## 1 Introduction  
Landslides are a common natural geological disaster, and their harm is great. With the increasing frequency of human engineering activities, the landslide problem becomes more and more prominent, and it has been the concern of scholars in various countries [1, 2]. The purpose of landslide research is to understand the development mechanism and movement failure mode of landslides, and then determine prevention and control measures. It mainly includes three aspects: landslide expression, landslide stability analysis and landslide engineering treatment. Among them, landslide expression is the basis of landslide research,and the purpose is to describe the spatial distribution characteristics of landslide mass, the position and shape of the sliding surface and the material composition and geological structure characteristics of landslide mass. It lays a foundation for the establishment of a landslide mechanics mathematical model, monitoring model and landslide stability evaluation. The existence of a weak interlayer in the landslide mass provides a potential sliding surface for the landslide mass, which is not conducive to the overall stability of the landslide mass [3; 4; 5]. When there are soft and hard rock deposits in the slope, under the influence of external factors such as rainfall and wind, the softer rock layer is more likely to be weathered and broken and to shed, forming soft structural planes or a weak interlayer, sometimes forming hard rock and soft rock interbedding, which is not conducive to the stability of the elastic rock slope. The stability of the elastic rock slope is worse than that of the conventional one because of the weak interlayer. After the construction of houses and roads are cut, the safety and stability of the slope is more threatened. On the one hand, the weak interlayer has strong water sensitivity, which is easily saturated and softened once it absorbs water, and the strength is greatly reduced, resulting in the sliding failure of the slope along the interlayer. On the other hand, the infiltration of rainwater increases the self weight of the slope, and creep deformation of the slope occurs, providing power for the slope to start sliding. Therefore, the weak interlayer is the key factor to control slope stability. In the study of the spatial-temporal distribution law and internal structural characteristics of the landslide, it is of great significance to effectively identify the weak interlayer [6; 7; 8]. The weak structural surface in the rock mass is characterized by weak fractures, thinness, easy disturbance and erosion, and the strength is significantly different from the rocks on both sides. It is difficult to directly identify the weak structural plane in the rock mass. At present, the main identification method is through outcrop observation or excavation sampling, which has a large workload and high cost. It is mainly applicable to the identification of weak structures in shallow strata. The rock structure at the corresponding depth is mainly obtained through modeling and geophysical exploration [9; 10; 11; 12]. The conventional borehole method has a low success rate in taking samples of weak structural plane and poor positioning and qualitative effects. The survey method of large-diameter borehole or excavation of exploratory tunnels and shafts is adopted, which has a long construction period, high cost and is unsafe. In landslide exploration, conventional boreholes are a very mature exploration method, which are simple, convenient and practical. However, this is an indirect method. When encountering complex geological conditions with a low coring rate, it is difficult to obtain geological information of structural planes such as faults, weak planes, weak joints and weak zones in the borehole, which easily leads to misjudgment of deep geological conditions [13; 14; 15]. At present, with the rapid development of various sensors, optical imaging technology, acoustic testing technology, laser scanning technology, computer technology, etc.