Geotechnical group puts a spin on soils

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Shideh Dashti, John McCartney, and Richard Regueiro are pictured with the 400 g-ton centrifuge.
The 400 g-ton centrifuge is the geotechnical group’s major experimental workhorse.

You could call it Disaster Central. On any given day in the Engineering Center’s geotechnical labs, you’re likely to find students and faculty simulating an earthquake, an offshore tidal wave, an exploding land mine, or thermal and hydrological forces on soils powerful enough to crack a dam or tilt a foundation.

These activities attest to a thriving geotechnical engineering and geomechanics (GEGM) group, a faculty enclave in the civil, environmental, and architectural engineering department with a wide range of capabilities and accomplishments.

The most recent example of the group’s success is the Multidisciplinary University Research Initiative (MURI) on soil blast modeling and simulation, funded with a $7.2 million grant from the Department of Defense. After a final competition between 17 leading U.S. university groups, the grant was awarded last fall to Assistant Professor Richard Regueiro and team members Ronald Pak, John McCartney, and Stein Sture in the GEGM group.

The MURI is aimed at creating a more accurate representation of the impact of buried land mines and improvised explosive devices on light-armored military vehicles so they can be better designed to withstand blasts. The team will integrate advanced theoretical mechanics with fundamental experimental investigations using a 400 g-ton centrifuge to develop robust computer simulations of explosive blasts under challenging field conditions.

The 400 g-ton centrifuge is the geotechnical group’s major experimental workhorse. Developed in the late 1980s by Hon-Yim Ko, who is now professor emeritus, it remains one of the most powerful in the world with the capability of accelerating a 2-ton payload to a maximum of 200 g in about 14 minutes. In the centrifuge environment, scaled models can be used effectively to study how soil affects the earthquake response of a bridge or a tidal wave crashing on an ocean pier.

Assistant Professor Shideh Dashti, who joined the faculty last year, is planning a series of centrifuge experiments and numerical simulations to explore the impact of skyscrapers on underground transportation tunnels during earthquakes.

The initiative, funded by the National Science Foundation, will study the seismic response of temporary and permanent cut-and-cover box structures near mid- to high-rise buildings with the goal of producing well-calibrated predictive tools that more reliably characterize interactions between soil, foundations, and shallow underground structures during earthquakes.

A better understanding of these interactions will advance research and practice for a range of underground facilities and critical lifelines including tunnels, pipelines, and utilities, Dashti says. She also is collaborating with Assistant Professor John McCartney to study the impact of earthquakes on underground structures such as enclosed water reservoirs, with funding from the Los Angeles Department of Water and Power.

A long-standing theme of CU’s GEGM program is to incorporate the use of fundamental mechanics principles and computing power with experimental methods, according to Professor Ronald Pak, who has been active in research in dynamic soil-structure interaction, geotechnical earthquake engineering, and applied geomechanics at CU-Boulder for more than 27 years.

Pak also is director of the Engineering Science track in civil engineering at both the undergraduate and graduate levels. Sharing a similar vision with GEGM, the track has attracted applicants with superb analytical and computational backgrounds from both within and beyond civil engineering.

McCartney, a BS/MS graduate of the program who came back to join the faculty four years ago, particularly enjoys the breadth of activities. He specializes in the behavior of partially saturated soils and their interaction with civil infrastructure ranging from building foundations to pavements to landfills, and he is currently finalizing an NSF-supported project on the interaction of geothermal energy foundations with surrounding soils. Energy foundations are used to improve the efficiency of heat pumps for heating and cooling of buildings.

While drilling a deep geothermal well can be prohibitively expensive for some building applications, McCartney and his students have been testing the effectiveness of using holes already drilled for the building foundation to install heat exchangers, enabling the foundation to be used for multiple purposes. In addition to using centrifuge models to demonstrate the feasibility of this approach, they have incorporated geothermal energy foundations into a building recently constructed for the Denver Housing Authority.

McCartney also is collaborating with a colleague at the U.S. Air Force Academy to construct an entire building that can be used as a test facility for the long-term behavior of energy foundations, and he is incorporating the lessons learned from energy foundations into his NSF CAREER Award, which will investigate the application of heat exchangers in other geotechnical engineering systems.

Research efforts by professors Tad Pfeffer on glacier mechanics and climate change, Dobroslav Znidarcic on the consolidation of mine tailings, Bernard Amadei on rock mechanics and sustainability engineering, and Stein Sture on constitutive modeling round out one of the most diverse, yet disciplinary-strong, geotechnical engineering and geomechanics groups in the nation.

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