Process of pore pressure diffusion in saturated clay soil and impact of adsorbed water

LianSheng Tang,HaoKun Chen,Jing Song 한국지질과학협의회 2016 Geosciences Journal Vol.20 No.5

Water molecules are adsorbed onto the surface and interlayer of clay minerals and form a film, which causes that pore pressure diffusion in clayey soils differs from that in granular material. In this paper, adsorbed water is classified into strongly adsorbed water and loosely adsorbed water, which provide a better understanding of the physical mechanisms of the adsorbed water. To investigate the impact of adsorbed water on pore pressure diffusion, a series laboratory tests were conducted, including the uplift pressure test, pore pressure diffusion test and adsorbed water content test. The experimental results implies that strongly adsorbed water can neither flow nor participate in pressure diffusion, but loosely adsorbed water shears at pressure gradients and participates in laminar flow. Therefore, as long as the dense clayey soil contains loosely adsorbed water, the pore pressure change at a local site can diffuse throughout the material. A concept called “loosely adsorbed water index (Ilo) is defined to characterize both the content and physical properties of loosely adsorbed water: (1) when Ilo ≥ 1, the peripheral water molecules of loosely adsorbed water layer essentially behave the same as free water; (2) as Ilo → 0, the physical properties of adsorbed water may evolve from a gel-like state to a solid-like state (strongly adsorbed water). According to the density of clay and the content of adsorbed water, the process of pore pressure diffusion can be divided into three modes: flow channels of free fluid, deformations of the adsorbed water layer and shear motions of the peripheral-adsorbed water molecules. Pore pressure response to additional water pressure strongly depends on the permeability, seepage path and boundary conditions. The time-lag effect of pore pressure diffusion should be considered in applications of effective stress in engineering.

흐름과 파에 의한 해저지반내 간극수압의 발생과 액상화에 관한 해석적인 연구

이광호(Kwang-Ho Lee),김동욱(Dong-Wook Kim),김도삼(Do-Sam Kim),배기성(Ki-Seong Bae),전종혁(Jong-Hyeok Jeon) 한국해안해양공학회 2015 한국해안해양공학회 논문집 Vol.27 No.5

진행파 혹은 임의 반사율을 갖는 부분중복파 혹은 완전중복파-흐름-해저지반의 상호작용에 관한 해석해가 Lee et al.(2014; 2015a; 2015b; 2015c; 2015d) 및 Yamamoto et al.(1978)과 같은 다수의 연구자들에 의해 유도되었으며, 그들은 진동간극수압과 잔류간극수압을 별개로 취급하여 각 파동에 의한 지반응답을 논의하였다. 그러나, 실제 현장이나 실험에서 해저지반내 간극수압은 진동성분과 잔류성분이 별개로 나타나는 것이 아니고 그의 합 (전간극수압)으로 주어지기 때문에 전간극수압의 관점에서 반드시 검토될 필요가 있다. 따라서, 본 연구에서는 진동간극수압과 잔류간극수압뿐만 아니라 전간극수압의 측면에서 파동조건, 지반조건 및 흐름조건의 변화에 따른 지반응답의 변동특성을 논의하였으며, 더불어 이에 따른 액상화의 연직깊이에서 특성변화를 검토하였다. 이로부터 진행파와 순방향의 흐름의 공존장에서는 흐름속도가 증가할수록 무차원진동간극수압이 증가하고, 무차원잔류간극수압은 감소하여 결과적으로 무차원전간극수압이 작아지며, 무차원액상화 깊이도 감소하는 등의 지반응답특성을 확인할 수 있었다. Analytical solutions for interaction between seabed and waves such as progressive wave or partial standing wave with arbitrary reflection ratio or standing wave have been developed by many researchers including Lee et al.(2014; 2015a; 2015b; 2015c; 2015d) and Yamamoto et al.(1978). They handled the pore-water pressure as oscillating pore-water pressure and residual pore-water pressure separately and discussed the seabed response on each pore-water pressure. However, based on field observations and laboratory experiments, the oscillating and residual pore-water pressures in the seabed do occur not separately but together at the same time. Therefore, the pore-water pressure should be investigated from a total pore-water pressure point of view. Thus, in this paper, the wave-induced seabed response including liquefaction depth was discussed among oscillating, residual, and total pore-water pressures’ point of view according to the variation of wave, seabed, and flow conditions. From the results, in the field of flow with the same direction of progressive wave, the following seabed response has been identified; with increase of flow velocity, the dimensionless oscillating pore-water pressure increases, but the dimensionless residual pore-water pressure decreases, and consequently the dimensionless total pore-water pressure and the dimensionless liquefaction depth decrease.

