The October GeoStudio TechTalk introduced you to the GeoStudio Core bundle, including common use cases that can be analysed using the products included in the bundle.
This video will take you through the step-by-step process of defining the analysis tree, materials, and geometry, followed by reviewing the results of an example project.
The GeoStudio Core bundle combines the three GeoStudio products that are most commonly used in engineering projects: SLOPE/W, SEEP/W and SIGMA/W. The integration of these three products can help you achieve realistic results for various real-world problems.
1 hr 4 min
<v Vincent>Hello, and welcome to this GeoStudio Tech Talk.</v>
These monthly webinars are designed to improve
understanding of the software
and ultimately promote success in engineering projects.
This month’s Tech Talk will feature GeoStudio Core
integrating SLOPE/W, SEEP/W, and SIGMA/W
to solve complex problems.
I’m Vincent Castonguay.
I work as a research and development specialist
with the GeoStudio Business Unit here at Seequent.
Today’s webinars will be approximately 60 minutes long.
Attendees can ask questions using the chat feature.
I will respond to these questions via email
as quickly as possible, and a recording of the webinar
will be available so participants can review
the demonstration at a later time.
GeoStudio is a software package
developed for a geotechnical engineers
and earth scientists comprising several products.
The range of products allows users
to solve a wide array of problems
that may be encountered in these fields.
Today’s would be in our relates specifically
to three of our products, SLOPE/W, SEEP/W, AND SIGMA/W.
Those looking to learn more about the products,
including background theory, available features,
and typical modeling scenarios
can find an extensive library of your sources
There you can find tutorial videos,
examples with detailed explanations
and engineering books on each product.
Let me start this webinar by showing you
this beautiful picture of a slope plunging toward the sea.
This is either a tourist dream spot
or the geotechnical engineers nightmare,
depending on who’s looking at it.
A geotechnical engineer will naturally see option two.
This complex, natural geological feature
will often be turned into a 2D representation
stripped of as much of the complexities as possible
to understand the key mechanisms, controlling behavior.
A question a geotechnical engineer might need to answer
regarding this slope is, is the slope stable?
To better represent the problem
and be able to properly answer the questions
we might have to consider the water conditions
that exist in the slope.
Where’s the water table?
How does it affect shear resistance?
We might also need to consider if there are stresses
and strain conditions that affect the slope as well.
Once all of these elements are considered,
then we can begin to answer the engineering question
and proceed to a slope stability analysis.
The process I just described
is exactly what this webinar’s all about.
How can we use the GeoStudio Core products
in an integrated way to solve a complex engineering problem?
In this webinar,
we will first review the GeoStudio Core products.
Next, I will spend a moment discussing
the numerical modeling process
and the important aspects to consider,
to conduct a successful numerical analysis.
Finally, I will demonstrate how to put this on into practice
by creating an example where the construction sequence
of two embankment is simulated
using the full GeoStudio Core lineup of products.
Let’s dive into it by reviewing each product
that composes the GeoStudio Core lineup.
As I mentioned earlier,
GeoStudio Core refers to the three most popular products
part of the GeoStudio portfolio.
SLOPE/W, SEEP/W, and SIGMA/W.
SLOPE/W is a limit equilibrium stability application,
where a slope is split into a number of slices,
driving in resisting forces are calculated
within each slice,
and factors of safety are computed.
Slope is all fundamentally about comparing resistance
versus driving forces.
Water seepage is often a governing factor
in many geotechnical problematics.
SEEP/W is a finite element software
where a domain is disguised into small elements
in order to resolve the water balance within the domain.
SEEP/W will help establish water conditions
that can then be used by other modules in GeoStudio.
Finally, SIGMA/W is the stress-train modeling module
Similar to how SEEP/W functions,
SIGMA/W disguises a domain into finite elements,
but this time to resolve the force-displacement equilibrium.
SIGMA/W helps establishing the stresses and strains
that exist within a domain.
The strength of the GeoStudio Core package
lies within the tight implementation
of the various physics that interact with each other.
Groundwater conditions calculated with SEEP,
can be made to influence the stresses and strains
that are calculated with SIGMA/W.
Both of these physics can in turn,
be brought in to SLOPE/W
to calculate the stability of a slope or earth structure.
Each model can be made to impact the others in various ways
that we will discuss in this webinar.
Let us now focus on the numerical modeling process
and what are some of the important aspects to consider
when setting up a more complex numerical analysis.
Using SEEP/W and SIGMA/W in conjunction with SLOPE/W
brings some new challenges that need to be addressed,
especially for users who are more experienced
with using SLOPE/W alone.
Imagine I have an engineering problem to solve,
and I wished to proceed via numerical modeling
to help me with this task.
