Recent climate change has led to extreme floods surpassing levee design criteria, posing a threat to safety. Consequently, there is a demand for the development of technologies capable of handling such severe floods. In this study, a method assessing failure probabilities, represented by fragility curves, was developed for the levee slope under rapid drawdown. The time-dependent probabilistic stability assessment of the levee slope due to a water level drop was explored. Integrating seepage analysis results from finite element analysis with slope stability analysis, Monte Carlo simulations were conducted to scrutinize the time-dependent behavior of the levee slope under rapid drawdown conditions. The probability of failure was calculated to develop fragility curves for the levee slope. The developed fragility curves were significantly influenced by the drawdown rate. Since the drawdown rate is determined through hydraulic analysis based on flood scenarios, the stability of the water-side slope of the embankment due to a water level drop will be greatly affected by climate change. The fragility curves obtained using the proposed methods are valuable for risk assessment, offering information to evaluate the performance of the levee under various water level drawdown conditions.

Background: Mass spectrometry methods exhibit higher accuracy and lower variability than immunoassays at low testosterone concentrations. We developed and validated an ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) assay for quantifying serum total testosterone. Methods: We used an ExionLC UPLC (Sciex, Framingham, MA, USA) system and a Sciex Triple Quad 6500+ (Sciex) MS/MS system in electrospray ionization and positive ion modes with multiple reaction monitoring transitions to evaluate precision, accuracy, linearity, lower limit of quantitation (LLOQ), carryover, ion suppression, stability, and reference intervals. For method comparison, we measured serum testosterone concentrations using this method in 40 subjects whose testosterone concentrations ranged from 0.14 to 55.48 nmol/L as determined using the Architect i2000 immunoassay (Abbott Diagnostics, Abbott Park, IL, USA) and in an additional 160 sera with testosterone concentrations < 1.67 nmol/L. Results: The intra- and inter-run precision CVs were < 2.81%, and the accuracy bias values were < 3.85%, which were all acceptable. The verified linear interval was 0.03-180.84 nmol/L; the LLOQ was 0.03 nmol/L. No significant carryover and ion suppression were observed. The testosterone in serum was stable at 4 degrees C, at -20 degrees C, and after three freeze-thaw cycles. The reference intervals were successfully verified. The correlation was good at testosterone concentrations of 0.14-55.48 nmol/L; however, the Architect assay showed positive percent bias at concentrations < 1.67 nmol/L. Conclusions: The UPLC-MS/MS assay shows acceptable performance, with a lower LLOQ than the immunoassay. This method will enable the quantitation of low testosterone concentrations.

The maintenance of water-retaining structures involves evaluating their performance against current and future operating water levels. Fragility curves are commonly used for this purpose, as they indicate the conditional probability of failure for various load conditions and accurately characterize a structure’s performance. Monte Carlo simulation (MCS) can be used to determine the fragility curve of water-retaining structures by calculating the probability of failure as the water level changes. However, performing repetitive MCS involves extensive calculations, thus making it inefficient for practical applications. Therefore, it is essential to develop efficient methods that require a minimum number of MCS runs to estimate the fragility curve. This study proposed two methods to estimate the fragility curves of water-retaining structures, thereby allowing for the assessment of failure probabilities related to important quantities such as the steady-state seepage rate, exit gradient, and uplift force, which make them suitable for practical applications. The fragility curves obtained using the proposed methods are valuable for risk assessment, design, and decision-making purposes, as they offer information to evaluate the performance of the water-retaining structure under various water level conditions.

The failure time of slope is essential for slope risk assessment. However, in previous studies, the safety factor and failure probability of slope have been regarded as the main research topic rather than the failure time. In this study, a stochastic failure distribution model related to the slope failure time is proposed. The stochastic failure distribution model based on fragility curves was used to analyze the failure process of shallow landslides under rainfall infiltration. The fragility curve is derived as a function of the intensity-duration of rainfall from the result of a probabilistic analysis, which considers the uncertainties of the hydraulic and mechanical properties of the soil. Then, the failure distribution analysis was performed for various rainfall conditions based on the generated fragility curves. Using the proposed failure distribution model, a chart showing the relationship between rainfall intensity and slope failure time was developed. The relationship is a kind of intensity-duration rainfall threshold for the initiation of shallow landslides. It is based on a probabilistic analysis considering the uncertainty of the soil properties. The proposed probabilistic failure distribution model could be beneficial for analyzing the failure process of hillslopes due to rainfall infiltration, and for predicting the time of landslide occurrence.

