This work investigates the thermal transient response of different soils when exposed to intense heat flux. A special porous media code, TOUGH2, is applied for numerical analyses. Improvements are made to previous experimental facilities, and new experimental results are used to characterize the heat and mass transfer physics in the soil and verify simulations. A two-zone structure exists for the coarse sand, namely a liquid zone on top and a two-phase zone at bottom. A large convection cell is developed within the liquid zone. A two-zone structure is also observed in the fine sand. However, at later times the soil begins to dry out, and develops a vapor zone below the two-phase zone. The lower permeability in the fine sand tends to suppress convection, increase pore water pressure and temperatures. Finally, a full scale tunnel simulation is conducted to provide insight into the application of soil response during tunnel fires.