jihad shwan - Academia.edu (original) (raw)
Papers by jihad shwan
Japanese Geotechnical Society Special Publication, 2019
The shear strength equations, based on two stress state variables, proposed by Fredlund et al. (1... more The shear strength equations, based on two stress state variables, proposed by Fredlund et al. (1978) and Öberg and Sällfors (1997), respectively were compared at peak and critical states. Data of a set of drained direct shear tests for a fine sand tested under saturated and unsaturated conditions were used for the comparison. The comparison between the two equations suggests that suction contributing to the effective stress for sand used is often much smaller than predicted by the (sSr) term used in effective stress expressions of Öberg and Sällfors (1997). It is suggested that effective stress in unsaturated soils should be related to soil fabric and microstructure which caused an increase of shear strength parameters. Clusters or assemblages of particles, held by menisci, increased dilation and frictional resistance during shearing related to the different phases of water retention behaviour.
This paper investigates the effect of scale on the bearing capacity and settlement of footings. F... more This paper investigates the effect of scale on the bearing capacity and settlement of footings. For this study, three types of prototype footing circular, square and rectangular were investigated . For the circular footing, diameters (8, 10, 15 and 20 cm) were used, while for the square and rectangular footings, the dimensions used were 8×8, 10×10, 15×15, 20×20 cm and 8×12, 10×15,15×22.5 and 20×30 cm, respectively. The experimental work was complimented by finite element studies using the software (SAGE-CRISP), which is a 2D finite element program designed to solve both 2D plane strain and axi-symmetric problems. This was used to analyse square footings of size 8, 15, and 20 cm. Additionally, equations due to Zhu et al. (2001) were used to determine the bearing capacity factors Sγ and Nγ for different footing shapes. Relaibilty of the results showed that these equations could be used for larger footings with using reduction factor for Nγ. It was found that the bearing capacity shape...
The Journal of The University of Duhok, Jul 20, 2017
A modification of an existing soil water retention curve (SWRC) equation is presented in this pap... more A modification of an existing soil water retention curve (SWRC) equation is presented in this paper which takes into consideration the effects of the soil capillarity (parameter a) and air entry value (s o). The reformulated equation then was incorporated into the research version of the LimitState:GEO software to perform two parametric studies on the bearing capacity of a strip footing placed on the surface and total passive earth pressure for a frictional wall of 1 m height. The parametric analyses were to study the effect of SWRC hysteresis on the strength of unsaturated soils through parameter a and air entry value (s o). The numerical bearing capacity and the passive earth pressure results were compared with the experimental data and the derived Rankine equations which take into account the effect of capillary rise, respectively. The numerical results showed that the effect of SWRC hysteresis has significant influence on the strength for both parametric studies.
ABSTRACT This paper reports an investigation into the effect of stress state and matric suction o... more ABSTRACT This paper reports an investigation into the effect of stress state and matric suction on the unsaturated shear strength of a fine sand using a modified direct shear apparatus. The direct shear apparatus was adapted to enable application of a specified suction to the sand sample using the hanging column technique (HCT). This also allowed monitoring of the water content of the sample and hence the average degree of saturation at different stages during the test. This additionally allows direct measurement of the soil water characteristic curve (SWCC) for the fine sand within the suction range of 0 to 10 kPa. A modified effective stress equation is evaluated that accounts for applied stress, suction and degree of saturation and is calibrated against the experimental results. Somewhat unexpectedly the shear strength of the unsaturated sand was significantly affected by the degree of saturation far in excess of what would have been expected by simple account of suction and saturation used in the modified effective stress equation.
Advanced Materials Research
The stress paths to which specimens are subjected in triaxial tests together with the yield surfa... more The stress paths to which specimens are subjected in triaxial tests together with the yield surfaces, which may be exercised in different models of such a test are simulated. A laboratory testing on undisturbed clay soil samples was performed in order to characterize the stress-strain behaviour of the residual soils in Sao Paulo sedimentary deposit. The sample is tested under isotropically consolidated drained triaxial compression. Strain controlled procedure was used to simulate stress-strain relationships of the soil. Seven models are used; namely: linear elastic, Duncan-Chang hyperbolic, Mohr-Coulomb, Cam clay, modified Cam clay, new Mohr-Coulomb and Cap model. It was concluded that the results of Cam clay and Duncan Chang models are the closest to the experimental data under low confining pressures; 49 and 98 kPa. Both models exhibit parabolic stress-strain relationships while the linear elastic model results are far away from experimental ones especially at large stress levels....