Over 160 shallow landslides resulted from heavy rainfall that occurred in 26–27 July 2011 at Umyeon Mountain, Seoul, South Korea. To accurately reflect the fluid flow mechanism in the void spaces of soils, we considered the two-phase flow of water and air for rainfall infiltration analysis using available historical rainfall data, topographic maps, and geotechnical/hydrological properties. Variations in pore water and air pressure from the infiltration analysis are used for slope stability assessment. By comparing the results from numerical models applying single- and two-phase flow models, we observed that air flow changes the rate of increase in pore water pressure, influencing the safety factor on slopes with a low infiltration capacity, where ponding is more likely to occur during heavy rainfall. Finally, several slope failure assessments were conducted to evaluate the usefulness of using the two-phase flow model in forecasting slope stability in conditions of increased rainfall sums. We observed that the two-phase flow model reduces the tendency of over-prediction compared to the single-phase model. The results from the two-phase flow model revealed good agreement with actual landslide events.

Shallow slope failures occur almost every year during the rainy season. Continuous observation of the meteorological parameters and hydrological characteristics is required to more clearly understand the triggering mechanisms of shallow slope failure. In addition, influential factors, such as type of relative permeability models, air flow, and variation of hydraulic conductivity associated with stress–strain behavior of soil, have significant effects on the actual mechanism of rainfall infiltration. Real-time data including hourly rainfall and pore water pressure in response to rainfall was recorded by devices; then, the change in pore pressure from the devices was compared to the results from the infiltration analysis with applications of three relative permeability models, air flow, and the coupled hydro-mechanical analysis to examine an appropriate site-specific approach to a rainfall infiltration analysis. The infiltration and stability analyses based on the site-specific hydrologic characteristics were utilized to create maps of safety factors that depend on the cumulative rainfall. In regions vulnerable to landslides, rainfall forecast information and safety factor maps built by applying various rainfall scenarios can be useful in preparing countermeasures against disasters during the rainy season.

In Korea, where shallow deposits of weathered residual soil exist on bedrock in hillslopes, the full saturation of the soil layer caused by reaching of rainwater from the slope surface to an impermeable bedrock is one of the important causes of landslides. Landslides can lead to a shallow failure surface that passes through the contact between soil and impervious bedrock. In this study, a stability analysis method for slopes with a shallow bedrock was developed to predict landslides. The method is based on a one-dimensional conceptual infiltration model that considers an initial inhomogeneous water content distribution. Constant intensity of rainfall was considered and shallow impermeable boundary conditions were imposed on the Green-Ampt model to simulate the impermeable bedrock underlying the weathered residual soil. To consider a hillslope with weathered residual soil when the rainfall intensity is less than the infiltration capacity, the Green-Ampt model was modified to simulate rainfall intensity that is smaller than the soil's saturated hydraulic conductivity. A series of stability analyses were performed for slopes with known hydraulic properties to evaluate the applicability of the proposed procedure. The prediction results were then compared with those obtained by the stability analysis based on the infiltration results from numerical analysis. The results showed that the proposed method can be used to predict landslides due to rainfall infiltration by efficiently considering the movements of the saturated region in hill slopes that have shallow impermeable bedrock.

