This paper used finite element modeling to evaluate the consolidation effect on the performance o... more This paper used finite element modeling to evaluate the consolidation effect on the performance of existing rafts underpinned with micropiles under combined vertical and lateral loads. For this purpose, a real-life case study was discussed, in which micropile underpinning was used to stop the continuous tilt of a 13-floor residential building supported by a surface raft. It was found that the building tilted towards the northeast direction because of the consolidation of a deep soft clay layer under the northeast building corner. After discussing the as-built micropiling system, a 3D numerical model, developed using the PLAXIS software, was used to conduct the numerical research. The time-dependent behavior of the raft with and without the consideration of micropiles was assessed. Moreover, the variation of load-sharing ratios with time was investigated. The numerical results emphasize that the underpinning process was effective and reduced the final raft rotation and maximum settle...
This paper presents a real case study of a micropiling process that was developed to stop the con... more This paper presents a real case study of a micropiling process that was developed to stop the continuous tilting of a 9-story residential building in Dakahlia, Egypt. Shortly after the construction of the building, the surface raft foundation exhibited severe settlement problems. In order to carry out a geotechnical investigation, boreholes were drilled around the constructed building. It was discovered that in addition to a thick, soft clay layer in the soil profile, there was also a crucial eccentricity between the centroid of the total building loads and the centroid of the raft. The issue needed to be addressed immediately, and a micropiling system was proposed to satisfy the geotechnical and structural conditions associated with the case history. In addition to describing the field measurements, detailed methodology, and micropile installation process, this paper also presents three different design approaches for determining the number and location of the micropiles. Although ...
This article presents a comparative study of using three different kinds of biopolymers (xanthan ... more This article presents a comparative study of using three different kinds of biopolymers (xanthan gum, sodium alginate, and gelatin), environmentally friendly materials, in stabilizing collapsible soil. Modified Proctor, single oedometer, unconsolidated undrained triaxial, and California bearing ratio (CBR) tests were conducted to estimate the engineering characteristics of the soil after being mixed with various biopolymer contents. Biopolymer effect on the collapse index was investigated using different mixing conditions (dry mixing and wet mixing). Additionally, X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests were utilized to demonstrate the changes in the microstructure of the treated samples. The results showed that after mixing the soil with 4% xanthan gum content in the dry case, the collapse index decreased significantly from 13.48–1.27% and the cohesion stress increased from 47 to 144 kPa, resulting in the shear strength improvement. The results proved t...
The aim of this paper is to compare between results of the 2D finite element method (FEM) and res... more The aim of this paper is to compare between results of the 2D finite element method (FEM) and results of the 3D (FEM) when they are used to assess the factor of safety of clay slopes stabilized with vertical piles. It is expected that this comparison will aid engineers to judge and convert the results of the simplified 2D analysis to the more realistic results of the sophisticated 3D analysis that simulates the real behavior of slopes having infinite length. Extensive numerical modelling of homogeneous clay slopes stabilized with a row of piles and underlined by a bed of rock are carried out using the PLAXIS 2D program (version 8.2) and the PLAXIS 3D program (version 2010), which are both based on the shear strength reduction method to evaluate the factor of safety of the slope. The increase in factor of safety (FSI) of the stabilized clay slope is investigated considering many parameters, which include, the slope width, location of the piles, piles diameter, piles spacing and shear...
Biopolymers are natural polymers produced by living organisms and are considered environmentally ... more Biopolymers are natural polymers produced by living organisms and are considered environmentally friendly and sustainable materials; however, the physical properties of biopolymers widely vary for different biopolymer types and compositions. This study aims to evaluate the basic physical characteristics of biopolymer soil mixtures using three different biopolymers (xanthan gum, modified starch, and guar gum) and two types of soils. The two types of soils were selected to examine the effect of biopolymers on the behavior of cohesion and cohesionless soil mixtures. Soils were mixed with various concentrations of biopolymer solutions—over a range of (0.25 to 2 %)—and tested during scheduled curing periods (1–10 weeks). The study shows a remarkable improvement in shear resistance and permeability reduction for both types of soil. The results also indicate that the biopolymer-induced viscosity changes significantly affected the compaction characteristics of the mixtures. Regression equations were developed to predict the values of shear strength and permeability for biopolymer/soil mixtures with different concentrations under various curing times.
