Uncovering the Secrets of Earthquake Safety, One Earthquake Simulation at a Time


The Soil Box system, photographed during the assembly phase. Credit: Eric Marks/UNR

To ensure that our buildings and infrastructure are earthquake resistant, we need to understand how seismic activity affects different structures. Miniature models and historical observations are helpful, but they only scratch the surface of understanding and quantifying such a powerful and profound geological event as a major earthquake.

Two major research efforts aim to fill the gaps and provide resources for researchers and engineers to study earthquakes at all scales, from seismic wave initiation to fault rupture site at depth, to interactions between the shaking ground and the individual structures on the surface.

The first effort is an experimental facility for real-world studies of how the soil around a structure influences its performance during an earthquake. The ground under our feet may feel solid, but vibrations can quickly make it unstable. This is because soils are composed of complex layers of rock and mineral particles of varying sizes with varying moisture levels that each respond differently to seismic activity. During an earthquake, the movements of buildings are dictated by the site-specific interactions between these soil layers and the direction and strength of the vibrations. Now nearing completion after more than five years of design and construction, the large-scale laminar floor box system will be the largest facility in the United States to study these interactions, and comparable in size to the largest in the world.

The facility is a collaboration between the University of Nevada, Reno (University) and Lawrence Berkeley National Laboratory (Berkeley Lab). It consists of a 350 ton capacity soil container mounted on a hydraulic base that can replicate shaking with a force of up to one and a quarter million pounds. The facility will open with a celebratory demonstration event at the University on September 15.

Studies conducted with the Soil Box System will provide data for the other effort, EQSIM: an ongoing collaboration between scientists at Berkeley Lab, Lawrence Livermore National Laboratory and the University to develop realistic and highly detailed using DOE supercomputers.

“These projects are synergistic. The Soil Box system helps us understand and refine the modeling of the complex interaction between soil and a structure. Our goal is to create realistic models of specific interactions – for example, what happens to a 20-story building to be built very close to the Hayward Fault in California during a large-magnitude earthquake? – and add them to our existing large-scale simulations,” said David McCallen, lead scientist in the field. of Earth and Environmental Sciences at Berkeley Lab and head of EQSIM. “We want to model all the way from the fault rupture through the ground to the structure to see how buildings and other infrastructure in an entire region will react.”

Credit: Lawrence Berkeley National Laboratory

A new path for real-world testing

The floor box project was started in 2015 to protect Department of Energy buildings that contain sensitive scientific instruments against any potential earthquake scenario. “This was driven by how little knowledge we had about how the soil surrounding a building’s foundation affects its performance during an earthquake,” said Ian Buckle, principal investigator of the Soil Box System, Foundation Professor in the Department of Civil and Environmental Engineering at the University. “For buildings on shallow foundations, there is probably not much effect. But for those with deeper foundations, such as nuclear facilities and long-span bridges, the answer may be much. .”

The design team, led by Buckle and fellow university professors Sherif Elfass and Patrick Laplace, designed and fabricated the system to have the largest soil container possible, so that representative structures could be placed on top. A management committee has been formed to help guide the team through this challenging project. Apart from those named above, the committee also included university professors Ramin Motamed and Raj Siddharthan.

Uncovering the Secrets of Earthquake Safety, One Earthquake Simulation at a Time

The Soil Box system, photographed during the assembly phase. Credit: David McCallen/Berkeley Lab

The 15-foot-tall, 21.5-foot-wide box rests on a 24-foot square shaking platform controlled by 16 hydraulic actuators. The soil container has 19 layers, called laminates, which are each supported by elastomer (rubber-like) bearings so that the soil layers can move relative to each other like soil does during earthquakes. real. The system can move and accelerate 350 tons of soil – and the structure above it – in two horizontal directions simultaneously with the same force as a strong earthquake, and is so powerful that designers had to incorporate shields for the prevent self-destruction during experiments. The hydraulics are controlled by custom software and the box is equipped with a suite of sensors so scientists can collect detailed data sets to feed their computer simulations.

“A floor box and shaker table of this size and complexity is not something you order from an online catalog. There are very few organizations or companies with the knowledge and expertise. expertise to do it, so we decided to do it ourselves with our own expertise and resources,” Buckle said. “This design not only allows us to work with large-scale structural models that can be placed on- above ground, but also the large scale makes it possible to model more realistic ground properties.”

Once operational, the facility will become a resource for DOE researchers focused on seismic safety as well as scientists from academia and industry. James McConnell, Associate Principal Deputy Administrator, DOE’s National Nuclear Security Administration, said, “It is important that DOE and NNSA invest in this work to ensure that the large, complex and unique facilities we are building are designed to protect the country’s research, defense and power generation needs, but the results have the added benefit of helping engineers and architects in industry and the private sector build a wide range of structures earthquake resistant.

Uncovering the Secrets of Earthquake Safety, One Earthquake Simulation at a Time

Diagram of the Soil Box system. Credit: David McCallen/Berkeley Lab

Leveraging a new generation of supercomputers

Current models of seismic properties rely on approximations and simplifications due, in part, to the lack of actual data on the fundamental physics involved, but also because very few computers on the planet are actually capable of running seismic simulations. with the precision required to perform infrastructure damage assessments. That’s why McCallen and his colleagues at EQSIM used the Summit supercomputer at Oak Ridge National Laboratory and the Perlmutter supercomputer at the Berkeley lab to develop very large, detailed models, like their simulations of the San Francisco Bay Area. Francisco for earthquakes from the M7 Hayward Fault, which has 391 billion pattern grid points.

They will also soon begin work on an even more capable platform: the new Frontier supercomputer, also at Oak Ridge. Frontier is the first computer system to break the exascale barrier, which means it is capable of computing at least one billion trillion (also known as quintillion, or 1018) operations per second, and is currently ranked as the most powerful supercomputer in the world.

Using these exceptionally fast machines, the team will be able to add new knowledge and information about soil response and soil-structure interaction obtained through Soil Box experiments into their existing large-scale models. The long-standing goal of structural failure modeling is now becoming a computational reality. Their simulations will then be made available to the public through the Pacific Earthquake Engineering Research (PEER) Open Access Simulation Database. PEER is a multi-institution research center focused on performance-based earthquake engineering, led by UC Berkeley.

“Part of our plan is to be able to enhance the available datasets of measured seismic motions with our very dense and highly detailed simulated motions and to make these motions available to the broad scientific and engineering communities. earthquakes,” explained McCallen, who is also the director of the University of Nevada, Reno’s Center for Civil Earthquake Engineering Research. “And so we will be collaborating with PEER, which has a long history and the infrastructure to provide open access to recorded seismic ground motions so that they can share them freely with the wider community for the benefit of all. Because not everyone has a Frontier session on their desk.”

Hayward Fault earthquake simulations increase ground motion fidelity

Provided by Lawrence Berkeley National Laboratory

Quote: Cracking the Secrets of Earthquake Safety, One Earthquake Simulation at a Time (September 15, 2022) Retrieved September 15, 2022 from https://phys.org/news/2022-09-secrets-earthquake-safety-simulation.html

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