## 4 Discussion  
Deformation is the most obvious and common monitoring parameter in the process of slope failure, which can reflect the disaster mechanism and evolution law of a landslide. The essence of slope instability lies in the broken balance between sliding force and anti-sliding force, and the stress generated in a slope is a parameter closer to the mechanics  
Figure 10: Precision analysis of deformation quantification by acoustic emission under the condition of constant velocity of the sliding body. essence of the landslide [38]. The flexible anchor-like device designed in this study can simultaneously monitor the AE and axial tension. The measured AE parameters can directly quantify the slope deformation [28; 29; 32; 33; 37; 40] and the axial tension within the anchor cable correlates well with the thrust to the sliding body. Data points in Figure 7 showed a wide variation, which is partially due to the choice of backfill material. Backfill materials could significantly influence the AE rate-landslide velocity relationship. Backfill of large, angular particles generated AE signal with the greatest magnitude and began producing detectable AE the earliest [29]. The position rearrangement of the granite gravel may lead to large pressure build up and sudden particle sliding events, which may cause unevenness in the transmission of the slope movement to the inner AE system. Otherwise, use of a fine-grained sand may produce a more even AE response without great magnitude and early detection. It is preferable to use large, angular particles considering signal attenuation and early warning needs in the field. In terms of active AE waveguide and a large-deformation bolt, their feasibility for field installation and the reliability for landslide monitoring have been sufficiently investigated and extensively tested, respectively [8; 23; 24; 25; 27; 28; 38; 39; 41]. The proposed device integrates the structure of a large-deformation bolt into active waveguide. The novel device improved the mechanical structure of waveguides instead of conventional metal tubes. The flexible device with excellent resilience may endure large deformations during a landslide to sustainably monitor subsurface deformation. Furthermore, AE and mechanical parameters can be synchronously collected using one device and synthetically analysed. However, this device has not been applied in the field, and the reliability of the device needs to be validated further. Here is a conceptual anticipation to explain how it will be used in reality. When the flexible monitoring device is applied to the field, Figure 11 shows it is possible change during landslide process. Geological exploration and other means are needed before monitoring to determine the approximate position of a sliding surface in advance, so as to determine monitoring points at representative positions. The initial installation state of the device is shown in Figure 11a. With the deformation and movement of the sliding body, the anchor cable is subjected to the maximum earth pressure and bending moment at the sliding surface, resulting in the largest shear and bending deformation. When the anchor cable is tensioned, the metal head is pulled into the sleeve and moves along the axial direction, and the whole device has a tensile deformation. Due to the special structure of the proposed device, it is not easy to be sheared, stretched or bent even under a large deformation. The proposed device potentially has a larger measurement range and a longer service life, and thus it has strong adaptability and reliability to subsurface deformation monitoring. The advantages of the proposed composite device lie in the simultaneous collection of AE and mechanical parameters, which can be compared and verified with each other. Then, comprehensive analysis can be carried out to obtain more objective state of the slope and to study the characteristic changes of the feature parameters in the whole landslide process.