ShapeAccelArray Research Articles

The Use of Shape Accel Array for Deformation Monitoring and Parameter Inversion of a 300 m Ultrahigh Rockfill Dam

The global construction of rockfill dams has now surpassed the 300 m height level. Despite great achievements in dam design and construction, monitoring techniques have lagged behind the development of high rockfill dams. Existing deformation monitoring techniques are ill-suited to the high earth and water pressures, and extended monitoring periods are required for ultrahigh rockfill dams. This study introduces, for the first time, the use of a shape accel array (SAA) to monitor internal displacement in a 300 m high earth core rockfill dam. The SAA employs a rope-like array of capacitive MEMS accelerometers for deformation measurement. Compared to conventional monitoring techniques, SAA is a data-intensive monitoring technique. Based on the intensive data obtained from SAA, we employed a parameter inversion method, utilizing multiobjective optimization algorithm, the nondominated sorting genetic algorithm-III (NSGA-III), to inverse the constitutive model parameters of the rockfill dam. The multiobjective parameter inversion method maximizes the use of multisource monitoring data for predicting rockfill dam deformation.

Correlation of acoustic emissions with patterns of movement in an extremely slow-moving landslide at Peace River, Alberta, Canada

The Peace River region, Alberta, Canada, has experienced extensive landslide activity since deglaciation. Shear zones within weak lacustrine silt and clay layers typically experience continuous creep, damaging highway and utilities infrastructure. However, occasionally, movement accelerates and potentially catastrophic failures occur. Conventional deformation monitoring approaches provide incremental measurements with low temporal resolution and do not necessarily allow rapid changes in stability to be detected and communicated sufficiently in advance to provide early warning. The study objectives were to (i) acquire a long-term dataset of continuous deformation measurements with high temporal resolution of a case study slope in Peace River, (ii) enhance understanding of a typical creeping Peace River slope’s behavior in response to climatic drivers, and (iii) investigate the potential of an acoustic emission (AE) monitoring system to provide early warning of accelerating deformation behavior. ShapeAccelArray (SAA) and AE instruments were installed, in addition to conventional inclinometers and piezometers. Measurements show that the landslide is “extremely slow”, moving on average 5 mm annually, and reveal seasonal activity with periods of acceleration and deceleration driven by pore-water pressures. Measured AE correlated strongly with the rate and magnitude of SAA-measured displacement, demonstrating the potential of the AE technique to warn of accelerating deformation behavior.

In situ observation of storm-wave-induced seabed deformation with a submarine landslide monitoring system

Submarine landslides move large volumes of sediment and are often hazardous to offshore installations. Current research into submarine landslides mainly relies on marine surveying techniques. In contrast, in situ observations of the submarine landslide process, specifically seabed deformation, are sparse, and therefore restrict our understanding of submarine landslide mechanisms and the establishment of a disaster warning scheme. The submarine landslide monitoring (SLM) system, which has been designed to partly overcome these pitfalls, can monitor storm-wave-induced submarine landslides in situ and over a long time period. The SLM system comprises two parts: (1) a hydrodynamic monitoring tripod for recording hydrodynamic data (e.g., waves, tides, and currents) and (2) a shape accel array for recording seabed deformation at different depths. This study recorded the development of the SLM system and the results of in situ observation in the Yellow River Delta, China, during the boreal winter of 2014–2015. The results show an abrupt small-scale storm-wave-induced seabed shear deformation; the shear interface is in at least 1.5-m depth and the displacement of sediments at 1.23-m depth is more than 13 mm. The performance of the SLM system under real-time field monitoring conditions confirms the feasibility and stability of this approach.

Developing an early warning system for a very slow landslide based on displacement monitoring

The Ripley Landslide is a soil slide moving on a fully developed, sub-horizontal, shear surface. The landslide represents a hazard for two important railway lines across its toe. The landslide is being monitored by an array of displacement measurement systems including GPS units, a ShapeAccelArray (SAA), satellite InSAR, and crack extension metres, as well as an array of piezometers targeting pore water pressures in the vicinity of the shear surface. The displacement monitoring system shows an annual cycle of slope deformations most active between September and May. Annual horizontal displacements range between 60 and 100 mm. Vertical displacements range between 20 and 80 mm of settlement. The average horizontal velocities during the active displacement period are between 0.2 and 0.35 mm/day, with maximum velocities of up to 0.6 mm/day. This paper describes the development of an early warning system based on landslide displacement measurements. The system is based on GPS and SAA measurements, which provide near real-time displacement data. The early warning system focuses on detecting changes in landslide annual displacement cycles and potential accelerations, as well as the effects of slope deformation on the railway alignment. As such, the system monitors both the integrity and performance of the slope.

Measurement of Deformations by MEMS Arrays, Verified at Sub-millimetre Level Using Robotic Total Stations

Measurement of sub-millimetre-level deformations of structures in the presence of ambient temperature changes can be challenging. This paper describes the measurement of a structure moving due to temperature changes, using two ShapeAccelArray (SAA) instruments, and verified by a geodetic monitoring system. SAA is a geotechnical instrument often used for monitoring of displacements in soil. SAA uses micro-electromechanical system (MEMS) sensors to measure tilt in the gravity field. The geodetic monitoring system, which uses ALERT software, senses the displacements of targets relative to control points, using a robotic total station (RTS). The test setup consists of a central four-metre free-standing steel tube with other steel tubes welded to most of its length. The central tube is anchored in a concrete foundation. This composite “pole” is equipped with two SAAs as well as three geodetic prisms mounted on the top, in the middle, and in the foundation. The geodetic system uses multiple control targets mounted in concrete foundations of nearby buildings, and at the base of the pole. Long-term observations using two SAAs indicate that the pole is subject to deformations due to cyclical ambient temperature variations causing the pole to move by a few millimetres each day. In a multiple-day experiment, it was possible to track this movement using SAA as well as the RTS system. This paper presents data comparing the measurements of the two instruments and provides a good example of the detection of two-dimensional movements of seemingly rigid objects due to temperature changes.

