Abstract
The construction of large earth/rock fill dams, albeit its remarkable progress, still relies largely on past experiences. Therefore, a comprehensive yet dependable monitoring program is particularly beneficial for guiding the practice. However, conventional measurements can only produce limited discrete data. This paper exploits the potential of the terrestrial laser scanning (TLS) for an accurate inventory of as-built states of a concrete-faced rockfill dam under construction and for a full-field analysis of the 3D deformation pattern over its upstream face. For the former, a well-designed 3D geodetic system, with a particular consideration of the topography, promises a regulated acquisition of high-quality and blind-zone-free point cloud at field and also eases the cumbersome data registration process while maintaining its precision in house. For the latter, a problem-tailored processing pipeline is proposed for deformation extraction. Its core idea is to achieve a highly precise alignment of the point clouds with Iterative Closed Point algorithms from different epochs in datum areas that displays a featured, undeformed geometry at stable positions across epochs. Then, the alignment transformation matrix is applied to the point clouds of respective upstream face for each epoch, followed by pairwise comparisons of multiple adjusted point clouds for deformation evaluation. A processing pipeline is used to exploit the peal scene data redundancy of the GLQ dam acquired at six different epochs. Statistical analysis shows that satisfactory accuracy for deformation detection can be repeatably achieved, regardless of the scanner’s positioning uncertainties. The obtained 3D deformation patterns are characterised by three different zones: practically undeformed, outward and inward deformed zones. Their evolutions comply well with real construction stages and unique 3D valley topography. Abundant deformation results highlight the potential of TLS combined with the proposed data processing pipeline for cost-efficient monitoring of huge infrastructures compared to conventional labor-intense measurements.
Highlights
We presented a well-designed application of terrestrial laser scanning (TLS) for monitoring the GuoLangQiao (GLQ) Dam (a 183.6 m high Concrete Faced Rockfill Dam (CFRD)) that is under construction
For the first time, the great potential of the TLS technique for understanding 3D deformation patterns of CFRD during construction stages is shown, and this includes their possible implications for cracking behaviour of concrete face slabs
A Triangular Irregular Network (TIN) model was first generated by the classic Delaunay triangulation method to represent reference data, the shortest distance from any one point in the test data to its nearest triangle plane in the reference TIN model was calculated as the displacement of that point between two epochs
Summary
Due to the limitations of theoretical and experimental techniques, a well-designed field monitoring scheme, which is capable of recording a complete picture of the dam’s behaviour at its different construction stages, can offer a valuable database for investigating the fundamental behaviour of large volume rockfills and for guiding construction practices on site This requires that a large volume of high-accurate field data to be acquired in a prompt manner, which cannot be realized by any conventional sensors. The work presented in this paper can serve as a good reference for the application of TLS to measurements of the as-built behaviour of the CFRDs. for the first time, the great potential of the TLS technique for understanding 3D deformation patterns of CFRD during construction stages is shown, and this includes their possible implications for cracking behaviour of concrete face slabs
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