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3D modelling of the ancient underground quarries of the famous Parian marble in the Aegean Sea, Greece and assessment of their stability using lidar scanning

Efi Goula, George Papathanassiou, Triantafyllos Kaklis, Vassilis Marinos and Ioannis Vazaios
3D modelling of the ancient underground quarries of the famous Parian marble in the Aegean Sea, Greece and assessment of their stability using lidar scanning
Quarterly Journal of Engineering Geology and Hydrogeology (February 2019) 52 (1): 61-73

Abstract

Laser scanning has proven useful in the stability assessment of underground openings. High accuracy points are used to generate 3D surface models to evaluate their stability by assessing rockmass structural features. A series of scans obtained from underground ancient quarries in Paros Island were processed. The structural analysis of the openings was complemented by field observations and measurements, serving as input parameters for numerical software used to evaluate the potential failure mechanisms and overall stability. Blocks with a higher risk of detaching are encountered mostly at tunnel portals where support is required to secure unstable blocks to preserve this geotope. Rockmass behaviour can be particularly complex and is influenced by different structures that vary in their geological origin and scale, including faults, joints, foliation etc. The identification and characterization of these structures is of great significance to rockmass evaluation and stability assessment and can be performed by employing several techniques that usually involve collecting geological data (ISRM 1978; Priest 1993). However, manual data collection can be a tedious task, especially in underground projects in which the rockmass can be difficult to access. Additionally, the integration of the geological survey in an active operational environment may have further complications (Fekete et al. 2010). Remote sensing techniques, such as LiDAR (Light Detection and Ranging) and photogrammetry, can produce detailed 3D geometrical models, and they have been proven to be a valuable asset in the field of geological and geotechnical engineering with a wide range of applications, including discontinuity mapping, rockmass quality assessment, deformation monitoring etc. More specifically, for underground excavations, remote sensing techniques can be employed to assess the excavation boundary and create 2D cross-sectional profiles along the alignment of the excavation, assess the installed support, assist in determining over- or under-excavations, etc. (Fekete et al. 2010). Furthermore, for unlined tunnels and other unsupported underground structures, LiDAR data and the generated 3D models can be particularly useful when determining the structural features of the rockmass and the potential failure mechanisms that can be observed as a result of the rockmass structure. The main objective of the present study was to identify and record the geometric characteristics of the discontinuities found within the ancient underground marble quarries of the Nymfes Tunnels located in the island of Paros, Greece. The mapping of the discontinuity geometrical features was conducted using terrestrial laser scanning (TLS) and the data obtained from LiDAR were used as input for performing a stability analysis of the investigated underground openings. The employed method highlights the value of laser scanning to map discontinuity elements within jointed rocks, especially within an underground environment, in which the speed and accuracy of data collection and personnel safety pose significant challenges within actively or inactively operational tunnel environments. Furthermore, within this specific site of great archaeological interest laser scanning can also minimize potential human interference when data are collected, which is essential during operations at historical sites. The presented workflow will be of great assistance to geologists and engineers involved in underground works due to its versatility regarding the rockmass conditions and its efficiency in data collection and management, which can be further coupled with both in situ rockmass and discontinuity assessment techniques. In this particular case, the study focused on both the identification of specific, high-risk locations within the galleries due to block failure as a result of the geological structures (discontinuity orientation relative to the orientation of the galleries), and on the quarry wall condition, in order to preserve this historical geotope. The stability of the openings was assessed based on LiDAR data and in situ measurements, including joint compressive strength (JCS) and joint roughness coefficient (JRC) measurements. The data collected in situ were used as input to assess the stability of the underground openings.


ISSN: 1470-9236
EISSN: 2041-4803
Serial Title: Quarterly Journal of Engineering Geology and Hydrogeology
Serial Volume: 52
Serial Issue: 1
Title: 3D modelling of the ancient underground quarries of the famous Parian marble in the Aegean Sea, Greece and assessment of their stability using lidar scanning
Affiliation: Aristotle University of Thessaloniki, Department of Geology, Thessaloniki, Greece
Pages: 61-73
Published: 201902
Text Language: English
Publisher: Geological Society of London, London, United Kingdom
References: 23
Accession Number: 2019-010922
Categories: Engineering geologyApplied geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. geol. sketch maps
N37°04'60" - N37°04'60", E25°08'60" - E25°08'60"
Secondary Affiliation: Queens University, CAN, Canada
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute.
Update Code: 2019
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