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:
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)
“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
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
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.
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, 6–8) . 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.
work on transportation resilience has been completed or is underway (4, 6, 7,
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
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
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|
|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.
|Index Terms:||Disaster resilience, Underground structures, Soil structure, Risk assessment, Disasters, Repairing, Underground construction, |
Maintenance and Preservation|
Security and Emergencies
Bridges and other structures