Modernized Resonant Column and Torsional Shearing Apparatus With Multipoint Contactless Displacement Detection System

Abstract

In this study, a modification of resonant column/torsional shearing (RC/TS) apparatus was proposed to perform a qualitative analysis of a noncohesive soil specimen vibration during RC tests. An additional multipoint displacement detection system was installed in the RC/TS WF8500 device. In the new measuring system, 48 mini-magnets are attached to the side surface of a cylindrical soil specimen, creating a regular grid of measuring points. Around 48 Hall sensors (Honeywell SS495A1) are used to measure changes in the magnetic field strength due to the movement of the corresponding magnets on the surface of the specimen subjected to dynamic torque. The Hall sensor generates an analog signal that is proportional to the change in the magnetic field. The measurements are collected with a newly developed data acquisition system that consists of a set of analog-to-digital converters and a set of ARM (Advanced RISC (Reduced Instruction Sets Computing) Machine) microcontrollers. The measurement system is controlled with a dedicated software, ControlRec, developed by the authors. The measurements are taken synchronically with and independently from the standard RC test procedure. The new measuring technique allows to observe displacements of the 48 points on the specimens’ surface with over 4 times higher sampling rate than in the original measuring system. As a result, additional effects related to the mechanical wave propagation through soil specimen were observed (local disturbances in distribution of vibration amplitudes or significant displacements near the bottom end of the specimen, which is assumed to be fixed in the standard RC/TS results analysis), that could not be identified using the standard equipment of the device.