Constitutive models for soil are typically based on the same mathematical plasticity theory frame... more Constitutive models for soil are typically based on the same mathematical plasticity theory framework used to model common metals. However, the constitutive behaviour of soil differs from that of metals in different ways. The soil used in this paper was selected from the work of Azevedo et al. (2002). The work dealt with 2D finite element analysis of a shallow tunnel in the city of S˜ao Paulo, Brazil, through residual soils. The tunnel, approximately 103 m long, has a maximum width of 11.4 m. The thickness of the soil cover above the tunnel crown was 7.6 m. The support system consisted of a 0.20 m-thick primary shotcrete and a 0.15 m-thick secondary shotcrete liner. Three stages of excavation process were taken into consideration to simulate the actual behaviour of the tunnel during the excavation. In each stage, five increments are included. Numerical simulation of excavations is performed by releasing equivalent nodal forces defined by the in situ soil stresses existing along the ...
Acta Montanistica Slovaca
There are many factors that govern the expansion behavior of soil. The primary factors are a chan... more There are many factors that govern the expansion behavior of soil. The primary factors are a change in water content and the amount and type of clay size particles in the soil. Other important factors affecting the expansion behavior include the type of soil (natural or fill), condition of the soil in terms of dry density and moisture content, magnitude of the surcharge pressure, and amount of no expansive material such as gravel or cobble size particles. In this paper, a swelling soil from the site Hamamuk earth dam, which is located in Koya town north of Iraq, is treated by four types of additives; cement, steel fibers, gasoline fuel and injection by cement grout. The treatment of the expansive soil with 5 % of cement or steel fibers or the injection with cement grout revealed a better improvement while 4 % of gasoline oil is sufficient to reveal the optimum treatment by this material. The angle of internal friction is not affected by the treatment while the cohesion between particles is slightly affected by these additives due to a change in the adhesion between the additive and soil particles.
Japanese Geotechnical Society Special Publication, 2019
The shear strength equations, based on two stress state variables, proposed by Fredlund et al. (1... more The shear strength equations, based on two stress state variables, proposed by Fredlund et al. (1978) and Öberg and Sällfors (1997), respectively were compared at peak and critical states. Data of a set of drained direct shear tests for a fine sand tested under saturated and unsaturated conditions were used for the comparison. The comparison between the two equations suggests that suction contributing to the effective stress for sand used is often much smaller than predicted by the (sSr) term used in effective stress expressions of Öberg and Sällfors (1997). It is suggested that effective stress in unsaturated soils should be related to soil fabric and microstructure which caused an increase of shear strength parameters. Clusters or assemblages of particles, held by menisci, increased dilation and frictional resistance during shearing related to the different phases of water retention behaviour.
This paper investigates the effect of scale on the bearing capacity and settlement of footings. F... more This paper investigates the effect of scale on the bearing capacity and settlement of footings. For this study, three types of prototype footing circular, square and rectangular were investigated . For the circular footing, diameters (8, 10, 15 and 20 cm) were used, while for the square and rectangular footings, the dimensions used were 8×8, 10×10, 15×15, 20×20 cm and 8×12, 10×15,15×22.5 and 20×30 cm, respectively. The experimental work was complimented by finite element studies using the software (SAGE-CRISP), which is a 2D finite element program designed to solve both 2D plane strain and axi-symmetric problems. This was used to analyse square footings of size 8, 15, and 20 cm. Additionally, equations due to Zhu et al. (2001) were used to determine the bearing capacity factors Sγ and Nγ for different footing shapes. Relaibilty of the results showed that these equations could be used for larger footings with using reduction factor for Nγ. It was found that the bearing capacity shape...