Spatial probability assessment of landslide considering increases in pore-water pressure during rainfall and earthquakes: Case studies at Atsuma and Mt. Umyeon

Nguyen, Ba-Quang-Vinh,Lee, Seung-Rae,Kim, Yun-Tae Catena Verlag 2020 Catena Vol.187 No.-

<P><B>Abstract</B></P> <P>Increased pore-water pressure due to rainfall infiltration and cyclic loading is a major cause of slope instability. Many studies have been carried out to assess rainfall-induced landslide spatial probability based on physical models, combining hydrological models to analyze changes in pore-water pressure on slopes due to rainfall. However, the generation of pore-water pressure due to seismic loading is often disregarded during assessments of earthquake-induced landslide susceptibility. Hence, in this paper, we propose a model to assess landslide spatial probability that takes into account increased pore-water pressure during both rainfall and earthquakes. The procedure for the proposed method includes two main steps. In step 1, we analyze the change in the groundwater table due to rainfall infiltration and subsurface flow during rainfall. In step 2, the slope safety factor is calculated using an infinite slope model, considering the generation of excess pore-water pressure under cyclic loading during earthquakes. Landslide spatial probability is established based on the slope factor of safety. We validated the proposed model by analyzing rainfall-earthquake-induced landslide events occurring on September 6, 2018 in Atsuma town, Japan. According to our results, the area under the receiver operating characteristic curve of the Atsuma landslide data is 82.4% and the true-positive rate of unstable slope classification is 98.1%. The proposed model was then applied to Mt. Umyeon, Korea, to assess the spatial probability of rainfall-earthquake-induced landslide. Our model classifies the likelihood of landslide occurrence according to four susceptibility levels: high, moderate, low and very low. We also compared our results to those of previous models and show that the proposed approach may provide reasonably accurate predictions of landslide spatial probability during rainfall and earthquake events.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Considering the change in pore-water pressure due to rainfall and earthquake. </LI> <LI> Good performance with real landslide events in Atsuma. </LI> <LI> Cumulative rainfall strongly affect the area of susceptibility class. </LI> <LI> Peak ground acceleration strongly affect the area of susceptibility class. </LI> <LI> Excess pore-water pressure is the main reason for slope instability. </LI> </UL> </P>

Capillary pressure at irregularly shaped pore throats: Implications for water retention characteristics

Suh, Hyoung Suk,Kang, Dong Hun,Jang, Jaewon,Kim, Kwang Yeom,Yun, Tae Sup Elsevier 2017 ADVANCES IN WATER RESOURCES Vol.110 No.-

<P><B>Abstract</B></P> <P>The random shapes of pore throats in geomaterials hinder accurate estimation of capillary pressure, and conventional pore network models that simply use the Young–Laplace equation assuming circular pore throats overestimate the capillary pressure. As a solution to this problem that does not complicate the pore network model or slow its implementation, we propose a new morphological analysis method to correlate the capillary pressure at an irregular pore channel with its cross-sectional geometry using lattice Boltzmann (LB) simulation and Mayer and Stowe–Princen theory. Geometry-based shape factors for pore throats are shown here to correlate strongly with the capillary pressure obtained by LB simulation. Water retention curves obtained by incorporating the morphological calibration into conventional pore network simulation and their correlative scheme agree well with experimental data. The suggested method is relevant to pore-scale processes such as geological CO<SUB>2</SUB> sequestration, methane bubbling from wetlands, and enhanced carbon recovery.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Lattice Boltzmann simulation can accurately compute capillary pressure in irregular pore channels. </LI> <LI> Our morphological analysis estimates the effective pore throat shape to compute capillary pressure without lattice Boltzmann simulation. </LI> <LI> Pore network models calibrated by these specific capillary pressures produce water retention curves similar to experiment. </LI> </UL> </P>

Landslide Susceptibility Assessment Considering Pore Water Pressure Increases due to Rainfall and Earthquake

( Ba-quang-vinh Nguyen ),( Ji-sung Lee ),( Seung-rae Lee ),( Yun-tae Kim ) 대한지질공학회 2019 대한지질공학회 학술발표회논문집 Vol.2019 No.2

