At present, landslide susceptibility assessment (LSA) based on the characteristics of landslides in different areas is an effective prevention measure for landslide management. In Enshi County, China, the landslides are mainly triggered by high-intensity rainfall, which causes a large number of casualties and economic losses every year. In order to effectively control the landslide occurrence in Enshi County and mitigate the damages caused by the landslide. In this study, eight indicators were selected as assessment indicators for LSA in Enshi County. The analytic hierarchy process (AHP) model, information value (IV) model and analytic hierarchy process-information value (AHP-IV) model were, respectively, applied to assess the landslide distribution of landslides in the rainy season (RS) and non-rainy season (NRS). Based on the three models, the study area was classified into five levels of landslide susceptibility, including very high susceptibility, high susceptibility, medium susceptibility, low susceptibility, and very low susceptibility. The receiver operating characteristic (ROC) curve was applied to verify the model accuracy. The results showed that the AHP-IV model (ROC = 0.7716) was more suitable in RS, and the IV model (ROC = 0.8237) was the most appropriate model in NRS. Finally, combined with the results of landslide susceptibility in RS and NRS, an integrated landslide susceptibility map was proposed, involving year-round high susceptibility, RS high susceptibility, NRS high susceptibility and year-round low susceptibility. The integrated landslide susceptibility results provide a more detailed division in terms of the different time periods in a year, which is beneficial for the government to efficiently allocate landslide management funds and propose effective landslide management strategies. Additionally, the focused arrangement of monitoring works in landslide-prone areas enable collect landslide information efficiently, which is helpful for the subsequent landslide preventive management.

Landslides, which can cause significant losses of lives or property damages, result from several different environmental factors whose influences are very complex. Thus, the statistical multi-layer perceptron (MLP) and heuristic analytical hierarchy process (AHP) are employed in the evaluation of landslide susceptibility. However, the landslide susceptibility maps drawn by these two methods are always affected by subjectivity and randomness. In the present study, we introduce variable weight theory (VW) to improve the MLP and AHP methods, and two novel hybrid models, AHP-VW and MLP-VW, are respectively proposed. VW theory is used to redistribute the weights of the factors in the two constant weight evaluations. This is so that the weights of the factors change with different evaluation units, thereby eliminating the subjectivity and randomness problems. The landslide susceptibility maps of the study area were categorized into very low, low, moderate, high, and very high susceptibility grades. The landslide susceptibility maps of the four models are validated by the receiver operating characteristic (ROC) curve. The area under the curve (AUC) is 0.825 for the AHP model, 0.879 for the MLP model, 0.873 for the AHP-VW model, and 0.915 for the MLP-VW model. The results show that the landslide susceptibility map drawn by statistical MLP is better than that drawn by heuristic AHP, which is consistent with many other current research results. Furthermore, VW can significantly improve the performance of constant-weight single models. Landslide susceptibility maps drawn by the statistical MLP model hybrid VW can be used for regional land use planning and landslide hazard mitigation purposes.

To study the lateral seepage field in the tension saturated zone (TSZ), an experiment with no evaporation and precipitation infiltration was carried out in a self-made seepage tank filled up with fine sand. Based on the data and plots obtained, the lateral seepage field distribution features in the TSZ can be divided into three area for discussion: ascending area, descending area, and the nearly horizontal flow area. In the ascending and descending area, the total water potential gradient diminished from the recharge area to the discharge area and the seepage velocity was faster. In the nearly horizontal flow area, the total water potential gradient was lower and the seepage velocity was slower. The pressure potential gradually decreased horizontally from the recharge area to the discharge area, while in the vertical profile, it gradually decreased from the bottom to the top in the whole seepage area. In the absence of evaporation, the vertical water exchange among the saturated zone, TSZ, and unsaturated zone in nearly horizontal flow area is weak. Contrarily, in the ascending area and descending area, vertical water flows through both the phreatic surface and the upper interface of the TSZ. When there is lateral seepage in the TSZ, the thickness of the TSZ generally increases from the ascending area to the nearly horizontal area and then to the descending area. It should be pointed out that in the nearly horizontal area, the TSZ thickness is approximately equal to the height of the water column. Overall, the lateral seepage in the TSZ can be regarded as a stable siphon process, hence the siphon tube model can be further used to depict this lateral seepage.