Broader Impacts: The topic of expansive soils is not only compelling from a scientific perspective, but a social perspective as well.  The microscopic, particle-particle understanding of expansive soil behavior will help to predict the macroscopic shrink-swell behavior that causes an estimated $15 billion dollars in annual damage to infrastructure.  To initiate this improvement, students will be taught about the important role that geotechnical engineer’s play within our society to broaden their career path opportunities as well as increase, enhance and diversify our undergraduate civil engineering population.  This enhanced undergraduate student population will feed a more talented and diverse graduate student population which will produce a more educated workforce.  In time, this extensive network of civil engineers can dispel the poor public perception of engineers and increase their status in society. Similar to current practices and successes, the PI will focus on the recruitment and retention of women and minorities in order to enhance and diversify the engineering experience.

    Pile foundations are integral part of many civil engineering structures. The seismic behavior of pile foundations is a very complex problem with interactions between soils (solid skeleton, pore water, and pore air), piles, and superstructure. This complexity is further exacerbated when weak soils such as soft clays and liquefiable loose sands surround the pile foundation. The behavior of pile foundations in liquefiable sands has been studied extensively; however, similar investigations for neither soft clays nor seismic response of piles in improved soils have been rarely performed. The current seismic design practice calls for avoiding inelastic behavior of pile foundations by restricting their lateral displacements because it is difficult to detect damage to foundations following an earthquake. Limiting the lateral displacement of a pile foundation is relatively easy to achieve in competent soils. In case of weak soils, the current practice is to use an increased number of more ductile, larger diameter piles that are difficult to design and expensive to construct. An innovative, more cost‐efficient, solution to this problem is to improve the soil surrounding the pile foundation. For structures undergoing seismic retrofit with existing pile foundations in weak soils, improving the soils may be the only option to improve the seismic behavior of the foundation. This technique is not widely used in seismic regions due to lack of fundamental understanding of the behavior of improved and unimproved soils and the interactions between them as well as with the piles during earthquakes. As a first step in our long term objective of understanding and improving the seismic behavior of pile foundations in all weak soils we will focus on soft clays. Soft clays are quite prevalent in earthquake prone areas of U.S., but have received little attention from the research community.

    Following are some of the unanswered research questions that have to be addressed before ground improvement can be used as a viable option to enhance the seismic response of pile foundations in soft clays in routine design practice: (1) what are the effective techniques for improving soft clays around pile foundations for both seismic design and retrofit? (2) how can we analyze, simulate, and design pile foundations in soft clays with ground improvement for earthquake loads? (3) how do piles and pile groups, with and without ground improvement, behave during seismic events and how can we validate our analysis and simulation tools and designs? and (4) how can we translate our understanding into a useful design methodology to benefit the broader earthquake engineering community?

    The intellectual merit of this proposal is that we will systematically address the above given research questions using a multidisciplinary team consisting of structural and geotechnical engineers. We have engaged industrial partners who have extensive experience in ground improvement techniques and seismic design of pile foundations in preparation of this proposal. We will work closely with these partners throughout the project to translate our research into a useful design methodology and tools that will benefit the entire earthquake engineering community immediately as well as influence the long term practices. We will combine innovative centrifuge and full‐scale field tests using NEES facilities and equipment, simplified analysis methods, and sophisticated fully coupled simulation techniques to understand and improve the seismic behavior of pile foundations in soft clays. Simple analysis methods will serve the immediate needs of the industry while sophisticated simulation techniques are expected to show the limitations of the simple analysis methods and impact the long term industry practices.

    In addition to benefiting the earthquake engineering community, the broader impacts of the proposed project include the integration of the proposed research into education at K‐12 and undergraduate and graduate levels using the knowledge gained from innovative curriculum projects currently underway or already implemented. Our education plan includes a seismic design project that spans multiple courses for undergraduate and graduate students, a web‐based simulation competition for high school students, and an adventure scenario based learning module for middle and elementary school students. One of our partner institutions is a predominately undergraduate institution and we will be able to recruit undergraduate and graduate research assistants from a talented pool of students at this institution. We will also continue our tradition of recruiting and retaining underrepresented students in engineering.

