Extreme Heat Geotechnics

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The sensitivity of structures to the insult of fire is well established and was stunningly demonstrated in the World Trade Center collapse. Fires in underground structures are not uncommon, and have led to unacceptable loss of life. The 1996 Channel Tunnel fire; the 2001 Howard St. (Baltimore) Tunnel; and the 1999 Mont Blanc road tunnel fire are recent examples of sustained, large-scale tunnel fires. As world populations continue to grow exponentially, and are concentrated in urban areas, public access highway and rail tunnels will become ever more common and essential links in urban transit networks. The impact of fire on these key transportation components and other underground spaces, however, has received relatively little civil engineering attention. The study of the effects of thermal loading on soil has been largely limited to soil response when subjected to the narrow temperature and heat flux ranges associated with climatic changes. Thermal loadings from a fire, in contrast, may be 50 to 100 times that of typical thermal loads from the sun. This intense thermal loading can result in dramatic temperature gradients within the soil, fluid phase change, moisture migration, increases in soil pore pressures, and both temporary and long term changes to mechanical properties of the soil. We propose to identify through experimentation, the whole system response, both transient and permanent, of saturated and unsaturated soil to prolonged, intense temperature gradients that accompany severe tunnel fire conditions, under stress conditions typical of shallow tunnels. That soil response is expected to impact the stability of the entire underground structure, both during and after a fire event. A realistic model of soil behavior will be developed that can be linked, in turn, to understanding and predicting soil-tunnel interaction during and after fires. This research represents a strong collaborative effort between students and faculty in the Civil Engineering and the Fire Protection Engineering Departments at the University of Maryland. This cross-disciplinary interaction will result in creative approaches and research findings that may not have been conceived otherwise. The work builds on an active NSF Small Grants for Exploratory Research (SGER) investigation, which began in June 2003. This research represents the first scientific work where non-uniform thermal transport has been experimentally investigated in three-phase porous media. A credible 1-D thermo-hydro-mechanical model will be developed based on the experimental measurements and observations. This model will be used to understand and predict soil-tunnel interaction during and after fires. From an education point of view, the research will expose graduate students to a cross-disciplinary research environment in an area of emerging importance, at the same time developing intellectual capital for engineering of key civil works, applying a broader approach to the problem. The PIs emphasis on recruiting student members of underrepresented groups because of the special opportunity this presents for role modeling and mentoring.