• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.25 no.1
• /
• pp.20-27
• /
• 2013

Seabed settlement underneath a coastal structure may occur due to wave loading generated by storm surge. If the foundation seabed consists of sandy soil, the possibility of the seabed settlement may be more susceptible because of generation of residual excess pore-water pressure and cyclic mobility. However, most coastal structures, such as breakwater, quay wall, etc., are designed by considering wave load assumed to be static condition as an uniform load and the wave load only acts on the structure. In real conditions, however, the wave load is dynamically applied to seabed as well as the coastal structure. In this study, therefore, a real-time wave load is considered and which is assumed acting on both the structure and seabed. Based on a numerical analysis, it was found that there exists a significant effect of wave load on the structure and seabed. The deformation behavior of the seabed according to time was simulated, and other related factors such as the variation of effective stress and the change of effective stress path in the seabed were clearly observed.

• Journal of Korean Society of Environmental Engineers
• /
• v.30 no.9
• /
• pp.918-924
• /
• 2008

This research investigates the influences of the presence of aquatic macrophytes on the changes of biogeochemistry in the sediments through the comparative analysis of porewater and sediments. From the in situ measurements, elevated SO$_4{^{2-}}$ concentrations were observed in the rhizosphere during the growing season, which was resulted from the oxidation of reduced sulfide in the sediments by the oxygen release from the plant roots. There was sufficient AVS in the sediments to induce observed SO$_4{^{2-}}$ concentrations. The amount of oxygen in the oxidation of AVS to produce observed SO$_4{^{2-}}$ concentrations is 0.85 g/m$^2$ day which is relevant to the results of other researches. The AVS concentrations in the vegetated sediments increased with the depth whereas there is higher mass of AVS in the surface of the non-vegetated sediments. This shows that evapotranspiration induces the transportation of SO$_4{^{2-}}$ in the surface water into the anaerobic sediments. In addition, the elevated organic content caused by the presence of plants increased $\beta$-glucosidase activities which play an important role in the carbon cycle of the sediments.

• Journal of the Korean Geotechnical Society
• /
• v.18 no.6
• /
• pp.73-81
• /
• 2002

Various CPT-based prediction models far profiling stress history of marine clay at the southern part of the Korean peninsula were investigated by using both statistical analysis and case history study. Preconsolidation pressures($\sigma'$p) and overconsolidation ratio(OCR) estimated by empirical correlations and cone penetration tests were compared with those of laboratory odometer test results. Stress history of marine clay determined by odometer test results was in general overconsolidated at below 10m depth from the mudline, whereas marine clay at below l0m depth from the mudline which has an around 0.3 overconsolidation ratio showed variable stresses and unstable states. Preconsolidation pressures were computed by both empirical methods of the Chen and Mayne(1996) and theoretical method of Konrad and Law(1987). It is estimated that Chen and Mayne(1996)'s prediction method based on pore water pressure is more reliable than any other prediction methods, and their method proved to be the most reliable for overconsolidation ratio estimation. However, it is recommended that Mayne & Holtz(1988) and Mayne & Bachus(1988) methods are more suitable than any other methods for predicting the overconsolidation ratio at an underconsolidated (OCR<1) clay. For these reasons, rather than making use of existing prediction models, development of site specific empirical correlations which considers local characteristics and site conditions may be required due to different local stress history and variable soil properties.

• The Journal of Engineering Geology
• /
• v.23 no.3
• /
• pp.247-256
• /
• 2013

The carbonate sands of the Sabkha layer in the Middle East have very low shear strength. Therefore, instant settlement and time-dependent secondary settlement occur when inner voids are exposed, as in the case of particle crushing. We analyzed settlement of the Sabkha layer under a large-scale foundation by hydrotesting, and compared the field test results with the results of laboratory tests. With ongoing particle crushing, we observed the following stress-strain behaviors: strain-hardening (Sabkha GL-1.5 m), strain-perfect (Sabkha GL-7.0 m), and strain-softening (Sabkha GL-7.5 m). General shear failure occurred most frequently in dense sand and firm ground. Although the stress-strain behavior of Sabkha layer carbonate sand that of strain-softening, the particle crushing strength was low compared with the strain-hardening and strain-perfect behaviors. The stress-strain behaviors differ between carbonate sand and quartz sand. If the relative density of quartz sand is increased, the shear strength is also increased. Continuous secondary compression settlement occurred during the hydrotests, after the dissipation of porewater pressure. Particle crushing strength is relatively low in the Sabkha layer and its stress-strain behavior is strain-softening or strain-perfect. The particle crushing effect is dominant factor affecting foundation settlement in the Sabkha layer.