Problem Statement

    Quite often, the result of this settlement manifests itself in the form of damage to the approach slab leading up to the bridge and/or abrupt displacements between transitions from pavement to slab or slab to bridge depending on the design. The bump and/or abrupt slope change poses a  danger to traffic and can cause increased dynamic loads on the bridge. Thus, frequent and costly   maintenance   is   needed   or   sometimes extensive   repair   and   reconstruction   may   be required in extreme cases.

Overview of Problem and Proposed Research

    In  older  bridges,  it  was  not  uncommon  to  see approach slabs without a mechanical connection to the    bridge,    which    resulted    in    an    abrupt displacement (bump) at the approach slab‐bridge interface   (joint).   This displacement  is  largely  related  to  the  fact  that abutments are pile supported and experience little settlement   while   the   approach   slab   rests   on abutment  backfill  and  embankment  soil  that  in turn  is  supported by  the  underlying foundation soil.  Thus,  the  problem  is  really  a  differential settlement problem resulting from compression of the soil strata below the approach slab. It is now relatively common for the approach slab to rest on  the edge of the abutment and be mechanically linked (via reinforcing steel) to the bridge slab.

    When settlement of the embankment and backfill occurs, rather than an abrupt displacement at the  joint,  the  unsupported  end  of  the  approach  slab  at  the  at  the  pavement  end  moves downward while the end supported by the bridge rotates. This scenario is representative of distresses observed recently for the Herford Lane Bridge over U.S. 69 in Pittsburg County, OK (Source, ODOT Materials Division). Interestingly, and of great concern, is that this bridge is relatively new having only been opened to traffic in October of 2008. Settlement at one end results in an overall rotation of the slab about a relatively fixed position on the abutment. In this case the abrupt displacement at the joint is minimized; however, if the settlement below the approach slab is significant a loss of support (void) may occur under the slab resulting in a structural failure (severe cracking or breaking) of the slab. Furthermore, while the abrupt displacement at the end of the bridge is minimized, the rapid change of roadway slope due to rotation of an approach slab may be unacceptable for safe flow of traffic and results in increased dynamic loads on the bridge from truck traffic. In either scenario, i.e. abutment‐supported or unsupported approach slab, significant maintenance and repair are often required.While differential settlement due to the compression of underlying soil strata is an obvious problem, there are many other factors that may cause or amplify the problem. Some other factors that may contribute to approach slab settlement include but are not limited to erosion of supporting soil (pavement layers and underlying fill), compaction of material immediately below the slab due to cyclic traffic loading, and lateral deformation of wing walls and loss of confinement in the abutment backfill. These problems may be exacerbated by poor drainage beneath the approach slab and in the backfill.

    The research proposed will critically investigate the design and construction methods employed in Oklahoma to determine causes and solutions to the bridge approach settlement problem. This will be accomplished through an extensive review of the literature to examine problems  and  solutions  employed by   other   state   departments   of transportation,  a  detailed  forensic analysis of bridge approaches in Oklahoma that have experienced these problems, and critical analysis of current design methods, specifications and inspection methods currently used in Oklahoma. Solutions that work in concert with current Oklahoma bridge design and construction practices will be presented, which may include suggested alterations to existing designs and modification of specifications and quality control methods to improve performance. In addition, more comprehensive and innovative approaches to designing the approach embankment‐abutment‐approach slab system will be presented.


Introduction

    Shallow slope failures in roadway cuts and on embankments are frequent problems along Oklahoma highways, and most other States for that matter; and they and represent a significant burden on maintenance budgets. Often these failures are associated with clayey soils having relatively high plasticity. Generally, during construction these soils have relatively high shear strength, a stiff consistency, and produce stable slopes. However, over time the soils experience cyclic wetting and drying resulting in a net increase in soil moisture content and corresponding decrease in shear strength. Eventually, the reduction in shear strength results in a slope failure usually triggered by a rainfall event. Exacerbating the problem are desiccation cracks that develop during extreme drying periods allowing water to penetrate the soil deeper and faster.

