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Improving Buried Structure Resilience


The 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. Buried 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). Knowing 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. In 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 network’s reliability. ** **

Develop knowledge of how to improve buried structure’s (culvert and bridge size) resilience by identifying:

  1. Buried structure vulnerabilities;

  2. A buried structure’s risk;

  3. Buried structure resilience design guidance.


Transportation agencies will have knowledge of how to manage and improve the resilience of their buried structure assets. Benefits include:

  1. Fewer direct negative impacts from unexpected events such as loss of life, economic loss, or environmental damage.

  2. Lower maintenance costs as resilient buried structures are less vulnerable.

Related Research:

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 be considered.

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 implemented:

  1. A resilient buried structure AASHTO update
  2. 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
Research Priority:High
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.
Date Posted:01/03/2019
Date Modified:02/14/2020
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

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