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Liangtong Zhan - One of the best experts on this subject based on the ideXlab platform.
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comparative study of rainfall infiltration into a bare and a grassed unsaturated expansive Soil Slope
Soils and Foundations, 2007Co-Authors: Liangtong ZhanAbstract:It is generally thought that vegetation has a stabilization effect on a Slope; however, very limited quantitative field data are available for verifying this perception. In order to improve our understanding on the vegetation effect on rainfall infiltration and hence on Slope stability, a well-instrumented field study was carried out on an unsaturated expansive Soil Slope in China. The field program consisted of two neighboring monitoring areas (both 16 m wide by about 30 m long): namely a bare area and a naturally grassed area (real Slope). Artificial rainfall events were produced in succession in the two areas with a specially-designed sprinkler system. In this paper, the relevant monitored results from the two areas are directly compared and discussed. Prior to the artificial rainfall, the measured higher initial Soil suction in the grassed area than that in the bare areas was attributed to the evapo-transpiration effect of the grass. During the rainfall, the presence of the grass greatly increased the infiltrability of the upper Soil layer and delayed the onset of surface runoff. The observed delayed responses (i.e., about 3 days) of surface runoff, Soil suction and water content to the rainfall in the grassed area was about twice the duration of the delayed response in the bare area (i.e., about 1.5 days). The influence of the simulated rainfall on the changes of Soil suction and water content in the grassed area was found to be more significant and about 1.5 m deeper than that in the bare area. The greater depth of influence observed in the grassed area may be attributable to the greater depth of open cracks due to the evapo-transpiration effect of grass.
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performance of an unsaturated expansive Soil Slope subjected to artificial rainfall infiltration
Geotechnique, 2003Co-Authors: Charles Wang Wai Ng, D G Fredlund, Liangtong Zhan, B W GongAbstract:A major infrastructure project, the South-to-North Water Transfer Project, has been proposed to carry potable water from the Yangtze River region in the south to many arid and semi-arid areas in the northern regions of China, including Beijing. The proposed 1200 km ‘middle route’ of the project is likely to be an open channel with a trapezoidal cross-section. At least 180 km of the proposed excavated canal will pass through areas of unsaturated expansive Soils. An 11 m high cut Slope in a typical expansive clay with medium plasticity in Zaoyang, close to the ‘middle route’ in Hubei, was selected for a comprehensive and well-instrumented field study of the effects of rainfall infiltration. Two artificial rainfall events were created during a month of field investigation and monitoring. Prior to the rainfall events, high Soil suction was measured within the top 1 m of Soil. This high initial Soil suction created an upward flux of water and moisture. The abundant cracks and fissures near the ground surface p...
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artificial rainfall infiltration tests on a well instrumented unsaturated expansive Soil Slope
Rock and Soil Mechanics, 2003Co-Authors: Liangtong Zhan, C G Bao, B W GongAbstract:To improve our understanding of the fundamental mechanism of rain-induced landslides in unsaturated expansive Soils, artificial rainfall simulation tests were carried out on an 11 m high cut Slope in a typical medium-plastic expansive clay in Hubei of China. The Slope was well-instrumented with tensiometers, thermal conductivity suction sensors, moisture probes, earth pressure cells, inclinometers, a tipping bucket rain gauge, a vee-notch flow meter and an evaporimeter. Two artificial rainfall events were created during a month of field investigation and monitoring. Monitored results demonstrate: rainfall infiltration leads to a significant increase in pore-water pressure and water content within the top 2 m Soil layer, which may result in a reduction of shear strength due to a decrease in effective stress and wetting-induced softening. On the other hand, rainfall infiltration causes a significant increase in total stress ratio (sh/sv), which may lead to a local passive failure and then trigger a progressive Slope failure under a continuous rainfall condition.
Eng Choon Leong - One of the best experts on this subject based on the ideXlab platform.
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effects of flux boundary conditions on pore water pressure distribution in Slope
Engineering Geology, 2013Co-Authors: H Rahardjo, Alfrendo Satyanaga, Eng Choon LeongAbstract:Abstract Many geotechnical analyses commonly ignore the flux boundary conditions at the ground surface to avoid the complexity in determining the actual flux values at the Soil-atmosphere interface. However, actual flux boundary conditions can be an important input to many geotechnical analyses, especially those related to unsaturated Soils. Therefore, the effects of flux boundary conditions on pore-water pressure distribution in a residual Slope are investigated in this paper. The study focuses on infiltration and evaporation processes. The characterization of climatic data in Singapore is presented in this paper to illustrate the quantification of flux boundary conditions. Evaporation rate for the seepage analyses is calculated using Penman's method. The classification of Singapore climate is carried out using Thornthwaite index. The typical differences between air and Soil temperatures in Singapore are presented in this paper using case study from a residual Soil Slope at Yishun, Singapore. Finite element seepage analyses were conducted to investigate the effect of rainwater infiltration and evaporation on pore-water pressure distribution of a residual Soil Slope at Jalan Kukoh, Singapore. The numerical analysis results show good agreement with those obtained from field measurements if the evaporation is applied in the analyses during the drying process. This indicates that rainfall and evaporation play important roles in pore-water pressure changes within Soil Slope.
