Tom Martlev - detailed geological modelling in urban areas focused on structures relevant to the near surface groundwater flow

…by I•GIS
Detailed geological modelling in urban areas
– focus on structures relevant to the near-surface groundwater flow and
surface water recharge.
Senior Geologist Tom Martlev Pallesen (I•GIS)
Detailed Geological Modelling In Urban Areas

…by I•GIS
Disposition
Background
Challenges -
detailed modelling in urban areas
Datatypes
Model types
Summary
Model setup and workflow
Development of new tools

…by I•GIS
Background
The case shows an example from Odense City (DK) where new geological modelling techniques
has been developed in the geological modelling software GeoScene3D, and used to create a
detailed voxel model of the anthropogenic layer (the soil zone where human activity has
changed the original geological layers).
The example is part of a pilot project partly financed by VTU (Foundation for Development of
Technology in the Danish Water Sector) and involves many different datatypes such as human
related elements (landfill, pipelines, roadbeds etc.).
I•GIS have modelled the anthropogenic layer in the pilot area Thomas B. Thriges Gade.
GeoScene3D is a geological modelling software, widely used
to make geological models in the context of groundwater
mapping.
In Denmark GeoScene3D is being used at Geological Survey
(GEUS), the Ministry of Environment and Food, Danish
Regions, municipalities, water companies, consultants
and educational institutions.
Background Challenges
detailed modelling Datatypes Model types Development of new
tools
Model setup and
workflow Summary

…by I•GIS
Selected developments
• Import of pipelines and structural elements and the use of attributes
• Tools to create buffers surrounding 3D elements
• 3D objects transformed to voxels in a voxel data grid
• (Tool to georeference jpg, bmp and pdf files at a specific XYZ point and correct
vertical scale, e.g. well logs)
tools
Model setup and
workflow Summary

…by I•GIS
Modelling surface near geology and landfill layers in urban
areas are complex. This is partly due to :
• Often high geological variability.
• Many human-induced changes in the original geology (excavations, constructions,
landfill) – often a long history.
• A general need of great level of detail in the models (thin layers and there
propagation are highly relevant when calculating surface near groundwater flow,
infiltration of surface water, propagation of contaminations etc.).
• All boreholes in the Thomas B. Thriges Gade pilot area shows layers of landfill.
tools
Model setup and
workflow Summary

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The complex culture layer (anthropogenic layer)
tools
Model setup and
workflow Summary

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The knowledge of the structural elements can be handled and
used in the process of making very detailed geological models.
tools
Model setup and
workflow Summary
Voxel model based on sand-clay fraction (sand=reddish, clay=brownish)

…by I•GIS
What kind of data are we using…
• Geological related data
• Structural elements and constructions
• (historical maps, geotechnical boreholes and many more)
Datatype Data-subtype Bemærkninger
Terræn 1,6 m grid
Boringer PC-Jupiter 208 boringer
Boringer Region Midt GeoCloud 192 boringer. Næsten alle overlapper med
PC-Jupiter
Boringer Lokal database (Watertech) Diverse korte boringer
Boringer GeoGIS (Rambøll) Diverse korte boringer
Fyldlag/type Tolket på baggrund af tilgængelige
borejournaler i PC-Jupiter eller detail-
beskrivelser i de øvrige databaser.
Bygninger
Bygningsfundamenter Samles i ét vektortema
Befæstede arealer Veje m.m. Samles i ét vektortema
Befæstede arealer Parkeringspladser o.lign. Samles i ét vektortema
Rørledninger Vandforsyning Samles i ét vektortema
Rørledninger Spildevand Samles i ét vektortema
Rørledninger Fjernvarme Samles i ét vektortema
Samlet vektortema Rørledninger og befæstede arealer. Alle temaer fra ”Samles i ét vektortema”)
tools
Model setup and
workflow Summary

…by I•GIS
Geological related data (lithology):
• Geological soil sample descriptions
• An overall evaluation and classification
of land fill type in “fill classes” based on
assumed sand-clay fraction.
tools
Model setup and
workflow Summary

