Hesham El Naggar

Energy dissipation in engineered sand of large damping ratio

Many geotechnical problems such as seismic resistant designs and machine vibrations require the installation of dampers or isolators to control the amplitude of vibrations. Engineered fills designed with increased capability of dissipating energy can provide a more economical approach to control excessive vibrations. This study presents a novel technique to increase the damping ratio of sand without affecting its stiffness and shear strength. The increase in damping ratio is evaluated by performing resonant column tests on the engineered sand. The damping ratio of the sand is increased by adding a controlled amount of viscoelastic material to the voids. The resonant column tests indicate that the damping ratio of the sand can be increased manifold without affecting the shear modulus. The micromechanical evaluation of the results shows a good correlation between the particle surface area in contact with the pore-mixture and the damping ratio of the sand. The suitability of engineered sand as foundation material is also evaluated by performing direct shear tests. The direct shear tests on mixtures indicate similar or better shear strength parameters compared to pure sand.

Numerical Modeling of Soil and Surface Foundation Pressure Effects on Buried Box Culvert Behavior

AbstractBox culverts can be subjected to considerable induced earth pressure from overlaying structures and foundations. Therefore, the effect of surface foundations on soil pressures around box culverts needs to be properly investigated and incorporated into the analysis and design of culverts. In this study, the effect of a surface foundation on the response of box culverts was investigated experimentally and numerically. A series of centrifuge tests were performed to evaluate the additional soil pressures around box culverts installed in sand due to adjacent surface foundations. The experimental results were used to calibrate and verify a two-dimensional (2D) numerical model developed using computer software. This model was then used for a parametric study to investigate the effect of the relative foundation location on various aspects of the culvert response. The soil pressures, culvert bending moments, and soil-culvert interaction factors were all considered for different soil depths and surface foun...

Helical Screw Piles Performance - A Versatile Efficient Seismic Foundation Systems Alternative for Structures Rehabilitation, New Sustainable Structures Construction and Infrastructure Delivery

Helical screw anchors have been utilized in uplift forces applications for many years and they have gained popularity for bearing load, seismic performance and dynamic applications and evolved into Helical Screw Piles (HSPs). The speed and ease of their installation, as well as the low cost for new construction and repair, make them versatile for many rehabilitation or new construction applications and as an efficient alternative for deep foundations in infrastructure projects when it is suitable. The main objectives of this paper are to explore the available helical piles systems as well the performance of the helical pile foundation systems under monotonic and cyclic axial and lateral loads. In addition, to explore the new helical screw pile systems suitable for seismic retrofitting of existing foundations and for new structures construction; and to explore their design methodology. Among the helical piles configurations available the circular steel shaft helical piles and the square steel shaft helical piles. Among the different systems the fiber reinforced polymer grouted helical screw piles (FRP-G-HSP); and the reinforced grouted helical screw piles (RG-HSP) in which steel fibers were added to the grout. The research methodology involved conducting more than one hundred full scale field load tests on different instrumented helical piles configurations installed in layered soils profiles. The piles included plain helical screw piles (P-HSP); grouted helical screw piles (G-HSPs); FRP-G-HSPs; and RG-HSPs. The axial and the lateral monotonic and cyclic load tests will be presented as well the piles stiffness and the load transfer mechanisms together with the design theories criteria. The results of 3-D Plaxis finite element modeling were used to establish the load transfer mechanism and to validate the design methodology for the considered piles. Case studies for their applications will be presented.