Abstract: The rotation azimuth of slope surface points can effectively reveal the evolution process of landslide deformation. We independently developed a measuring instrument for the rotation azimuth of slope surface points. Moreover, we revealed the response characteristics of multi-point rotational azimuth in the process of landslide breeding. We installed two measuring instruments respectively on the surface of the physical loess landslide model's back edge, middle edge and front edge. In the experiment, we simulated the influence of irrigation water infiltration on slope deformation with continuous long-time irrigation. Our findings manifested that: 1) with the continuous infiltration of irrigation water, seepage passages inside the slope body developed and expanded steadily, and the seepage flow at the bottom of the slope foot increased from 24 mL/min to 1 515 mL/min, showing a double exponential growth trend. 2) In the process of landslide evolution, cracks occurred firstly in the middle-to-back part of the slope, developing perpendicular to the direction of slope surface. At 1^#, 2^#, 3^# and 4^# points, the rotational azimuth increased gradually in a linear trend. Penetrating the back edge of slope, cracks developed gradually in the front edge, and the rotational azimuth at points 1^# and 2^# surged, with the soil mass been extruded. 3) The extrusion of soil in the front edge changed the stress state and seepage path of the slope body, resulting in the plummet of rotation direction at points 3^# and 4^# in the middle of slope body as well as the extrusion of soil in the middle and back edge, which gave rise to a second sliding. 4) According to the change trend of rotational azimuth of surface points, the evolution of irrigated loess landslide can be summarized into three stages: stable breeding stage, steady deformation stage, and accelerated destruction stage, of which the stable breeding stage accounted for 99.5% of the total landslide duration, steady deformation stage 0.2%-0.3%, and accelerated destruction stage only lasted for 10-15 seconds, a further sign of abruptness of irrigated loess landslide.

Key words: azimuth of rotation, measuring instrument, loess landslide, deformation damage feature, irrigation seepage