Yida Zhang News

Yida Zhang’s CAREER award targets role of tiny grains in dam failures

Anonymous — Thu, 14 Sep 2023 21:15:05 +0000

Yida Zhang’s CAREER award targets role of tiny grains in dam failures Anonymous (not verified) Thu, 09/14/2023 - 15:15

Susan Glairon

Yida Zhang is deeply passionate about assessing the stability of dams, but his approach is unconventional. Rather than studying the large aging structures, his research zeroes in on the tiny sand grains beneath and surrounding them. He investigates how the grain size distribution evolves under stress and its potential to compromise the stability of dams, especially in cases of extreme weather events.

“In geotech, we design based on the properties of soils at the moment of construction,” says Zhang, an assistant professor in CU Boulder’s Department of Civil, Environmental and Architectural Engineering. “That’s the end of the story. We don’t ask how the material evolves and degrades over time.”

Zhang was recently granted a prestigious CAREER award, a $600,000, five-year grant from the National Science Foundation, to support his research, “Decoding the Grain Size Evolution of Granular Soils under High Stresses.” The CAREER program stands as NSF's highest honor in support of early-career faculty with the potential to serve as academic role models in research and education.

The funding enabled Zhang to establish his research group, the Multiphysical Geomechanics Lab, to pursue research on granular soils under extreme stresses and environmental loadings over extended time spans.

Rising dams, extreme weather
Amid the construction of increasingly taller dams and the escalating threat of extreme weather events, Zhang underscores the critical importance of his research. During construction, carefully controlled grain size distributions and construction protocols are utilized to achieve desirable geotechnical properties of the soil and to ensure mechanical and hydrological stability. However, the long-term effects of high stress, which can crush, degrade and erode the grains, are often overlooked, he says.

For example, one of the most common methods for safe, long-term storage of tailings, a mining waste consisting of crushed rocks and residual chemicals, is to construct tailings dams. Tailings first go through a hydrocyclone process to separate the coarse grains for dam construction. Then, the finer fraction, mixed with water, is stored upstream of the dam to prevent it from transforming into a dense, toxic mudflow. Crushed sand grains would substantially hinder dam drainage, which is crucial to swiftly evacuate water from behind the dam; draining the water reduces the risk of liquefaction in the event of an earthquake.

Zhang’s goal is to develop a numerical approach that leverages grain-size distribution data to inform the engineering designs of large critical geostructures. Engineers would be able to use this tool when designing tall dams, enabling them to anticipate how grain size will evolve under stress and how the factor of safety will change over time. Unlike current technology, this grain-sized informed approach will empower engineers to design dams with a safety margin exceeding the minimum requirements over the long run, effectively preventing failures arising from grain size shifts or soil breakage, he says.

Education components
The project also includes educational tools designed to illustrate to high school students the ways in which civil engineers address climate change and to make civil engineering topics more accessible. This initiative aims to counter the national decline in the recruitment of civil engineers and secure a steady supply of skilled geotechnical engineers into the workforce.

“We need to create a pipeline for the next generation of geotechnical engineers,” Zhang says. “Without a continuous influx of talent into this field, we risk a shortage of skilled professionals as we confront new challenges related to climate change.”

Furthermore, he plans to equip graduate students with toolkits for adapting geo-structures to climate change.

“No one wants the failure of critical dams or levees, recalling memories of Katrina and, more recently, the Brumadinho dam failure in Brazil,” Zhang said. “We want to design our dams and levees with better knowledge about the material response to extreme loading after it ages. We don’t want the dams to fail.”

Photo above: Hoover Dam. Photo credit: Susan Glairon

With the construction of increasingly taller dams, Geotechnical Engineering Assistant Professor Yida Zhang is concerned about the potential effects of soil grain breakage caused by pressure. He recently received a prestigious NSF CAREER award to fund his research on the evolution of grain sizes in dams.

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DOE Grant to Increase Safety of Nuclear Waste Storage

Anonymous — Fri, 16 Nov 2018 21:02:49 +0000

DOE Grant to Increase Safety of Nuclear Waste Storage Anonymous (not verified) Fri, 11/16/2018 - 14:02

Professors Yida Zhang and Yunping Xi from the Civil, Environmental and Architectural Engineering Department at the University of Colorado Boulder were awarded $789,000 from the Department of Energy for their research project “Time-Dependent THMC Properties and Microstructural Evolution of Damage Rocks in Excavation Damage Zone.” This research will contribute to increasing the safety of nuclear waste storage.

"Since the closure of the Yucca Mountain project, U.S. has been reevaluating all the options available for geological disposal of high-level nuclear wastes. This research will help accelerate this goal by evaluating the suitability of salt rock and claystone formations for long-term isolation of nuclear wastes,” said Zhang.

Nuclear energy is an efficient and greenhouse gas free method of electricity generation with one major issue: the waste from nuclear power plants is radioactive and potentially harmful. The current consensus is that the best potential solution for this high-level nuclear waste (HLW) is deep geological disposal.This would involve building a large repository deep underground in bedrock or inside a salt dome. This would allow the isolation of the nuclear waste until it is no longer hazardous. The U.S. Nuclear Regulatory Commission (NRC) requires that nuclear waste is isolated for 1 million years. Due to the massive time scale involved, engineers need to be very confident that their deep geological disposal repositories are stable and isolated from the outside environment. Due to the challenges in developing these repositories, none are currently in operation despite 50 years of research in multiple countries. For engineers to better control the uncertainties associated with million-year time scale, they need to improve their understanding of the coupled thermal-hydrological-mechanical-chemical (THCM) processes in relation to the evolving microstructures of the host rocks.

Figure 1: Left, schematic of excavation damage zone; right, the increase of permeability near the excavation.

The stress state of host rocks are deeply perturbed by the construction of an underground opening, creating a region known as the excavation damage zone (EDZ). EDZ’s include increased fracturing and fissuring parallel to the opening face of the rock. These cracks and holes can allow groundwater to flow into the repositories.The EDZ is dynamic and variable. It’s time dependent behavior is poorly understood, especially in a long-term sense. Zhang and Xi will try to obtain a better understanding of the

Figure 2: Excavation damage zone

behavior of the EDZ as a function of post-closure time.

“We will use coupled thermo-hydro-mechanical tests to probe the creep behavior of these rocks in laboratory time scale (e.g. one month), then extrapolate the results to geological time scale (e.g. one million years) via multi-scale theoretical and numerical models to be developed in this project,” said Zhang.

Zhang is the lead PI of this project. His research with CU focuses on geotechnical engineering, including constitutive modeling of geomaterials interacting with environmental factors and micromechanics of granular materials. Xi focuses on structural engineering and materials science, including evaluation of nuclear power plants and containment structures. They are using their background in micromechanics of particles to gain a better understanding of the long term effects of deep excavation.

“We are extremely excited to get this project, to help shape the future of U.S. energy solutions and meanwhile minimize environmental impacts.”

Zhang and Xi will use their background in geomechanics to analyze EDZ behavior in salt and argalite, two materials with promising potential for deep geological disposal. While there are many other aspects involved with the behavior of EDZs, their research will help make nuclear energy a more safe and reliable option.

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