Papers by Henok Fikre Gebregziabher
Springer eBooks, 2021
Concrete lining and rock bolts are usually provided to support excavated tunnels on different gro... more Concrete lining and rock bolts are usually provided to support excavated tunnels on different ground conditions. These two support systems are worthy and need in-depth consideration as their impact on tunnel cost and deformation are critical. The optimum use of these support systems is a challenge that demands the best design solution. In order to facilitate the determination of the optimal combination of the two, an optimization scheme has been devised in this study using Finite Element Analysis (FEA) and MATLAB software for a specific under-construction tunnel in Karakore, Ethiopia. The tunnel displacements found from the FEA and the cost of tunnel construction were modeled using polynomial functions with a multi-objective optimization since the problem has two objectives. Considering displacement and cost functions, the optimum combination of rock bolt and concrete lining has been found. The result shows that the optimum combination can be found by increasing the number of rock bolts. The finite element analysis gives a total displacement of 6.34 cm in the best scenario case, which is slightly greater than the observed total displacement of about 6 cm. The total cost of rock bolt and concrete lining for the optimum combination becomes $30,700 per meter length of tunnel rock bolt and concrete lining construction.
Open Journal of Safety Science and Technology, 2021
This paper is concerned with the current tunnel practices in Ethiopia, the main challenges and ri... more This paper is concerned with the current tunnel practices in Ethiopia, the main challenges and risks which were associated with tunneling, risk assessment and controlling measures. In this paper the qualitative risk analysis is performed based on the surveyed data from the tunnel experts and other professionals participated on the tunneling work. The qualitative risk analysis has been conducted as an input for the risk matrix analysis method. The qualitative analysis incorporates risk identification, risk classification, risk ranking, risk responding and risk monitoring mechanism. So, based on the qualitative analysis made and the result, those risks which occurred in the tunneling phase are ranked and controlling mechanism is developed. Accordingly, a guideline of risk management for tunneling work has been developed by referring different standards and based on the current tunnel practices in Ethiopia. The study helps to easily understand the most risks which are associated with tunneling and the risk controlling mechanism. This gives guidance to those who will be participated in the tunnel project for tunneling risk management throughout the entire project implementation.
International Journal of Geotechnical Engineering, Aug 24, 2020
Raft rigidity is one of the governing factors that control the performance of piled rafts; it inf... more Raft rigidity is one of the governing factors that control the performance of piled rafts; it influences the interactions of the raft with the piles and the soil. By employing extensive three-dimensional Finite Element Analyses, the effects of raft stiffness on the absolute and differential settlements of piled rafts were investigated with the aim of achieving optimal design with limited number of piles. An appropriate constitutive model was applied to simulate the soil behavior, whose parameters were calibrated using pile load test measurements. While raft thickness is found to have minor effects on the settlements of piled rafts with closely spaced piles, a range of raft-soil stiffness ratios between 0.03 and 0.08 are found to minimize settlements for the case of widely spaced piles. Rigid rafts with raft-soil-stiffness ratios higher than 0.1 are recommended to be avoided for not enhancing the performance of the foundation.
GeoCongress 2012, Mar 29, 2012
In the last four decades Combined Pile-Raft Foundations (CPRF) have been successfully applied in ... more In the last four decades Combined Pile-Raft Foundations (CPRF) have been successfully applied in different parts of the world for optimizing foundations of civil engineering structures. This paper is an extension of the research works being carried out to widespread the concept further. A number of three-dimensional non linear finite element analyses on four-layered subsoil conditions of the West-African city Lagos have been carried out. Evaluation of the dominant parameters of CPRF, i.e., the settlements and pile-raft coefficient, have shown that the economical use of this system is dependent on the level of the applied load, configurations and length of piles as well as stiffness of the different soil layers. The parametric study shows that the application of CPRF is appropriate on semi-soft multi layered soils if the right combination of loading, material and geometric configurations is used. Some recommendations are given for such combinations of input parameters, enhancing the behavior of CPRF on semi-soft multi-layered soil conditions.
