It is of great theoretical and engineering significance to carry out field rainfall tests and research on double-layer soil slopes in loess areas. Based on the developed rainfall simulation system with slow-moving injection, field rainfall tests were carried out on a natural double-layer loess slope. The characteristics of volumetric water content were monitored, and the rainfall infiltration characteristics and infiltration effect at the interface of the soil layer were analyzed by numerical simulation. The results showed the fastest infiltration at the top platform of the slope, followed by that at the upper surface of the slope, and the slowest infiltration at the lower surface of the slope during rainfall. Under various rainfall intensities, the erosion of the upper silty loess slope was greater than that of the lower clay loess slope, and the erosion patterns were quite different at the end of rainfall. During the infiltration process in the double-layer loess slope, a stagnant transition area was formed near the interface of the soil layer. The equipotential line of water content in the stagnant transition area of the upper region was roughly parallel to the slope surface, and the equipotential line in the lower region was roughly parallel to the interface of the soil layer. With an increase in rainfall intensity, the upper transition area at the interface of the soil layer continued to extend from the slope surface inward, showing the interface infiltration effect that became increasingly significant with the intensification of rainfall. The infiltration effect at the soil layer interface could provide an evaluation basis for rainfall infiltration analyses of multi-layer soil slopes.

When tests are conducted on the field slope under artificial rainfall, because artificial rainfall is often limited to implementation in the mode of local rainfall, there is a boundary constraint effect between the rainfall area and the non-rainfall area, which is manifested in the lateral infiltration of rainwater and the slope deformation retardation of non-rainfall area to the rainfall area. Firstly, a deep-buried isolated trench was proposed to solve these boundary constraints. Then, field cracking tests and the corresponding numerical simulation were conducted under rainfall. In the end, the response of water content and the cracking failure characteristics of the slope were analyzed during rainfall, and the effect of a deep-buried isolated trench on the cracking characteristics of the slope was evaluated. The results indicate that the proposed deep-buried isolated trench measure can effectively eliminate the deformation retardation resulting from the adjacent non-rainfall area so a through-crack parallel to the slope shoulder that extended on both sides of the boundary of the rainfall slope was observed at the slope crest and a cracking failure in the shape of the overall downward cutting was realized. As the crack occurred, the rainwater infiltration further aggravated expansion of depthwise cracks, and a local sliding zone was formed in the upper part of the slope. The deep-buried isolated trench solves the boundary constraints, such as lateral infiltration of rainwater and deformation retardation, and can provide an effective technical measure for the field slope test under artificial rainfall.

When loess is contaminated by oil, different modes of contamination will have a certain impact on the mechanical behaviors of loess in the oil-production areas. This study is aimed at evaluating the effect of diesel oil contamination on mechanical behaviors of loess through extensive laboratory tests. Two different modes of oil contamination were proposed and applied in compression tests, direct shear tests, and unconfined compressive strength tests to study the compressibility and strength characteristics of diesel-contaminated loess. Results show that two different modes of oil contamination have significant effects on the mechanical behaviors of loess. In comparison with clean loess, the compressibility of contaminated loess increases, and its unconfined compressive strength and shear strength all decrease under the first mode of oil contamination. The compression modulus, friction angle, and unconfined compressive strength of diesel oil-contaminated loess using the second mode of oil contamination are larger than those in the first mode of oil contamination at the same oil content and dry density. Understanding these effects on mechanical behaviors of loess under different modes of oil contamination can significantly guide soil and environment-remediation activities in loess oil-production areas.