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effects of groundwater table position and Soil properties on stability of Slope during rainfall
Journal of Geotechnical and Geoenvironmental Engineering, 2010Co-Authors: H Rahardjo, Eng Choon Leong, Alfrendo Satyanaga Nio, Ng Yew SongAbstract:Rainfall, hydrological condition, and geological formation of Slope are important contributing factors to Slope failures. Parametric studies were carried out to study the effect of groundwater table position, rainfall intensities, and Soil properties in affecting Slope stability. Three different groundwater table positions corresponding to the wettest, typical, and driest periods in Singapore and four different rainfall intensities (9, 22, 36, and 80 mm/h) were used in the numerical analyses. Typical Soil properties of two main residual Soils from the Bukit Timah Granite and the sedimentary Jurong Formation in Singapore were incorporated into the numerical analyses. The changes in factor of safety during rainfall were not affected significantly by the groundwater table near the ground surface due to the relatively small changes in matric suction during rainfall. A delay in response of the minimum factor of safety due to rainfall and a slower recovery rate after rainfall were observed in Slopes from the sedimentary Jurong Formation as compared to those Slopes from the Bukit Timah Granite. Numerical analyses of an actual residual Soil Slope from the Bukit Timah Granite at Marsiling Road and a residual Soil Slope from the sedimentary Jurong Formation at Jalan Kukoh show good agreement with the trends observed in the parametric studies.
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response of a residual Soil Slope to rainfall
Canadian Geotechnical Journal, 2005Co-Authors: Eng Choon LeongAbstract:Rainfall-induced landslides are a common problem in residual Soil Slopes of the tropics. It is widely known that rainfall-induced Slope failures are mainly caused by infiltration of rainwater; however, the response of a residual Soil Slope to infiltration is not fully understood. The difficulties lie in the quantification of the flux boundary condition across the Slope surface with respect to infiltration and its effect on the pore-water pressure conditions in the Slope. Therefore, it is important to understand the response of a Slope to different rainfall conditions and the resulting changes in pore-water pressures and water contents. A residual Soil Slope in Singapore was instrumented with pore- water pressure, water content, and rainfall measuring devices, and studies were carried out under natural and simulated rainfalls. Results indicate that significant infiltration may occur in a residual Soil Slope during a rainfall. Small total rainfalls can contribute a larger infiltration percentage than large total rainfalls. The percentage of infiltration usually decreases with increasing total rainfalls. The study has indicated the existence of a threshold rainfall of about 10 mm for runoff generation to commence. Infiltration during wet periods may lead to the development of positive pore-water pressures as a consequence of a perched water table condition. Matric suctions are recovered gradually during dry peri- ods due to redistribution. Soil water contents tend to be higher near the toe of the Slope than at the crest irrespective of rainfall events, indicating subsurface movement of water in the downSlope direction. The study has also indicated a correlation between rainfall amount and relative increase in pore-water pressure. The results can be used to quantify the flux boundary conditions required for the seepage analyses associated with rainfall-induced Slope failures.
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response of a residual Soil Slope to rainfall
Canadian Geotechnical Journal, 2005Co-Authors: T T Lee, Eng Choon LeongAbstract:Rainfall-induced landslides are a common problem in residual Soil Slopes of the tropics. It is widely known that rainfall-induced Slope failures are mainly caused by infiltration of rainwater; howe...
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controlling parameters for rainfall induced landslides
Computers and Geotechnics, 2002Co-Authors: Illias Tsaparas, H Rahardjo, D G Toll, Eng Choon LeongAbstract:Slope instability due to rainfall is a common geotechnical problem in tropical and subtropical areas. The numerical analysis of this problem requires the definition of various hydrological characteristics of the Soil in addition to the climatic information. This work attempts to identify the influence of some of those parameters on the stability of an unsaturated Soil Slope during rainfall. The results of the analysis show that the ratio between the saturated coefficient of permeability with respect to water and the rainfall patterns can significantly influence the seepage pattern within an unsaturated Soil Slope.
Huabei Liu - One of the best experts on this subject based on the ideXlab platform.