• Economic and Environmental Geology
• /
• v.40 no.5
• /
• pp.551-561
• /
• 2007

This case study is about the sampling and interpretation of soil pore water in order to understand and to predict the diffusion and behavior of soil pollution. For the measurement of polycyclic aromatic hydrocarbons(PAHs) in two representative hydrocarbon-contaminated sites, the extraction system of the soil pore water was set up with respect to soil depths and the behavior of contaminants was interpreted. The soil solution extraction system consisted of peristaltic pump, and extraction and sampling compartment, and can measure simultaneously the soil water pressure. The concentration of PAHs with respect to extraction pressure and time decreased due to dilution through soil pore water. Particularly, the concentration of PAHs was more reduced under the unsaturated oxic condition than saturated anoxic condition. Therefore, the soil solution extraction with respect to soil water pressure can interpret the extent of equilibrium between porewater and soil surface.

• Geotechnical Engineering
• /
• v.3 no.4
• /
• pp.41-54
• /
• 1987

A stochastic numerical analysis for predicting the groundswater fluctuations in hillside slopes is performed in this paper to account for the uncertainties associated with the rainfall and site characteristics. The effect of spatial variabilities of aquifer parameters and the effect of temporal variability of recharge on the groundwater fluctuations are studied in depth. The Kriging is used to account for the spatial tariabilities of aquifer parameters. This technique prolevides the best linear unbiased estimator of a parameter and its minimum variance from a litsitem number of measured data. A stochastic one-dimensional numerical model is delreloped b) combining the groundwater flow model, the Kriging, and the first-order second-moment analysis. In addition, a two dimensional detelministic groundwater model is developed to study the change of ground water surfas in the transverse direction as well as in the downslope direction. It is revealed that the undulations of the impervious bedrock in addition to the permeability and the specific yield have an important influence on the fluctuations of the groundwater surface. It is also found that th'e groundwater changes significantly in the transverse direction as well as in the downslope direction. The results obtained in this analysis may be used for evaluation of landslide risks due to high porewater pressure.

• Geotechnical Engineering
• /
• v.8 no.2
• /
• pp.5-20
• /
• 1992

The physical-based and lumped-parameter hydrologic groundwater flow model for predicting the rainfall-triggered rise of groundwater levels in hillside slopes is developed in this paper to assess the risk of landslides. The developed model consists of a vertical infiltration model for unsaturated zone linked to a linear storage reservoir model(LSRM) for saturated zone. The groundwater flow model has uncertain constants like soil depttL slope angle, saturated permeability, and potential evapotranspiration and four free model parameters like a, b, c, and K. The free model parameters could be estimated from known input-output records. The BARD algorithm is uses as the parameter estimation technique which is based on a linearization of the proposed model by Gauss -Newton method and Taylor series expansion. The application to examine the capacity of prediction shows that the developed model has a potential of use in forecast systems of predicting landslides and that the optimal estimate of potential 'a' in infiltration model is the most important in the global optimum analysis because small variation of it results in the large change of the objective function, the sum of squares of deviations of the observed and computed groundwater levels. 본 논문에서는 가파른 산사면에서 산사태의 발생을 예측하기 위한 수문학적 인 지하수 흐름 모델을 개발하였다. 이 모델은 물리적인 개념에 기본하였으며, Lumped-parameter를 이용하였다. 개발된 지하수 흐름 모델은 두 모델을 조합하여 구성되어 있으며, 비포화대 흐름을 위해서는 수정된 abcd 모델을, 포화대 흐름에 대해서는 시간 지체 효과를 고려할 수 있는 선형 저수지 모델을 이용하였다. 지하수 흐름 모델은 토층의 두께, 산사면의 경사각, 포화투수계수, 잠재 증발산 량과 같은 불확실한 상수들과 a, b, c, 그리고 K와 같은 자유모델변수들을 가진다. 자유모델변수들은 유입-유출 자료들로부터 평가할 수 있으며, 이를 위해서 본 논문에서는 Gauss-Newton 방법을 이용한 Bard 알고리즘을 사용하였다. 서울 구로구 시흥동 산사태 발생 지역의 산사면에 대하여 개발된 모델을 적용하여 예제 해석을 수행함으로써, 지하수 흐름 모델이 산사태 발생 예측을 위하여 이용할 수 있음을 입증하였다. 또한, 매개변수분석 연구를 통하여, 변수 a값은 작은 변화에 대하여 목적함수값에 큰 변화를 일으키므로 a의 값에 대한 최적값을 구하는 것이 가장 중요한 요소라는 결론을 얻었다.