International Journal of Advanced Science and Engineering, 2021
This study aimed at assessing the static and dynamic slope stability of Ribb Zoned Earthen Dam th... more This study aimed at assessing the static and dynamic slope stability of Ribb Zoned Earthen Dam that is located in the earthquake prone areas of Ethiopia by employing finite element method using the shear strength reduction (SSR) technique of PLAXIS. The slope stability analyses were coupled with seepage analyses by considering different critical loading conditions. The peak ground acceleration (PGA) required as an input for the dynamic analyses of the dam were determined from a real accelerogram of an earthquake of magnitude 6.5 Richter scale recorded in 1845 around the dam, at epicenter distance of 175 km. Since the Ribb dam site and reservoir area lie in an earthquake sensitive zone of magnitudes 4.5 to 6.5, additional dynamic analyses have also been carried out corresponding to an earthquake of magnitude 4.5. The results of the coupled analyses using these two values of PGA showed that, the dam is stable at all critical conditions. Deformation analyses also showed that all displacements in the dam crest are within permissible limits.
Engineering
One of the major problems in ballasted railroads is ballast flying, which is the projection of ba... more One of the major problems in ballasted railroads is ballast flying, which is the projection of ballast particles from the at-rest position as the train passes over the track of a railway structure, mainly due to high speed. In this research, the possibility of railway ballast flying for the double track Addis-Adama section of the new Addis-Djibouti railway line is assessed by determining the major causes of ballast flying and applying Discrete Element Modeling (DEM) with the aid of Particle Flow Code (PFC3D) software. The analysis comprised of an impact load and ballast material behavior which were used to determine the vibrational speed of individual ballast particles. The governing result from the series of discrete element analyses performed by considering fouled ballast gradation with grain-size diameter of 22.4 mm gives rise to a ballast maximum vibrational speed of 0.014 m/s. Since the ballast vibrational speed for Addis Ababa-Adama line is less than 0.02 m/s that is recommended by the literature, no ballast flight is expected under the present traffic and ballast conditions.
Journal of Management Science & Engineering research, 2021
Expansive soils undergo high volume change due to cyclic swelling and shrinkage behavior during t... more Expansive soils undergo high volume change due to cyclic swelling and shrinkage behavior during the wet and dry seasons. Thus, such problematic soils should be completely avoided or properly treated when encountered as subgrade materials. In the present study, the biomedical waste incinerator ash and lime combination was proposed to stabilize expansive soil. Particle size analysis, Atterberg limits, free-swell, compaction, unconfined compression strength, and California bearing ratio tests were conducted on the natural soil and blended with 3%, 5%, 7%, 9%, and 11% biomedical waste incinerator ash (BWIA). The optimum content of BWIA was determined based on the free-swell test results. To further investigate the relative effectiveness of the stabilizer, 2% and 3% lime were also added to the optimum soil-BWIA mixture and UCS and CBR tests were also conducted. In addition, scanning electron microscopy (SEM) tests for representative stabilized samples were also conducted to examine the c...
Open Journal of Safety Science and Technology
This paper presents an effective means of analyzing the safety of a tunnel under dynamic loading ... more This paper presents an effective means of analyzing the safety of a tunnel under dynamic loading in areas with seismic records. A particular case of the railway tunnel in the earthquake-prone regions of the escarpment seismic zone of Ethiopia was the specific focus area of the research. Probabilistic seismic hazard analysis (PSHA) and deaggregation have been conducted to determine the design earthquake required as an input for the dynamic analysis. The PSHA performed by considering the operating design earthquake with conservative assumptions of the local geological features resulted in a peak ground acceleration of 0.36. Two pairs of design earthquake have been obtained from the deaggregation process, which were used to filter acceleration time histories for the selected design earthquake from the ground motion database of Pacific Earthquake Engineering Research Center. Finally, full dynamic analyses of the tunnel have been performed by applying the scaled acceleration time histori...
International Journal of Geotechnical Engineering
Raft rigidity is one of the governing factors that control the performance of piled rafts; it inf... more Raft rigidity is one of the governing factors that control the performance of piled rafts; it influences the interactions of the raft with the piles and the soil. By employing extensive three-dimen...
