TOWARDS DESCRIBING FULL-SECTION DEFORMATIONS USING TERRESTRIAL LASER SCANNING IN THE BADALING TUNNEL (CHINA)

Abstract. This paper focuses on the analysis of point clouds from terrestrial laser scanning to interpret possible deformations of the new Badaling Tunnel that was built for the Winter Olympics 2022 in the nearby of Beijing, China. A reference framework is established to compare data corresponding to various days with blocks of uniform columns and rows from an estimated tunnel axis. Filling holes and detecting outliers are performed for quasi-planar estimation, and refinement transformation is used to adjust the data errors between different days. Finally, the full-section deformations are detected in the form of distance discrepancies of representative points and are verified against total station measurements

Selected aspects of geometrical analyses of surfaces measured using terrestrial laser scanning (TLS)

[EN] Modern measurement technologies are widely used for the monitoring and determination of surface deformations. One more frequently used measurement technology is terrestrial laser scanning (TLS), which provides quasi-continuous information about the tested surface in the form of a point cloud at a given resolution. At the same time, TLS is based on measuring the distance in a given direction, thanks to which we can obtain a high precision of measurement, often compared to tacheometric measurements. This paper presents a study on the determination of surface flatness parameters extracted from a point cloud. It takes into account the roughness characteristics of the different structures on the measured surfaces and analyzes them using the most popular algorithms for determining the distance of points from the reference surface. Additionally, the review presents the issue of expanding selected surfaces onto a plane to analyze their geometric parameters, and thus to determine the deformation. The applied solution can be used to monitor the deformation of objects such as tunnels and interiors of collectors or large-diameter downpipes, the shape of which is similar to a cylinder surface. Thanks to the expansion of the cylinder surface into a plane, it is possible to perform a comprehensive analysis of surface deformation, and not only selected fragments in the form of sections. The conducted analyses show the great potential of data obtained using terrestrial laser scanning, when an appropriate procedure and data processing method are applied. This paper focuses on two types of studies; the study of surface flatness and analysis of the deformation of cylindrical surfaces. These types of studies are extremely useful in assessing the technical condition of structures, especially in studying the deformation of structures built underground (tunnels, passages, warehouses), where the loads from the surrounding earth are significant.Zaczek-Peplinska, J.; Kowalska, M.; Ryczko, K.; Sekular, C. (2023). Selected aspects of geometrical analyses of surfaces measured using terrestrial laser scanning (TLS). En 5th Joint International Symposium on Deformation Monitoring (JISDM 2022). Editorial Universitat Politècnica de València. 389-396. https://doi.org/10.4995/JISDM2022.2022.1388238939

A review of laser scanning for geological and geotechnical applications in underground mining

Laser scanning can provide timely assessments of mine sites despite adverse challenges in the operational environment. Although there are several published articles on laser scanning, there is a need to review them in the context of underground mining applications. To this end, a holistic review of laser scanning is presented including progress in 3D scanning systems, data capture/processing techniques and primary applications in underground mines. Laser scanning technology has advanced significantly in terms of mobility and mapping, but there are constraints in coherent and consistent data collection at certain mines due to feature deficiency, dynamics, and environmental influences such as dust and water. Studies suggest that laser scanning has matured over the years for change detection, clearance measurements and structure mapping applications. However, there is scope for improvements in lithology identification, surface parameter measurements, logistic tracking and autonomous navigation. Laser scanning has the potential to provide real-time solutions but the lack of infrastructure in underground mines for data transfer, geodetic networking and processing capacity remain limiting factors. Nevertheless, laser scanners are becoming an integral part of mine automation thanks to their affordability, accuracy and mobility, which should support their widespread usage in years to come

Shaking table model tests of reinforced concrete tunnels under multiple earthquake shakings

The cumulative effect of multiple relatively low or moderate seismic events on tunnels is not well-understood within an earthquake prone region. To investigate the effect of multiple earthquakes on the integrity of tunnel structures, 1 g shaking table tests were performed. This research also explored the impact of tunnel presence on the soil response, namely analyzing soil-structure interaction effects. Within the tests, a free-field model and a soil-tunnel model were employed synchronously. The shaking table study was designed and conducted following a new set of scaling laws able to faithfully simulate cracking of tunnel lining, and white noise tests were applied after each seismic shaking for dynamic identification. Except for the measurement of acceleration and bending strain, a new cracking monitoring system equipped with wireless mini-cameras was proposed to detect the evolution of tunnel damages during the tests, while Light Detection and Ranging (LiDAR) technology was utilized to examine the ground deformations in the two model configurations. Based on the point cloud data, it was observed that sand densification effects were obvious in the two models and the influence of tunnel presence on the soil response was restricted in a limited region. The trend in the evolution of an image-based damage index kept similar to that in the progression of surface settlements, implying that the seismically-induced ground failure might play an important role in the seismic response of shallow tunnels. Also, the frequency shifting behaviour of lining did not follow the intuitive pattern, where a reduction in natural frequencies is expected when structural damage occurs. Moreover, the variation of acceleration amplification factors of the tunnel was almost consistent with that of the soil, and the trend of strain agreed with that of surface settlements. The findings from this study provide an insight to better understand the resilience and life-long performance of earthquakes exposed underground structures

