Compared with plain soil, polypropylene (PP) fiber‐reinforced soil has markedly improved mechanical properties and can be used in slope protection projects. To investigate the reduction law of the antierosion ability parameters of PP fiber‐reinforced loess under dry‐wet (D‐W) cycles and freeze‐thaw (F‐T) cycles, we took loess from Yan’an, China, mixed them with PP fiber, and did shear strength tests, disintegration tests, and permeability tests under D‐W cycles and F‐T cycles. The experimental results show that D‐W cycles or F‐T cycles had a less deteriorating effect on the cohesion, disintegration rate, and permeability coefficient of the fiber‐reinforced samples than on plain loess; however, the reduction in their internal friction angle was more obvious. Under D‐W cycles or F‐T cycles, the cohesion and internal friction angle of the reinforced soil decreased as the number of cycles increased, while the disintegration rate and permeability coefficient increased as the number of cycles increased. The relation between the reduction in the antierosion ability parameters of reinforced soil and the number of D‐W cycles or F‐T cycles accorded with the hyperbolic function fitting results. The most obvious reduction effect the D‐W cycles had on the reinforced soil was on the disintegration rate, followed by cohesion, internal friction angle, and permeability coefficient. The most obvious effect of F‐T cycles was also on the disintegration rate, followed by cohesion, permeability coefficient, and internal friction angle. Compared with D‐W cycles, F‐T cycles had a stronger effect on the reduction in the cohesion, disintegration rate, and permeability coefficient of reinforced soil, but the reduction in the friction angle was greater in D‐W cycles.

The water disaster susceptible areas in loess multi-arch tunnels were studied. Taking Lishi multi-arch tunnel as an example, the tunnel is located in Luliang City, Shanxi Province, China, with a total length of 180 m. It is the first loess multi-arch tunnel in China. The groundwater recharge in the tunnel site is dominated by rainfall, and the surrounding rock of the tunnel is unsaturated. Considering the lateral recharge of groundwater, in this study, midas geo-technical analysis system was adopted to simulate the construction process of a middle pilot tunnel-bilateral pilot tunnel of a loess multi-arch tunnel, accounting for fluid-solid coupling. The variations in the surrounding rock stress and seepage fields of loess multi-arch tunnels during the construction process were studied. A water disaster susceptible area in a loess multi-arch tunnel was confirmed based on the catastrophe area of the displacement, stress, gross head, pore water pressure, and seepage velocity. The result show that the water disaster susceptible areas for loess multi-arch tunnels during the construction period mainly concentrated in the mid-partition, arch springs of the left and right tunnels, and the tunnel face.