Softening Mechanism Of The Slope Toe Of Malan Loess

In response to policies of urbanization construction and economic transformation promulgated by the central government of China;regions in Loess Plateau of China have recently seen an increased in infrastructural developments such as transportation,water conservation and hydropower.However,the geographical landscape of the Loess Plateau is prone to natural disasters,resulting in the region's undeveloped status.Previous studies on the instability of the loess slope relative to rainfall and water supply mostly focused on surface runoffs and erosion,running water infiltration and water level uplift,rate of soil quality deterioration and fissure initiation,etc.,ignoring the role of toe softening in inducing and aggravating geological disasters.There are no clear answers regarding: 1)macro-development law of toe softening and associated disease of loess slope;2)the methods for detecting in-situ soil strength of a slope toe;3)the distribution characteristics and dynamic evolution mechanism of soil strength and water content of the loess slope toe;4)the coupling relationship between strength field and water content field.Taking Yuci District of Shanxi Province as the research area,this study extensively discusses the above issues by conducting slope survey,in-situ test,on-site rainfall test and physical simulation.With my findings,the scientific and probably “mystery” about softening mechanism of the loess slope toe was addressed.The main results and conclusions drawn from this study are summarized as follows.(1)With the help of UAV aerial survey and visual analysis system,a comprehensive investigation on the characteristics of toe softening and associated diseases of loess slope was conducted by using route crossing.The survey showed that the softening of the loess slope toe had a remarkable versatility.Highly stable and straight wetting front was often observed on the surface of the slope toe during and after rainfalls.Soil below the wetting front were characterized by dull color,wetting and small hardness,and even with disease of spall and salt crystallization.The resulting slope disease seriously threatens the stability of the slope and can further cause serious geo-hazards.(2)Drawing on the basic principles and structure of conventional cone penetration instruments,a horizontal penetration device for the strength detection of soft rock and soil slopes was developed.This device,is advantageous for its compactness,convenience and accuracy,which are essential for detecting the in-situ strength of soils at a slope toe,and exceeds the limitations of the traditional cone penetration instruments with a single penetration direction and bulky structure.(3)Based on the in-situ test of the strength and water content of soils at the loess slope toe,contour clouds of the penetration resistance and water density of the soil at the slope toe were constructed using Sufer,Arc GIS,Origin,etc.Characteristics of penetration resistance and water distribution of soils at the slope toe were analyzed.Then the coupling relationship between them were established by utilizing theory of section cutting,model optimization and image overlapping.Distribution models of penetration resistance and water content at the slope toe were built based on aforementioned research,which promoted the proposed mechanism of water induced softening of the Malan loess.(4)On-site rainfall and monitoring test of soil-water capacity were performed by the author during this research.With the help of Arc GIS,Surfer,a time-series evolution map of water field of the slope toe was constructed.Based on the theory of time-series analysis,change of volumetric water content of soils at the slope toe and time-history expansion path of water content contours of soils,the law of dynamic evolution of soil water content of slope toes was proven.(5)By utilizing infiltration model test of the intact Malan loess,with the help of identification and extraction technology of wetting front,the migration path and expansion mode of capillary water and gravity water on the section of model slope are completely characterized.Combined with the test results of on-site soluble salt and soil water potential,the driving mechanism of soil water migration of the Loess slope toe was systematically elucidated,and the model of soil water migration and infiltration was constructed.With a comprehensive analysis of the in-situ results,on-site rainfall and model test,an evolution model of genetic mechanism of toe softening on Loess slope was constructed,which revealed the softening mechanism of the loess slope toe.