Because direct measurement is time-consuming and costly, the permeability function of unsaturated soil is commonly determined by estimation using the soil–water characteristic curve (SWCC). Various ...prediction models (i.e., indirect methods) for the permeability function have been proposed by different researchers. Mualem (1986) categorized these prediction models into three groups: empirical, macroscopic, and statistical models. Of these, the statistical model is the most rigorous and provides the most accurate results (Leong and Rahardjo 1997). In this paper, a new equation for the calculation of the permeability function is proposed in which the permeability function of unsaturated soil is correlated with the fitting parameters of SWCC. In other words, unsaturated hydraulic conductivity is computed using an electronic spreadsheet with input parameters (i.e., the fitting parameters of SWCC). The proposed equation is shown to be the general form of the equations by Marshall (1958) and Kunze et al. (1968). In the equation, suction is considered as a variable and SWCC, in the form of degree of saturation, S, is adopted as a probability function. Soil volume change is also incorporated in this equation. Lastly, the proposed equation is verified using experimental data from the literature.
•A new statistical model for the prediction of kw from SWCC in the form of S is proposed.•SWCC in the form of S is analogous to the pore-suction distribution function.•In the proposed equation, the kw of unsaturated soil is correlated with the SWCC fitting parameters.•Soil volume change is also incorporated in the proposed equation.•The proposed equation is able to predict kw from a bimodal SWCC.
Many shallow foundations are constructed within the soil layer above the groundwater table, where the soil remains unsaturated, and the failure of shallow foundation is mostly related to shear ...failure. The shear strength of the unsaturated soil is one of the main engineering properties required in geotechnical designs. Previous researchers suggested that the shear strength of the unsaturated soil depends on matric suction in the soil. The shape of the soil–water characteristic curve (SWCC) has a significant effect on the characteristics of unsaturated shear strength with respect to matric suction. In this paper, a new model was proposed for the estimation of the unsaturated shear strength from SWCC. In this new model, meniscus was considered to transfer soil suction into both additional net normal stress and additional cohesion. Based on the categorization from soil science, water in soil can be categorized into three groups: (1) gravity water, (2) capillary water and (3) hygroscopic water. The elemental analysis on the contractile skin indicated that only the capillary water in the soil can transfer stress into soil skeleton. Consequently, the SWCC is modified by considering capillary water only for the estimation of unsaturated shear strength. In the derivation, unsaturated soil is considered as four-phase material. Finally, a new mathematical equation for the estimation of the unsaturated shear strength was proposed and verified with the experimental data from the published literature. In addition, the proposed equation does not consist of any empirical parameter and can be used to predict the shear strength of unsaturated soil.
Soil–water characteristic curve (SWCC) contains the fundamental information needed for describing the mechanical behavior of unsaturated soil. Some parameters such as air-entry value, slope at the ...inflection point, residual water content and residual suction are commonly used to describe the SWCC and other associated properties such as shear strength and permeability. Currently these parameters are determined using the graphical method which can be subjective and time consuming. Equations for determining these parameters are proposed and the relationships between SWCC parameters and fitting parameters are discussed in this paper. These equations can be used for computational analyses to replace the conventional graphical method in providing consistent results.
Hydraulic property of soil is key information required for understanding the groundwater flow in the soil (including saturated and unsaturated zone). The water flow in soil is governed by the ...geometrical pore-space characteristics of soil structure (i.e., pore-size distribution function). Even though the concept of pore-size distribution function had been proposed decades ago, the pore-size distribution function is rarely used to estimate the hydraulic properties in engineering practice. In practice, the effective particle size (i.e., d10) and void ratio (e) are commonly used for the estimation of saturated coefficient of permeability, ks, for sandy soils. Neither d10 nor e can accurately represent the geometrical pore space in soil. With the development of unsaturated soil mechanics, it is observed that the pore-size distribution function can be expressed in another form which is named as soil-water characteristic curve (SWCC). In this study, the coefficients of permeability of sandy soils were estimated using the concept of “pore-size distribution function” (or SWCC). The comparison between the estimated results using the proposed equation and the measured data from laboratory tests in Nanyang Technological University (NTU) showed that the proposed equation in this note provided good estimation of ks.
•Estimation of saturated coefficient of permeability.•Verification of estimation results with experimental data.•Role of Pore-size distribution function in the estimation.•Better estimation using proposed equation than conventional methods
The understanding of unsaturated soil mechanics principles is of interest to a wide spectrum of geotechnical problems associated with soils above water table and compacted soils. This paper describes ...the stress state variables and constitutive equations based on the unsaturated soil mechanics principles. In addition, the basic concepts for characterization of unsaturated soils and measurements of matric suction (or negative pore-water pressures) are also explained. The application of unsaturated soil mechanics theories is illustrated through the use of capillary barrier system for minimizing rain infiltration into residual soil slopes.
