in slopes more soil softening and the strength of spring thaw frozen layer of melted rock decreased and due to great water pressure caused by re-draining of the enriched underground water, the loess landslide happens.Second, this paper carries out the freeze-thaw action permeability coefficient test, revealing the mechanism of thawing causes underground water flow field changes and constructing underground water evolution under freeze-thaw cycle. The undisturbed samples were tested after freeze-thaw cycle in line with practical condition to obtain freeze-thaw loess permeability coefficient. Under American dehumidifying and moisture transient test device, the SWCC to study loess absorption and desorption was gained. Then, the coefficient was used for numerical simulation to determine the slope groundwater seepage field in the freeze-thaw period. The simulation results shows that the effect of frozen stagnant water caused groundwater rise with a maximum lifting height of about 2.75 meters and the influence scope is inside 50 meters of the slope toe.Third, after shear strength test, the internal friction angle of frozen loess changed little, but the cohesive force increased by about 80 times and melting ability dropped by 99%.Typical freeze-thaw-induced landslide area was selected.Based on different temperatures and seepage fields of the above conditions, using both traditional slice method and partial safety factor method, the stability of slopes in each period of freezing time was compared and analyzed so as to achieve the temperature, seepage and stress coupling analysis slope stability. The initial slope is stable and with seasonal freeze action, slope stability would increase. During spring melting time, the groundwater level was the highest while the frozen layer melting strength plummeted and the stability of the slopes was the worst. As the stagnant water is excreted, the slope again went back to stabilize.