    The loss of shear strength in clayey soils due to wetting is associated with two inter-related phenomena. First, as the moisture content is increased the matric suction is reduced, which reduces the intergranular or effective stress in the soil. Decreasing effective stress equates to reduced shear strength. Second, as the moisture content increases the diffuse double layers surrounding clay particles expand and take on water with a corresponding increase in soil void ratio. Reduced dry density and increased water content results in softening and substantially lower shear strength. An additional consequence of wetting is that the driving mass of the soil increases with increased moisture content. Thus, while shearing resistance (or strength) is decreasing, imposed gravitational shearing stresses are increasing, further reducing the slope stability.

            Research is needed so engineers can better understand the problem, better predict shallow slope stability, and implement preventive measures if necessary. Proposed research will examine the mechanics of the soil in shallow slopes as related to matric suction changes, soil type, and expected degree of wetting. Research will involve studying at least two field cases where shallow slope instability has been a problem; at least one case will involve a cut slope section and one case will involve an embankment slope. Successful completion of this research will provide engineers with tools for improved analysis of shallow slope stability and recommendations for preventing landslides.

 Goals of Proposed Research

            There are three primary goals of the proposed research:

1)    To provide geotechnical engineers with a method for predicting stability of cut slopes and embankment slopes composed of unsaturated soil, incorporating soil moisture condition and suction into the analysis. The focus is on high plasticity clays for which these problems are most prevalent.

2)    To provide geotechnical engineers with methods for predicting changes in soil moisture conditions and suction in said slopes as a function of climate changes so that a proper “design moisture condition” can be selected. This will also all for predicting the slope stability over time based on predicted moisture content changes.

3)    To provide recommendations to minimize the climate impacts on slope stability including, as necessary, reducing adverse impacts of desiccation cracking in clayey materials.

    The University of Oklahoma (OU) College of Engineering (CoE) seeks to recruit and retain highly qualified and diverse graduate students to pursue degrees in transportation related engineering fields.  OU’s CoE has ongoing research projects within a variety of transportation issues that span the disciplines of Civil Engineering, Computer Science, Electrical and Computer Engineering, Industrial Engineering and Mechanical Engineering.  OU is poised to educate the next generation of transportation engineers to fill both Oklahoma’s and the United State’s critical need for qualified engineers to help our aging infrastructure.  The graduate students recruited to these programs will become Oklahoma Transportation Center Fellows, gaining significant experience in transportation research and industry.

    The CoE recruiting staff, in collaboration with transportation faculty, will indentify highly qualified graduate applicants from diverse backgrounds that have interest in transportation fields.  Not only will undergraduate students from our own institutions be aggressively targeted through a transportation engineering activity series in the existing ENGR 1410 Engineering Seminar and an undergraduate research program, but national societies will be used to find domestic applicants, including, American Indian Society of Engineering and Science, National Society of Black Engineers, Society of Hispanic Professional Engineers, and Society of Women Engineers.  OU has active chapters of each of these societies, and will use these as well as each society’s national conference to search for applicants. We will also utilize the Graduate Records Examination (GRE) score search to identify excellent students within our geographic location. 

    Top prospects for this program will be brought to our campus’s to tour lab spaces, meet prospective faculty advisors and other transportation faculty, and interact with current graduate students.  These interactions will be important in recruiting candidates because they will gain firsthand knowledge of the quality of our faculty, students, and research facilities. 

    OTC funding for this project will allow us to augment successful, existing undergraduate research programs at our institutions, support campus visitations for prospects, and provide a competitive level of financial support to graduate students.  This funding not only helps with the recruitment, but perhaps more importantly, the retention of prospects.  OTC supplemental funding combined with research funding will be a competitive recruitment and retention tool. 

    Recruiting three highly qualified diverse graduate students each year over three years, to pursue transportation research, will foster technological competitiveness in the future transportation workforce and set a standard for continued diverse student recruitment.  Complex transportation issues will demand that increased education in a variety of disciplines.   As the OTC and the OU College of Engineering put more resources into transportation projects and diversity, they will raise awareness not only in the state, but nationwide.