…by I•GIS
Structural elements, constructions and land fill-types
• Overall evaluation of dimensions and material type used for fill in traces, roadbeds etc.
• Development over time relative to the establishment and due to the
use of different material types over time
tools
Model setup and
workflow Summary

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Use of attributes
Vector data (e.g. pipelines) can be imported into GeoScene3D and can be handled due
to dimension, age, material type, manufacturer etc.
tools
Model setup and
workflow Summary

…by I•GIS
What are attributes?
One or more properties (e.g. diameter, age, material type) that can be linked to
an element (e.g. water pipes):
tools
Model setup and
workflow Summary

…by I•GIS
What kind of geological model types can
handle these different and complex
datatypes?
tools
Model setup and
workflow Summary

…by I•GIS
Issues
In general, geological modelling software to make
detailed geological models in urban areas have
limitations due to
1. Handling of ”untraditional” data types
2. Meet the need of a high level of detail
3. Create a model that gives the users an good overview and a model that is relatively
easy to update
Most geological models (in Denmark) are made as layered models, where interpretation points
are interpolated into surfaces, which defines top or bottom of individual layer units.
These models are has limitations when it comes to handling many and discontinuous layers, due
to the need for the geologist to define top, bottom and horizontal extent for each layer. The
number of individual layer units can be extremely high in a detailed geological model.
Typically the need for a high level of geological detail have been handled by e.g. zonation in the
groundwater modelling software. These software aren't designed for neither geological
interpretation, nor visual presentations, and won’t create overview.
Detailed geological modelling is typically are complex and time consuming process with lots of
manual work, also when the model needs to bee updated.
Possible solution:
Voxel models
tools
Model setup and
workflow Summary

…by I•GIS
Interpretation strategies and model types
Layered models
• Modelling of layer top and bottom
• Interpretationpoints interpolated to surfaces
• Well known methodology
• Often assumes near parallel layers.
• Significant simplification of the real geological
• Settings.
Voxelmodels
• ”Boxes” with a user defined size (X, Y, Z).
• Each voxel can be assigned different properties (lithology, hydraulic conductivity, age,
porosity…).
• In principle, all geology can be handled and with a
• high level of detail.
Layered model
Voxelmodel
tools
Model setup and
workflow Summary

…by I•GIS
The classical layered models assumes that the layers in the underground are more or less
plane parallel…
In reality we generally see them as very inhomogeneous and non-parallel due to geologically
and human related processes. ….
This is the reality we can handle with voxel models
tools
Model setup and
workflow Summary

…by I•GIS
Voxel models gives the modeller new opportunities by using new datatypes in a
high level of model detail, e.g.:
• Pipelines and traces.
• Buildings and underground structures
• Roads and road beds
Buildings (blue structures), pipelines and boreholes
tools
Model setup and
workflow Summary

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Development of new tools in GeoScene3D for handling ”Urbane Data”.
tools
Model setup and
workflow Summary

…by I•GIS
Development of new tools in geoScene3D
Buildings, basements, traces etc. can be handled due to attributes such as depth,
dimension, age etc. and can be used directly to select voxels in a 3D grid.
Colour of buildings
indicates basement depth
in meters below terrain
(e.g. medium blue = 1,2
mbt.).
Pipelines colour coded and
dimensioned on the basis
of attributes ”Dimension”
and ”Age”.
tools
Model setup and
workflow Summary

…by I•GIS
• Objects (basements, pipelines, roadbeds etc.) can be converted to voxels in a user-
defined voxel grid (3D grid).
• All voxels in the voxel grid, that are cut by a object, can be selected and assigned an
user defined property.
• This assignment can be relative, and by that takes into account that often only a
part of a voxel are cut by the object.
100/0
50
tools
Model setup and
workflow Summary

…by I•GIS
• ”Vector Theme” and ”Box”/”Pipe” selection.
Selection using the ”Pipe” function: Selection using the ”Box” function:
(voxels assigned to a grid with excisting
information)
tools
Model setup and
workflow Summary

