Reconfigurable Web wrapper agents

Web wrapper agents exploit online Web data sources, facilitating information integration and reuse. With the DeepSpot Agent Toolbox, users can automate virtually all types of Web browsing sessions simply by browsing the target Web sites.     

Unsaturated elasto-plastic constitutive equations for compacted kaolin under consolidated drained and shearing-infiltration conditions

Transient process of water flow changes the equilibrium conditions of an unsaturated soil, resulting in volume change of a soil. The volume change alters the hydraulic properties of the soil and thus influences the transient process of water flow through the soil. Therefore, the interactive processes between stress-strain behavior and pore-water pressure are the primary processes affecting the mechanical behavior of unsaturated soils. This paper presents coupled elasto-plastic constitutive equations for unsaturated compacted kaolin under consolidated drained and shearing-infiltration conditions. The study focused on the development of the suction increase (SI) yield curve that incorporates changes in matric suction during transient processes. In addition, the relationship of change in specific water volume with respect to net mean stress and matric suction was also proposed by incorporating the hysteresis of soil-water characteristic curve. The simulated results by the proposed constitutive model were compared with those obtained from isotropically consolidated drained tests and shearing infiltration tests of compacted kaolin to verify the proposed model. The simulated results are in close agreement with the experimental results.     

Effects of Groundwater Table Position and Soil Properties on Stability of Slope during Rainfall

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.     

Shear Strength Equations for Unsaturated Soil under Drying and Wetting

Shear strength of unsaturated soil is an important engineering property in various geotechnical designs. In response to varying climatic conditions, unsaturated soil behaves differently under the drying and wetting processes due to hysteresis. Many research works were conducted and numerous equations were proposed for unsaturated shear strength, however, most of them were limited to the soil under the drying process. In this study, shear strength equations were categorized according to the nature of equation, i.e., fitting and prediction type equations. The purpose of this study is to propose prediction type shear strength equations for unsaturated soil under drying and wetting. Twelve published shear strength equations were selected for evaluation. A series of unsaturated consolidated drained triaxial tests were conducted on statically compacted sand-kaolin specimens under drying and wetting to examine the validity of the proposed equations. The experimental results indicated that the specimens on the drying path had a higher shear strength and exhibited more ductility, less stiffness, and contraction during shearing while the specimens on the wetting path had a lower shear strength and exhibited more brittleness, more stiffness, and dilation during shearing. The proposed equations were shown to provide the best predictions on the drying and wetting shear strength results from this study as well as published data in the comparison study.     

非饱和土孔隙气、水、汽、热耦合运动之模拟(英文)

旨在介绍一个描述非饱和土孔隙气、水、汽、热耦合运动的理论模型。该模型假定孔隙气和孔隙水运动分别遵循达西定律 ,而影响水蒸汽运动的两种主要因素分别是分子扩散和孔隙气运动 ,其中受分子扩散影响的孔隙水蒸汽运动可用Fick定律描述。热转移则主要包括了三种形式 ,即传导、对流和汽化潜热。根据有限单元法 ,编制了一个三维的计算机程序用以模拟非饱和土孔隙气、水、汽、热的耦合运动。通过数值分析与干沙试验结果之比较 ,验证了文中之理论模型和计算机程序的可靠性     

Effect of Antecedent Rainfall Patterns on Rainfall-Induced Slope Failure

Rainfall-induced slope failure occurs in many parts of the world, especially in the tropics. Many rainfall-induced slope failures have been attributed to antecedent rainfalls. Although it has been identified as a cause of rainfall-induced slope failure, the pattern or distribution of the antecedent rainfall has not received adequate attention. In this study, parametric studies were performed by using three typical rainfall patterns, identified by analysis of available rainfall data for Singapore and two different soil types to represent high- and low-conductivity residual soils of Singapore. Antecedent rainfall patterns were applied on soil slopes and a transient seepage analysis was conducted. The computed pore-water pressures were used in stability analyses to calculate the safety factor of the slope. Results indicated that antecedent rainfall affected the stability of both high-conductivity (HC) and low-conductivity (LC) soil slopes. However, the stability of the LC soil slope was more significantly affected than the HC soil slope. Patterns of antecedent rainfall controlled the rate of decrease in factor of safety, the time corresponding to Fs(min) and the value of Fs(min). Delayed rainfall pattern resulted in the lowest minimum factor of safety, Fs(min), for the HC soil slope, and advanced rainfall pattern resulted in the lowest Fs(min) for the LC soil slope.     

