Construction and post-construction deformation analysis of an MSE wall using terrestrial laser scanning and finite element modelling
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Date
2020
Authors
Adamson, Devon
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Abstract
Terrestrial Laser Scanning (TLS) is a new technology surveying tool that can collect highly accurate cartesian coordinates of data points surrounding the scanner in a 360° field of view. This technology can be useful in the field of monitoring heavy civil structures, in the case of this research, the settlement of bride interchange abutments.
Two bridge abutments were monitored with TLS, designed with Cast-In-Place (CIP) belled piles and Mechanically-Stabilized Earth (MSE) retaining walls with a segmented precast concrete panel facing system. The foundation was further reinforced with vibration-compacted rockfill columns supporting the approach embankments, which increased the stiffness of the soil and acted as drains to dissipate pore water pressure. The wall facing panels had discernable edges that could easily be identified by the scanner, allowing for a total wall survey rather than the limited discrete location surveying used by traditional methods. Multiple scan surveys were taken along each wall face and were registered together to create a larger Project Point Cloud (PPC). Once PPCs were collected for successive survey dates, point clouds were aligned in the same coordinate system and relative movement was measured. These measurements were then compared against the surveying performed on site by the contractor to observe discrepancies in measured readings.
Once surveying was completed, numerical models were developed with site investigation information and laboratory testing results to compute pore water pressure behaviour and predict foundation settlement using Finite Element Method (FEM) and 3-Dimensional (3D) vertical settlement analysis. Since 2D modelling software was used for FEM to analyze a 3-Dimensional site, discontinuous materials were treated as equivalent material walls using converted plane strain parameters. The 3D vertical settlement analysis retained axisymmetric parameters but required the foundation soil and rockfill columns reinforcement to combine into a single material layer of equivalent stiffness within the reinforced soil zones.
Both surveying and numerical modelling observed the abutments to settle more outside the extents of the bridge deck where there were less columns. The laser scanner had some small deviations in relation to the surveying performed on site and the computed settlements from FEM. It is recommended when using TLS for future research and design projects to include more scans during baseline readings and to include more settlement instrumentation near the end of the reinforcement strips to measure differential settlement effects
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Keywords
terrestrial laser scanning, MSE wall, finite element modelling