Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Civil and Environmental Engineering

Supervisor

Dr. M. Hesham El Naggar and Dr. Tim Newson

Abstract

Failures of box culverts under static and earthquake loads can cause significant economic loss. Therefore, it is important to investigate the soil-culvert interaction of box culverts to understand their responses to such loads. The response of buried box culverts is a complex soil-structure interaction problem, where the relative stiffness between the soil and the structure is a critical factor. Soil arching is an important aspect of the soil-culvert interaction problem, and results in the redistribution of free-field stresses due to the presence of buried structures and leads to an increase or decrease in the loading around box culverts.

A series of static and seismic scaled physical model centrifuge tests were performed to investigate the soil culvert interaction. Two different box culvert thicknesses and two Nevada sand relative densities were used to explore the interaction between the sand and box culverts under a wide range of different conditions. The static loading consisted of the soil self-weight of and the surcharge from a surface foundation, while the seismic loading considered the application of seven earthquake shaking events for each test. Several sensors were used in these tests, including tactile pressure sensors, LVDTs, accelerometers and strain gauges. A newly developed method for installing the strain gauges inside the box culvert model is introduced. The responses of the box culvert have been compared for all of the loading conditions.

It was observed that the kinematic soil culvert interaction due to the presence of a box culvert, as well as the surface foundation, had a significant effect on reducing the peak ground acceleration at the surface when compared to the free-field peak ground acceleration. The kinematic interaction can provide up to a 50% reduction and is dependent on the amplitude of the input motion at the base of the model. Small values for the rocking of the box culvert and surface foundation were also observed, and their values changed with the amplitude of the input motion. The values observed for the foundation were higher than those for the culvert, due to the soil confinement. The lateral movement of the foundations increased as the peak ground acceleration at the base of the model increased. The racking deformation ratio of the culvert was found to change with the thickness and therefore the relative stiffness of the culvert and the soil density.

Soil pressures measured by different methods were in good agreement and those obtained from the tactile sensors can be considered to bound the expected behaviours. The soil pressure observed on the culvert top slab had a parabolic shape, i.e., higher values at the edges and lower at the center than the theoretical vertical soil pressure. On the side wall, the horizontal soil pressure increased with depth. The soil-culvert interaction factors decreased at the center and increased at the edges of the top slab, as the thickness and the relative stiffness of the culvert decreased. The seismic analysis showed that the seismic bending moment increased as the peak ground acceleration at the model base and the relative stiffness of the culvert increased.

The static and seismic responses of the box culvert were analyzed using the finite difference code FLAC 2D and the results matched the experimental responses. The validated numerical model was then used to perform a parametric study, to evaluate the effects of: culvert geometric parameters, foundation locations and soil properties for the static loading and only the culvert geometric parameters for the seismic loading. The results have been evaluated for bending moment, soil pressure and soil culvert interaction factors. Based on these analyses, charts and equations are presented to help in assessing the design values of the static soil pressure, static bending moment, and the seismic bending moments around box culverts.

Keywords

Soil arching, Soil Culvert Interaction (SCI), box culvert, foundation, Nevada sand, centrifuge modeling, finite difference modeling, kinematic interaction, rocking of structures, racking of culverts, bending moment, soil pressure, soil-culvert interaction factors, geometry effect, foundation effect, soil properties.


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