Doctor of Philosophy
Civil and Environmental Engineering
El Naggar, M. Hesham
Large structures such as tall buildings, towers, and bridges transfer their loads to competent soil layers through pile skin friction and/or end bearing. When a pile is installed in a compressible soil layer, it may experience additional skin frictional force called “drag force” due to excessive soil settlement relative to the pile resulting from external loadings such as embankment construction. The location of maximum drag force, where skin friction is equal to zero or soil settlement and pile settlement become equal, is called the “neutral plane”. This thesis discusses the results of a comprehensive long-term field-monitoring program of three instrumented abutment piles and adjacent soil in order to evaluate the developed drag forces along the shafts of the three piles. The data collected from the field-monitoring program are presented and discussed in terms of measured responses with time, and load distribution along the pile shafts. In addition, the results were used to examine the unified design method and assess the design codes with respect to drag force. The findings indicated that the piles most likely behaved independently, and each experienced different magnitude of drag forces that extended to different elevations (i.e., neutral plane locations). A reasonable prediction of drag force can be achieved using the unified design method by considering the soil in the pile vicinity to be normally consolidated using both the total stress method (a) and effective stress method (b). The design of piles subject to drag force can be costly when following the AASHTO (2014), while the design following CHBDC (CSA 2006) and FHWA (2016) would result in safe and efficient design. Furthermore, the data were utilized to validate three-dimensional (3D) finite element models that were then employed to conduct a comprehensive parametric study to assess different aspects related to negative skin friction on single piles as well as group effects on drag force distribution among piles installed in small and large groups. The results revealed that the soil along the pile shaft moved with the pile and no soil plug was observed at the pile toe. Moreover, the analysis showed that the group effect might be neglected for piles installed in one row; however, it cannot be neglected for piles installed in large groups. Finally, design charts to calculate the toe resistance and group factor to calculate the drag force for a group of piles are presented in this study.
Summary for Lay Audience
Heavy structures such as towers, bridges, and tall buildings distribute their loads to strong soil layers via pile skin friction and/or end bearing. Due to excessive soil settlement relative to the pile caused by external loads such as embankment construction, a pile built in a compressible soil layer may experience additional skin frictional force known as "drag force". In this thesis, the outcomes of a long-term field-monitoring program of three instrumented bridge piles and surrounding soil are discussed. The program was carried out to assess the developed drag forces along the shafts of the three piles. The information gathered from the field-monitoring program is presented and discussed in terms of the load distribution along the pile shafts and measured responses with time. The information was utilized to calculate the magnitude of drag force for each of the three piles. The findings were also used to evaluate the design codes in terms of drag force and to look into the unified design technique. The results showed that, each pile is more likely behaved independently. By assuming that the soil near the pile is normally consolidated using both the total stress approach and the effective stress method, the unified design method may produce an acceptable prediction of the drag force. The design of piles subject to drag force can be costly when following some design codes. The collected data were used to validate three-dimensional (3D) finite element models that were then used to conduct a comprehensive parametric study. The results showed that the soil along the pile shaft moved along the pile. However, there was no plug found at the pile toe. Additionally, the research demonstrates that the group effect may be ignored for piles installed in a single line but not for piles installed in large groups. In this study's conclusion, design charts for calculating toe resistance and group factors for calculating drag forces for groups of piles are presented.
Drbe, Osama F. El Hadi, "Comprehensive Study of Induced Drag Force on Integral Abutment Piles" (2022). Electronic Thesis and Dissertation Repository. 8880.
Available for download on Wednesday, December 31, 2025