Response of saturated soil to the intense heat of tunnel fires

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The sensitivity of structures to the effect of fire is well established and was stunningly demonstrated in the World Trade Center collapse of 9/11. Fires in underground structures are not uncommon, and appear to be increasing in frequency and severity. In prolonged tunnel fires, the temperature of the adjacent soil can rise as much as 400C or more. These high temperatures and associated temperature gradients in the soil are expected to impact the stability of the entire underground structure. The specific objective of this research program is to examine the response of saturated soil to temperature gradients associated with severe tunnel fires.This exploratory experimental research will address the system response of saturated soil subjected to prolonged, intense temperatures characteristic of public access rail and highway tunnel fires. It is supported under the Small Grants for Exploratory Research program. A physical model will be constructed that represents a simple one-dimensional cylindrical core from a section of the tunnel lining and the saturated soil above it. This model will be subjected to the fire loads expected in tunnel fires. It will be instrumented, and changes in the mechanical properties of the soil measured. This simple approach will provide a preliminary view of the temperature distribution, the thermally induced movement of water, vaporization of pore fluid, soil movement due to consolidation and to other pore fluid behavior, and changes in soil properties in response to representative insitu heat, fluid pressure, and surcharge conditions. More sophisticated model investigations to be initiated subsequent to this study will be based on these preliminary experimental results.From a technical point of view, this basic research ultimately will contribute to public safety through improved original design and remedial design of underground civil engineering structures that may be subject to intense and prolonged fire. In addition, it will generate a scientific discussion between distinct engineering disciplines: Geotechnical Engineering and Fire Protection Engineering.