Measurement of odor intensity in the ground of natural slopes with a history of landslide disasters

The smell of soil is one of the premonitory phenomena of debris flows. To clarify the relationship between landslide disasters and odors, we observed odor intensity in a ground with a history of debris flow disasters and investigated the relationship between odors and geotechnical characteristics of the soil. The odor intensity in the ground was measured at depths of 0–2.5 m on the slope of Mt. Gagara, Hiroshima University, which has a history of collapse owing to heavy rain. The method involves inserting an aluminum pipe and a Teflon tube into a hole with a diameter of 10 mm formed using a lightweight dynamic cone penetration test (LWDCPT) device and measuring the odor intensity of the sucked interstitial air using an odor measuring instrument. More than 100 odor intensities were measured at many points, which were considered recognizable without individual differences. To investigate the odor distribution in the ground, we measured the odor intensity at 19 locations within an area of 2 m × 2 m. The average odor intensity was 340 and the coefficient of variation was 0.60. This result shows that the odor distribution in the ground varied significantly. The odor in the ground was measured at depths of 30 and 50 cm on natural Masado slopes at eight locations in Hiroshima Prefecture. We observed that odor was not always present in all grounds. A weak but positive correlation was observed between the logarithm of the LWDCPT penetration resistance and odor intensity, and the relationship between odor intensity and ground constant was investigated at these eight locations. Although the odor intensity in the ground varied significantly depending on the location, a correlation between the pH and ignition loss was observed, which appeared to be linked to the activity of bacteria in the ground.