The Journal of The University of Duhok, Jul 20, 2017
A modification of an existing soil water retention curve (SWRC) equation is presented in this pap... more A modification of an existing soil water retention curve (SWRC) equation is presented in this paper which takes into consideration the effects of the soil capillarity (parameter a) and air entry value (s o). The reformulated equation then was incorporated into the research version of the LimitState:GEO software to perform two parametric studies on the bearing capacity of a strip footing placed on the surface and total passive earth pressure for a frictional wall of 1 m height. The parametric analyses were to study the effect of SWRC hysteresis on the strength of unsaturated soils through parameter a and air entry value (s o). The numerical bearing capacity and the passive earth pressure results were compared with the experimental data and the derived Rankine equations which take into account the effect of capillary rise, respectively. The numerical results showed that the effect of SWRC hysteresis has significant influence on the strength for both parametric studies.
ABSTRACT This paper reports an investigation into the effect of stress state and matric suction o... more ABSTRACT This paper reports an investigation into the effect of stress state and matric suction on the unsaturated shear strength of a fine sand using a modified direct shear apparatus. The direct shear apparatus was adapted to enable application of a specified suction to the sand sample using the hanging column technique (HCT). This also allowed monitoring of the water content of the sample and hence the average degree of saturation at different stages during the test. This additionally allows direct measurement of the soil water characteristic curve (SWCC) for the fine sand within the suction range of 0 to 10 kPa. A modified effective stress equation is evaluated that accounts for applied stress, suction and degree of saturation and is calibrated against the experimental results. Somewhat unexpectedly the shear strength of the unsaturated sand was significantly affected by the degree of saturation far in excess of what would have been expected by simple account of suction and saturation used in the modified effective stress equation.
Advanced Materials Research
The stress paths to which specimens are subjected in triaxial tests together with the yield surfa... more The stress paths to which specimens are subjected in triaxial tests together with the yield surfaces, which may be exercised in different models of such a test are simulated. A laboratory testing on undisturbed clay soil samples was performed in order to characterize the stress-strain behaviour of the residual soils in Sao Paulo sedimentary deposit. The sample is tested under isotropically consolidated drained triaxial compression. Strain controlled procedure was used to simulate stress-strain relationships of the soil. Seven models are used; namely: linear elastic, Duncan-Chang hyperbolic, Mohr-Coulomb, Cam clay, modified Cam clay, new Mohr-Coulomb and Cap model. It was concluded that the results of Cam clay and Duncan Chang models are the closest to the experimental data under low confining pressures; 49 and 98 kPa. Both models exhibit parabolic stress-strain relationships while the linear elastic model results are far away from experimental ones especially at large stress levels....
Constitutive models for soil are typically based on the same mathematical plasticity theory frame... more Constitutive models for soil are typically based on the same mathematical plasticity theory framework used to model common metals. However, the constitutive behaviour of soil differs from that of metals in different ways. The soil used in this paper was selected from the work of Azevedo et al. (2002). The work dealt with 2D finite element analysis of a shallow tunnel in the city of S˜ao Paulo, Brazil, through residual soils. The tunnel, approximately 103 m long, has a maximum width of 11.4 m. The thickness of the soil cover above the tunnel crown was 7.6 m. The support system consisted of a 0.20 m-thick primary shotcrete and a 0.15 m-thick secondary shotcrete liner. Three stages of excavation process were taken into consideration to simulate the actual behaviour of the tunnel during the excavation. In each stage, five increments are included. Numerical simulation of excavations is performed by releasing equivalent nodal forces defined by the in situ soil stresses existing along the ...
Acta Montanistica Slovaca
There are many factors that govern the expansion behavior of soil. The primary factors are a chan... more There are many factors that govern the expansion behavior of soil. The primary factors are a change in water content and the amount and type of clay size particles in the soil. Other important factors affecting the expansion behavior include the type of soil (natural or fill), condition of the soil in terms of dry density and moisture content, magnitude of the surcharge pressure, and amount of no expansive material such as gravel or cobble size particles. In this paper, a swelling soil from the site Hamamuk earth dam, which is located in Koya town north of Iraq, is treated by four types of additives; cement, steel fibers, gasoline fuel and injection by cement grout. The treatment of the expansive soil with 5 % of cement or steel fibers or the injection with cement grout revealed a better improvement while 4 % of gasoline oil is sufficient to reveal the optimum treatment by this material. The angle of internal friction is not affected by the treatment while the cohesion between particles is slightly affected by these additives due to a change in the adhesion between the additive and soil particles.