Improving Buried Structure Resilience
need for resilient infrastructure is increasingly evident as negative
impacts of unexpected events continue to highlight our transportation
network’s vulnerability. Resilience, “the
ability to prepare and plan for, absorb, recover from, or more successfully
adapt to actual or potential adverse events”, is a critical concept for
transportation asset management (2). Resilience design centers around eliminating or minimizing road
closure frequency and duration. Agencies across the country need
solutions to protect existing infrastructure and long-term transportation
investments by federal, state and local governments. In 2015, Congress
passed the Fixing America’s Surface Transportation (FAST) Act requiring
agencies to implement resiliency strategies as part of the transportation
planning process (3).
The FHWA has been developing knowledge to
help owners identify vulnerable assets (1) and better understand
weather-related hazards and implementable methodologies through projects such
as FHWA’s “Synthesis of Approaches for
Addressing Resilience in Project Development” (4). Additional
knowledge is being developed to better predict extreme weather events (9). Currently,
there is limited understanding of how to assess a buried structure’s risk
and design more resilient buried structures. Complimenting the FHWA’s work to
date with buried structure resilience knowledge is a crucial step in
improving our transportation network vulnerability.
structures, commonly referred to as culverts or buried bridges, are an integral part of our transportation
networks. Approximately 22% of the U.S. bridge inventory are buried
structures, and smaller culverts not listed in the bridge inventory are
commonly found every eighth to quarter of a mile on most roads in the U.S.(_5_).
Despite buried structures
being very common, limited knowledge exists for evaluating or intentionally
designing resilient buried structures. Examples of buried structure failure
that had significant impact were witnessed during Hurricanes Harvey in
Texas, Florence in North Carolina, and Michael in Florida and Georgia, as
well as, seismic, mudslide, and fire events in California and Alaska. These instances impacted the
immediate watershed, disrupted everyday business trade and private
enterprise systems, and affected evacuation and emergency routes.
The risk and resiliency
associated with buried structures is uniquely different from that of traditional
beam bridge structures, with the
fundamental difference being buried structures derive a significant portion
of their load carrying capacity from soil-structure interaction.
Soil-structure interaction provides natural resiliency to fire as well as
vehicle and seismic loads; buried structures can support tremendous loads.
However, a buried structure’s load carrying capacity is reduced if
soil-structure interaction is compromised through means such as soil loss, water submersion, seismic activity, structural
deterioration, or long-term consolidation. Hydraulic buried structures have
additional considerations such as maintaining hydraulic conveyance and recovering
quickly from debris blockages or soil/foundation deterioration.
A resilient buried structure should survive extreme events while minimizing loss of functionality and
recovery time proportionate to the intensity of the events. Structures should
resist major component failures while accepting minor component failures which
require minimal recovery time. Although not an AASHTO design requirement, buried structures may be
intelligently designed to minimize transportation vulnerability by preventing
damage or minimizing repair time. For example, a buried structure
which experiences soil damage but can be repaired quickly and more resilient
than a buried structure with a failed structural component, which typically
takes longer to repair (10).
how to evaluate and, when necessary, increase the resilience of buried
structure assets during design or rehabilitation is a crucial step towards
increasing a transportation network’s resilience. Knowledge of how buried
structures are potentially vulnerable to various unexpected events needs to
be understood. Particular emphasis on soil-structure interaction as well as
foundation vulnerability is needed in addition to understanding hydraulic
and structural vulnerabilities. Once vulnerabilities are understood, a means
to evaluate and determine the level of risk for a buried structure will be developed.
Design guidelines of how to improve a buried structure’s resilience will be developed. One such design approach is the use of “Stream
Simulation”, where the structure width is at least as wide as the bank-full
stream flow. Such designs have performed well in major storm events such
Hurricane Irene in Vermont. This methodology has been used or promoted by
the US Forest Service, Washington State Department of Fish and Wildlife
(WDFW), Penn State Center for Dirt and Gravel Road Studies, and the Maine
DOT, but may be applicable at a national level. AASHTO has historically
outlined design standards which produce safe structures exposed to expected
events but contains no guidance for the design of a ‘bend but do not break’
resilience design approach towards unexpected events. AASHTO would benefit from having
resilience related design guidance.
summary, buried structures are a critical component of transportation
networks but knowledge of how to design for and improve the resilience of
buried structures is lacking.
