Experimental study on physical properties of soft soil after high temperature exposure

The temperature effect induced by tunnel fire is important in geotechnical engineering. Due to the difficulties of extinguishing a fire in a tunnel, the fire duration time could be more than 120 min and after the heating the temperature of the soil around the tunnel could exceed 100 degrees C. However, the physical and mechanical properties of soils exposed to temperatures in the range of 100 degrees C to 200 degrees C have been rarely explored. A custom high temperature apparatus was developed for measuring soft clay specimens with variations of mass, moisture content, dimensions and temperature distributions exposed to high temperatures of 105 degrees C, 120 degrees C, 150 degrees C and 200 degrees C for 150 min and 240 min, respectively. These measurements are performed after high-temperature exposure, and the water in both liquid and vapor phases are allowed to escape the specimens when the pore pressure exceeds 100 kPa during the heating process. The results show that the volume change, saturation and dry density of the specitnens vary nonlinearly with the ambient temperature and are affected by the exposure time. The results also show that the variation of temperature within the specimen may be divided into four stages characterized by a rapid temperature rise stage followed by a plateau at 100 degrees C with another rapid temperature rise and a final plateau corresponding to the ambient temperature. Finally, novel changes in particle agglomeration and cluster shapes of the exposed samples were observed using a Scanning Electron Micro-scope. (C) 2016 Elsevier B.V. All rights reserved.