| Formed in the Quaternary arid and semi-arid conditions,the loess,while nurturing the people,also makes collapse,landslides,mudslides and other geological disasters occur frequently,affecting the normal production and lives of the people and the smooth development of engineering construction in loess areas,causing serious threats to the safety of people’s lives and property.Almost all geological hazards and construction problems in loess areas are closely related to the destruction of soil structure caused by the change of moisture in the loess.Rainfall is the most common factor causing soil moisture changes under natural conditions.Therefore,research on rainfall infiltration in loess areas plays an important role in understanding the hydrological cycle in loess areas,and is of great significance to regional disaster prevention and construction.At present,most of the research on the infiltration of loess water is focused on artificial rainfall simulation,indoor small-scale experimental research and numerical simulation research,but there is less research on the infiltration of loess water by rainfall under natural conditions.Based on this paper,the long series continuous monitoring of the resistivity of the loess layer during rainfall infiltration was carried out with the aid of electrical resistivity tomography to study the infiltration pattern of loess moisture,and the basic properties of loess were also measured,including the resistivity test of remodelled loess,the in-situ resistivity test in the field and the drilling sampling.The HYDRUS-1D moisture transport model was combined with numerical simulation techniques to analyse and study the distribution characteristics and transport pattern of loess moisture during rainfall infiltration.The main conclusions are as follows:(1)The resistivity change characteristics of the three groups of electrical resistivity tomography monitoring profiles are similar,initially showing the resistivity distribution characteristics of low in the middle and upper parts and high in the deep parts.With the infiltration of water from rainfall,the resistivity of the middle and upper parts decreased further and changed significantly,while the resistivity of the bottom part began to decrease as the water continued to move downwards.After the rainfall stops,the water content of the soil gradually decreases under the influence of both evaporation and transpiration by plants,and the resistivity increases until it finally shows a high-low-high resistivity distribution.After the first concentrated rainfall period with a total rainfall of 139.4 mm over a period of 5 days,the resistivity within 2 m of the surface of the three groups of profiles changed significantly,while the resistivity at depth changed slowly,with a lag in water infiltration.(2)The pattern of water content change at different sampling time points in the three groups of profiles has good consistency.After the first concentrated rainfall period with a total rainfall of 139.4 mm over 5 days,the water infiltration depth reached 2.7 m.The water content within 1.4 m of the surface was significantly affected by evapotranspiration,and continued to decrease within 1.4 m of the surface after the rainfall ceased,while below 1.4 m the water content continued to increase due to the lagged infiltration of water.The overall water content of the study profiles differed according to the degree of evapotranspiration and transpiration of the vegetation cover: taller but sparse vegetation > sparse and bare vegetation > low and dense vegetation.(3)The relative error between the back-calculated water content of the electrical resistivity tomography and the actual water content measured by drilling is less than 10%,and the correlation coefficient r is greater than 0.85,which is a very strong correlation.The results of the electrical resistivity tomography are in good agreement and accuracy with the variation pattern of water and salt content in the profile,which proves that the electrical resistivity tomography is suitable for the study of rainfall infiltration in the study area,and its advantages of low cost,high efficiency,a large amount of information and high resolution can play a great role in the relevant research and practice.(4)The changes in soil moisture during the simulation period of the HYDRUS-1D model mainly occurred in the range of 0-3 m at the surface,and the rainfall,evapotranspiration,soil storage,and infiltration at the lower boundary were in a dynamic equilibrium.The total rainfall during the simulation period of 56 d was 239.3 mm,and the soil water storage in the simulated10 m depth profile increased by 107 mm.44.71% of the rainfall was converted into soil water storage. |
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