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early warning system with quasi distributed fiber optic sensor networks and cloud computing for Soil Slopes
IEEE Access, 2017Co-Authors: Longjun Dong, Lalit Borana, Huabei LiuAbstract:Slope failure and debris flow cause lots of casualties and property loss. An early-warning system for Slope collapse and debris flow is essential to ensure safety of human beings and assets. Based on fiber optic sensing technology and Internet of Things, a new sensing transducer for internal earth pressure measurement in a Soil Slope is proposed, fabricated, and tested in this paper. The working principles, theoretical analysis, laboratory calibrations, and discussions of the proposed pressure transducers are elaborated. Extensive evaluations of the resolutions, physical properties, and response to the applied pressures have been performed through modeling and experimentations. The results show that the sensitivity of the designed pressure sensor is 0.1287 kPa/ $\mu \varepsilon $ across a pressure range of 140 kPa. Finally, a field Soil Slope was instrumented with the developed fiber optic sensors and other sensors. Through internet and cloud computing platform, the stability of the Soil Slope was analyzed. In the cloud computing platform, the numerical simulation is carried out by considering the Slope internal deformations, rainfall infiltration, and limit force equilibrium. The factor of safety of the Soil Slope was calculated, which could be used to determine health condition of the instrumented Slope. The performance was evaluated and classified into three categories. It proves that the proposed early-warning system has potential to monitor the health condition of the Soil Slopes.
Guang Qing Wei - One of the best experts on this subject based on the ideXlab platform.
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Test on application of distributed fiber optic sensing technique into Soil Slope monitoring
Landslides, 2009Co-Authors: Bao Jun Wang, Ke Li, Bin Shi, Guang Qing WeiAbstract:Brillouin optical time-domain reflectometer (BOTDR), a newly developed\ndistributed fiber optic sensing technique, has been proved to be\na very suitable and useful technique for monitoring and early warning\nof structural engineering by laboratory tests and practical projects\ndue to its unique functions, such as distributing, long distance,\nanti-electromagnetic interference, waterproof, etc. However, its\napplication to geotechnical engineering, especially Soil-Slope engineering,\nhas been less carried out due to the complexity of the characteristics\nof geotechnical materials in the field. In this paper, BOTDR technique\nis applied to monitor the deformation of a laboratory Soil-Slope\nmodel in small scale in order to test the feasibility and early-warning\ncharacteristics of this technique with monitoring the deformation\nof Soil Slope. Different types of optical fibers are planted directly\nin the Soil-Slope model or bonded to geotextiles and geogrids that\nare planted in the fillings of the test model. Strain measurements\nof the model Slope under various loads are obtained by BOTDR. By\ndata processing and analysis, the abnormal strains can be obtained\ndistributively, and the position of the abnormal strains can be located\nas well. The results show much valuable information for applications\nof BOTDR technique into Soil-Slope engineering. The test proves that\nthe BOTDR technique can be used to ensure the stability of artificial\nSoil Slope and is useful for monitoring and early warning of the\nartificial Soil-Slope engineering.
Ga Zhang - One of the best experts on this subject based on the ideXlab platform.
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effect study of cracks on behavior of Soil Slope under rainfall conditions
Soils and Foundations, 2012Co-Authors: Ga Zhang, Jianmin Zhang, Rui Wang, Jiyun Qian, Jiangu QianAbstract:Abstract Deep-seated landslides in Slopes are often induced by rainfall due to pre-existing cracks or weak layers. A series of centrifuge model tests under rainfall conditions were conducted on Slopes with different types of cracks. The histories of suction and displacement of the Slope were measured during the tests to investigate the infiltration–deformation–failure process of the Slopes. The wetting front curved notably near the crack under rainfall conditions. The deformation of the Slope was mainly caused by the saturation of Soil and crack-affected water infiltration under rainfall conditions. The displacement process of the Slopes with cracks can be divided into a small displacement stage, a rapid increase stage, and a stable stage. The influence of the crack on the infiltration and deformation of the Slope decreased with increasing distance from the crack. Rainfall induced significant vertical deformation near the vertical crack rather than horizontal deformation. In contrast to the oblique crack, the vertical crack on the Slope top was unlikely to lead to global landslide under rainfall conditions. The deformation–failure behavior of the Slope with cracks was also affected by the rainfall style and rain intensity.
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centrifuge model tests on a cohesive Soil Slope under excavation conditions
Soils and Foundations, 2011Co-Authors: Ga Zhang, Jianmin Zhang, C F LeeAbstract:ABSTRACT Problems induced by Slope excavations are quite common. An in-flight excavation device was realized to simulate the live excavation of Slopes at high g levels during centrifuge model tests. A series of centrifuge model tests was conducted to simulate the excavation of a Slope at different inclinations and heights, and the effect of the excavation size was taken into consideration. The displacement histories of points over the Slope were measured by an image capture and displacement measurement system. Measurement results showed that the excavation-induced deformation process could be divided into several phases with different displacement distribution features. The excavation was found to only affect a restricted zone of the Slope whose boundary could be outlined by an A-surface. A strain analysis was conducted to determine the excavation-induced strain localization area of the Slope. The degree of strain localization increased as the excavation time increased, but the width of the strain localization area was nearly invariable. Shear failure first occurred near the excavation surface and then extended upwardly to the Slope surface under excavation conditions, while tension failure played a dominant role in the upper part of the slip surface. The strain localization area moved towards the Slope surface with an increasing Slope inclination. The lower part of the final slip surface was located in the strain localization area.