Developing knowledge of how to improve the resilience of buried
structures is an essential step towards improving our transportation
Develop knowledge of how to improve buried
structure’s (culvert and bridge size) resilience by identifying:
buried structure’s risk;
structure resilience design guidance.
agencies will have knowledge of how to manage and improve the resilience of
their buried structure assets. Benefits include:
Fewer direct negative
impacts from unexpected events such as loss of life, economic loss, or
costs as resilient buried structures are less vulnerable.
Much work on transportation resilience has
been completed or is underway (4, 6, 7, 9). However,
none of the efforts have considered the unique behaviors associated with buried
structures. Risk and resilience are also gaining priority
and clarity due to both agency and academic effort (4, 6–8).
NCHRP 15-61 is developing a design guide of
national scope to provide hydraulic engineers with the tools needed to amend
practice to account for climate change (9).
This work will help hydraulic engineers better predict sizing
requirements for hydraulic structures.
Means to increase the resilience of buried
structure during extreme hydraulic events such as intentionally designing
buried structures for soil loss are being developed (10).
Task 1, Identify Buried Structure Vulnerabilities: Identify how buried
structures may be vulnerable to various unexpected stressors such as extreme
hydraulic events, seismic events, vehicular overload, excessive foundation
settlement, loss of soil support, drainage failures, and debris blockages from
fires, mud slides, and flashfloods.
Unexpected deterioration of the foundation, structure, or supportive
backfill should be considered. The impact of construction methods should also
Task 2, Buried Structure Risk: Develop guidelines to evaluate the
resilience risk of an existing buried structure, and determine the target
resilience level of a buried structure.
Task 3, Buried
Structure Resilience Design Guidance: Develop design guidelines
which improve a buried structure’s resilience.
To meet the objectives the following should be
- A resilient
buried structure AASHTO update
- A buried structure module for the U.S.
Climate Resilience Toolkit.
FHWA has developed VAST to help owners identify vulnerable assets. Additional knowledge is being developed to better predict the impact of extreme weather events (9). Complimenting this work with buried structure resilience knowledge is a crucial step in improving our transportation network vulnerability.
|Sponsoring Committee:||AKB70, Culverts, Buried Bridges and Soil Structure Interaction
|Research Period:||12 - 24 months|
|RNS Developer:||Kevin Williams, Timothy A. Wood|
|Source Info:||1. United States Global Change Research Program (2019, February 27). U.S. Climate Resilience Toolkit. Retrieved from https://toolkit.climate.gov/ |
2. TRB Resilience: Key Products and Projects. Washington, D.C., Mar, 2018.
3. United State Congress. FAST Act. Pub. L. No. 114-94, 2015.
4. Choate, A., B. Dix, B. Rodehorst, A. Wong, W. Jaglom, J. Keller, J. Lennon, C. Dorney, R. Kuchibhotla, J. Mallela, S. Sadasivam, and S. Douglass. Synthesis of Approaches for Addressing Resilience in Project Development. Publication FHWA-HEP-17-082. Federal Highway Administration, Washington, D.C., 2017.
5. Hebeler, G. An Update of National Trends in Culvert Durability and Service Life. Columbus Ohio, Oct 27, 2015.
6. Filosa, G., A. Plovnick, L. Stahl, R. Miller, and D. Pickrell. Vulnerability Assessment and Adaptation Framework. Publication FHWA-HEP-18-020. Federal Highway Administration, Washington, D.C., 2017.
7. Flannery, A. Resilience in Transportation Planning, Engineering, Management, Policy, and Administration. Publication NCHRP Synthesis 20-05/Topic 48-13. National Cooperative Highway Research Program, Washington, D.C., 2016.
8. Lounis, Z., and T. McAllister. Risk-Based Decision Making for Sustainable and Resilient Infrastructure Systems. J. of Structural Engineering, Vol. 142, No. 9, 2016. https://doi.org/10.1061/(ASCE)ST.1943-541X.0001545.
9. Kilgore, R. Applying Climate Change Information to Hydrologic and Hydraulic Design of Transportation Infrastructure. Publication NCHRP 15-61. National Cooperative Highway Research Program, Washington, D.C., 2015.
10. Williams, K., MacKinnon, S., Spence, N. How Resilient are Buried Bridges in Extreme Hydraulic Events? 2018 Conference of the Transportation Association of Canada, Saskatoon, SK.
|Index Terms:||Disaster resilience, Underground structures, Soil structure, Risk assessment, Disasters, Repairing, Underground construction, |
|Cosponsoring Committees:||AKD30, Low-Volume Roads|
Maintenance and Preservation
Planning and Forecasting
Security and Emergencies
Bridges and other structures