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Kibong Park - One of the best experts on this subject based on the ideXlab platform.

  • analysis of compressive strength development of concrete containing high volume fly ash
    Construction and Building Materials, 2015
    Co-Authors: Kibong Park
    Abstract:

    Abstract Fly ash is a principal by-product of the coal-fired power plants and is well accepted as a pozzolanic material that may be used as a mineral admixture in concrete. High-volume fly ash (HVFA) concrete, which has typically 50–60% fly ash as the total cementitious materials’ content, is widely used to achieve the sustainable development of concrete industry. Compressive strength development is the most important Engineering Property of hardening concrete. This paper presents a numerical procedure to evaluate the compressive strength development of HVFA concrete. The numerical procedure starts with a blended hydration model considering cement hydration, fly ash reaction, and interactions between cement hydration and fly ash reaction. Using the hydration model, the hydration degree of cement and reaction degree of fly ash are determined as functions of curing age. Furthermore, calcium silicate hydrate (CSH) contents of hardening HVFA concrete are calculated using reaction degrees of binders and mixing proportions of concrete. Finally, the compressive strengths of hardening HVFA concrete are determined using CSH contents. The proposed numerical procedure is valid for concrete with different water to binder ratios (ordinary strength concrete and ultra high strength concrete) and different fly ash contents (low volume fly ash and high volume fly ash).

Delwyn G. Fredlund - One of the best experts on this subject based on the ideXlab platform.

  • comparison of different procedures to predict unsaturated soil shear strength
    Geo-Denver 2000, 2000
    Co-Authors: Sai K. Vanapalli, Delwyn G. Fredlund
    Abstract:

    Several procedures have been proposed in the recent years to predict the shear strength of an unsaturated soil. The soil-water characteristic curve has been used as a tool either directly or indirectly in the prediction of the shear strength along with the saturated shear strength parameters in these procedures. This paper provides comparisons between the measured and predicted values of unsaturated shear strength using these procedures for three soils both for limited and large suction ranges. The three soils used in the study for comparisons have different gradation properties, percentages of clay and plasticity index, Ip values. The advantages and limitations associated with predicting the shear strength of unsaturated soils using the procedures is discussed in the paper. INTRODUCTION A theoretical framework for unsaturated soil mechanics that parallels saturated soil mechanics is available in terms of stress state variables, namely; net normal stress, (σn ua), and matric suction, (ua uw) where σn is the normal stress, ua is the pore-air pressure an uw is the pore-water pressure. (Fredlund and Rahardjo, 1993). The framework is based on experimental studies that are costly and time consuming. Several advancements have been made in the prediction of the Engineering behavior of unsaturated soils in recent years. The soil-water characteristic curve has been found to be a useful tool in the estimation of Engineering properties for unsaturated soils. Examples are the coefficient of permeability and the shear strength functions. Shear strength forms an important Engineering Property in the design of numerous geotechnical and geo-environmental structures such as earth dams, retaining walls, pavements, liners, covers, etc. Several procedures have been proposed in the literature during the past five years to predict the shear strength of an unsaturated soil. __________________________________________________________________________ Department of Civil Engineering, University of Saskatchewan, SK, Canada, S7N 5A9 These procedures use the soil-water characteristic curve as a tool either directly or indirectly along with the saturated shear strength parameters, c’ and φ’, to predict the shear strength function for an unsaturated soil (Vanapalli et al. 1996, Fredlund et al. 1996, Oberg and Sallfors 1997, Khallili and Khabbaz 1998 and Bao et al. 1998). The philosophy used in each of the prediction procedures proposed by these investigators is different. Comparisons have been provided between predicted and measured values of shear strength for a limited suction range for various soils (i.e., between 0 to 500 kPa). Escario and Juca (1989) measured the soil-water characteristic curves and the shear strength of three soils prior to the time when any proposals had been made for the shear strength functions. The three soils have different gradation properties, percentages of clay and plasticity indices, Ip. These results are used in this paper to provide comparisons between the predicted and measured shear strength values both for a limited suction range and a large suction range. The study presented in the paper highlights the advantages and limitations associated with the various procedures for predicting the shear strength of unsaturated soils. The simple procedures discussed in this paper are of value in bringing the shear strength theories for unsaturated soils into Engineering practice. EQUATIONS FOR INTERPRETING THE SHEAR STRENGTH OF UNSATURATED SOILS Bishop (1959) proposed shear strength equation for unsaturated soils by extending Terzaghi’s principle of effective stress for saturated soils. Bishop’s original equation can be arranged as shown below. ( ) ( ) ( )( ) [ ] ' tan ' tan ' φ χ φ σ τ w a a n u u u c − + − + = [1] where: τ = shear strength of unsaturated soil, c’ = effective cohesion, φ’ = angle of frictional resistance, (σn ua ) = net normal stress, (ua uw ) = matric suction, and χ = a parameter dependent on the degree of saturation The value of χ was assumed to vary from 1 to 0, which represents the variation from a fully saturated condition to a total dry condition. Several investigators found limitations with respect to the quantification of the parameter χ both theoretically and experimentally. Fredlund et al. (1978) have proposed a relationship to explain the shear strength of unsaturated soils in terms two independent stress state variables as shown below: ( ) ( ) b w a a n u u u c φ φ σ τ tan ' tan ' − + − + = [2] The shear strength contribution due to matric suction, φ , was initially assumed to be linear based on the analysis of limited results published in the literature. Later experimental studies performed over a large range of suction values have shown that the variation of shear strength with respect to soil suction is nonlinear (Gan et al. 1988 and Escario and Juca 1989). Equation [1] can be applied for both the linear and non-linear variation of shear strength with respect to suction. Figure 1. Typical soil-water characteristic curve showing zones of desaturation. The Relationship between the Soil-Water Characteristic Curve and the Shear Strength of Unsaturated soils The soil-water characteristic curve defines the relationship between the soil suction and either the degree of saturation, S, or gravimetric water content, w, or the volumetric water content, θ (Figure 1). The soil-water characteristic curve provides a conceptual and interpretative tool by which the behavior of unsaturated soils can be understood. As the soil moves from a saturated state to drier conditions, the distribution of the soil, water, and air phases change as the stress state changes. A typical soil-water characteristic curve with various zones of desaturation are shown in Figure 1. The wetted area of contact between the soil particles decreases with an increase in the soil suction. There is a relationship between the rate at which shear strength changes in unsaturated conditions to the wetted area of water contact between the soil particles or aggregates. In other words, a relations hip exists between the soil-water characteristic curve and the shear strength of unsaturated soils. Different Procedures for Predicting the Shear Strength of an Unsaturated Soil Vanapalli et al. (1996) and Fredlund et al. (1996) have proposed a more general, nonlinear function for predicting the shear strength of an unsaturated soil using the entire soilwater characteristic curve (i.e., 0 to 1,000,000 kPa) and the saturated shear strength parameters as shown below: ( ) [ ] ( ) ( )( ) { } [ ] ' tan ' tan ' φ φ σ τ κ Θ − + − + = w a a n u u u c [3] where: κ = fitting parameter used for obtaining a bestfit between the measured and predicted values, and Θ = normalized water content, θw/θs. The shear strength contribution due to suction constitutes the second part of [Eq. 3], which is: ( ) ( )( ) { } [ ] ' tan φ τ κ Θ − = w a us u u [4] Equation [3] can also be written in terms of degree of saturation, S, or gravimetric water content, w, to predict the shear strength yielding similar results. The entire soil-water characteristic curve data (i.e., 0 to 1,000,000 kPa) is required along with the saturated shear strength parameters in the use of Equation [3]. A bestfit soilwater characteristic curve can be obtained in terms of a, n, and m parameters using the equation proposed by Fredlund and Xing (1994) which is shown below:

  • comparison of different procedures to predict unsaturated soil shear strength
    Geo-Denver 2000, 2000
    Co-Authors: Sai K. Vanapalli, Delwyn G. Fredlund
    Abstract:

    Several procedures have been proposed in the recent years to predict the shear strength of an unsaturated soil. The soil-water characteristic curve has been used as a tool either directly or indirectly in the prediction of the shear strength along with the saturated shear strength parameters in these procedures. This paper provides comparisons between the measured and predicted values of unsaturated shear strength using these procedures for three soils both for limited and large suction ranges. The three soils used in the study for comparisons have different gradation properties, percentages of clay and plasticity index, Ip values. The advantages and limitations associated with predicting the shear strength of unsaturated soils using the procedures is discussed in the paper. INTRODUCTION A theoretical framework for unsaturated soil mechanics that parallels saturated soil mechanics is available in terms of stress state variables, namely; net normal stress, (σn ua), and matric suction, (ua uw) where σn is the normal stress, ua is the pore-air pressure an uw is the pore-water pressure. (Fredlund and Rahardjo, 1993). The framework is based on experimental studies that are costly and time consuming. Several advancements have been made in the prediction of the Engineering behavior of unsaturated soils in recent years. The soil-water characteristic curve has been found to be a useful tool in the estimation of Engineering properties for unsaturated soils. Examples are the coefficient of permeability and the shear strength functions. Shear strength forms an important Engineering Property in the design of numerous geotechnical and geo-environmental structures such as earth dams, retaining walls, pavements, liners, covers, etc. Several procedures have been proposed in the literature during the past five years to predict the shear strength of an unsaturated soil. __________________________________________________________________________ Department of Civil Engineering, University of Saskatchewan, SK, Canada, S7N 5A9 These procedures use the soil-water characteristic curve as a tool either directly or indirectly along with the saturated shear strength parameters, c’ and φ’, to predict the shear strength function for an unsaturated soil (Vanapalli et al. 1996, Fredlund et al. 1996, Oberg and Sallfors 1997, Khallili and Khabbaz 1998 and Bao et al. 1998). The philosophy used in each of the prediction procedures proposed by these investigators is different. Comparisons have been provided between predicted and measured values of shear strength for a limited suction range for various soils (i.e., between 0 to 500 kPa). Escario and Juca (1989) measured the soil-water characteristic curves and the shear strength of three soils prior to the time when any proposals had been made for the shear strength functions. The three soils have different gradation properties, percentages of clay and plasticity indices, Ip. These results are used in this paper to provide comparisons between the predicted and measured shear strength values both for a limited suction range and a large suction range. The study presented in the paper highlights the advantages and limitations associated with the various procedures for predicting the shear strength of unsaturated soils. The simple procedures discussed in this paper are of value in bringing the shear strength theories for unsaturated soils into Engineering practice. EQUATIONS FOR INTERPRETING THE SHEAR STRENGTH OF UNSATURATED SOILS Bishop (1959) proposed shear strength equation for unsaturated soils by extending Terzaghi’s principle of effective stress for saturated soils. Bishop’s original equation can be arranged as shown below. ( ) ( ) ( )( ) [ ] ' tan ' tan ' φ χ φ σ τ w a a n u u u c − + − + = [1] where: τ = shear strength of unsaturated soil, c’ = effective cohesion, φ’ = angle of frictional resistance, (σn ua ) = net normal stress, (ua uw ) = matric suction, and χ = a parameter dependent on the degree of saturation The value of χ was assumed to vary from 1 to 0, which represents the variation from a fully saturated condition to a total dry condition. Several investigators found limitations with respect to the quantification of the parameter χ both theoretically and experimentally. Fredlund et al. (1978) have proposed a relationship to explain the shear strength of unsaturated soils in terms two independent stress state variables as shown below: ( ) ( ) b w a a n u u u c φ φ σ τ tan ' tan ' − + − + = [2] The shear strength contribution due to matric suction, φ , was initially assumed to be linear based on the analysis of limited results published in the literature. Later experimental studies performed over a large range of suction values have shown that the variation of shear strength with respect to soil suction is nonlinear (Gan et al. 1988 and Escario and Juca 1989). Equation [1] can be applied for both the linear and non-linear variation of shear strength with respect to suction. Figure 1. Typical soil-water characteristic curve showing zones of desaturation. The Relationship between the Soil-Water Characteristic Curve and the Shear Strength of Unsaturated soils The soil-water characteristic curve defines the relationship between the soil suction and either the degree of saturation, S, or gravimetric water content, w, or the volumetric water content, θ (Figure 1). The soil-water characteristic curve provides a conceptual and interpretative tool by which the behavior of unsaturated soils can be understood. As the soil moves from a saturated state to drier conditions, the distribution of the soil, water, and air phases change as the stress state changes. A typical soil-water characteristic curve with various zones of desaturation are shown in Figure 1. The wetted area of contact between the soil particles decreases with an increase in the soil suction. There is a relationship between the rate at which shear strength changes in unsaturated conditions to the wetted area of water contact between the soil particles or aggregates. In other words, a relations hip exists between the soil-water characteristic curve and the shear strength of unsaturated soils. Different Procedures for Predicting the Shear Strength of an Unsaturated Soil Vanapalli et al. (1996) and Fredlund et al. (1996) have proposed a more general, nonlinear function for predicting the shear strength of an unsaturated soil using the entire soilwater characteristic curve (i.e., 0 to 1,000,000 kPa) and the saturated shear strength parameters as shown below: ( ) [ ] ( ) ( )( ) { } [ ] ' tan ' tan ' φ φ σ τ κ Θ − + − + = w a a n u u u c [3] where: κ = fitting parameter used for obtaining a bestfit between the measured and predicted values, and Θ = normalized water content, θw/θs. The shear strength contribution due to suction constitutes the second part of [Eq. 3], which is: ( ) ( )( ) { } [ ] ' tan φ τ κ Θ − = w a us u u [4] Equation [3] can also be written in terms of degree of saturation, S, or gravimetric water content, w, to predict the shear strength yielding similar results. The entire soil-water characteristic curve data (i.e., 0 to 1,000,000 kPa) is required along with the saturated shear strength parameters in the use of Equation [3]. A bestfit soilwater characteristic curve can be obtained in terms of a, n, and m parameters using the equation proposed by Fredlund and Xing (1994) which is shown below:

Yuyang Long - One of the best experts on this subject based on the ideXlab platform.

  • weathering treatment coupled with nano silica filling to promote the Engineering Property of municipal solid waste incinerator bottom ash
    RSC Advances, 2018
    Co-Authors: Qingna Kong, Jun Yao, Qian Yang, Dongshen Shen, Yuyang Long
    Abstract:

    A new approach including weathering treatment and nano-silica filling was employed to promote the Engineering properties of municipal solid waste incinerator (MSWI) bottom ash. X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron dispersive spectroscopy (EDS) was used to characterize the mineralogical and morphological changes due to the treatment. Changes of chemical stability, compressive strength and heavy metal leaching of MSWI bottom ash were also explored. After the weathering treatment, the content of organic matter decreased from 2.70% to 1.07%, while the carbonates increased from 0.70% to 2.05%. The nano-silica treatment filled the intrinsic and neo-formed micropores and coated the surface of MSWI bottom ash. Due to this process, the chemical stability was promoted. The compressive strength increased from 4.83 to 5.32 MPa. The leaching of Cu, Zn, Pb, Cr and Cd sharply decreased from 250.05 to 89.97 mg L−1, 1080.45 to 173.14 mg L−1, 1.25 to 0.70 mg L−1, 72.58 to 12.96 mg L−1 and 0.94 to 0.30 mg L−1, respectively. The results suggested that the weathering treatment coupled with nano-silica filling could greatly promote the Engineering properties of MSWI bottom ash, which is beneficial with respect to the reuse of MSWI bottom ash as the building material.

Sai K. Vanapalli - One of the best experts on this subject based on the ideXlab platform.

  • comparison of different procedures to predict unsaturated soil shear strength
    Geo-Denver 2000, 2000
    Co-Authors: Sai K. Vanapalli, Delwyn G. Fredlund
    Abstract:

    Several procedures have been proposed in the recent years to predict the shear strength of an unsaturated soil. The soil-water characteristic curve has been used as a tool either directly or indirectly in the prediction of the shear strength along with the saturated shear strength parameters in these procedures. This paper provides comparisons between the measured and predicted values of unsaturated shear strength using these procedures for three soils both for limited and large suction ranges. The three soils used in the study for comparisons have different gradation properties, percentages of clay and plasticity index, Ip values. The advantages and limitations associated with predicting the shear strength of unsaturated soils using the procedures is discussed in the paper. INTRODUCTION A theoretical framework for unsaturated soil mechanics that parallels saturated soil mechanics is available in terms of stress state variables, namely; net normal stress, (σn ua), and matric suction, (ua uw) where σn is the normal stress, ua is the pore-air pressure an uw is the pore-water pressure. (Fredlund and Rahardjo, 1993). The framework is based on experimental studies that are costly and time consuming. Several advancements have been made in the prediction of the Engineering behavior of unsaturated soils in recent years. The soil-water characteristic curve has been found to be a useful tool in the estimation of Engineering properties for unsaturated soils. Examples are the coefficient of permeability and the shear strength functions. Shear strength forms an important Engineering Property in the design of numerous geotechnical and geo-environmental structures such as earth dams, retaining walls, pavements, liners, covers, etc. Several procedures have been proposed in the literature during the past five years to predict the shear strength of an unsaturated soil. __________________________________________________________________________ Department of Civil Engineering, University of Saskatchewan, SK, Canada, S7N 5A9 These procedures use the soil-water characteristic curve as a tool either directly or indirectly along with the saturated shear strength parameters, c’ and φ’, to predict the shear strength function for an unsaturated soil (Vanapalli et al. 1996, Fredlund et al. 1996, Oberg and Sallfors 1997, Khallili and Khabbaz 1998 and Bao et al. 1998). The philosophy used in each of the prediction procedures proposed by these investigators is different. Comparisons have been provided between predicted and measured values of shear strength for a limited suction range for various soils (i.e., between 0 to 500 kPa). Escario and Juca (1989) measured the soil-water characteristic curves and the shear strength of three soils prior to the time when any proposals had been made for the shear strength functions. The three soils have different gradation properties, percentages of clay and plasticity indices, Ip. These results are used in this paper to provide comparisons between the predicted and measured shear strength values both for a limited suction range and a large suction range. The study presented in the paper highlights the advantages and limitations associated with the various procedures for predicting the shear strength of unsaturated soils. The simple procedures discussed in this paper are of value in bringing the shear strength theories for unsaturated soils into Engineering practice. EQUATIONS FOR INTERPRETING THE SHEAR STRENGTH OF UNSATURATED SOILS Bishop (1959) proposed shear strength equation for unsaturated soils by extending Terzaghi’s principle of effective stress for saturated soils. Bishop’s original equation can be arranged as shown below. ( ) ( ) ( )( ) [ ] ' tan ' tan ' φ χ φ σ τ w a a n u u u c − + − + = [1] where: τ = shear strength of unsaturated soil, c’ = effective cohesion, φ’ = angle of frictional resistance, (σn ua ) = net normal stress, (ua uw ) = matric suction, and χ = a parameter dependent on the degree of saturation The value of χ was assumed to vary from 1 to 0, which represents the variation from a fully saturated condition to a total dry condition. Several investigators found limitations with respect to the quantification of the parameter χ both theoretically and experimentally. Fredlund et al. (1978) have proposed a relationship to explain the shear strength of unsaturated soils in terms two independent stress state variables as shown below: ( ) ( ) b w a a n u u u c φ φ σ τ tan ' tan ' − + − + = [2] The shear strength contribution due to matric suction, φ , was initially assumed to be linear based on the analysis of limited results published in the literature. Later experimental studies performed over a large range of suction values have shown that the variation of shear strength with respect to soil suction is nonlinear (Gan et al. 1988 and Escario and Juca 1989). Equation [1] can be applied for both the linear and non-linear variation of shear strength with respect to suction. Figure 1. Typical soil-water characteristic curve showing zones of desaturation. The Relationship between the Soil-Water Characteristic Curve and the Shear Strength of Unsaturated soils The soil-water characteristic curve defines the relationship between the soil suction and either the degree of saturation, S, or gravimetric water content, w, or the volumetric water content, θ (Figure 1). The soil-water characteristic curve provides a conceptual and interpretative tool by which the behavior of unsaturated soils can be understood. As the soil moves from a saturated state to drier conditions, the distribution of the soil, water, and air phases change as the stress state changes. A typical soil-water characteristic curve with various zones of desaturation are shown in Figure 1. The wetted area of contact between the soil particles decreases with an increase in the soil suction. There is a relationship between the rate at which shear strength changes in unsaturated conditions to the wetted area of water contact between the soil particles or aggregates. In other words, a relations hip exists between the soil-water characteristic curve and the shear strength of unsaturated soils. Different Procedures for Predicting the Shear Strength of an Unsaturated Soil Vanapalli et al. (1996) and Fredlund et al. (1996) have proposed a more general, nonlinear function for predicting the shear strength of an unsaturated soil using the entire soilwater characteristic curve (i.e., 0 to 1,000,000 kPa) and the saturated shear strength parameters as shown below: ( ) [ ] ( ) ( )( ) { } [ ] ' tan ' tan ' φ φ σ τ κ Θ − + − + = w a a n u u u c [3] where: κ = fitting parameter used for obtaining a bestfit between the measured and predicted values, and Θ = normalized water content, θw/θs. The shear strength contribution due to suction constitutes the second part of [Eq. 3], which is: ( ) ( )( ) { } [ ] ' tan φ τ κ Θ − = w a us u u [4] Equation [3] can also be written in terms of degree of saturation, S, or gravimetric water content, w, to predict the shear strength yielding similar results. The entire soil-water characteristic curve data (i.e., 0 to 1,000,000 kPa) is required along with the saturated shear strength parameters in the use of Equation [3]. A bestfit soilwater characteristic curve can be obtained in terms of a, n, and m parameters using the equation proposed by Fredlund and Xing (1994) which is shown below:

  • comparison of different procedures to predict unsaturated soil shear strength
    Geo-Denver 2000, 2000
    Co-Authors: Sai K. Vanapalli, Delwyn G. Fredlund
    Abstract:

    Several procedures have been proposed in the recent years to predict the shear strength of an unsaturated soil. The soil-water characteristic curve has been used as a tool either directly or indirectly in the prediction of the shear strength along with the saturated shear strength parameters in these procedures. This paper provides comparisons between the measured and predicted values of unsaturated shear strength using these procedures for three soils both for limited and large suction ranges. The three soils used in the study for comparisons have different gradation properties, percentages of clay and plasticity index, Ip values. The advantages and limitations associated with predicting the shear strength of unsaturated soils using the procedures is discussed in the paper. INTRODUCTION A theoretical framework for unsaturated soil mechanics that parallels saturated soil mechanics is available in terms of stress state variables, namely; net normal stress, (σn ua), and matric suction, (ua uw) where σn is the normal stress, ua is the pore-air pressure an uw is the pore-water pressure. (Fredlund and Rahardjo, 1993). The framework is based on experimental studies that are costly and time consuming. Several advancements have been made in the prediction of the Engineering behavior of unsaturated soils in recent years. The soil-water characteristic curve has been found to be a useful tool in the estimation of Engineering properties for unsaturated soils. Examples are the coefficient of permeability and the shear strength functions. Shear strength forms an important Engineering Property in the design of numerous geotechnical and geo-environmental structures such as earth dams, retaining walls, pavements, liners, covers, etc. Several procedures have been proposed in the literature during the past five years to predict the shear strength of an unsaturated soil. __________________________________________________________________________ Department of Civil Engineering, University of Saskatchewan, SK, Canada, S7N 5A9 These procedures use the soil-water characteristic curve as a tool either directly or indirectly along with the saturated shear strength parameters, c’ and φ’, to predict the shear strength function for an unsaturated soil (Vanapalli et al. 1996, Fredlund et al. 1996, Oberg and Sallfors 1997, Khallili and Khabbaz 1998 and Bao et al. 1998). The philosophy used in each of the prediction procedures proposed by these investigators is different. Comparisons have been provided between predicted and measured values of shear strength for a limited suction range for various soils (i.e., between 0 to 500 kPa). Escario and Juca (1989) measured the soil-water characteristic curves and the shear strength of three soils prior to the time when any proposals had been made for the shear strength functions. The three soils have different gradation properties, percentages of clay and plasticity indices, Ip. These results are used in this paper to provide comparisons between the predicted and measured shear strength values both for a limited suction range and a large suction range. The study presented in the paper highlights the advantages and limitations associated with the various procedures for predicting the shear strength of unsaturated soils. The simple procedures discussed in this paper are of value in bringing the shear strength theories for unsaturated soils into Engineering practice. EQUATIONS FOR INTERPRETING THE SHEAR STRENGTH OF UNSATURATED SOILS Bishop (1959) proposed shear strength equation for unsaturated soils by extending Terzaghi’s principle of effective stress for saturated soils. Bishop’s original equation can be arranged as shown below. ( ) ( ) ( )( ) [ ] ' tan ' tan ' φ χ φ σ τ w a a n u u u c − + − + = [1] where: τ = shear strength of unsaturated soil, c’ = effective cohesion, φ’ = angle of frictional resistance, (σn ua ) = net normal stress, (ua uw ) = matric suction, and χ = a parameter dependent on the degree of saturation The value of χ was assumed to vary from 1 to 0, which represents the variation from a fully saturated condition to a total dry condition. Several investigators found limitations with respect to the quantification of the parameter χ both theoretically and experimentally. Fredlund et al. (1978) have proposed a relationship to explain the shear strength of unsaturated soils in terms two independent stress state variables as shown below: ( ) ( ) b w a a n u u u c φ φ σ τ tan ' tan ' − + − + = [2] The shear strength contribution due to matric suction, φ , was initially assumed to be linear based on the analysis of limited results published in the literature. Later experimental studies performed over a large range of suction values have shown that the variation of shear strength with respect to soil suction is nonlinear (Gan et al. 1988 and Escario and Juca 1989). Equation [1] can be applied for both the linear and non-linear variation of shear strength with respect to suction. Figure 1. Typical soil-water characteristic curve showing zones of desaturation. The Relationship between the Soil-Water Characteristic Curve and the Shear Strength of Unsaturated soils The soil-water characteristic curve defines the relationship between the soil suction and either the degree of saturation, S, or gravimetric water content, w, or the volumetric water content, θ (Figure 1). The soil-water characteristic curve provides a conceptual and interpretative tool by which the behavior of unsaturated soils can be understood. As the soil moves from a saturated state to drier conditions, the distribution of the soil, water, and air phases change as the stress state changes. A typical soil-water characteristic curve with various zones of desaturation are shown in Figure 1. The wetted area of contact between the soil particles decreases with an increase in the soil suction. There is a relationship between the rate at which shear strength changes in unsaturated conditions to the wetted area of water contact between the soil particles or aggregates. In other words, a relations hip exists between the soil-water characteristic curve and the shear strength of unsaturated soils. Different Procedures for Predicting the Shear Strength of an Unsaturated Soil Vanapalli et al. (1996) and Fredlund et al. (1996) have proposed a more general, nonlinear function for predicting the shear strength of an unsaturated soil using the entire soilwater characteristic curve (i.e., 0 to 1,000,000 kPa) and the saturated shear strength parameters as shown below: ( ) [ ] ( ) ( )( ) { } [ ] ' tan ' tan ' φ φ σ τ κ Θ − + − + = w a a n u u u c [3] where: κ = fitting parameter used for obtaining a bestfit between the measured and predicted values, and Θ = normalized water content, θw/θs. The shear strength contribution due to suction constitutes the second part of [Eq. 3], which is: ( ) ( )( ) { } [ ] ' tan φ τ κ Θ − = w a us u u [4] Equation [3] can also be written in terms of degree of saturation, S, or gravimetric water content, w, to predict the shear strength yielding similar results. The entire soil-water characteristic curve data (i.e., 0 to 1,000,000 kPa) is required along with the saturated shear strength parameters in the use of Equation [3]. A bestfit soilwater characteristic curve can be obtained in terms of a, n, and m parameters using the equation proposed by Fredlund and Xing (1994) which is shown below:

