Geotechnical Resilience: It’s a Matter of Choice

Resilience requires informed decisions based on risk assessments that rely on the best knowledge, science and technology. It’s a choice engineers and society cannot ignore.

A Modern Tower of Babel?

Editor's note: This article originally appeared in the May/June 2019 issue of Geostrata, the official bi-monthly magazine of the Geo-Institute of ASCE.

 Resilience: This word was introduced to the engineering world more than 15 years ago as the most pressing challenge for research and practice in the earthquake field for decades to come. Since then, resilience has become a catchphrase that, under its placard, has initiated major efforts for the future of infrastructure and the communities served by them globally.

The abstract concept of resilience has evolved and stretched so much that today it seems to be an answer to anything and for anyone. A precarious suggestion by the pioneers who conceived the first engineering resilience framework, Bruneau and Reinhorn, is that resilience may have turned into a modern Tower of Babel, where the occupants talk without really understanding each other.

Defining its principles in measurable terms is the fundamental step in incorporating resilience in engineering practice. The National Academy of Engineering defines resilience as the ability to anticipate, prepare for, adapt to changed conditions, and withstand and rapidly recover from disasters. In this context, the global quest for resilience is competing against time, with the frequency and destructiveness of extreme events increasing with each passing year. Extreme natural events generated losses of more than 300 billion dollars in 2017 (67 percent more than 2016) and claimed 11,000 lives.

Scientific predictions of multihazard occurrence and climate change, combined with the state of our natural and urbanized environment, have elevated disasters to a matter of when and not if. Therefore, resilience is not a catchphrase — nor a trend that sounds good at water-cooler conversations. It’s making informed decisions based on risk assessments that rely on the best knowledge, science, and technology available, while optimizing funding allocation. Resilience is a choice that engineers and society cannot afford to ignore.

From Life-Safety to Life-Quality

Although engineering tools and knowledge have advanced, our civilization has not reached the technology paradise described by Nobel Laureate Hannes Alfven as a utopia where "no acts of God can be permitted, and everything happens according to the blueprints." The current blueprints, in the form of design codes, revolve around the concept of no loss of life immediately after an extreme event.

Yet as important as life safety is, society now expects even more. The major lesson learned in the aftermath of orgextreme events, especially in large urban centers — such as when Hurricane Sandy struck the New York metropolitan area in 2012 — is that life safety may be satisfied, but interruption of services can also have detrimental financial and downtime effects. The new frontier of long-term life quality, rather than life safety, represents social needs of resilience as not a "bouncing back," but rather a "bouncing forward" strategy.

During the 2017 Puebla-Morelos earthquake in Mexico, some 200 people ran into the iconic Torre Mayor skyscraper rather than outside, as the building has proven to be resilient following past earthquakes and large winds during its 14-year life.

The factor of downtime and a community’s ability to maintain functionality and vital services in the face of stresses and shocks is directly linked as a fundamental resilience quantifier of life quality immediately after a disaster and long-term on a community level. To this end, preparedness measures of incremental retrofit and planning, based on decided priorities, is key.

The Role of Geotechnical Engineers

When urban environments are impacted by disasters, some of the first necessities involve geotechnical aspects of individual or distributed grid projects, such as infrastructure. The potential direct impacts are on life, economic growth, and viability.

Geotechnical engineers can and should be in the forefront of developing resilience-based frameworks (RBF) for design toward decision-making. When integrated with innovative tools and documented past cases of success and failures, these frameworks can support the demands of future cities and safely sustain existing communities.

Leadership in the path to resilience is an organic evolution of geotechnical engineering as, by nature, geo-problems require innovation and resourcefulness combined with engineering judgement based on past experience. Geoprofessionals deal with decision-making in daily practice, addressing uncertainties in the properties and accuracy of empirical methodologies through performance quantifiers for varying loading conditions, rather than prescriptive factor-of-safety type of approaches. Successful performance of geo-designs during extreme natural events is living proof of the value of a philosophy that targets resilient performance, enhancing the confidence of the stakeholders and the public on the engineering and technologies used.

