An Improved Apparatus for Testing the Friction Variation of Soil-Structure Interface Induced by One-Dimensional Vibration
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AbstractForced vibration of underground structures is a common activity during the construction or service period of rail infrastructure, such as vibro piling, the vibration of piles, and tunnel lining under moving train loads, etc. To better predict the structure’s performance under vibration, a lot of attention has been paid to investigating the behavior of interfaces between soils and structures. However, limited by the capabilities of the current test apparatus, the soil-structure interface friction is mainly determined under static and low-frequency cyclic loading conditions. While for dynamic conditions, the interface friction is generally configured as a reduction of the static friction coefficient. By now, the interface friction under vibration is not fully addressed, especially under high-frequency vibration. In this study, an apparatus is developed from a direct shear device to test the interface friction variation between soil and structure under vibration. Static and vibration forces are imposed on the structure to implement coupled monotonic shear and high-frequency vibration to the interface. The apparatus allows for the controlling of soil property, surface property of structure, normal stress, shear rate, and vibration intensity and frequency. The variation of shear stress and displacement, normal stress ,and displacement are mainly monitored. To show the capability and test procedure of the developed apparatus, dry sand and a smooth-steel plate are installed and tested on the apparatus with a vibration frequency 45 Hz and an acceleration of 0–0.15 g. The results show that the apparatus can stably obtain the friction weakening of the sand-steel interface, including the reduction of shear strength, volume change, and shear-displacement slip.