Increased pore-water pressure due to rainfall infiltration and earthquakes is a major cause slope instability. The effect of changes in pore-water pressure on slopes due to rainfall has been considered in many studies, while the generation of pore-water pressure due to seismic loading is often disregarded in earthquake-induced landslide susceptibility assessment. Hence, this study propose a model to assess landslide susceptibility that takes into account increased pore-water pressure during both rainfall and earthquakes. The procedure for the proposed method includes two main steps. In step 1, we analyze the change in the groundwater table due to rainfall infiltration and subsurface flow during rainfall. In step 2, the slope safety factor is calculated using an infinite slope model, considering the generation of excess pore-water pressure under cyclic loading during earthquakes. Landslide susceptibility is established based on the slope factor of safety. We validated the proposed model by analyzing rainfall-earthquake-induced landslide events occurring on September 6, 2018 in Atsuma, Japan. According to our results, the area under the receiver operating characteristic curve of the Atsuma landslide data is 82% and the true-positive rate of unstable slope classification is 98.1%. The proposed model was then applied to Mt. Umyeon, Korea, to assess the rainfall-earthquake-induced landslide susceptibility. Our model classifies the likelihood of landslide occurrence according to four susceptibility levels: high, moderate, low and very low. We also compared our results to those of previous models and show that the proposed approach may provide reasonably accurate predictions of landslide susceptibility during rainfall and earthquake.

Incorporating Hysteresis in One-dimensional Seepage Modeling in Unsaturated Soils

L. Z. Wu,R. Q. Huang,Q. Xu 대한토목학회 2012 KSCE JOURNAL OF CIVIL ENGINEERING Vol.16 No.1

To understand better the influence of soil-water characteristic hysteresis on rainfall infiltration and pore-water pressure distributions in unsaturated soils, an analytical solution to the one-dimensional governing partial differential equation considering hysteresis is derived using a Fourier integral transformation. The analytical solution considers time-dependent and arbitrary initial pore-water pressure distributions, as well as a time-varying rainfall flux process at the ground surface. An exponential function is used to represent the hysteretic Soil-Water Characteristic Curve (SWCC) and the relationship between hydraulic conductivity and pore-water pressure. The calculated results demonstrate that the critical point, the intersection between wetting and drying domains in one-dimensional unsaturated seepage, is influenced by many factors. The hysteresis in soil-water characteristics is an important factor in infiltration process influencing the pore-water pressure profiles in unsaturated soils. The effects of hysteretic parameters on pore-water pressure profiles are also analyzed. The value of α in the hysteresis model is found to be the most significant factor influencing the pore pressure distributions.

침하량과 과잉간극수압을 이용한 압밀도의 추정

이달원 ( Lee Dal Won ),임성훈 ( Lim Seong Hun ) 한국농공학회 2002 韓國農工學會誌 : 전원과 자원 Vol.44 No.3

This study was performed to estimate the degree of consolidation using excess pore water pressure in the very soft ground. The final settlement prediction methods by Hyperbolic, Asaoka and Curve fitting methods from the measured settlement data were used to compare with the degree of consolidation estimated by excess pore water pressure. The dissipated excess pore water pressure during embankment construction and the peak excess pore water pressure on the completed embankment were used for the estimation of the degree of consolidation. After completion of embankment, it was concluded that the degree of consolidation estimated from dissipated excess pore water pressure was more reliable than that from the peak excess pore water pressure. And, the degree of consolidation estimated from the surface settlement was nearly the same as settlement of each layer. The degree of consolidation estimated from dissipated excess pore water pressure was a little larger than that from settlement.

발파하중이 인접 댐에 미치는 진동영향에 대한 연계해석적 검토

박인준,김성인,남기천,곽창원 사단법인 한국터널지하공간학회 2004 한국터널지하공간학회논문집 Vol.6 No.1

The numerical investigation for the effects of blasting-induced vibration on adjacent dam and pore water pressure fluctuation was conducted through solid-water coupled analysis under dynamic loading. The stability of dam was examined by peak particle velocity of core. Pore water pressure distributions were calculated by steady state flow analysis using coupled analysis on ground water and blasting-induced vibration. The influence of pore water pressure and the effective stress distribution in the ground were also investigated. Furthermore, effective stress alteration was examined by applying Finn & Byrne Model to monitor the generation and dissipation of pore water pressure. 본 논문에서는 기존댐 인접지에 터널구조물을 건설하기 위한 발파시, 폭괴하중으로 인한 지반진동이 댐 제체와 간극수압에 미치는 영향을 고찰하였다. 댐의 안정성 검토는 발파시 발생하는 코어부의 최대입자속도 (Peak Particle Velocity)를 계산하여 수행하였다. 간극수와 지반진동간의 상호 연계해석을 위하여 댐 제체에 대한 정상상태 흐름해석을 수행하여 간극수압 분포를 파악하고, 유발된 과잉간극수압 및 유효응력분포로 발파하중이 인접지반에 미치는 영향을 분석하였다. 또한 발파와 같은 급속하중 재하 후 과잉간극수압의 증가 및 소산현상 해석을 위하여 Finn & Byrne Model을 적용하여 하중재하 전후의 유효응력 변화양상을 검토하였다.