Journal of Geotechnical and Geoenvironmental Engineering, Feb 23, 2009
ABSTRACT An experimental and numerical study of the behavior of an eccentrically loaded strip foo... more ABSTRACT An experimental and numerical study of the behavior of an eccentrically loaded strip footing resting on geosynthetic-reinforced sand is presented. Particular attention was given to simulate footings constructed on unsymmetrical geogrid layers with eccentricity either direction of the footing. Several configurations of geogrid layers with different number, length, layer eccentricity along with the effect of the sand relative density, and the load eccentricity were investigated. A numerical study on a plane strain prototype footing was performed using finite element analysis. Test results indicate that the footing performance could be appreciably improved by the inclusion of layers of geogrid leading to an economic design of the footing. However, the efficiency of the sand-geogrid system is dependent on the load eccentricity ratio and reinforcement parameters. A close agreement between the experimental and numerical trend lines is observed. Based on the numerical and experimental results, critical values of the geogrid parameters for maximum reinforcing effect are established.
Journal of Geotechnical and Geoenvironmental Engineering, 2008
ABSTRACT An experimental study of the lateral behavior of vertical pile groups embedded in reinfo... more ABSTRACT An experimental study of the lateral behavior of vertical pile groups embedded in reinforced and nonreinforced sandy earth slopes was carried out. The model tests include studies of group configurations, pile spacing, embedment length of pile, relative densities of sand, and location of pile groups relative to the slope crest. Several configurations of geogrid reinforcement with different lengths, widths, and number of layers were used to reinforce a sandy slope of 1 (V): 1.5 (H). Pile groups of 2 x 2 and 3 x 3 along with center-to-center pile spacing of 2D, 3D, and 4.5D and piles with embedment length to diameter ratios of L/D = 12 and 22 were considered. Based on test results, geogrid parameters that give the maximum lateral capacity improvement are presented and discussed.
This paper used finite element modeling to evaluate the consolidation effect on the performance o... more This paper used finite element modeling to evaluate the consolidation effect on the performance of existing rafts underpinned with micropiles under combined vertical and lateral loads. For this purpose, a real-life case study was discussed, in which micropile underpinning was used to stop the continuous tilt of a 13-floor residential building supported by a surface raft. It was found that the building tilted towards the northeast direction because of the consolidation of a deep soft clay layer under the northeast building corner. After discussing the as-built micropiling system, a 3D numerical model, developed using the PLAXIS software, was used to conduct the numerical research. The time-dependent behavior of the raft with and without the consideration of micropiles was assessed. Moreover, the variation of load-sharing ratios with time was investigated. The numerical results emphasize that the underpinning process was effective and reduced the final raft rotation and maximum settle...
This paper presents a real case study of a micropiling process that was developed to stop the con... more This paper presents a real case study of a micropiling process that was developed to stop the continuous tilting of a 9-story residential building in Dakahlia, Egypt. Shortly after the construction of the building, the surface raft foundation exhibited severe settlement problems. In order to carry out a geotechnical investigation, boreholes were drilled around the constructed building. It was discovered that in addition to a thick, soft clay layer in the soil profile, there was also a crucial eccentricity between the centroid of the total building loads and the centroid of the raft. The issue needed to be addressed immediately, and a micropiling system was proposed to satisfy the geotechnical and structural conditions associated with the case history. In addition to describing the field measurements, detailed methodology, and micropile installation process, this paper also presents three different design approaches for determining the number and location of the micropiles. Although ...
This article presents a comparative study of using three different kinds of biopolymers (xanthan ... more This article presents a comparative study of using three different kinds of biopolymers (xanthan gum, sodium alginate, and gelatin), environmentally friendly materials, in stabilizing collapsible soil. Modified Proctor, single oedometer, unconsolidated undrained triaxial, and California bearing ratio (CBR) tests were conducted to estimate the engineering characteristics of the soil after being mixed with various biopolymer contents. Biopolymer effect on the collapse index was investigated using different mixing conditions (dry mixing and wet mixing). Additionally, X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests were utilized to demonstrate the changes in the microstructure of the treated samples. The results showed that after mixing the soil with 4% xanthan gum content in the dry case, the collapse index decreased significantly from 13.48–1.27% and the cohesion stress increased from 47 to 144 kPa, resulting in the shear strength improvement. The results proved t...
