Hany El Naggar

Soil-Structure Interaction of Very Flexible Pipes: Centrifuge and Numerical Investigations

AbstractThe unprecedented increasing cost of steel coupled with the superior mechanical and anticorrosion properties of fiber-reinforced plastic (FRP) creates a huge opportunity for FRP pipes to take the market share of steel and be the pipe of choice for geotechnical engineers for a variety of applications ranging from potable-water systems to feed lines and penstock for hydroelectric power plants. Recently, very flexible large-diameter FRP pipes have been installed in eastern Canada and the United States to replace old wood-stave pipes to convey water to drive the turbines of small hydroelectric plants. The behavior of buried very flexible pipes is one of the complex soil-structure interaction (SSI) problems in geotechnical engineering and has not been studied thoroughly until now. The flexibility classification of pipes is determined based on their effective stiffness. Accordingly, flexible pipes will have an effective flexibility of 10 kPa/m or less. In this paper, the results of centrifuge modeling o...

Earth Pressure Reduction System Using Geogrid-Reinforced Platform Bridging for Buried Utilities

AbstractConstruction of new highway embankments in urban areas often requires building over existing underground utilities and lifelines. Embankments constructed over such utilities often induce substantial additional earth pressures causing overstressing and/or unacceptable deformations of the buried pipes, resulting in interruption of service for both the utility and highway. There are several techniques that can be used to mitigate this problem. Geogrid-reinforced bridge platforms are one of the newer techniques to deal with this problem. In order to gain a better understanding of the earth pressure reduction that may be achieved by geogrid bridging, the Ontario Ministry of Transportation (MTO) constructed an instrumented full-scale test embankment over a geogrid-reinforced bridged trench. In this paper, the results of this full-scale test along with a numerical study to evaluate the stress reductions achieved by the use of geogrid bridging platform installation are reported. In addition, results of a ...

Pressure Distribution around Rigid Culverts Considering Soil–Structure Interaction Effects

AbstractHeger pressure distributions are considered a fundamental tool in the design of RC culverts, according to the direct-design method. However, some factors known to affect soil–structure interaction are neglected when using Heger pressure distributions. These factors include the effect of the trench geometry, the relative stiffness of the existing soil to the backfill, and the burial depth of the structure. This paper presents a detailed finite-element analysis parametric study that investigates the accuracy and applicability of Heger pressure distributions for culverts in partial trench installations when the aforementioned factors are considered.

Numerical Study on Buckling of End-Bearing Piles in Soft Soil Subjected to Axial Loads

End bearing piles are commonly used as an efficient foundation system for supporting structures built on soft soils. Although, soft soils can provide some confinement to the pile not to be treated as an Euler column, the excessive large lateral movement may cause the soil to fail under axial loads before reaching the buckling load. Moreover, the buckling resistance of end bearing piles under loading–unloading conditions may be influenced since residual stresses in the structural elements of the piles and the surrounding soil exist even after removing the load. In addition, buckling of end bearing piles under extreme loading conditions of loading–unloading nature may result in residual stresses in the structural elements of the piles and the surrounding soil even after removing the load. In this paper, a 3-D numerical model utilizing the finite difference method was developed to study buckling behavior of end bearing piles. First the model’s calculated buckling load was verified against the theoretical solution for an idealized Euler’s case. Then, a comprehensive parametric study was performed to understand the effect of both the soil stiffness and the flexural stiffness of the pile on the behavior of buckled end bearing piles under both loading and unloading conditions. The results showed that both the lateral stiffness of the supporting soil as well as the flexural stiffness of the pile have a significant impact on the buckling length and hence the buckling load. The flexural stiffness of the pile should match (be relatively close) the stiffness of the soil in order to avoid high values of lateral displacement of the pile’s axis.