강우의 침투가 사면안정에 미치는 영향을 평가하기 위해 강우의 침투해석을 수행하고 그 결과를 한계평형해석에 적용하는 안정해석 절차가 널리 사용되고 있으나 지반은 흙 입자, 물과 공기로 이루어진 3상의 물질이므로 사면을 통한 강우의 침투를 엄밀하게 해석하기 위해서는 물, 공기의 흐름과 흙의 응력-변형거동이 완전 연관된(fully coupled) 식을 고려해야 한다. 본 연구에서는 공기와 물의 흐름이 사면의 역학적 안정에 미치는 영향을 연구하기 위하여 우리나라에 널리 분포하는 풍화잔류토 사면에 대하여 3상이 연동된 흐름해석을 수행하였다. 강우침투가 사면안정에 미치는 영향을 평가하기 위하여 강도감소법에 의한 사면 안정해석을 수행하였다. 해석결과에 의하면 침투하는 강우가 공기를 밀어내 공기의 흐름이 발생하고 공기압이 증가하였다. 이러한 간극에서의 물과 공기의 상호작용은 사면의 응력-변형거동에 영향을 미쳐 공기의 흐름을 고려하지 않은 흙 입자-물의 연관해석의 결과와는 다른 사면안정 거동을 보였다. Stability analysis based on the limit equilibrium method combined with the result of infiltration analysis is commonly used to evaluate the effect of rainfall infiltration on the slope stability. Soil is a three-phase mixture composed of solid particle, water and air. Therefore, a fully coupled mixture theories of stress-deformation behavior and the flow of water and air should be used to accurately analyze the process of rainfall infiltration through soil slope. The purpose of this study is to study the effect of interaction of air and water flow on the mechanical stability of slope. In this study, stability analyses based on the coupled hydro-mechanical model of three-phases were conducted for slope of weathered granite soil widespread in Korea. During the process of hydro-mechanical analysis strength reduction technique was applied to evaluate the effect of rainfall infiltration on the slope stability. The results showed an increase of air pressure during infiltration because rain water continuously displaced the air in the unsaturated zone. Such water-air interaction in the pore space of soil affects the stress-deformation behavior of slope. Therefore, the results from the three-phase model showed different behavior from the solid-water model that ignores the transport effect of air in the pores.

지진에 대한 사면안정 해석은 지진에 의한 관성력을 정적하중으로 고려하는 유사정적해석을 널리 사용하고 있다. 사면과 같은 지반 구조물은 지반정수의 불확실성이 포함되어 있어 확률론적 해석을 이용하여 지반정수의 불확실성을 고려해야 한다. 본 연구에서는 지반의 불확실성을 고려한 확률론적 사면안정해석을 수행하였으며, 구조물이 임의 수준의 지반 운동을 받을 때 파괴상태에 도달하는 확률을 그래프로 나타낸 취약도 곡선을 작성하였다. 유사정적해석으로 확률론적 사면안정해석을 수행하기 위해 Monte Carlo Simulation(MCS)을 시행하였다. MCS의 소요 시간을 단축하기 위하여 인공신경망 기반의 응답면 기법을 이용해 파괴확률을 산출하여 수평지진계수별 취약도 곡선을 작성하는 방법을 제시하였다. 인공신경망을 이용하여 작성한 취약도 곡선을 MCS의 결과와 비교해 본 결과 상당한 시간 절약에 비해 유사한 결과를 얻을 수 있었다. Usually the seismic stability analysis of slope uses the pseudostatic analysis considering the inertial force by the earthquake as a static load. Geostructures such as slope include the uncertainty of soil properties. Therefore, it is necessary to consider probabilistic method for stability analysis. In this study, the probabilistic stability analysis of slope considering the uncertainty of soil properties has been performed. The fragility curve that represents the probability of exceeding limit state of slope as a function of the ground motion has been established. The Monte Carlo Simulation (MCS) has been implemented to perform the probabilistic stability analysis of slope with pseudostatic analysis. A procedure to develop the fragility curve by the pseudostatic horizontal acceleration has been presented by calculating the probability of failure based on the Artificial Neural Network (ANN) based response surface technique that reduces the required time of MCS. The results showed that the proposed method can get the fragility curve that is similar to the direct MCS-based fragility curve, and can be efficiently used to reduce the analysis time.

Even though soil is a mixture of solids with voids that are filled by air and water, most previous studies on rainfall infiltration and its influence on slope stability were based on a single-phase water flow model by assuming that the pore air pressure was atmospheric. The purpose of this study is to examine the effect of interactions between air and water flow due to heavy rainfall on the mechanical stability of an unsaturated soil slope. Water-air two-phase flow analyses were conducted to investigate the contribution of pore-air pressure on infiltration by rainfall. In order to study the infiltration behavior with respect to soil type, flow analyses were performed with two types of soil under similar settings. Results obtained from the two-phase infiltration analysis were then used as input to the stability analysis by the strength reduction method. Infiltration and stability analyses based on a single-phase water flow model were also carried out, which helped clarify the effects of air flow induced by rainfall infiltration on an unsaturated soil slope. The results showed an increase in pore air pressure during infiltration because rainwater displaced the air in the unsaturated zone; hence, remarkable delaying effects on water flow were induced. Such water-air interactions in the pore space of soil significantly affected the stability and behavior of the soil slope.