A rapid loess mudflow triggered by the check dam failure in a bulldoze mountain area, Lanzhou, China

Urban expansion results in a large number of land creation projects in the Chinese Loess Plateau. This has strikingly catalyzed hilltops being cut and valleys or low lands being filled by bulldozed mountain. Meanwhile, a large number of check dams were built into the loess gully to store soil and water. This paper studied a case of check dam failure, which resulted in rapid loess mudflow in a bulldozed mountain area. To investigate kinematic characteristics of the mudflow and trigger mechanism of the dam failure, in situ feature measurements, physical property tests, triaxial tests, and groundwater simulations were carried out. The field investigation revealed that moisture content of the loess in the filled area was very high and that the dam failure was most likely due to groundwater seepage. The VS2DI simulation of the check dam showed that its material was over saturated due to moisture migration in it, which significantly affected its stability. The simulation results are consistent with those of the field investigation. Rapid mobility of the mudflow could be attributed to liquefaction of the loess behind the dams. Meanwhile, the movement velocities calculated from by in situ mud splash height are related to the deposited volume of the mobilized materials at corresponding sites.