The objectives of this study are: (1) to compare data recorded with a recently developed in-place inclinometer–accelerometer system to data measured with other established instrumentation through full-scale laminar box tests and field test sites, and (2) to evaluate possible causes for discrepancies between the measured and theoretical soil settlement at a bridge replacement site on soft clay. The performance of the three-dimensional (3D) micro-electro-mechanical systems (MEMS)-based in-place inclinometer–accelerometer array is evaluated for monitoring the settlement and lateral spreading of a very soft, 30-m-deep clay deposit at a New York State Department of Transportation (NYSDOT) bridge realignment site. Brief design details are given of the developed instrumentation system, which utilizes MEMS devices to measure angles relative to gravity, in addition to signals proportional to acceleration. The estimated theoretical accuracy of the system-displacement measurement is assessed empirically using thousands of datasets from several long-term field installations. This new instrumentation system was also included in a full-scale laminar box test of a sloping saturated fine sand deposit. This full-scale test provides a means of evaluating measured acceleration data. In all cases, data recorded with the developed in-place inclinometer–accelerometer system is compared to data measured with state-of-the-practice instrumentation. These comparisons were extremely favorable and justified the future use of this instrumentation for many geotechnical applications. This study also includes an evaluation of commercially available geotechnical software settlement predictions as compared to measured data at the NYSDOT bridge realignment site. The results of this study indicate that the effectiveness of the prefabricated vertical drains (PVDs) is not constant throughout the monitoring period and that the changes in effectiveness cannot be captured in commercial software using a constant ch.