Volume 34, Issue 6 (November 2011)
An Evaluation of Real-Time Deformation Monitoring Using Motion Capture Instrumentation and Its Application in Monitoring Railway Foundations
ABSTRACT:The purpose of this study is to evaluate the use of motion capture instrumentation to monitor the response of a railway embankment and the underlying soft peat mire foundation soils to freight train loading. Initial data sets were obtained from the motion capture system, called the ShapeAccelArray (SAA, Measurand Inc.), installed in a railway embankment. Review of the data sets from the site installation raised questions as to the ability of the SAA to provide accurate displacement measurements. Testing of the SAA in the laboratory confirmed that the output from the SAA system (inclusive of software) would not provide a true measurement of horizontal deformations during large cyclic motions. This inaccuracy was due to the magnitude of acceleration associated with the cyclical motion on the microelectromechanical systems (MEMS) accelerometers and the effect of this on the ability of the system to determine its shape. A method for determining the magnitude of cyclic displacement from the output of the MEMS accelerometers was developed from the laboratory testing data. This involved the double integration of the change in acceleration measured by the accelerometers to obtain a change in displacement. This method was applied to the data sets obtained from the field installation to obtain a profile of cyclic displacement with depth.