Experimental assessment of the performance of terrestrial laser scanners in monitoring the geometric deformations in retaining walls

Abstract The Terrestrial Laser Scanner (TLS) has a great potential to be used in monitoring structures, specifically retaining walls, due to its fast acquisition and contactless function. However, previous research showed that the accuracy of deformation estimation using the TLS varied between few millimeters to a few centimeters. The Structural Health Monitoring (SHM) of retaining walls is executed according to their serviceability limits, and has to be taken with a tolerance of a few millimeters. Therefore, the aim in this study is to propose methods and approaches that ensure that the accuracy of the deformation estimation using the TLS is within $$1-2 \hspace{0.2em} \text {mm}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>-</mml:mo> <mml:mn>2</mml:mn> <mml:mspace/> <mml:mtext>mm</mml:mtext> </mml:mrow> </mml:math> . This study is based on experimental assessment, where the main scenarios of geometric deformations in retaining walls are simulated through an experimental device (i.e., wooden sheet). The wooden sheet was scanned by a TLS from distance varying from $$10-27 \hspace{0.2em} \text {m}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>10</mml:mn> <mml:mo>-</mml:mo> <mml:mn>27</mml:mn> <mml:mspace/> <mml:mtext>m</mml:mtext> </mml:mrow> </mml:math> with scanning angle varying between $${0}^{\circ } \hspace{0.2em} \text {and} \hspace{0.2em} {20}^{\circ }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mo>∘</mml:mo> </mml:msup> <mml:mspace/> <mml:mtext>and</mml:mtext> <mml:mspace/> <mml:msup> <mml:mrow> <mml:mn>20</mml:mn> </mml:mrow> <mml:mo>∘</mml:mo> </mml:msup> </mml:mrow> </mml:math> . The wooden sheet was designed to simulate three main scenarios of deformation (i.e., lateral displacement, settlement and tilt) with amplitudes varying from $$2 \hspace{0.2em} \text {to} \hspace{0.2em} 16 \hspace{0.2em} \text {mm}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>2</mml:mn> <mml:mspace/> <mml:mtext>to</mml:mtext> <mml:mspace/> <mml:mn>16</mml:mn> <mml:mspace/> <mml:mtext>mm</mml:mtext> </mml:mrow> </mml:math> and $${0.2}^{\circ } \hspace{0.2em} \text {to} \hspace{0.2em} {1.6}^{\circ }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mrow> <mml:mn>0.2</mml:mn> </mml:mrow> <mml:mo>∘</mml:mo> </mml:msup> <mml:mspace/> <mml:mtext>to</mml:mtext> <mml:mspace/> <mml:msup> <mml:mrow> <mml:mn>1.6</mml:mn> </mml:mrow> <mml:mo>∘</mml:mo> </mml:msup> </mml:mrow> </mml:math> for tilt. This study presents a holistic attempt based on controlled experiments to evaluate the performance in monitoring deformation, using a multi-parametric analysis and identifying approaches to enhance the application of TLS in monitoring deformation of wall-type structures, such as retaining wall. The TLS measurements were compared to robotic total station measurements as well as absolute measurements using a ruler. These strategies should enhance the efficient use of the TLS in monitoring small geometric deformations.