Water leakage mapping in concrete railway tunnels using LiDAR generated point clouds

Dissertation (MEng (Transportation Engineering)) University of Pretoria, 2021.Light detection and ranging (LiDAR) is a key non-destructive testing (NDT) method used in modern civil engineering inspections and commonly known for its ability to generate high-density coordinated point clouds of scanned environments. In addition to the coordinates of each point an intensity value, highly dependent on the backscattered energy of the laser beam, is recorded. This value has proven to vary largely for different material properties and surfaces. In this study properties such as surface colour, roughness and state of saturation are reviewed. Different coloured and concrete planar targets were scanned using a mobile LiDAR scanning system to investigate the effect distance, incidence angle and ambient lighting have on targets of differing properties. The study comprised controlled laboratory scans and field surveying of operational concrete railway tunnels. The aim of field tests was to automatically extract water leakage areas, visible on tunnel walls, based on the intensity information of points. Laboratory results showed that darker coloured targets resulted in a lower recorded intensity value and larger standard deviation of range. Black targets recorded the lowest intensities (0 - 4 units) with 50% higher standard deviations of range, on average, compared to all other coloured targets which recorded standard deviations of around 12 mm. The roughness of each coloured target showed to largely influence the recorded intensity, with smooth surfaces recording higher standard deviations of measurements. Concrete targets proved that a difference in roughness and saturation was detectable from intensity data. The biggest change was seen with saturated targets where a 70 to 80 % lower intensity value was recorded, on average, when compared to the same targets in their dry state. The difference in target roughness showed to have no effect on intensity when saturated. The laboratory data provided an important reference for the interpretation and filtering of field point clouds. Ambient lighting had no significant effect on all measurements for both the coloured and concrete targets. Field tests conducted on an operational concrete railway tunnel confirmed and demonstrated the ability to rapidly identify, extract and record areas of water leakage based on the intensity and spatial information of point cloud data. This is particularly useful as water ingress is known to degrade concrete, resulting in the earlier onset of corrosion, spalling and loss of strength. The mobile LiDAR scanning system used here proved capable of reducing survey time, which would allow for shorter interval revisits, while providing more quantitative information of the leakage areas. Long-term continuous monitoring of the internal structure of a tunnel will reduce the life cycle costs by removing the need for personnel to enter the tunnels for visual assessments and enable remedial work to be better planned by analysing a virtual 3D point cloud of the tunnel before stepping foot onto site.Transnet Freight RailChair in Railway EngineeringCivil EngineeringMEng (Transportation Engineering)Unrestricte

Non-contact monitoring of railway infrastructure with terrestrial laser scanning and photogrammetry at Network Rail

Current monitoring practices in the railway industry primarily rely on total station and prism based methods. This approach requires the installation and maintenance of prisms directly onto the structure being monitored which can be invasive and expensive. This thesis presents the outcomes of an industrial based doctorate, motivated by the Network Rail Thameslink Programme, to investigate the potential of terrestrial laser scanning and photogrammetry as an alternative non-contact and “target-less” solution to monitoring railway infrastructure. The contributions made by this thesis in the context of Network Rail requirements include: a laboratory based exploration of the state of the art in target and surface-based measurements; a validation of conventional, terrestrial laser scan and photogrammetric surveys of a deforming set of brick arches; and a novel prism-less method of track measurement using terrestrial laser scanner data. The complete project has been carried out as part of the highly complex and dynamic £900m London Bridge Redevelopment Project. The thesis comprises of a review of existing monitoring system performance and highlights challenges in the adoption of this technology through interviews of leading professionals in the monitoring industry. Laboratory tests utilise network adjustment prediction and analysis to compare state of the art total station, terrestrial laser scanning and close-range photogrammetry instrumentation to both target and target-less deformation monitoring scenarios. The developed tests allow the performance of each technique to be assessed within the context of state of the art and Network Rail operational practice and are extensible to developments in each of these technologies. Results demonstrate performances to sub-millimetre level and are validated through the use of a Leica AT401 laser tracker. Each technique is then explored within the London Bridge Redevelopment Project through a series of live monitoring sites where their ability to either augment or replace existing survey techniques is evaluated. Results from the on-site monitoring of historic brick arch structures demonstrate surface measurements compatibility at the millimetre level, highlighting close agreement between instrument performance established in the laboratory. A key use of prism-based techniques is in the determination of engineering track parameters where costly prism systems, both in terms of installation and subsequent maintenance, attached to the track are a key concern. Here laboratory validated track surface measurement, with terrestrial laser scanning, has been deployed on a 15 metre long dual track site and shown to be highly capable of replacing prism systems for the determination of accurate track geometry. This work has included a novel optical non-contact measurement process utilising individual rail cross section designs to automatically extract relevant track geometry parameters within 1mm of prism-based methods. The method offers excellent potential for incorporation into an automated track monitoring system. Outcomes from the thesis have been published in peer-reviewed journals and conferences