Numerical simulations of triaxial shearing-infiltration tests

The failure of steep slopes during rainfall is commonly associated with a decrease in matric suction in the unsaturated soil zone above the water table. The shear strength characteristics of residual soil under water infiltration have been studied in the laboratory using unsaturated triaxial tests. This paper presents a development of a numerical model for simulating a triaxial shearing-infiltration test to investigate the shear strength characteristics of a compacted kaolin under infiltration condition. Both the hydraulic and mechanical responses of the compacted kaolin are modeled using the commercial software SIGMA/W and in-house software YS-Slope. The numerical analyses result and their validation against laboratory test results are presented and discussed in this paper. The results from the numerical analyses show good agreements with those from the laboratory tests, indicating that the proposed numerical model can be used to simulate the triaxial shearing-infiltration tests in laboratory.     

Shear Strength and Pore-Water Pressure Characteristics during Constant Water Content Triaxial Tests

Shear strength parameters used in geotechnical design are obtained mainly from the consolidated drained (CD) or consolidated undrained (CU) triaxial tests. However in many field situations, soils are compacted for construction purposes and may not follow the stress paths in CD or CU triaxial tests. In these cases, the excess pore-air pressure during compaction will dissipate instantaneously, but the excess pore-water pressure will dissipate with time. Under this condition, it can be considered that the air phase is drained and the water phase is undrained. This condition can be simulated in a constant water content (CW) triaxial test. The purpose of this paper is to present the characteristics of the shear strength, volume change, and pore-water pressure of a compacted silt during shearing under the constant water content condition. A series of CW triaxial tests was carried out on statically compacted silt specimens. The experimental results showed that initial matric suction and net confining stress play an important role in affecting the characteristics of the shear strength, pore-water pressure, and volume change of a compacted soil during shearing under the constant water content condition. The failure envelope of the compacted silt exhibited nonlinearity with respect to matric suction.     

Implementation of cryptography in steganography for enhanced security

Multimedia Tools and Applications - The rapid development in technology has had a great influence on the exchange of information. In this modern era, maintaining security during...     

Effects of Hysteresis on Steady-State Infiltration in Unsaturated Slopes

Hysteresis is a common feature exhibited in hydraulic properties of an unsaturated soil. For a specific matric suction, water content or coefficient of permeability on a wetting curve is always lower than those found on a drying curve. This paper focuses on hysteresis observed in steady-state infiltration tests in a laboratory slope model. The slope model consisted of a 400 mm thick fine sand layer overlying a 200 mm thick gravelly sand layer at a slope angle of 30°. The slope model was subjected to artificial rainfalls of different intensities. The slope model was instrumented to continuously measure the changes in pore-water pressure or matric suction, volumetric water content, and water balance during an experiment. Two experiments with similar applied precipitation intensities were conducted on soils that experienced adsorption and desorption processes. For the adsorption process, the slope model was first subjected to an antecedent steady-state rainfall with an intensity lower than the intensity of the incident steady-state rainfall. In the adsorption process, the water content of the soils increased during the incident rainfall prior to achieving the steady-state condition. For the desorption process, the slope model was first subjected to an antecedent steady-state rainfall with an intensity higher than the intensity of the incident steady-state rainfall. In the desorption process, the water content of the soils actually decreased during the incident rainfall prior to achieving the steady-state condition. The results indicate that the matric suction distributions in soils experiencing the desorption process were higher than those observed in soils experiencing the adsorption process. The matric suctions within the slope during a steady-state infiltration were affected by the initial water content of the soil prior to the infiltration process. Numerical analyses, employing both drying and wetting hydraulic properties of the soils, were performed to study the difference in matric suctions as observed in the experiments. The results suggest that the hysteretic behavior of the soil affects the matric suction distribution within the slope at steady-state conditions. The appropriate hydraulic properties of the soils (i.e., drying or wetting) should be used in accordance with the process that the soils actually experience (i.e., desorption process or adsorption process) even though the slope is under a steady-state rainfall condition.