Teaching Documents by Sayed M Ahmed
CES 641 -Underground Structures /DEFORMATIONS AND BUILDING DAMAGES ASSOCIATED WITH TUNNELING
Deformation associated with tunneling 2017-2018
Papers by Sayed M Ahmed
E3S Web of Conferences
Uniaxial tensile and/or pull-out tests are performed to obtain the stress-strain curve of geogrid... more Uniaxial tensile and/or pull-out tests are performed to obtain the stress-strain curve of geogrids. The clamp lining in contact with a specimen in the uniaxial tensile test or the grit of a sandpaper clamp liner in a pull-out test affects the results. In this study, one geogrid made of polyester and another one made of high-density polyethylene (HDPE) are tested in the uniaxial tensile test using various clamps and in pull-out test using sandpapers of different grits. Based on the results obtained, it is recommended to test HDPE in uniaxial tests with serrated steel-lined clamps and in pull-out tests with sandpaper (grit 180) lined clamps. A polyester geogrid shall be tested in uniaxial tests with plastic-lined clamps and in pull-out tests with sandpaper (grit 400) lined clamps.
Research Square (Research Square), Aug 11, 2022
The potential of computing in education can be easily visualized by comparing manual calculations... more The potential of computing in education can be easily visualized by comparing manual calculations to using spreadsheets. The various bene ts range from easing repetitive tasks to visualizing data. It also grants the ability to explore without being hindered by heavy computational burdens. Programming is one computing tool that is mostly neglected in civil engineering education, where to the modern civil engineer computing may be viewed as only using commercially available software. But how can programming be used in a civil engineering class? This paper aims to answer this question by illustrating three different examples of programs written using python programming language to create impactful visualizations and engaging projects. Programming can be used in-class by educators to create visualizations and interactive sessions, or by students to train their algorithmic-thinking problem-solving skills. Though there are many barriers that obstruct implementing computing into civil engineering classes, they can be mitigated by using python.
20th International Conference on Soil Mechanics and Geotechnical Engineering, 2022
Assessing the load-deformation behavior is an essential aspect of geotechnical designs of shallow... more Assessing the load-deformation behavior is an essential aspect of geotechnical designs of shallow foundations, reasonably accurate estimates of the settlement of foundations under different loading conditions are crucial for highly compressible clays. Nevertheless, current design procedures, utilizing linear elasticity, cannot accurately predict soil deformations under loads as the stress-strain of soils is highly nonlinear, even under small loads. Thus, it is not uncommon to have significant differences between observed and estimated settlement values. In the presented study, a new procedure is proposed to estimate the nonlinear behavior of shallow foundations resting on soft to firm clays using in-situ seismic piezocone (SCPTu) testing. The parameters of the nonlinear behavior are assessed using the results of the SCPTu. Followingly, load-deformation of shallow foundations is determined. A well-documented case study is back analyzed to validate the procedure. A close agreement is shown between the predicted and observed load-deformation relationships, implying that the approach may be utilized.
Proceedings of the 2nd World Congress on Civil, Structural, and Environmental Engineering, 2017
The shear wave velocity VS is an essential parameter in various geotechnical analyses. It can be ... more The shear wave velocity VS is an essential parameter in various geotechnical analyses. It can be determined using laboratory testing of undisturbed samples, in-situ geophysical measurements, or by using correlations of the shear wave velocity with the common in-situ penetration tests such as the standard penetration tests (SPT) and the cone penetration test (CPT). The latter approach is often preferred by engineers for many reasons including cost optimization of the geotechnical investigations and infeasibility of undisturbed sampling in some formations such as non-cohesive soils. Accordingly, many correlations were envisaged to determine the shear wave velocity using the CPT; these correlations were developed through statistical and regression analyses of compiled CPT and shear wave velocity databases. Yet, to date, substantial discrepancies between the existing CPT correlations and the measured shear wave velocities are still revealed when the CPT correlations are compared with more recent case histories and databases. As such, there is a continuous need to update these correlations. In this study, a proposed approach is presented to define the stress-dependency parameters of the shear wave velocity in terms of the CPT measurements. Hence, enhanced CPT correlations for the shear wave velocity and the small strain modulus in both cohesionless and cohesive soils are realised. Two case studies are analysed using the proposed CPT correlation for the shear wave velocity as well as the commonly applied correlations. It is shown that the proposed CPT-VS correlation provides consistent predictions with the measured shear wave velocity; hence, it may be considered as an enhancement to the currently adopted methods.
