| In recent years,the extreme heavy rainfall weather in Ningzhen area has gradually increased,which has caused a large number of landslide disasters.Due to the occurrence of heavy rainfall,a new type of landslide,intermittent creep landslide,occurs in the gentle slope zone of the Piedmont.According to the data of many landslides in Ningzhen area,this kind of landslide has very similar stratigraphic structure.The structure of slope is as follows:the whole slope presents the structural characteristics of steep upward and gentle downward,the upper slope is often bare rock,whose grade is generally more than 30 degrees,even more than 50 degrees.The lower part is mostly covered by loose sediment of Quaternary system,whose grade is very gentle,generally less than 15 degrees,some even only 8 degrees.Near the surface is mainly clay soil,gravel or gravel clay soil,with poor permeability.At the bottom is slope residual soil,and lithology is mainly gravel soil or strongly weathered rock mass,with good permeability.The special stratum structure makes the slope have the stratum condition to form temporary confined water.Extreme strong rainfall provides the water source condition for the formation of temporary confined water.Groundwater monitoring data showed that temporary confined water did form during the period of heavy rainfall.Traditional studies have shown that such gentle slopes are not easy to slide.However,in recent years,many landslides had occurred frequently on the gentle slopes of the Piedmont in Ningzhen area.It is preliminary judged that temporary confined water is the main cause of such landslide.In this paper,the formation conditions and influencing factors of temporary confined water and its influence on slope stability were studied by means of theoretical analysis,numerical simulation and laboratory tests,and the landslide prevention measures suitable for gentle slopes of the Piedmont were put forward.This paper mainly obtained the following understandings:(1)The physical model of dissipation of confined water on gentle slope was established.Under the conditions of different confined water level,the relationship between pressure head,water level and cumulative water flow in clay layer and test time was studied,and then the dissipation rule of confined water in clay layer,the actual permeability characteristics and the water-proof effect of clay layer under confined water were obtained.It laid a foundation for studying the formation of temporary confined water and its influence on the stability of gentle slopes of the Piedmont.(2)According to the special stratum structure of the gentle slope of the Piedmont,the simplified groundwater seepage model of the slope was established,and the seepage equation of the gentle slope in each stage was established by theoretical analysis method.The influence of rainfall intensity,rainfall time,permeability coefficient of the middle layer and thickness of the middle layer on the temporary confined water level was analyzed by numerical simulation method.(3)According to the action characteristics of temporary confined water and the distribution characteristics of confined water level in the gentle slope,the landslide mechanism of intermittent creep landslide was comprehensively analyzed,and the failure modes of intermittent creep landslide dominated by temporary confined water were put forward:top crack sliding failure,floating sliding failure and high angle shear failure.The failure conditions of various failure modes were analyzed from the point of view of slope stress.(4)Taking a landslide in Paoma Mountain of Zhenjiang City as an example,the formation process of confined water and the distribution of confined water level on the slope were analyzed by numerical simulation.Based on the failure model of intermittent creep landslide,the in:fluence of temporary confined water on the stability of the gentle slope under two conditions of blocking and non-blocking was explored.(5)Based on the above research results on the formation conditions of temporary confined water and the influencing factors of confined water level on gentle slope,the monitoring methods of the temporary confined water level in the gentle slope of the Piedmont and the landslide prevention measures suitable for gentle slope were put forward. |
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