Measurement of cyclic response of railway embankments and underlying soft peat foundations to heavy axle loads

This paper presents the deformation and pore-water pressure response within peat foundations below three different railway embankments in response to cyclic heavy axle loading. The study sites include two at Canadian National (CN) Railway's Edson and Lac-La-Biche subdivisions in northern Alberta, and one at CN′s Lévis subdivision in southeastern Quebec. The three sites were instrumented to monitor the spatial distribution of strain, pore pressure generation, and stress, and the distribution of horizontal cyclic displacement with depth during the passage of trains. The horizontal cyclic displacement with depth was measured using a ShapeAccelArray (SAA). An analysis was conducted to determine how close the peat is to yielding under heavy axle loads. This analysis was based on the elastic response determined from undrained triaxial testing, a constitutive model developed for peat, and finite element modelling. The field response and the numerical modelling suggest that the embankments at the northern Alberta sites are stable under current loading conditions. The highest potential for yielding at these sites occurs just beneath the embankment and at the interface between the peat and underlying stiffer soil. At the Lévis site the analysis suggests that a recently constructed ditch concentrates shear stress at a location where the principal stress orientation corresponds to a reduced strength of peat and may have increased the potential for yielding.

Asset Management and Safety Assessment of Levees and Earthen Dams Through Comprehensive Real-Time Field Monitoring

Assessing the health of and maintaining civil infrastructure has been an increased concern in the wake of natural disasters such as Hurricane Katrina in 2005 and the summer 2007 flood events in the UK. The variability of properties within geotechnical systems makes predictions of soil behavior extremely difficult, especially when soil models are not calibrated with field-measured performance. Unfortunately the current state of the art in geotechnical system health assessment is either based on very expensive monitoring systems for real-time information or on periodic measurement of ground surface displacements. Accordingly, a need has arisen for a system capable of in situ, real-time monitoring of levees, embankments, and other earthen structures. The work presented herein highlights the development of novel, affordable sensing technologies for use in a framework to monitor, manage and ensure the safety of geotechnical infrastructure. MEMS (micro-electro-mechanical systems)-based in-place inclinometer system, Measurand’s ShapeAccelArray (SAA), is now established as a sensing tool for simultaneous measurement of 3D soil acceleration and 3D ground deformation up to a depth of one hundred meters, with an accuracy of ±1.5 mm per 30 m. Each sensor array is connected to a wireless sensor node to enable real-time monitoring as well as remote sensor configuration. This system is now being further developed to include digitally integrated pore pressure measurement in the form of vibrating wire piezometers equipped with microprocessors (called SAAPs). The SAAPs are able to convert vibrating wire data to digital data downhole, and they integrate easily into the SAA system. In situ testing was conducted in a levee in England subjected to significant tidal loading (up to 6 m of fluctuation during spring tides) through collaboration with the European Union’s UrbanFlood project. In addition to the SAAs and SAAPs installed in three sections of the levee, the site was also instrumented with other sensors from Alert Solutions and TenCate, providing values for comparison. The likelihood of this levee to experience deformation and the density of instrumentation installed in the bank made this the ideal location to test the new SAAP system. The additional insight into subsurface behavior provided by the SAAPs is integral in the development of a comprehensive system for monitoring and management of civil infrastructure. The preliminary testing indicates the suitability of this new multi-parameter system for inclusion in a multi-scale monitoring and health assessment framework, which will be implemented in New Orleans, LA in 2012.

An Evaluation of Real-Time Deformation Monitoring Using Motion Capture Instrumentation and Its Application in Monitoring Railway Foundations

Abstract 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.

Innovative sensing for real-time health monitoring of geostructural systems

Recent advances in miniaturizing sensors and electronics and the development of a pervasive wireless infrastructure have enabled a paradigm shift in the health monitoring of soilstructure systems. Created by researchers at Rensselaer Polytechnic Institute (RPI)1 and Measurand Inc.,2 the wireless ShapeAccelArray (SAA) sensing system is capable of measurements that represent a significant advance in implementing this shift. Over the last 50 years engineers have used traditional, manual slope inclinometers to monitor the health of landslides and construction activities. However, the frequency and accuracy of this labor-intensive monitoring rely on a trained engineer manually collecting and managing the data. The low sensor density provided by this method results in very limited data. State departments of transportation and federal agencies continue to spend significant resources monitoring possible slope failures using manual inclinometers or in-place inclinometer arrays. The expense and inflexibility of the slope inclinometer arrays, and the need for torsional alignment, make installation of multiple setups at a single site relatively rare, severely limiting the ability to conduct pervasive real-time monitoring. The wireless SAA system can remotely collect both 3D deformation and acceleration readings anywhere there is cell-phone coverage. The SAA system enables gravity-based shape calculation along a sensorized substrate through an extension of technologies that use fiber-optic orientation sensing to calculate 3D polylines representing the shape of a sensor array.3 The SAA uses microelectromechanical systems (MEMS) accelerometers in a precalibrated, geometrically constrained arrangement4 to provide long-term stability previously unattainable with fiber-optic Figure 1. Advancing polyvinyl chloride casing segments along the wireless ShapeAccelArray (SAA).