I will first need to conceptualize the problem at hand
so that I can subject my conceptual model to analysis.
So for example,
this slope that I showed at the beginning of the webinar
could be conceptualized as the following geometry.
Conceptualization has at its core
the idea of simplification.
When performing numerical simulations,
we tend to over complicate the geometries that we use
probably in fear of missing out on important details.
If you go back in mere 10 or 20 years,
trying to solve very complex geometries
would have been almost impossible
because of lack of computational power.
Nowadays however, the most basic laptops
can solve quite complex problem.
So in a way, there’s a tendency to avoid simplifying
because we know the computer can handle it.
But the point remains that simpler geometries
often lead to easier results interpretation.
We should thus simplify as much as we can
and come back later on when we have a good grasp
on what the results mean
and add more complexity, if necessary.
The next step to solve the numerical modeling problem
would be to carefully choose the physics
that apply to the problem at hand.
I like to view these physics
in terms of GeoStudio products.
For example, if I’m trying to model
the effect of disappearing permafrost under a culvert,
I’ll need to include in my model SEEP/W
to account for water transfers,
TEMP/W to simulate the heat exchanges,
and SIGMA/W to compute the resulting stress-strain behavior.
Any engineering problem should be carefully studied
to decide what physics apply into consequently,
which GeoStudio module should be included in the analysis.
As we add physics into our models,
we also need to choose which constitutive laws
will correctly represent to soil behavior.
A constitutive law is a set of mathematical equations
that wishes to translate real soil behavior
into computer language
so that GeoStudio can adequately model the soils
in a way that fits the field reality.
Constitutive laws exists to represent
the stress-train behavior of soils, for example,
or the ability to transfer water and heat
or any other behavior feature we deem important
in our simulations.
Various parts of a domain can require
distinct constitutive laws
as the materials might behave quite differently.
Choosing the appropriate constitutive law
for a particular soil requires knowledge and experience.
While it is not necessary to know and understand
every intricate detail of the workings
of the various constitutive laws,
it is important to have a general understanding
of the models we choose to use.
Otherwise we might be unable
to correctly interpret the results.
The next item on the list to define
is the boundary conditions that apply to our domain.
Boundary conditions can take many forms
depending on what type of analysis we are conducting,
but they generally serve the same general purpose
and forcing certain conditions to part of the domain
in order to drive the simulations.
In the case of a SIGMA/W simulation, for example,
boundary conditions could include limiting displacements
on the edge of the domain or applying forces and stresses.
Specifying the hydraulic condition
is also a form of boundary condition application.
Appropriately defining the boundary conditions
that apply to a numerical model can be quite challenging
and might be easy to overlook.
Specifying the wrong bunch of conditions for a problem
will cost just as much problem for the overall solution
as would using a batch geometry
or failing to choose the appropriate inputs
for the constitutive laws.
Once the steps one to four I’ve been properly dealt with,
we can move on to solve the numerical analysis.
We call this step, interpretation.
For the user, this is generally the simpler step
of the whole modeling process.
Once the calculations are completed,
GeoStudio will output results,
that can be viewed through contour plots
or line plots for example.
But calculated results in themselves aren’t worth much
if they are not properly verified by a competent user.
This step is crucial in any numerical analysis.
One must have sufficient knowledge and experience
to be able to look at simulation results
and assess if the response
as computed by the software makes sense.
In most cases, the software will input some results.
It is up to the user to understand what these results mean.
And we often say that the numerical modelers
should know the answer they expect
before even launching the software they intent to use.
Having a general idea of how the results should look
will help user on interpret
what the software is telling them.
Finally, this verification step might reveal some flaws
and choices made along the way
from conceptualization to interpretation.
It is quite common then that we will need
to take a step back as we inspect computed results
to rethink our constitutive law choices, for example,
or that particular boundary condition we were unsure about,
if it was appropriate or not.
Critically assessing these choices
will help produce higher quality numerical simulations.
A feature of numerical modeling
that users will most often encounter
is what we call parent-child relationships.
In real life a child inherits certain characteristics
of their parents, which they can in turn pass along
to their own child.
Child’s of the same parents
will share the same characteristics.
Well, the same holds true for GeoStudio analysis.
These characters takes parent analysis
will pass on to child analysis,
will take the form of stressors, pore-water pressure,
accumulator strains, and so on.
This helps create hierarchy and structure
in complex analysis trees where many analysis types
might cohabit and share information.
So for example, in this analysis tree,
all the analysis displayed share the same geometry.
The seepage analysis sits one hierarchy level higher
in the analysis tree than the In-Situ analysis.
As such, the seepage analysis acts as the parent
while the In-Situ analysis is the child.
The In-Situ analysis can then inherits certain features
of the seepage analysis, in this case,
pore-water pressure conditions.
