This paper is the result of geohazard survey engineering.

Objective The change mechanism of mudflow mass in the motion process is an important research topic in the fast landslides and mudflows. During the shearing process, basal erosion is recognized as a dynamic interaction between the original moving material and the entrained basal topsoil along the contact surface.

Methods In the current study, massive geohazards occurring in Tianshui on July 25, 2013 were selected as the research objects. The erosion rate was first introduced, and then the dynamic numerical model of basal erosion based on three-dimensional continuous medium was established to analyze the response relationship between the motion behavior and the dynamic process of mudflow on the basal erosion.

Results The motion process of mudflow on the slope of Nanyu Village is mainly divided into a rapid acceleration stage, a fluctuation stage, and a rapid deceleration stage. During the rapid acceleration stage, the effect of basal erosion on the mudflow motion behavior was weak. During the fluctuation stage, the effect of basal erosion on the dynamic process of mudflow was significant, and the erosion volume and the total dynamic energy increase dramatically. This exacerbated the intensity and scope of disaster, and the slope toe was severely eroded. During the rapid deceleration stage, the basal friction quickly dissipated the total dynamic energy, and the erosion volume grew slowly and tended to be stabilized. With the gradual increasing in erosion rate, the basal erosion effect gradually enhanced, and the running time, moving distance, average thickness, erosion volume, and total dynamic energy of the mudflow increased by an exponential function. The average velocity decreased slightly as an exponential function with high fitting accuracy, which can be used for the qualitative analyses and quantitative calculations of the basal erosion effect on the mudflow.

Conclusions The numerical results are more consistent with the actual cases considering the basal erosion. The numerical model is more suitable for the evaluation and prediction of the disaster intensity of such mudflows and landslides. The findings provide theoretical support for the dynamic mechanism and technical guidance for the prevention and control of mudflow disasters.