Landslide Analysis of River Bank Affected by Water Level Fluctuation Ⅰ

Kim You-Seong(김유성),Wang Yu-Mei(왕유메이) 한국지반신소재학회 2010 한국지반신소재학회 논문집 Vol.9 No.3

저수지의 수위변화는 저수지 주변 강기슭 사면파괴의 주요 요인이다. 중국의 삼협댐 저수위는 홍수량 조절을 위해 145m와 175m사이에서 변화한다. 삼협댐 저수위의 정상적 운영상태에서 저수위 변동속도는 0.67m~3.0m의 범위에 있다. 마지아고 사면은 자시강의 2.1㎞ 상류 좌측기슭에 위치한다. 자시강은 삼협지역내에 있는 양츠강의 지류이다. 2003년 저수위가 95m에서 135m로 상승한 직후, 마지아고 사면의 후면부에서 길이 20m, 폭 3~10의 균열이 발생하였다. 지금은 균열 보수 후 특별한 징후는 보이지 않고는 있으나, 이 큰 균열은 마지아고 사면의 산사태 가능성을 암시하고 있었다. 이 연구에서는 저수위 변화와 관련하여 사면내에서 간극수압의 변화를 모의하기 위해 불포화 및 포화 침투해석이 수행되었다. 얻어진 간극수압은 저수위에 따른 안전율 변화를 평가하기 위해 사용되었다. 연구결과 침윤선은 저수위 변화보다 상당히 지연된 반응을 보였고, 저수위의 상승-하강과정에서 침윤선은 각각 요면과 철면의 형상을 나타내었다. 또한 저수위의 변동은 사면의 전면부에만 영향을 미치고 있었고 후면부에는 영향을 미치지 않았다. The change of water level in reservoirs is an important factor causing failure of bank slopes, i.e. landslide. The water level of Three Gorges reservoir in China fluctuate between 145 m and 175 m, as a matter of flood control. During its normal operational state, the rate of water level fluctuation is supposed to range from 0.67 m/d to 3.0 m/d. Majiagou slope is located on the left bank of Zhaxi River, 2.1 ㎞ up from the outlet. Zhaxi River is a tributary of the Yangtze River within the Three Gorges area, of which the water level changes with the reservoir. At the back of Majiagou slope, a 20 m long and 3~10 cm wide fissure developed just after the reservoir water level rose from 95 m to 135 m in 2003. This big fissure was a full suggestion of potential failure of this slope. In this study, unsaturated-saturated seepage analyses were carried out to simulate the change of pore-water pressures in the bank slope subjected to the reservoir water level change. The obtained pore-water pressures were then used to evaluate the change in factor of safety (FS) with reservoir water level. It was found that the phreatic line showed a delayed response with respect to the change of the reservoir water level, because the seepage through soil layer was generally slower than water flows itself. During the rising and drawdown process, the phreatic lines take the shapes of concave and convex, respectively. And the fluctuation of reservoir water level just affected the front part of the bank slope, but had little influence on the back of the slope.

Development of Excess Pore Water Pressure in Sand during K0-Controlled Cyclic Loading

김종관,유민택 대한토목학회 2024 KSCE Journal of Civil Engineering Vol.28 No.5

Understanding the characteristics of the development of excess pore water pressure during cyclic loading is important to evaluating the dynamic behavior of soils. Many researchers have proposed experimental models to estimate pore water pressure. However, existing experimental models are mainly based on experimental results obtained under isostatic and constant amplitude loading. In this study, K0-controlled cyclic loading is undertaken by simulating a horizontal stratified ground, and the development of excess pore water pressure is evaluated by measuring the accumulated shear strain; a modified accumulated shear strain is proposed based on these results. The results show that the excess pore water pressure can be predicted from the modified accumulated shear strain, regardless of soil type, initial soil pressure coefficient, initial shear stress, or the shape of input waveform.