Due to backfilling and surcharge pressures from the foundations of adjacent buildings, retaining ... more Due to backfilling and surcharge pressures from the foundations of adjacent buildings, retaining walls are built to withstand the ground pressure and lateral thrust. Expanded low stiffness polystyrene (EPS geofoam) panels mounted vertically against the rigid nonyielding retaining structures to minimize lateral earth pressure due to their compressible nature. Numerical models are being developed in the present study to validate the recorded physical test results for a rigid non-yielding wall (Ertugrul and Trandafir 2011). The results illustrate the effectiveness of EPS geofoam in controlling the lateral earth pressure as a material of inclusion behind retaining structures. A series of numerical analyses were performed using finite element program Plaxis 2D V8.5. Parametric analyses were adopted to demonstrate the effectiveness of the geofoam density and the thickness of the geofoam buffer in reducing the lateral earth pressure produced behind the retaining structures.
Undrained Shear Strength Assessment using Piezocone and Shear Wave Measurements
Proceedings of the Institution of Civil Engineers - Geotechnical Engineering, 2020
In this paper, a new approach is proposed to determine the undrained shear strength of intact cla... more In this paper, a new approach is proposed to determine the undrained shear strength of intact clays using the undrained rigidity index inferred from piezocones and shear wave velocity measurements ...
Assessment of Undrained Nonlinear Stiffness of Clays using Rigidity Index
Proceedings of the Institution of Civil Engineers - Geotechnical Engineering, 2020
Due consideration of non-linear soil stiffness is one of the essential requisites in many geotech... more Due consideration of non-linear soil stiffness is one of the essential requisites in many geotechnical applications. A considerable amount of the geotechnical literature, as well as numerous recent...
Proceedings of the 2nd World Congress on Civil, Structural, and Environmental Engineering, Apr 1, 2017
The shear wave velocity VS is an essential parameter in various geotechnical analyses. It can be ... more The shear wave velocity VS is an essential parameter in various geotechnical analyses. It can be determined using laboratory testing of undisturbed samples, in-situ geophysical measurements, or by using correlations of the shear wave velocity with the common in-situ penetration tests such as the standard penetration tests (SPT) and the cone penetration test (CPT). The latter approach is often preferred by engineers for many reasons including cost optimization of the geotechnical investigations and infeasibility of undisturbed sampling in some formations such as non-cohesive soils. Accordingly, many correlations were envisaged to determine the shear wave velocity using the CPT; these correlations were developed through statistical and regression analyses of compiled CPT and shear wave velocity databases. Yet, to date, substantial discrepancies between the existing CPT correlations and the measured shear wave velocities are still revealed when the CPT correlations are compared with more recent case histories and databases. As such, there is a continuous need to update these correlations. In this study, a proposed approach is presented to define the stress-dependency parameters of the shear wave velocity in terms of the CPT measurements. Hence, enhanced CPT correlations for the shear wave velocity and the small strain modulus in both cohesionless and cohesive soils are realised. Two case studies are analysed using the proposed CPT correlation for the shear wave velocity as well as the commonly applied correlations. It is shown that the proposed CPT-VS correlation provides consistent predictions with the measured shear wave velocity; hence, it may be considered as an enhancement to the currently adopted methods.
Proceedings of the 3rd World Congress on Civil, Structural, and Environmental Engineering, Apr 1, 2018
The consolidation test is one of the most common laboratory tests in geotechnical investigations.... more The consolidation test is one of the most common laboratory tests in geotechnical investigations. It is mainly utilized to assess the clay operative constrained modulus, which is an essential parameter in the settlement calculations of foundations and embankments. Recently, the non-linear numerical modelling has become more common than ever in geotechnical engineering. The state-of-art advanced geotechnical analyses focus on consideration of the nonlinear variation of soil moduli with the stress and strain levels. One of the fundamental quantities in advanced non-linear geotechnical analyses is the small strain shear modulus. It is obtained by measuring the shear wave velocity using special tests or amendments to traditional tests. Such tests and/or amendments are generally much less common and more expensive than consolidation tests. In this paper, the shear wave velocity and small strain shear modulus of soft to firm clays are evaluated from results of consolidation tests. The site-specific constants that relate the void ratio to the in-situ shear wave velocity is attained from the undisturbed virgin compression curve acquired from a consolidation test. The in-situ shear wave velocities and small strain shear moduli are concluded from the water content measurements. The proposed approach is validated by analysing two well-reported case studies; namely Ariake and Singapore clays. The results of the analyses show the viability of the proposed approach as the estimated moduli compare favourably with the values inferred from the field measurements.
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Teaching Documents by Sayed M Ahmed
Papers by Sayed M Ahmed
1. Factors affecting the deformations associated with deep excavations;
2. Assessment of the ground deformations outside the deep excavation using different approaches (viz., empirical/semi-empirical, numerical; analytical, physical modeling and ANN approaches);
3. Influence of the presence of buildings on the displacements;
4. Structural damage criteria;
5. Monitoring programs for deep excavation projects; &
6. Risk management and mitigation for deep excavation projects
In addition to the International studies presented in this state-of-the-art covering the abovementioned points, National experiences in assessments of the deformations induced by deep excavations, monitoring programs, risk assessment and risk mitigation are also highlighted.