…by I•GIS
Workflow
1) Modelling process
• Define model area, including extent of voxelgrid and cell size.
• Prepare data. Setup using attributes and depth information.
• Define temporal order (time of establishment) for the individual datasets:
Which structures cuts other structures. Which came first, which came last?
• Define ”background geology” and initially fill voxels based on this.
• Incorporate structural elements. For this part; use the new tools ”Box”,
”Pipe”, ”Blend” etc.).
tools
Model setup and
workflow Summary

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Workflow
1) Preparation of data
• Define attributes for each dataset. These are used for positioning,
dimensioning and visualizing the individual datasets.
• Define fill layer using e.g. lithology or sand-clay fraction.
tools
Model setup and
workflow Summary

…by I•GIS
Workflow
• Depth and composition of landfill: 3 fill-type classes with an estimated sand-
clay proportion (highly unscientific, subjective evaluation).
Land fill type Estimated sand content
(%)
Sand, some brick fragments, very silty
Clay, topsoil, with bricks (fragments)
Clay, sandy
Peat, sandy, with bricks
30
Sand topsoil, topsoil with brick fragments
Sand, pretty coarse, concrete, bricks, charcoal
Topsoil with brick fragments
Topsoil, sandy
Peat
Topsoil, peat, clayey, sandy, brick fragments
60
Sand and gravel, concrete fragments
Sand, coarse, stony
80
tools
Model setup and
workflow Summary

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Workflow
• Interpolation of fill layer data in 3D.
• After that – fill the rest of the fill layer and incorporate structural elements.
tools
Model setup and
workflow Summary

…by I•GIS
Urban voxel model – simplified example of workflow
1. Boreholes, water- and waste water pipes are imported and positioned according to diameter2. Bottom of landfill and the user defined land fill classes are imported3. Fill layer interpolated in 3D.
4. The rest of the land fill layer are filled with an estimated average land fill (here; reused
moraine clay).
5. Buildings and other structures are incorporated. Surfaces from an existing regional geological model are
imported and layers are converted to voxels
100% sand
100% clay
tools
Model setup and
workflow Summary

…by I•GIS
The Thomas B. Thriges Gade model – some facts
• The voxel grid in the Thomas B. Thriges Gade pilot area contains 3,74 mio. voxels
• Cell size is 5 x 5 x 0,5 m.
• Grid size: 1200 x 1300 x 30 m
• GeoScene3D can handle voxel grids up to 16 mio. voxels
• The voxel grids are regular with even cell sizes (user defined X, Y, Z)
• More voxel grids can be combined.
• Existing layer models can easily be converted to voxels
Number of voxels based on different grid geometries.
X (meter) Y (meter) Z (range) Z (vertical cell size) XY (horizontal cell size) Cells (total)
100 100 30 0,5 5,0 24.000
250 250 30 0,5 5,0 150.000
1.200 1.300 30 0,5 5,0 3.744.000
250 250 30 0,5 2,5 600.000
1.200 1.300 30 0,5 2,5 14.976.000
10.000 10.000 30 2 25 2.400.000
TBT pilot area
tools
Model setup and
workflow Summary

…by I•GIS
Urbane voxel models - opportunities and perspectives
• Development of highly detailed geological models.
• The possibilities of using many different datatypes, and hereby to implement e.g.
the human impact.
• Development of detailed models for many purposes (urban development,
geotechnical, Water Sensitive Urban Design (WSUD), contaminated field sites,
groundwater flow, vulnerability assessments etc.).
• One model optimized for several purposes.
• Import and export of data in different formats.
tools
Model setup and
workflow Summary

…by I•GIS
20-50% sand. Total volume = 1.960.000 m3.
Horizontal slices. Clay-sand distribution. Level 4 (DNN).
tools
Model setup and
workflow Summary
60-100% sand within region. Total volume
154.038 m3.
Vertical slices.
Cross sections
Urbane voxel models - opportunities and perspectives
• Easy model update (when data and work flow are ready).
• Voxels can be changed individually. Easy creation of different model scenarios for
hydraulic calculations
• Preparation of data can be time consuming
• Visualization
- isolating individual lithology classes or values
- Horizontal and vertical cross sections.
• Volume calculations based on user defined limits (values, surfaces, regions)

…by I•GIS
Thank you for your attention
•
tools
Model setup and
workflow Summary

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