Background The artificial accumulation site in the loess area is a new measure for Lanzhou city to expand the urban land space in recent years. It is inevitable to form more artificial landfill slopes at the edge of the site, which may become a potential material to be involved in debris flow.

Methods This paper took the "4·19"debris flow disaster in Jianshui valley of Lanzhou city as an example. Combined with grain size analysis experiment, SEM image and field infiltration experiment, this paper discussed its characteristics and operation mode, and proposed corresponding treatment suggestions.

Results 1) Materials with grain size < 1 mm in the loess area accounted for 11.4 %-55.2 %, which was conducive to the initiation of debris flow. 2)Compared with two mud level survey sections with a distance of 170 m, the flow of the downstream section increased by 2.5 times, indicating that the loess subsidence caused by infiltration promoted the conversion rate of debris flow material. 3) The infiltration experiment showed that loess accumulation site had strong permeability. It basically reached a stable infiltration state in about 8 min under low water head conditions, and basically reached a stable infiltration state in about 12 min under high water head conditions. It caused soil softening in a short time, affecting the slope stability of artificial landfill site, and thus improved the material conversion rate of debris flow. 4) The flow pattern of debris flow induced by artificial accumulation site in the loess area is complex and changeable, which has the characteristics of wavy flow and intermittent flow.

Conclusions On this basis, authors propose a prevention model that combines process management and key protection.