Andrew Chan - One of the best experts on this subject based on the ideXlab platform.

  • Study on The Engineering Property of Mixed-Soil Fly Ash
    Rock and Soil Mechanics, 2010
    Co-Authors: Jing Li, Andrew Chan
    Abstract:

    Fly ash is a byproduct dumped out of thermal power plants which use coal as one kind of fuel. It is urgent to consider how the vast quantity of harmful fly ash resources can be utilized. There are a large number of potential solutions to this problem, an effective disposal method is to use it as a fill material for dam construction or filled ground. Fly ash is a uncompacted lightweight material with a lot of pores. On one hand, it has a superior Engineering capability in many aspects; On the other hand, pure fly ash lacks any necessary cohesion so that it has a very sensitive reaction with water which is an undesirable effect on the safe operation of the project which employs pure fly ash. Based on above considered, the Engineering performance of the fly ash can potentially be enhanced by mixing different quantity of clay into fly ash, therefore the study on mechanical properties of fly ash mixed with different quantities of clay could help to promote the Engineering application of fly ash. In this paper, fly ash from the Xianyang Weihe thermal power plant is the object of study, and different quantity of loess it is used to obtain the mixed-soil fly ash, then the Engineering characteristics of fly ash with different quantity of soil mixed are studied via compaction test, compression test, and direct shear test as well as triaxial compression test. Furthermore, the trends of influence of different quantity of soil mixed on deformation and strength characteristics of fly ash are also obtained. The research results in this paper will offer the basis for both the effective utilization of fly ash and the improvement of its Engineering Property.