Study On The Effect Of Rainfall Infiltration On Stability Of Loess Excavation Slope

Landslide is one of the major geological disasters in China.In the northwest and north China where the Loess distributes widely,a large number of construction projects will form a large number of excavated loess slope in the implementation process.it is the current focus and difficulties that how to avoid the occurrence of landslides.Recently,persistent heavy rainfall and other harsh extreme weather disasters occur frequently,which further increases the probability of landslides.In this paper,exemplified by the engineering of land reclamation in gully,the formation mechanism of landslide of excavated slope is studied by field investigation,indoor experiment and slope stability numerical simulation.The persistent heavy rain in the summer of the project area led to that the slope collecting water at the top of the slope,the toe of the slope and platform.In view of this phenomenon,the impact of ponding infiltration caused by persistent heavy rainfall on slope stability is studied emphatically.The laboratory tests were conducted to simulate the vertical one-dimensional persistent rainfall infiltration process,and the change of soil moisture content and the characteristics of wetting front movement were observed and tested.The indoor shear tests were conducted to study the effect of moisture content on shear strength of slope soil.According to the distribution of soil saturation area at different time points obtained from the rainfall infiltration test and the specific values of unit weight,cohesion and internal friction angle in saturated zone,the changes of potential sliding surface and the stability of slope under persistent rainfall infiltration conditions were calculated and analyzed by FLAC3 D software.Lastly,in view of the stability of the excavated slope in the natural state,the optimization of the slope excavation method is studied by calculating the safety factor under different slope shapes and different slope ratios.The research conclusions can be summarized as follows:(1)The results of vertical one-dimensional ponding infiltration test of soil show that: the wetting front moves faster in the shallow soil under the condition of rainfall infiltration,and the velocity of the wetting front gradually decreases with the depth increasing.When the wetting front arrives,the soil moisture content at different depths shows a first steep rise and then a gradual increase.After a certain period of infiltration,the soil moisture content of a certain depth remains the same,and the saturation reaches 80%.(2)Comparing the three kinds of instability criterion of strength reduction method,we can know that: The solving process of convergence criterion of numerical computation is efficient,simple and quick.The solving process of displacement mutation criterion is complicated,but the calculation accuracy is high.The solving process of connectivity criterion of the plastic zone can reflect the development process of the shear band intuitively,but the calculation accuracy is low.The three kinds of instability criterion have their own advantages.Therefore,combining the three kinds of instability criterion to calculate the safety factor,the slope stability can be mastered comprehensively.(3)The rainfall infiltration reduced the shear strength of the soil,and with the increase of the rainfall duration,the saturated area in the slope soil increased,and the deformation of some parts in slope soil increased.When the local plastic deformation occurs gradually to a certain extent,the slope will produce displacement mutation and shear strain increment mutation and then form a through the shear band,resulting in landslides.Therefore,the loess slope should be set drainage measures to avoid landslides caused by rainfall infiltration and other natural disasters.(4)By calculating the safety factor of excavated slope in natural state with different slope shapes and different slope ratios,it is proved that the addition of platform in the middle of slope can improve the safety factor of slope and enhance the stability of slope.In the case where the top of the slope and the toe of the slope are fixed,the safety factor of the slope increases first and then decreases as the width of the platform increases.Therefore,We suggest that setting up the platform reasonably and controlling the width of the platform in the practical project.