How Resilient are Buried Bridges in Extreme Hydraulic Events?

Transportation agencies across the country are facing more frequent extreme hydraulic events which negatively impact and damage transportation networks. Transportation networks disrupted from more extreme hydraulic events could result in large repair costs, negative costs to the economy from disrupted travel, and expose the public to safety hazards. Agencies desire infrastructure which accommodate an agency’s limited financial and environmental resources, minimize disruption to the public, and can accommodate changes such as climate change impacts.

Buried bridges, commonly referred to as buried structures, are soil-structure bridges which derive their support from composite interaction between their structural bridge component and their surrounding soil. Buried bridges have spans up to 40 m and are found across Canada. Buried bridges have several accelerated bridge construction benefits such as an ability to be rapidly constructed, and installed costs 33% to 67% lower than traditional beam bridges.

The paper’s objective is to evaluate a buried bridge’s resilience to extreme hydraulic events and inform practitioners of best practices for designing and constructing buried bridges more resilient to extreme hydraulic events. Resilience is defined by the Federal Highway Administration as ‘the ability to anticipate, prepare for, and adapt to changing conditions and withstand, respond to, and recover rapidly from disruptions’ (Federal Highway Administration, January 2017). Climate change is increasing the frequency and severity of extreme hydraulic events. This increases the risk of public disruption from a buried bridge’s surrounding backfill being compromised through piping, washout, or scour.

The 2014 CHBDC outlines buried structure hydraulic design criteria and requires designers to prevent structure and embankment failure during predicted floods. The draft 2019 CHBDC enhances this criteria by requiring designers to consider resilience and minimize damage from unforeseen events. In other words, the CHBDC requires designers to prevent public disruption under predicted conditions and minimize public disruption from unforeseen events.

This paper will present best practices to design and evaluate a buried structure’s hydraulic design criteria such that it better satisfies the CHBDC’s current and future design requirements. A design approach which increases buried structure’s resilience against extreme hydraulic events is introduced. Findings of a desktop study evaluating how resilient various buried bridges are when their surrounding soil is piped, washed out, or scoured away are presented.