Study On The Post-evaluation Of Loess Slope Treated By Retaining Wall Under Rainfall

The post-evaluation of loess slopes treated by retaining walls is a issue urgently needs commencing.In this paper,field investigation is carried out on the loess slope treatment by retaining wall in northern Shaanxi.Model experiment,field monitoring and prediction,and finite element numerical simulation were carried out for typical loess slope engineering to analyze the deformation and failure mechanism of loess slope engineering treated by retaining wall under long-term rainfall.According to the deformation and failure mechanism,nine main controlling factors affecting the treatment effect are screened out,and a fuzzy comprehensive post-evaluation theoretical framework is constructed for the treatment of loess slope by retaining wall.The main results obtained are as follows:(1)Based on the field investigation,the failure type of loess slope caused by rainfall was explored,and the deformation and failure mechanism of loess slope treated by retaining wall under the influence of rainfall was preliminarily analyzed.Meanwhile,adopted the Apriori association statistics theory,the governance association rules mined from the field investigation data are:① when using cutting measures to treat the loess slope,the necessary conditions for good treatment effect are:the local annual rainfall is less than 550 mm or the slope height is less than 50 m or the average slope is less than 65° or the operation duration is less than 6 years;②when the gravity retaining wall is used for treatment,the necessary conditions to achieve good treating effect are:the annual rainfall is less than 550mm,and the average slope is less than 65°;or the annual rainfall is less than 650mm,and the slope height is less than 20m.(2)Selecting a typical cutting loess slope and a loess slope treated by the retaining wall,carried out the indoor model experiment to analyze the influence of the deformation and failure mechanism of retaining wall of the loess slope:① for cutting treatment of the loess slope,due to the surface consolidation effect during rainfall intervals,the rain flushing action of slope is more and more weak,after the third year it enters the scouring stability phase;The infiltration rainwater gathers at the shoulders of the slope,resulting in large excess pore water pressure and "shoulder cutting" effect.The failure mode of loess slope under the influence of rainfall is the combination of rotation around the sliding center and rheology of sliding body,which is classified as traction landslide.②For the loess slope treated by the retaining wall,from the third year,the saturated flow of soil within a depth of 4m in the surface layer will occur to the back of the wall,which makes the earth pressure on the surface of the back of the wall increase greatly.At this time,the earth pressure on the back of the wall is small in the middle and large at the top and bottom.Under the influence of rainfall,the failure mode of loess slope retaining wall is an inclined forward and a bulge in the middle.Since the third year,the loess slope treated by retaining wall has entered a stable period of deformation.(3)Putting forward the theory of collapsible loess slope field monitoring,according to the loess collapsing settlement,the theory correction formula of inclinometer monitoring values was deduced.For the earth pressure and deformation on the back of the retaining wall,the prediction ARIMA model was employed,and the further analysis of the deformation failure mechanism was carried out:The development process of earth pressure behind the wall can be divided into three stages:rapid growth stage,slow growth stage and gradually stable stage.The wall bulge is caused by the combination of thinner wall thickness and larger earth pressure behind the wall.The forward tilt and fracture of the wall are caused by the initiation of movement of the potential sliding surface.ARIMA model is more reasonable to predict soil pressure and displacement,so it is recommended to use ARIMA model for prediction.(4)The finite element fluid-structure coupling analysis of typical loess slopes treated by cutting and retaining wall under the influence of rainfall was carried out to further analyze their deformation and failure mechanism.① The wet front in the rainfall can not be used as the boundary between the saturated zone and the unsaturated zone,but only as the boundary of a certain rain infiltration rate;It is proved that the shoulder cutting effect of rainfall is caused by the accumulation of excess pore water pressure.② The pore water pressure near the retaining wall is always negative due to the effect of "drainage".Due to the resistance of retaining wall,the rheological phenomenon of slope is concentrated in the first year rainfall.Wall waterproof can effectively prevent wall damage.(5)According to the deformation and failure mechanism of loess slope affected by rainfall,nine main controlling factors of loess slope control effect are summarized.The theory of determining the membership function of each main control factor more objectively based on the field survey statistics and single factor Apriori association rule is proposed.Combined with the deformation and failure mechanism of loess slope,the weight of each main control factor was determined by the improved analytic hierarchy process(AHP),and then the fuzzy comprehensive evaluation theoretical framework of loess slope treatment effect based on Apriori association rule was constructed,and the engineering verification was carried out.