• Journal of the Korean Geotechnical Society
• /
• v.34 no.8
• /
• pp.37-49
• /
• 2018

Since the observation of ground motions in South Korea, liquefaction manifestation was the first to be observed in Pohang earthquake in 2017 with $M_L$ 5.4. Because liquefaction causes ground settlement and lateral spread damaging in-ground or super structures, various researchers have been analyzing the Pohang liquefaction case history to better understand and predict liquefaction consequence and to prevent future disasters. In prior research at the 2018 EESK conference, a map of Liquefaction Potential Index (LPI), indicating the severity of liquefaction, in Pohang was created and compared with damage observations. The LPI correlated well with the observations, but the severity categorized by LPI range was significantly higher than the actual observations in most regions. The prior LPI map was created evaluating ground motions using the simplified approach. In this research, we perform the effective site response analyses with porewater pressure generation model for the detailed evaluation of liquefaction on the liquefied sites in Pohang. We found that the simplified approach for LPI evaluation can overestimate the severity.

• Journal of the Korean GEO-environmental Society
• /
• v.19 no.12
• /
• pp.41-46
• /
• 2018

The wireless sensor network system has the advantage of confirming the behavior of the entire facility by improving the disadvantages of conventional monitoring system. As a result, it is widely proposed as safety diagnosis and measurement of structures, water management systems, and management systems for dam structures. However, there is a lack of research that can evaluate the condition of facilities such as safety at the same time as monitoring. In this study, it is proposed a wireless sensor network system which can evaluate the behavior characteristics of facilities and evaluate the safety status for improving the technical disadvantages on conventional monitoring system. The geotechnical risk factors for the reservoir dam facility were evaluated and the limit values for the risk factors causing the failure of the facility were set. In other words, the system was set up so that the risk factors can be measured and the limit status can be evaluated immediately for each factor. In this study, numerical analysis is carried out for seepage and slope stability analysis using the typical cross section for reservoir dams. The stress-porewater coupling finite difference numerical analysis is performed for establishing the limit displacement for reservoir dam structures. It is developed a system that can estimate the time to reach the critical value by regression analysis using the measured datas.

• The Journal of Engineering Geology
• /
• v.29 no.2
• /
• pp.123-136
• /
• 2019

This study examines the effect of collector well installed to reduce groundwater level in the regions with the occurrence of landcreep, a soil mass movement triggered by instability on slopes. Slopes are prone to failure as a result of instability caused by its internal, topographic and geological properties as well as due to external factors such as rainfall and earthquake. In Korea during the rain season, rainfall infiltration affects the groundwater level in soil, building up porewater pressure and load, and finally drives slopes to collapse. Slope failure caused by rainfall infiltration has been leading to a drastic forest degradation. The studied slope is located adjacent to a valley, its terrain corresponds to piedmont gentle slope, while the upper part of the failure surface is steep. After reinforcing the terrain where landcreep had occurred and installing collector well on the slope, we measured the changes in the groundwater level. In order to analyze the relationship between the well and the slope, we calculated the ratio of groundwater level to rainfall before and after the installation of the collector well. As a result, it is confirmed that the ratio increases after the installation of the well, which in turn reduces the groundwater level. Analysis of the change in groundwater level after 3, 7, 15 days antecedent rainfall showed that the higher the overall groundwater level, the less the value ($r_p$) of groundwater level-rainfall ratio is, while the value becomes relatively greater when the groundwater level is low. In particular, if a slope has a large catchment basin as is in the case of the studied site, antecedent rainfall affects groundwater level in the order of 3 < 7 < 15 days.