Date of Award

May 2019

Degree Type


Degree Name

Doctor of Philosophy



First Advisor

Habib Tabatabai

Committee Members

Hani Titi, Adeep Rahman, Konstantin Sobolev, Matthew Petering


Approach slabs, Bridges, Downdrag, Maintenance problems, Piles, Soil settlement


The roughness of the transition between the bridge and the roadway is a well-known issue that affects roughly 25% of the bridges in the United States. As soil underneath the approach slab settles, deferential settlement develops between the bridge and the approaching roadway. This may negatively affect the ride quality for travelers and result in substantial long-term maintenance costs. Because of the differential settlement, bumps could develop at the ends of the bridge when abrupt changes in slope (exceeding 1/125) occurs.

This study was aimed at mitigating the formation of bumps at the ends of the bridge through a new design concept for the approach area. The proposed design takes advantage of settlement-reducing piles that would support various approach slab segments and control their settlement. These pile elements are intended to control the roughness of the transition such that acceptable slope changes develop between various segments of the approach slab and thus improve the performance of the approach slab system.

In this study, a comprehensive review of literature as well as a review of various state practices regarding the approach area was performed. A set of finite element models were developed and parametric studies were performed to evaluate the soil/approach slab settlement behind bridge abutments for various soil conditions, and to quantify the pile head settlement and load distribution along piles as a function of pile-soil parameters. It has been determined that the degree of compressibility the embankment and natural soils, length of the approach slab, height of the abutment, and height and side slope of the embankment influence the potential development of bumps at approaches to bridges.

Empirical relationships are developed that relate various soil parameters to the longitudinal soil deformation profile behind bridge abutments. Empirical relationships and design charts are also developed to estimate pile head settlement for piles that are used to control soil settlement under the approach slab. Ultimately, a set of recommendations and design procedures are provided regarding the use and design of multi-segment pile-supported approach slabs for control of differential settlement.