Monitoring of Soil Moisture and Groundwater Level Using Ultrasonic Waves to Predict Slope Failures

概要

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Field monitoring of soil moisture and groundwater levels is important to predict slope failures due to heavy rainfall. We have investigated a novel monitoring method using ultrasonic waves. The detector is composed of an ultrasonic transducer and a brass pipe whose lower end is inserted vertically into the ground. Ultrasonic waves generated by the transducer at the upper end of the pipe travel through it underground, and are reflected from the soil’s surface at the bottom of the pipe. The soil’s moisture is monitored by the intensity of the reflected ultrasonic waves and the groundwater level is monitored by the propagation time of the same waves. Indoor experiments were carried out using an artificial rainfall simulator and a soil tank. Shigaraki soil and Toyoura sand were used as soil samples in the experiments. The intensity of the reflected waves increased with the soil’s water content and changed dramatically depending on whether the soil was fully dry, wet, or fully saturated. The propagation time decreased as the groundwater level rose. This method has advantages in that the detector can easily be installed on the ground surface and can simultaneously monitor both the soil moisture and groundwater level.
2009-09-25