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3D Discontinuity Characterization of Chalk Sea Cliffs using Terrestrial Laser Scanning Systems
A. Stavrou, J. Lawrence, B. Awakian and W. Murphy
Chalk of the Northern Province - its regional context Hull University, 10-13 September 2015
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To demonstrate the utilisation of Terrestrial Laser Scanning Systems for the 3D characterisation of discontinuities in chalk sea cliff environments.
To introduce the Laser Scanning or LiDAR technology as a potential replacement of conventional field techniques.
To prove that there is a strong correlation between results obtained by LiDAR and scanline surveys.
Aim of the Project
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Study Area
Brighton Marina
Saltdean Peacehaven
Peacehaven Newhaven
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Geological Setting
The Coastal cliffs are dominated by the Newhaven Chalk formation
Study area
Characterised by marl seams and repeated layering of flints
The bedding is sub-horizontal and gently dips to the South
Chalk is fragmented by normal and reverse faults and steeply inclined (60-700) conjugate shear joints
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Structurally Controlled Cliff Instability
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Discontinuity Characterisation
GEOMETRY
Orientation
Spacing
Persistence
Termination
SHEAR STRENGTH
Surface Roughness
Aperture
Filling
Wall Strength
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Scanline Surveys
Traditional method to characterise discontinuities
Brady and Brown, 2004
Disadvantages: Human bias Sampling difficulties
Quality and quantity
of measurements
Accessibility Safety risks Time consuming
and costly
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Terrestrial 3D Laser Scanning
Known as Light Detection and Ranging: LiDAR
A very popular and promising tool for collecting geo-data
Applicable to many geotechnical fields such as:
Rock Slope Engineering
Coastal Engineering
Structural Geology
Mining
Tunnelling
Advantages: Detailed 3D discontinuity
characterization Large amounts of very
high quality data
Almost no accessibility limitations
Reduced safety risks Rapid and cost effective
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Fundamentals and Principles
1. Transmitter 2. Target
3. Receiver
3D LiDAR
Point Cloud:
(i.e. a collection of reflection points)
2m high wall
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Fundamentals and Principles
Before Data Analysis
.. Noise removal
(e.g. vegetation, vehicles)
+ Triangular Mesh
generation
3D Discontinuity Characterization
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Discontinuity = A group of neighboring mesh triangles with similar normal vector measurements
3D Discontinuity Identification & Characterization
Split Engineering http://www.spliteng.com
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In flat, vertical cliff faces with no/low relief,
discontinuity surfaces are not readily available and
only discontinuity traces are visible
3D Discontinuity Identification & Characterization
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Methodology
• Manually identify lines to the point cloud that depict the fracture’s exposed trace
• The software will modify the digitized line and calculate a best-fit plane that fits the points along the fracture trace
3D Discontinuity Identification & Characterization
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Field-based manual discontinuity measurements (scanline surveys)
9 scan line surveys ranging in length from 30 to 50 meters
Computer-based processing and analysis of 3D laser scanning data (point clouds)
Project Structure
The project consisted of two distinct phases:
Example of a cliff face near Brighton Marina where a scanline survey was carried out
Example of a manually identified discontinuities using the Split-FX software
Vs
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The survey was carried out using two mobile laser-scanning systems:
1. a van mounted laser scanning system and
2. a boat mounted laser scanner
Laser Scanner Data Collection
Data provided by the Brighton and Hove City Council
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Results and Comparison
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Results and Comparison
Kinematic Analysis
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• The results show a very good fit between the two methods
• The comparison validates the good performance of laser scanners in flat, planar, low relief, chalk cliffs of limited accessibility
• Laser scanners are therefore considered to have the potential of replacing traditional discontinuity characterisation methods
• However, with the lack of any official standards and guidelines, laser scanners cannot be recommended as a stand-alone technique
Conclusion
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Thank you
Any Questions?