Effects of soil deformation and saturation on elastic wave velocities in relation to prediction of rain-induced landslides

Abstract The present means of physical landslide early warning systems make use of moisture sensors or slope deformations sensors. All such sensors are point sensors and are sensitive to variation of physical parameters in the vicinity of sensors only. A large number of sensors are therefore required to cover a wide potential landslide area. An idea to observe soil moisture changes and deformations in slope surface by means of elastic wave propagation in soil is proposed in this paper. Two series of triaxial experiments were conducted as part of this study. The first series of experiments explored the behavior of elastic wave propagation with varying soil moisture. In another series of experiments, soil specimens were subjected to the field stress path experienced by soil elements during rain-induced landslides. The response of elastic wave velocities during rain-induced landslides was envisaged in this test series. It was discovered that both shear, and compression wave velocities decrease by nearly half when soil saturation was increased from 20% to ~ 80%. From the field stress path tests, two distinct phases of rain-induced slope failures were identified. Large change in moisture content of soil was observed in the first phase of failure with the soil deformations being very small. Whereas in the second phase of failure large deformations occurred, with very small increase in moisture content of soil. Both shear, and compression wave velocities decreased gradually in the initial phase, whereas a rapid decrease was observed in the second phase of failure. By observing the change in wave velocities, time of failure initiation and post-failure strain rate could distinctly be identified. Such distinct variation of wave velocities during rain-induced slope failures can be helpful in designing a robust landslide prediction system.