Influence of rainfall on sliding modes of cutting slope of weathered granite stratum: Taking Yunxiao section in the Yunping freeway in Fujian for example

It is a common phenomenon that rainfall may cause locally shallow sliding of cutting slopes, but the study on the immanent cause is still insufficient. Take a two-grade cutting slope in the weathered granite stratum in Yunxiao section in the Yunping freeway in Fujian as an example, the shear strength theories of saturated soil and unsaturated soil and the strength reduction method of finite element were adopted to study the sliding modes of cutting slope under general working condition, groundwater seepage, and rainfall infiltration. The results show that the sliding mode of the slope exhibits the globally deep sliding under the general working condition. The sliding mode turns to be the shallow sliding from the deep sliding under groundwater seepage. Three slip surfaces may develop in the slope after a long-term light and/or moderate rainfalls, and the slip surface within the first-grade slope runs through firstly so that the sliding mode evolves into the locally shallow sliding from the globally deep sliding. A run-through slip surface only occurs within the first-grade slope after short-term strong rainfalls, i.e., the sliding mode completely turns to be the locally shallow one from the globally sliding one, and the more unfavorable the working condition of a rainfall is, the more remarkable it exhibits. It also agrees well with the phenomenon of the practical landslide, and the safety factor cannot meet the requirement of the specification, and thereby the inevitability of the locally shallow sliding of the cutting slope was theoretically verified. In addition, to avoid the occurrence of the locally shallow sliding of cutting slopes in the weathered granite stratum under the infiltration of rainfalls, various hypothetical schemes were numerically modeled. The results show that no slip surface will occur within the first-grade slope if it is sloped at an appropriate gentle slope, and as a result, the sliding mode is still a globally sliding in a deeper location and the safety factor may be effectively enhanced to meet the requirement of the specification. Therefore, in practice, it is extremely necessary to carry out the simulation analysis of a designed cutting slope in similar stratum under the infiltration of rainfall beforehand. Thus, the gradient of sloping will be more scientific and reasonable, so probability of the occurrence of the locally shallow sliding may be significantly reduced.