Agricultural irrigation in loess platform has led to a continuous rise of the groundwater level and triggered a series of loess landslides. To gain a better understanding of the infiltration behavior of irrigation water in loess

a field infiltration test with a diameter of 20 m was conducted on the South Jingyang tableland

Shaanxi province. The spatiotemporal characteristics of moisture content and matric suction were monitored. Then the infiltration laws under the conditions of soaking and intermittent irrigation were simulated. Results show that the soak infiltration can be divided into three stages

namely

uniform infiltration

preferential flow infiltration

and stable infiltration

respectively. Preferential flow associated with the vertical cracks in the Malan loess was observed when the width of the crack was more than 2 mm and the soil above the crack was saturated. The hydraulic conductivity of the lower part of paleosol layer (S1) was relatively weak compared to the upper part of S1

and a transient perched water was observed above the lower part of S1. The three-dimensional infiltration numerical model was established to reappear the soak infiltration process. Due to the multiple irrigation events

the downward percolation of water was significantly promoted by the superposition effect of wetting front. The infiltration capacity decreased with the increase of depth. The velocity of infiltration below 5.6 m depth was less than the hydraulic conductivity of the soil

the infiltration was driven solely by the gravity

and the moisture content and matric suction were almost unchanged. This finding explains the phenomenon that water infiltration in deep loess is difficult to be monitored in the previous studies.