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Quantifying and Increasing the Resiliency of Buried Structures


The need for resilient infrastructure is increasingly evident. Over the last decade an increasing number of extreme climate events, shifts in weather patterns and rapid population growth have highlighted the vulnerability of the transportation network. Regardless of cause, the magnitude, frequency, and duration of extreme climate events like flooding, drought, wildfires, and rising sea levels is increasing throughout the United States and around the world. These extreme climate events have strained infrastructure systems ability to perform as intended and to satisfy the growing demand. For example, the Colorado Recovery and Resiliency Cooperative documented one such event:

Colorado experienced its costliest disaster in September 2013. The floods and accompanying debris flows, avulsions, and landslides caused more than $4 billion in damages to homes, businesses, roads, highways, and watersheds; 1,852 homes were destroyed over 28,000 dwellings were impacted; close to 500 miles of state and federal highways were closed; and tragically 10 lives were lost. This disaster highlighted the need to reexamine the Colorado’s vulnerability to hazards - particularly through floodplain, erosion zone, and debris flow mapping -- in order to better understand and reduce risk from future hazard events.(1)

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). 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). Additionally, FHWA’s “Synthesis of Approaches for Addressing Resilience in Project Development” has examined current and future weather-related hazard solutions and methodologies implementable by transportation agencies (4).

Though the public can reliably identify the need for resilience of the above-ground transportation system, agencies must consider all components of the transportation system including those assets below ground. Underground assets are a crucial part of a resilient transportation system, especially where transportation integrity is a critical lifeline to communities in the wake of natural disasters. The assets of transportation agencies include many buried structures, like pipes and culverts. Approximately 22% of the U.S. bridge inventory consists of buried structures, often classified as culverts or buried bridges. Smaller culverts not on the bridge inventory are commonly found every eighth to quarter of a mile on most roads in the U.S.(5). Defining and increasing the resiliency of buried structures is critical to proper asset management.

The risk and resiliency associated with buried structures is uniquely different from those associated with traditional bridge structures and pavements. For all parts of the transportation system, relevant considerations include the buried structure’s ability to persevere through extreme events (seismic, weather), unexpected events (overload, higher foundation settlement, failed design elements such as surface drainage), and expected events (durability). However, buried structures differ in behavior and resilience from those of traditional bridges; buried structures experience lower direct exposure to vehicular impacts, wind loads and wind-born debris while simultaneously experiencing greater hydraulic exposure and dependence upon soil-structure interaction.

Soil instability and other below-ground issues will often lead to various failures that undermine the resilience of the transportation network above. As an example, a washed-out culvert not only impacts the immediate watershed (a hydraulic failure), but also disrupts everyday business trade and private enterprise systems (a transportation failure) and potential evacuation and emergency routes (a societal life-safety failure). This level of disruption has the capability to cause devastating health, safety, and economic impacts on the local community.

Though buried structures may be exposed to unique risks, they also have the potential of providing resilience through the rapid repair of damaged structures. A resilient buried structure can survive extreme and unexpected events while minimizing loss of functionality and recovery time proportionate to the intensity of the events; i.e. structures should resist major component failures while accepting minor component failures requiring minimal recover time after the event. For example, a buried structure that experiences backfill wash-out but is quickly repairable is more resilient than to a structural failure requiring replacement and long-term road closure.

Resilience related concerns can take several forms. First, agencies desperately need methods for quantifying risk and resiliency for all aspects of the transportation system. Generally, risk and resilience are gaining priority and clarity due to both agency and academic effort (4, 68) . However, as already discussed, buried structures experience a unique set of risk and reliability issues. The risk assessment of existing buried structures in terms of resilience and in terms comparable with traditional bridges is an important aspect of the research need.

A second significant aspect of resilience is the identification of resilient solutions for new transportation expansion. AASHTO has historically outlined design standards which produce safe structures particularly for expected events. However, on occasion an in-service buried structure has experienced a performance failure due to an unexpected event. The AASHTO design standards need additional resilience related guidelines intended to minimize unexpected public disruption following extreme climate events and unexpected events, again, particularly for buried structures.

A third aspect of resilience is the development of responsive solutions for improving buried structure resiliency and post extreme event recovery. Engineers and agencies need best practices for improving buried structure resiliency and reducing risk.


This study aims to assess and improve on the appropriateness and sufficiency of existing guidance for resilient infrastructure design and its application to buried structures. This assessment will result in recommendations and enhancements to the existing guidance. The resulting report must provide tools for evaluating buried structure resiliency and risk, guidance on appropriate resiliency levels for a given site, solution selection and design guidance capable of creating the appropriate degree of resilience, and methods for improving resilience in existing buried structures.


The results of the research will allow transportation agencies to quantify the resiliency and risk associated with a significant, but under-appreciated portion of their transportation assets, that is, buried structures. Through resiliency-conscious retrofit and design decisions, the resiliency of the transportation system will increase, resulting in fewer disruptions to the public in terms of life safety, economic and environmental impact. Furthermore, improved resiliency will indirectly increase service life; resilient structures experiencing extreme and unexpected events early in their service life should be able to recover and continue functioning well for many years.

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.


Task 1: Risk and Resiliency Assessment. Develop a systematic way for owners to evaluate the resiliency and risk of a buried structure relative to extreme events such as weather, overload, and unexpected events such as higher foundation settlement and drainage failures. Assessments should correspond will with similar resiliency and risk assessments for above-ground transportation components.

Task 2: Risk and Resiliency Need. Develop specific design guidelines for how to evaluate the level of resilience required by a particular project.

Task 3: Resiliency Design Guidance. **Develop specific design guidelines for how to determine and improve the level of resilience for a particular solution.

Task 4: Resiliency Retrofit Guidance. Develop specific design guidelines and methods for improving resiliency in existing buried structures.


Develop a proposal to update AASHTO to incorporate task results.

Develop a resilience evaluation guideline for asset management.


The results of this research will be useful for transportation agencies seeking to understand and improve the resiliency of their transportation assets. The project is a much-needed supplement to existing resiliency efforts. Consultants, designers, and contractors will be able to use the resulting guidance to provide resilient buried structures as alternatives and supplements to less resilient alternative transportation solutions.

Sponsoring Committee:AFF70, Culverts, Buried Bridges, and Hydraulic Structures
Research Period:12 - 24 months
Research Priority:High
RNS Developer:Kevin Williams, Timothy A. Wood
Source Info:1. Colorado Water Conservation Board, and Colorado Geological Survey. Colorado Hazard Mapping. Publication SB15-245. Colorado Resiliency and Recovery Office of the Department of Local Affairs, 2017.
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.
Date Posted:01/03/2019
Date Modified:01/11/2019
Index Terms:Disaster resilience, Underground structures, Soil structure, Risk assessment, Disasters, Repairing, Underground construction,
Cosponsoring Committees: 
Maintenance and Preservation
Security and Emergencies
Bridges and other structures
Transportation (General)

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