Geotechnical resilience principles can be conceptualized through the established four R’s for engineering resilience of physical and social systems:

  • Robustness: Inherent strength to withstand demands without degradation or function loss
  • Redundancy: Properties that allow for alternate options and substitutions under stress
  • Resourcefulness: Capacity to mobilize resources and services needed in emergencies
  • Rapidity: Speed to overcome disruption and restore safety, services, and financial stability

Applying these principles to geotechnical applications within an RBF cannot be prescriptive, as the above qualities are project- and community-specific. Rather, an RBF should be a toolkit to guide engineers, clients, owners, planners, insurers, stakeholders, and the public in making economically viable decisions. When engineers support decision-making, they set goals and evaluate the risk of multiple and cascading hazards viewed through various resilience lenses. In this process, community response and long-term recovery after an extreme event can be approached by data mining with visualization of future scenarios and tools for real-time instrumentation.

In practical terms, applied and tested solutions have demonstrated that resilience-based geo-designs pay off when an extreme event happens, or when multiple or cascading events occur. While seemingly these designs can appear the same as for working load conditions that satisfy a prescriptive factor, they are genuinely different in their ability to react to imposed stresses. As an analogy, think of identical twins who may look the same, but react very differently when exposed to a spreading disease.

Some geo-examples using an RBF include:

  • Incorporating sacrificial elements on the foundation system to accommodate large, ground-induced deformations
  • Daring to exploit soil yielding by allowing inelastic controlled behavior in the soil to reduce the demands transferred to the superstructure
  • Employing compliant retaining systems like mechanically stabilized earth walls instead of conventional pile walls and rigid abutment walls that can react by mobilizing soil strength before transferring stresses in the reinforced elements, providing redundancy and preparedness for the next event
  • Using protective systems like energy-absorption devices and smart materials
  • Implementing ground-reinforcement techniques that improve the soil and provide better distribute deformations and control drainage
  • Balancing rapid restoration solutions with future-ready designs, which facilitates working with nature rather than against it.

Several of these examples trace back to a fundamental understanding of physics and allowing engineering ingenuity to prevail. For example, Newmark’s design of the Trans-Alaska pipeline in the 1970s included a double-pipe solution, with the outer pipe being sacrificial for large deformations. This design allowed continued functionality of the inner pipe even after the pipeline was exposed to the effects of several large earthquakes and liquefaction-induced deformations. In Christchurch, New Zealand, more than four decades later, O’Rourke and his team addressed resilience goals by developing smart pipeline joints to accommodate ground deformations.

More vividly, during the 2017 Puebla-Morelos earthquake in Mexico, some 200 people ran into the iconic Torre Mayor skyscraper rather than outside, as the building has proven to be resilient following past earthquakes and large winds during its 14-year life. The structure’s use of innovative protective systems, combined with the deformation-compliant behavior of the four-level slurry wall basement constructed in the heart of the soft, lacustrine soil deposits, has paid off in the public’s conscience.

Resiliency Is a Choice

The incentive to invest in resilience measures before a disaster strikes is simple: it works. Worldwide data have shown that in a 50-year window, incremental measures to resist hazards can increase life quality by up to 40 percent. In the U.S., federal disaster-mitigation grants produce an average of $6 in societal savings for every dollar spent.

Geoprofessionals have the choice and social responsibility to consider resilience-based approaches in their designs. These not only satisfy life safety requirements, but also prevent hurricanes, earthquakes, wildfires, and other extreme events from becoming catastrophes.

The traditional alternative is no longer enough and is losing the race against time. In the resilience domain, geotechnical engineers have demonstrated leadership through proven innovation, and have a righteous seat at the table where frameworks and decisions are being made.

Read the article on the Geostrata web page.

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