The aim of this paper is to compare between results of the 2D finite element method (FEM) and res... more The aim of this paper is to compare between results of the 2D finite element method (FEM) and results of the 3D (FEM) when they are used to assess the factor of safety of clay slopes stabilized with vertical piles. It is expected that this comparison will aid engineers to judge and convert the results of the simplified 2D analysis to the more realistic results of the sophisticated 3D analysis that simulates the real behavior of slopes having infinite length. Extensive numerical modelling of homogeneous clay slopes stabilized with a row of piles and underlined by a bed of rock are carried out using the PLAXIS 2D program (version 8.2) and the PLAXIS 3D program (version 2010), which are both based on the shear strength reduction method to evaluate the factor of safety of the slope. The increase in factor of safety (FSI) of the stabilized clay slope is investigated considering many parameters, which include, the slope width, location of the piles, piles diameter, piles spacing and shear...
Biopolymers are natural polymers produced by living organisms and are considered environmentally ... more Biopolymers are natural polymers produced by living organisms and are considered environmentally friendly and sustainable materials; however, the physical properties of biopolymers widely vary for different biopolymer types and compositions. This study aims to evaluate the basic physical characteristics of biopolymer soil mixtures using three different biopolymers (xanthan gum, modified starch, and guar gum) and two types of soils. The two types of soils were selected to examine the effect of biopolymers on the behavior of cohesion and cohesionless soil mixtures. Soils were mixed with various concentrations of biopolymer solutions—over a range of (0.25 to 2 %)—and tested during scheduled curing periods (1–10 weeks). The study shows a remarkable improvement in shear resistance and permeability reduction for both types of soil. The results also indicate that the biopolymer-induced viscosity changes significantly affected the compaction characteristics of the mixtures. Regression equations were developed to predict the values of shear strength and permeability for biopolymer/soil mixtures with different concentrations under various curing times.
Journal of Geotechnical and Geoenvironmental Engineering, Feb 23, 2009
ABSTRACT An experimental and numerical study of the behavior of an eccentrically loaded strip foo... more ABSTRACT An experimental and numerical study of the behavior of an eccentrically loaded strip footing resting on geosynthetic-reinforced sand is presented. Particular attention was given to simulate footings constructed on unsymmetrical geogrid layers with eccentricity either direction of the footing. Several configurations of geogrid layers with different number, length, layer eccentricity along with the effect of the sand relative density, and the load eccentricity were investigated. A numerical study on a plane strain prototype footing was performed using finite element analysis. Test results indicate that the footing performance could be appreciably improved by the inclusion of layers of geogrid leading to an economic design of the footing. However, the efficiency of the sand-geogrid system is dependent on the load eccentricity ratio and reinforcement parameters. A close agreement between the experimental and numerical trend lines is observed. Based on the numerical and experimental results, critical values of the geogrid parameters for maximum reinforcing effect are established.
Journal of Geotechnical and Geoenvironmental Engineering, 2008
ABSTRACT An experimental study of the lateral behavior of vertical pile groups embedded in reinfo... more ABSTRACT An experimental study of the lateral behavior of vertical pile groups embedded in reinforced and nonreinforced sandy earth slopes was carried out. The model tests include studies of group configurations, pile spacing, embedment length of pile, relative densities of sand, and location of pile groups relative to the slope crest. Several configurations of geogrid reinforcement with different lengths, widths, and number of layers were used to reinforce a sandy slope of 1 (V): 1.5 (H). Pile groups of 2 x 2 and 3 x 3 along with center-to-center pile spacing of 2D, 3D, and 4.5D and piles with embedment length to diameter ratios of L/D = 12 and 22 were considered. Based on test results, geogrid parameters that give the maximum lateral capacity improvement are presented and discussed.
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Papers by Mostafa Sawwaf