The definitive guide to unsaturated soil— from the world's experts on the subjectThis book builds upon and substantially updates Fredlund and Rahardjo's publication, Soil Mechanics for Unsaturated ...Soils, the current standard in the field of unsaturated soils. It provides readers with more thorough coverage of the state of the art of unsaturated soil behavior and better reflects the manner in which practical unsaturated soil engineering problems are solved. Retaining the fundamental physics of unsaturated soil behavior presented in the earlier book, this new publication places greater emphasis on the importance of the 'soil-water characteristic curve' in solving practical engineering problems, as well as the quantification of thermal and moisture boundary conditions based on the use of weather data. Topics covered include:Theory to Practice of Unsaturated Soil MechanicsNature and Phase Properties of Unsaturated SoilState Variables for Unsaturated SoilsMeasurement and Estimation of State VariablesSoil-Water Characteristic Curves for Unsaturated SoilsGround Surface Moisture Flux Boundary ConditionsTheory of Water Flow through Unsaturated SoilsSolving Saturated/Unsaturated Water Flow ProblemsAir Flow through Unsaturated SoilsHeat Flow Analysis for Unsaturated SoilsShear Strength of Unsaturated SoilsShear Strength Applications in Plastic and Limit EquilibriumStress-Deformation Analysis for Unsaturated SoilsSolving Stress-Deformation Problems with Unsaturated SoilsCompressibility and Pore Pressure ParametersConsolidation and Swelling Processes in Unsaturated SoilsUnsaturated Soil Mechanics in Engineering Practiceis essential reading for geotechnical engineers, civil engineers, and undergraduate- and graduate-level civil engineering students with a focus on soil mechanics.
Soil-water characteristic curve (SWCC) defines the relationship between water content and suction in soil. Many unsaturated properties can be estimated from SWCC such as permeability function and ...unsaturated shear strength. Therefore, SWCC is considered as the key information of unsaturated soil properties. Permeability function, which defines the relationship between hydraulic conductivity and matric suction, is essential information for seepage analysis in understanding water flow in unsaturated soil. The permeability function is commonly determined indirectly from the SWCC rather than from direct measurement in the laboratory because the direct measurement is time consuming and costly. On the other hand, it has been reported that SWCC can have unimodal and bimodal characteristics. Many models have been proposed for the estimation of permeability function from a unimodal SWCC while limited numbers of model have been proposed for a bimodal SWCC. In this paper, experimental works in laboratory were carried out for measurements of the unsaturated permeability of soils with bimodal SWCC. Zhai and Rahardjo's (2015) equation was used to estimate the permeability function of soils with bimodal SWCC. The experimental results show good agreement with the estimated permeability function. Therefore, Zhai and Rahardjo's (2015) equation was recommended for the estimation of the permeability function from bimodal SWCC. This study also shows that the variability in bimodal SWCC has significant effect on the estimation of the permeability function.
•Equation for estimation of a bimodal permeability function•Verification of estimation results with experimental data•Comparison of estimation results using different best fit equations for a bimodal SWCC•Effect of variability in bimodal SWCC on the estimation results•Measurement at high suction during SWCC test is recommended.
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.
Celotno besedilo
Dostopno za:
DOBA, FGGLJ, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Numerous scientific evidence has given credence to the true existence and deleterious impacts of climate change. One aspect of climate change is the variations in rainfall patterns, which affect the ...flux boundary condition across ground surface. A possible disastrous consequence of this change is the occurrence of rainfall-induced slope failures. This paper aims to investigate the variations in rainfall patterns in Singapore and its effect on slope stability. Singapore's historical rainfall data from Seletar and Paya Lebar weather stations for the period of 1985–2009 were obtained and analysed by duration using linear regression. A general increasing trend was observed in both weather stations, with a possible shift to longer duration rainfall events, despite being statistically insignificant according to the Mann-Kendall test. Using the derived trends, projected rainfall intensities in 2050 and 2100 were used in the seepage and slope stability analyses performed on a typical residual soil slope in Singapore. A significant reduction in factor of safety was observed in the next 50 years, with only a marginal decrease in factor of safety in the subsequent 50 years. This indicates a possible detrimental effect of variations in rainfall patterns on slope stability in Singapore, especially in the next 50 years. The statistical analyses on rainfall data from Seletar and Paya Lebar weather stations for the period of 1985–2009 indicated that rainfall intensity tend to increase over the years, with a possible shift to longer duration rainfall events in the future. The stability analyses showed a significant decrease in factor of safety from 2003 to 2050 due to increase in rainfall intensity, suggesting that a climate change might have existed beyond 2009 with possibly detrimental effects to slope stability.
The hydraulic properties of soil (i.e. soil-water characteristic curve (SWCC) and coefficient of permeability) govern the moisture flow in it. Previous research has indicated that the hydraulic ...properties of soil are dependent on its pore-size distribution. An improved capillary model is now proposed to explain the concept of the pore-size distribution in soil and its relationship to SWCC. A new model, the “valve model”, is also proposed as the explanation for water flow in unsaturated soil. The pore-size distribution function is incorporated in the “valve model” and is used to calculate the relative coefficient of permeability for unsaturated soil. In this paper, the role of the pore-size distribution function in the estimation of SWCC and the permeability function are explained. Equations are proposed for estimating the pore-size distribution function from the experimental data of relative coefficient of permeability. The results from the proposed equations agree with the experimental data from laboratory measurement and published data.
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