The objects of the present study is to introduce a sophisticated three dimensional numerical model of the Bentonite Slurry Tunneling Machine by adapting the main factors affecting the pressurized Bentonite Slurry Tunneling such as unloading forces due to excavation, ground constitutive nonlinearity, interface condition, engineering properties of shield, rate of advance, machine overcutting, face pressure, yielding zones, the tail grouting and the hardening characteristics of the grout material. Soil constitutive behavior is represented using the hyperbolic elastoplastic model to account for the effect of the stress level, stress path and the confining pressure. Shield and tunnel lining elements are represented by elastic elements considering the different stiffness of the liner and the shield. The interface of the soil-shield and soil-lining is represented by a three dimensional hyperbolic gap element and grouting element with initial grouting stress. Special incremental technique is used to account for the variable mesh size due to excavation and lining erection using pseudo-time technique combined with Newton-Raphson iterative procedure. A nonlinear finite element program was developed and used to analyze the tunneling status in three giant projects, which are considered the foremost Bentonite Slurry tunneling projects in Egypt. The case studies are the Greater Cairo Metro-Line 2, El-Salam Syphon and the intersection of Al-Azhar Twin Road Tunnels and the CWO sewer.
Comparing the results of the developed numerical three-dimensional idealization of the Bentonite Slurry Tunneling with the field measurements compiled during the construction of the studied tunnels indicated the capability of such sophisticated modeling to develop realistic pattern of ground subsidence associated with tunneling. The results implied that, simulating the details of tunneling operation through the modeling formulation is considered as the basis for optimum idealization and is badly needed for realistic updating of the ground tunneling interaction. Furthermore, the three-dimensional tunneling analysis is considered as the entirely capable arrangement to simulate very sophisticated problems such as the intersection of multiple tunnels that cannot be preceded by means of two-dimensional analysis or empirical approach superposition. Consequently, the deformations and the internal forces developed in underground pipelines and sewers due to tunneling can be estimated. The results of the intersection of Al Azhar Road Tunnels and CWO sewer show that pre-excavation grouting proved to be a salutary process to control the deformation and the internal forces developed in underground structures due to tunneling. The results of the numerical modeling of the case studies are compared with the field measurements compiled during tunneling activities in order to assess the proposed numerical model.
frequencies and types. In most designs the interaction of nearby machine foundations is ignored, with the assumption of being far apart to minimize their cross effects. With no reliable analysis of machine foundation interaction, ignorance of interaction may lead to unsatisfactory results.
In this research the cross interaction of machine foundations is investigated using the finite element method (FEM). The soil is modeled as visco-elastic half space. The complex response method is adopted and the analysis is implemented in the frequency domain. A model of two square footings using three dimensional finite elements, loaded with vertical harmonic forces is analyzed to study the following factors:
1. The effect of loading parameters (angular velocity, amplitude and phase difference) and spacing on the interaction of surface footings.
2. The effect of the footing embedment for the case of embedded-surface footings and the case of embedded-embedded footings. The loading parameters are also considered for the two cases.
3. The effect of the soil depth to the underlain rock stratum on the interaction of adjacent footings.
4. The use of trenches to reduce the effect of adjacent footings' interaction.
Dimensionless curves have been developed for a mass ratio of 5.0 to account for the interaction of machine footings. The results show the importance of the interaction to get a satisfactory serviceability of machine foundation. The study also shows the effect of the loading characteristics, spacing, depth of compressible layer on the dynamic behaviour of adjacent footings. The following results were obtained:
1. The vibrations of surface footings may double in magnitude due to the interaction in case of applying forces with equal angular frequencies.
2. The load-vibration relation is linear in case of equal angular frequencies and non-linear for other cases.
3. The maximum out-of-phase vibration amplitudes are greater than the in-phase vibration amplitudes by a slight difference.
4. The vertical and the rocking vibrations are no longer uncoupled when considering the dynamic interaction of adjacent footing.
5. The embedment of the footings reduces the vibration if the two footings are equally embedded and may increase the vibration for the case of surface-embedded footings.
6. The vibration amplitudes decrease for cases of shallow depths of soil underlain by rock. In the same time, the dynamic response of the footings is not affected by the angular speed of the applied dynamic forces.
7. Trenches can be used to reduce the effect of machine foundation interaction with width greater than O.lB, depth greater than 2B and length greater than 3B, where B is the footing width.
From the results of this study, the interaction of machine foundations must be considered in design. Vibration reduction methods such as embedment and trenches, are investigated to obtain the optimum values of the parameters of each method.