GeoCongress 2012, 2012
In the last four decades Combined Pile-Raft Foundations (CPRF) have been successfully applied in ... more In the last four decades Combined Pile-Raft Foundations (CPRF) have been successfully applied in different parts of the world for optimizing foundations of civil engineering structures. This paper is an extension of the research works being carried out to widespread the concept further. A number of three-dimensional non linear finite element analyses on four-layered subsoil conditions of the West-African city Lagos have been carried out. Evaluation of the dominant parameters of CPRF, i.e., the settlements and pile-raft coefficient, have shown that the economical use of this system is dependent on the level of the applied load, configurations and length of piles as well as stiffness of the different soil layers. The parametric study shows that the application of CPRF is appropriate on semi-soft multi layered soils if the right combination of loading, material and geometric configurations is used. Some recommendations are given for such combinations of input parameters, enhancing the behavior of CPRF on semi-soft multi-layered soil conditions.
Journal of Management Science and Engineering Research (JMSER), 2021
Expansive soils undergo high volume change due to cyclic swelling and
shrinkage behavior during t... more Expansive soils undergo high volume change due to cyclic swelling and
shrinkage behavior during the wet and dry seasons. Thus, such problematic soils should be completely avoided or properly treated when encountered as subgrade materials. In the present study, the biomedical waste incinerator ash and lime combination was proposed to stabilize expansive soil. Particle size analysis, Atterberg limits, free-swell, compaction, unconfined compression strength, and California bearing ratio tests were conducted on the natural soil and blended with 3%, 5%, 7%, 9%, and 11% biomedical waste incinerator ash (BWIA). The optimum content of BWIA was determined based on the free-swell test results. To further investigate the relative effectiveness of the stabilizer, 2%, and 3% lime were also added to the optimum soil-BWIA mixture and UCS and CBR tests were also conducted. In addition, scanning electron microscopy (SEM) tests for representative stabilized samples were also conducted to examine the changes in microfabrics and structural arrangements due to bonding. The addition of BWIA has a promising effect on the index properties and strength of the expansive soil. The strength of the expansive soil significantly increased when it was blended with the optimum content of BWIA amended by 2% and 3% lime.
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Papers by Henok Fikre Gebregziabher
shrinkage behavior during the wet and dry seasons. Thus, such problematic soils should be completely avoided or properly treated when encountered as subgrade materials. In the present study, the biomedical waste incinerator ash and lime combination was proposed to stabilize expansive soil. Particle size analysis, Atterberg limits, free-swell, compaction, unconfined compression strength, and California bearing ratio tests were conducted on the natural soil and blended with 3%, 5%, 7%, 9%, and 11% biomedical waste incinerator ash (BWIA). The optimum content of BWIA was determined based on the free-swell test results. To further investigate the relative effectiveness of the stabilizer, 2%, and 3% lime were also added to the optimum soil-BWIA mixture and UCS and CBR tests were also conducted. In addition, scanning electron microscopy (SEM) tests for representative stabilized samples were also conducted to examine the changes in microfabrics and structural arrangements due to bonding. The addition of BWIA has a promising effect on the index properties and strength of the expansive soil. The strength of the expansive soil significantly increased when it was blended with the optimum content of BWIA amended by 2% and 3% lime.
shrinkage behavior during the wet and dry seasons. Thus, such problematic soils should be completely avoided or properly treated when encountered as subgrade materials. In the present study, the biomedical waste incinerator ash and lime combination was proposed to stabilize expansive soil. Particle size analysis, Atterberg limits, free-swell, compaction, unconfined compression strength, and California bearing ratio tests were conducted on the natural soil and blended with 3%, 5%, 7%, 9%, and 11% biomedical waste incinerator ash (BWIA). The optimum content of BWIA was determined based on the free-swell test results. To further investigate the relative effectiveness of the stabilizer, 2%, and 3% lime were also added to the optimum soil-BWIA mixture and UCS and CBR tests were also conducted. In addition, scanning electron microscopy (SEM) tests for representative stabilized samples were also conducted to examine the changes in microfabrics and structural arrangements due to bonding. The addition of BWIA has a promising effect on the index properties and strength of the expansive soil. The strength of the expansive soil significantly increased when it was blended with the optimum content of BWIA amended by 2% and 3% lime.