This paper investigates rainfall-induced landslides on partially saturated soil slopes using the 2011 Umyeonsan landslides at the center of Seoul, Korea. An integrated analysis of rainfall-induced landslide was carried out through laboratory tests, field tests, and numerical analysis. The results of comprehensive investigations in the Umyeonsan region demonstrate that landslide activity is closely related primarily to rainfall and soil properties and slope geometry, and vegetation. Numerical analysis was also performed to confirm the effect of these factors on landslide occurrence. Special attention was given to rainfall penetration analysis to determine the wetting band depth for shallow and deep-seated slope failure in watershed-scale landslide. The simulated results agree closely with the investigation results, which indicates that the applied method is appropriate for use in the simulation of landslides in unsaturated soils.

The load distribution and deformation of offshore piles are investigated using experimental tests and a numerical analysis. Special attention is given to the soil-pile rigidity of laterally loaded piles. Rigid-and flexible-pile analyses were conducted for comparison. A framework for determining the lateral load transfer curve (p-y curve) is proposed from field and laboratory model tests. A numerical analysis that takes into account the proposed p-y curves was performed for major parameters on pile flexibility such as the pile diameter, the pile length, pile bending stiffness, and the modulus of subgrade reaction. Based on the analysis, it is shown that there are significant differences in bending moment and lateral displacement in flexible piles rather than rigid piles. Through the comparative studies, it is found that the p-y curves influence the behavior of a flexible pile more than of a rigid pile and, thus, the magnitude and distribution of the p-y curves highly influence the pile behavior when it is designed as a flexible pile.

Shallow foundations are often situated on unsaturated zones above the groundwater table. In this study, the influence of rainfall infiltration on the settlement behavior of shallow foundations was investigated using numerical analyses. The numerical solutions were compared with experimental data from in-situ load tests. The relative importance of rainfall intensities and groundwater table positions in inducing the additional settlement of shallow foundations was examined through a series of parametric studies. Two different groundwater table positions contributing to settlements and three assorted rainfall intensities were used in the numerical analyses. Typical soil properties of two main residual soils in Korea were incorporated into the numerical analyses. Special attention is given to the sequential analysis procedure comprised of a flow analysis and deformation analysis. Load-settlement relationships obtained from the numerical methodology in the present study were in good agreement with the field measurements. Results from the parametric studies showed that the rainfall intensity plays a significant role in the settlement behavior of shallow foundations in unsaturated soils. The changes in the settlement during rainfall were also affected by the groundwater table position near the ground surface due to changes in matric suction. In addition, higher bearing capacity in response to rainfall infiltration was observed in the soil with smaller permeability function as compared to larger permeability function.

In this paper, the application of a WSN (Wireless Sensor Network) for landslide monitoring was studied. The WSN system consists of a sensor node for collecting and transmitting data using the IEEE 802.14e standard and a gateway for processing and transmitting the data to the final server. The topology of the sensor network adopts a highly flexible and reliable mesh type, and a test bed was built in three locations in Seoul. An instrumentation is done for each sensor node composing of two soil moisture sensors, one tensiometer, and one inclinometer and one rain gauge per test bed. For the estimation of optimal network topology among the sensor nodes, a susceptibility assessment of landslides, the density of trees and a viewshed analysis of the terrain were analyzed. As a result, the network connection worked quite well, and the response of the soil from rainfall was similar to the soil water characteristic curve obtained from laboratory tests. Therefore, a WSN system can be applied to landslide monitoring by collecting reliable data. In addition, the appropriate design method of WSN system for landslide monitoring was proposed.