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.