# Prediction of Shallow Failure on a Slope Using Volumetric Water Content Gradient Characteristics
###### Abstract  
Landslides that occur near residential regions are most commonly a result of shallow slope failure, which takes place as a consequence of heavy rainfall during the monsoon season, causing loss to human life and property. In this study, the characteristics of the volumetric water content (VWC) gradient were analyzed to predict shallow slope failure which was reproduced based on flume experiments performed at various slope conditions. The VWC gradient values were calculated for each measurement position and slope depth. Moreover, the VWC gradient characteristics during the occurrence and nonoccurrence of shallow slope failures were compared to those of an actual site that did not undergo slope failure. Our results show that the probability of failure increases with an increase in the VWC gradient value. Additionally, early warning criteria are proposed by dividing the range of the VWC gradient value into four stages in which the failure rate rapidly increased. Full-scale flume experiments were performed to simulate an actual site in terms of its scale, and the appropriate sensor installation positions were proposed to effectively predict the probability of failure.  
shallow slope failure; volumetric water content; flume experiment; early warning criteria 20221253082022022022022022022022022202  
characteristics, many researchers reported the possibility of predicting shallow failure [13; 14; 15]. [PERSON] et al. [16] reported that the possibility of failure increases significantly in the third stage, at which time the VWC increases rapidly. However, this study is limited in its capacity to be applied in practice because it is introduced only as a conceptual method for predicting failure according to the VWC change pattern. Previous studies revealed that the change in the VWC in the ground can be used as a precursor to shallow failure. However, to date, specific measurement standards have not been developed due to the difficulties in securing data that explain the VWC change pattern during the actual shallow failure process.  
Previous studies were mostly conducted to identify the characteristics of shallow failure caused by rainfall according to indoor model experiments [17; 18; 19]. This is because the experiments can be repeated using the same boundary conditions, and the deformation inside the slope can be directly observed [20].  
This study aimed to derive a measurement standard that can identify a sign of forthcoming shallow failure using the change in the VWC caused by rainfall penetration. To this end, soil slope failure was simulated by performing flume experiments, and the increasing tendency of the VWC in the slope where failure occurred was confirmed by collecting the VWC measurement data during the failure process. Testbeds were operated to identify the increasing VWC characteristics of the area where no failure occurred. Based on this, the VWC gradient and the failure rate were analyzed to propose measurement and management criteria. To use the proposed measurement and management criteria in the field, it is necessary to determine appropriate measurement positions. Therefore, a full-scale flume experiment was performed twice to examine the appropriateness of the proposed measurement and management criteria and the method of selecting measurement positions.