1831
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
1
Implementation of LRFD Methods to Quantify Value of Site Characterization
Activities
Mise en œuvre des méthodes de conception LRFD pour quantifier la valeur des activités de
caractérisation du site
J.E. Loehr, J.J. Bowders, B.L. Rosenblad
University of Missouri, Columbia, Missouri, U.S.A.
R. Luna, N. Maerz, R.W. Stephenson
Missouri University of Science and Technology, Rolla, Missouri, U.S.A.
W.J. Likos
University of Wisconsin, Madison, Wisconsin, U.S.A.
L. Ge
National Taiwan University, Taipei, Taiwan
ABSTRACT: A comprehensive research program was recently completed to develop "state specific" LRFD guidelines for the
Missouri Department of Transportation in the United States of America (USA). The new guidelines implement improvements to
current AASHTO LRFD specifications that provide minimum national standards for design of transportation projects in the USA.
The most notable of these improvements are specification of resistance factors that are dependent upon the variability of input
parameters. One product of these improvements is to produce designs that more closely achieve target levels of reliability. Perhaps
more importantly, the guidelines provide designers with explicit means to quantify the potential value of site characterization
activities during the design phase. The latter outcome allows designers to make more rational decisions regarding the type and scope
of site characterization activities and provides quantitative support for such decisions so that designers can more effectively convey
the value of site characterization to others.
RÉSUMÉ : Un vaste programme de recherche a été récemment mené pour adapter des directives LRFD spécifiques au Département
des Transports du Missouri (USA). Les nouvelles recommandations apportent des améliorations aux normes actuelles nationales
AASHTO LRFD qui fournissent des normes minimales pour la conception de projets de transport aux Etats-Unis. La plus notable de
ces améliorations est la spécification de facteurs de résistance qui dépendent de la variabilité des paramètres d'entrée. Un résultat de
ces améliorations est de produire des modèles qui permettent d'atteindre un plus grand niveau de fiabilité. Peut-être plus important
encore, les directives fournissent aux concepteurs de moyens explicites pour quantifier le niveau de qualité des reconnaissances
géotechniques permettant de caractériser un site. Le dernier résultat permet aux concepteurs de prendre des décisions plus rationnelles
concernant le type et l’étendue des reconnaissances
du site et leur offre un outil quantitatif pour évaluer et transmettre plus
efficacement à d'autres la valeur de la qualité des investigations.
KEYWORDS: load and resistance factor design, geotechnical site characterization, variability, uncertainty.
1 INTRODUCTION
Current practice for geotechnical design of transportation
infrastructure in the U.S. utilizes load and resistance factor
design (LRFD) techniques. In these methods, load factors and
resistance factors are respectively applied to different load
effects and resistance components to produce designs intended
to achieve some established target probability of failure. A
national code developed by the American Association of State
Highway and Transportation Officials (AASHTO) serves as a
baseline for such design, but individual state transportation
agencies
are allowed to develop their own “state specific”
LRFD methods to reflect differences in design practices.
This paper describes characteristics of one such state-
specific code developed by the authors for the Missouri
Department of Transportation (MoDOT).
Unique features
implemented in the new MoDOT design guidelines include:
Resistance factors are explicitly selected based on
variability and uncertainty in input parameters, and
A practical technique to quantify uncertainty in design
parameters from lab and field measurements is provided.
Practice using the new MoDOT design guidelines is compared
to traditional design practice and current AASHTO practice.
Methods used for calibration of resistance factors are then
described followed by description of the procedure
recommended for quantifying variability and uncertainty from
laboratory or field measurements. Finally, an example is
provided to illustrate how the methods can be used to quantify
the value of potential site characterization activities.
2 SOURCES OF VARIABILITY AND UNCERTAINTY
Variability and uncertainty arise from a multitude of sources in
geotechnical design. However, these sources can be generalized
into three broad categories:
Variability and uncertainty in design input parameters,
Variability and uncertainty in design methods, and
Variability and uncertainty attributed to construction.
These sources are at times inter-related, especially for
empirically based design methods. Nevertheless, it is useful to
consider them as being separate because of the degree of
influence that designers have over the different sources.
Designers generally have the greatest, and most direct,
influence over variability and uncertainty in design parameters,
principally through affecting the scope of site characterization
activities. Designers can also affect variability and uncertainty
in design methods by selecting from among several alternative
Implementation of LRFD Methods to Quantify Value of Site Characterization
Activities
Mise en œuvre des méthodes de conception LRFD pour quantifier la valeur des activités de
caractérisation du site
Loehr J.E., Bowders J.J., Rosenblad B.L.
University of Missouri, Columbia, Mis ouri, U.S.A.
Luna R., Maerz N., Stephenson R.W.
Missouri University of Science and Tech ology, Rolla, Missouri, U.S.A.
Likos W.J.
University of Wisconsin, Madison, Wisconsin, U.S.A.
Ge L.
National Taiwan University, Taipei, Taiwan
