Geotechnical News • June 2018
43
GEO-INTEREST
As observed in Figure 5, Geo Meshing
allows not only grouping the elements
by material type (upper image), but
also by construction sequence (lower
image). The lower image of Figure 5,
shows how Geo Meshing has assigned
a different name (and therefore a dif-
ferent color) to each of the construc-
tion lifts, for each stage. This process
is automatically done by Geo Meshing
while creating the 3D mesh. For this
specific model, it was done for the
sand dam and for the stored mate-
rial, thus dam construction sequence
and filling of the impoundment was
sequentially simulated.
The model has about 850,000 ele-
ments, with enough detail for getting
accurate response, but at the same
time, with a reasonable size for run-
ning it dynamically in reasonable
times.
Open Pit model
Figure 6 shows a 3D model of a
topography, before any excavation
has been simulated in the model. In
this image, the most relevant geologi-
cal units are displayed. In addition to
the geological units, the model shows
the mesh refinement performed using
Geo Meshing. Figure 7 shows the
same model, but at the excavation
final stage. This image shows how the
refined mesh zone is capable of repro-
ducing complex shapes within the pit.
The most challenging part of making
this model is the incorporation of an
interface, as shown in Figure 8. An
interface is a special spring element
that allows continuum models to be
locally discontinuous, thus creating
mesh separation or mesh relative dis-
placement. The interface in this model
is a non – planar surface, so it is hard
to comply the mesh with the interface
at each gridpoint and node. Geo Mesh-
ing has special features that facilitates
the interface creation for non – planar
surfaces. It generates a code that can
be called from FLAC3D® environ-
ment. In addition, Geo Meshing
allows the user to graphically select
the area where the interface will be
applied, without the need to extend it
to the whole model domain, and there-
fore, reducing unnecessary number of
interface nodes and elements (Figure
8).
Closure
Geo Meshing has evolved significantly
since it was first introduced as a set of
C++ programs. Now it is a self-con-
tained software capable of perform-
ing very complex tasks, in a friendly
environment.
The above shows just three examples
of what can be done with Geo Mesh-
ing, but many more projects have been
developed with Geo Meshing. In fact,
over 100 licenses has been distributed
so far, with users around the globe.
Some of them have reported success-
ful use of Geo Meshing, becoming a
key tool in their steps for performing
3D numerical analysis.
Alfredo Arenas
Geotechnical Civil Engineer, PhD
Golder Associates SA
Magdalena 181, Las Condes,
Santiago, Chile
56-2-26162010
A new monitoring system - CSattAR
Mehdi Alhaddad
CSattAR is a photogrammetric moni-
toring system that I developed during
my PhD research at the Cambridge
Centre for Smart Infrastructure
and Construction (CSIC). Part of
my research was to investigate the
behaviour of exiting cast-iron tunnels
when they are subjected to external
forces. This included monitoring
some extremely difficult-to-measure
deformations that were not readily
measurable when using conventional
techniques (I’ll show some examples
later). I also needed to monitor sig-
nificantly larger number of points than
was conventionally practical.
This led me to invest in developing
a new technique that needed to be
affordable with a research budget but
yet be able to monitor the deformation
of every ring that was influenced by
construction activities nearby ‘pre-
cisely’ and ‘accurately’. That led to
the creation of CSattAR. I installed the
system in several tunnel environments
and then spent some time developing
the system to work above ground (e.g.
monitor listed buildings). The system
is now able to operate outdoors as well
as indoors.
Fundamentals of the system
‘Photogrammetric’ is a mouth fill-
ing word but it simply means using
images to extract information and for
monitoring practices it means extract-
ing ‘deformation’ and ‘displacement’
measurements. ‘Displacement’ here
refers to absolute movement of a sin-
gle point with reference to the origin
of a coordinate system while ‘defor-
mation’ means the relative movement
between two or more points within a
structural unit (e.g. a masonry wall,
a tunnel ring, or a group of tunnel
rings).
