Author(s): Haoyin Shan; Junke Guo; Jerry Shen; Zhaoding Xie; Oscar Suaznabar; Kornel Kerenyi
Linked Author(s): Junke Guo
Keywords: Cohesive soils; Erosion; Slaking; Direct force gauge
Abstract: An ex-situ scour testing device (ESTD) was built to study erosion in cohesive soils. It was intended to help understanding forces acting on soils. Such information was urgently required in bridge scour formulation. The lack of knowledge was due to unavailability of sensors capable capturing these forces. The device featured an innovative direct force gauge which could instantaneously measure shear and vertical forces on soil specimens. Specimens were mounted on the sensor disk of the force gauge. The servo-controlled force gauge provided counterforce of the hydrodynamic force acting on a soil specimen. This mechanism enabled a minimal movement of the soil specimen. The force gauge automatically elevated the soil specimen after a period of erosion so that the soil surface maintained flush with the channel bed. The ESTD used a moving belt and a pump propelling flow through a test channel underneath the belt. The channel was 58 cm long, 12 cm wide and 2 cm deep. The entire channel bed was roughened by gluing sandpapers with various p-grades. Particle image velocimetry identified several log-law velocity profiles in the test channel. Two cascaded filter cylinders enabled clear flow condition for observation. Different types of soil specimens containing artificial porcelain clay, silt and non-uniform sand at different water contents were tested in the ESTD. The specimens had a diameter of 63. 5 mm and a height of 20 mm. The soil specimens were de-aired to prevent slaking. The tested specimen was initially flush with the channel bed. In erosion test, the shear stress on a soil specimen was kept constant. The specimen was automatically elevated by the force gauge. The shear stress and soil mass during the test were recorded. The mass loss was used to calculate the erosion rate. The preliminary erosion results were presented. Geotechnical properties including shear strength, plastic limit, and liquid limit of the soil specimens were reported.