Experimental Study On The Process Of Irrigation And Infiltration Of Undisturbed Loess

Loess is distributed in the arid and semi-arid regions of northwestern China.It is a kind of Quaternary sediments with loose pores,vertical joint development,and cemented structure between soil particles.Due to the shortage of water resources and the development of social economy,the expansion of agricultural irrigation projects has destroyed the local original hydrological and geological conditions,resulting in a large number of loess landslide geological disasters.Therefore,the loess landslide is a special kind of landslide.Most of these loess landslides are closely related to diversion irrigation.The southwest of Fuyang,Shaanxi Province and Heifangtai,Gansu Province are pregnant with typical irrigated loess landslides.Irrigation loess landslides have the characteristics of long sliding distance,fast sliding speed,great harm,and multiple recurrences in situ.Therefore,from the perspective of mechanism of water-induced loess slipping,the laws of soil moisture migration and water management under irrigation conditions are studied.The study of characteristics has practical significance.In this paper,from the perspective of the water quality of the undisturbed loess,the typical loess irrigated areas in the Minnan-Hebei area are taken as the main research object.Based on the field geological surveys and indoor tests on the landslide hazards of the Loess Plateau,the irrigation water in the aeration zone is systematically studied.The infiltration law in saturated loess was studied,and the change of water characteristics of shallow loess under irrigation and the mechanism of landslide occurrence were explored.In this paper,the field in-situ monitoring test was used to simulate and analyze the infiltration process of irrigation water.Through numerical calculations,the forward and inverse optimization of the soil-water characteristic parameters of the undisturbed loess under the condition of irrigation infiltration was performed.The main work of this paper is as follows:(1)Based on on-site sampling and laboratory tests,the basic physical properties of different soil layers(Q3 loess layer,transition layer,and S1 paleosol layer)were studied.The results showed that the basic physical properties of the soil column were in-depth withthe depth.The regularity changes and changes greatly at the soil interface.(2)Monitor and analyze the infiltration law of the in-situ soil column under the action of constant head: In this irrigation process,all sensors respond in sequence,and the soil moisture content has undergone a steady,sharp rise,and slowly increase.The four stages of Yamato re-stabilization;soil properties play a decisive role in the movement rate of the wet front,the infiltration rate in a single soil layer is roughly the same,and the topsoil> Q3loess> S1 paleosol> transitional layer;moisture absorption curve There is apparently no coincidence with the dehydration curve,showing significant hysteresis.(3)Study on indoor soil-water characteristic curve and parameter fitting of undisturbed loess in different layers: Use indoor soil-water characteristic curve test of undisturbed soil through PF tester;The "S"-type SWCC curve has higher R2 fitted,all being above 0.994,and the fitting effect is very good.The fitting result is compared with the basic physical property experiment and the result rule is consistent with theoretical experience.(4)Inversion calculation and forward prediction of undisturbed soil by numerical analysis: The comparison between numerical simulation results and experimental results shows that there is a certain degree of error between numerical simulation results and experimental results,and the matrix suction The simulation effect is better than the volumetric water content.According to the field monitoring data,the HYDRUS-2D numerical analysis inversion module is used to optimize the soil characteristic parameters.The above research results have certain research significance for studying the water transport law and water and physical properties during the process of loess irrigation.On this basis,it has certain application and academic value for the study of loess groundwater response and slope stability evaluation,and has deepened Understanding of the formation mechanism of loess landslides.