We can define this when defining each analysis.
Important to note here is the limit equilibrium analysis
displayed further down in the analysis tree.
This analysis is also a direct child
of the seepage analysis.
Since it sits at the same level as the In-Situ analysis,
you can call the siblings.
They both have access to the information
provided by the parents, seepage analysis.
Continuing on in the analysis tree,
the stress correction analysis sits one hierarchy level
below the In-Situ analysis.
The In-Situ analysis is then considered
the parent of the stress correction analysis,
and it can pass along information to it.
Finally, that analysis labeled tree, A, B, and C
are all siblings
whose parents is the stress correction analysis.
We are now ready to move on to the practical example
we will analyze to illustrate the various concepts
that were discussed in the webinar.
Cubzac-les-Ponts refers to test embankments
constructed in the 1980s in France
and studied by various researchers.
Two embankments in particular were analyzed.
Embankment A, which was both built fast and high
to purposely result in failure of the underlying soft clay.
Embankment B was constructed slowly
to monitor how pore-water pressure dissipation
would occur in the underlying soft clay.
The goal here is to use GeoStudio Core
to replicate the results.
The construction sequence for both embankments
is shown on this plot.
Embankment A, shown in blue was constructed in four lifts
and reached a maximum height of 4.5 meters
after eight days of construction.
Embarkment B, shown in red was constructed in six lifts
and only reached a maximum height of 2.4 meters
after six days of construction.
Embankment A failed on the ninth day
while Embankment B was monitored for years
after construction stopped.
Here is a cross section of embankment A
where we can see the four lifts of feel in orange,
built on top of a two-meter thick desiccated crust
And the rest of the soil deposit
is a soft clay material in green.
Similarly, here is embankment B’s geometry,
where we can see a smaller total height for the embankment,
as well as the small lifts used.
Since both embankments were constructed on the same site,
we encountered a same desiccated, crust
and soft clay deposits.
To cut computational effort in half,
we can make use of the symmetry of the geometry
by cutting the domain in half
where the summitry axis passes.
We will see later how boundary conditions
where that symmetry axis lies need to be modified
to properly account for the simplification.
The initial hydraulic conditions
are very simple at the test site
with the frantic surface being positioned
at eight meter of elevation,
midway into that desiccated crust.
These conditions apply to both embankments.
Let us now take a look at the analysis tree structure
for each embankment scenario.
For embankment A, the first analysis performed
uses SEEP/W to calculate the pore-water pressure
in the domain.
Next, a SIGMA/W In-Situ analysis is performed
to initiate the stress conditions within the domain.
Note here the father child relationship.
The In-Situ analysis will use a pore-water pressure
defined by the SEEP/W analysis.
Next embankment is constructed using SIGMA/W
following the sequence described earlier.
The consolidation analysis take advantage of SIGMA/W’s
fully coupled formulation
where a pore-water pressure migration
is properly simulated as soil consolidation occurs.
The final step to this analysis tree
is a stress-based stability performed in SLOPE/W.
The stresses and pore-water pressure conditions
that exist at the end of stage four of construction sequence
are passed along to the SLOPE/W analysis
to calculate the factor of safety.
A very similar approach is used for embankment B
where initial pore-water pressures
are calculated in SEEP/W,
In-Situ stresses are defined in SIGMA/W,
and the embankment’s constructioned
following the slower-paced sequence laid out earlier.
Once the embankment reaches its maximum height,
at dissipation phase is performed.
And essence, this is just a SIGMA/W conciliation analysis
where no extra load is added
and where we allow the accessible water pressures
to dissipate as time passes.
In this case, the dissipation is allowed to proceed
during 2000 days, which is roughly five and something years.
Finally, a stress-based stability analysis is performed
to verify the factor of safety exactly after
the six stage of construction.
The final aspect of these simulations
that need to be discussed before we jump into GeoStudio
is material definitions
or the choices of constitutive laws if you will.
We will review these choices for each GeoStudio model
in their respective order of appearance
in the analysis tree.
Note that both simulated embankments
share the exact same soil properties.
For the SEEP/W analysis,
the embankment fill is model using a saturated only model
with a large saturated hydraulic conductivity
to promote drainage.
The soft clay is also modeled
using the saturated only model
since we expect this material to remain saturated
throughout the duration of the analysis.
As you will see a few minutes,
the desiccated crust must employ
a saturated/unsaturated model,
as the water table will fluctuate within this layer
during the analysis.
For the SIGMA/W analysis, isotropic elastic materials
are used for both the embankment fill
and desiccated crust as these are quite stiff materials,
and we expect most of the deformations
to occur in the underlying soft clay.
The soft clay is modeled
using the modified cam clay material model.
This constitutive model
is formulated on the classical elastic plastic framework
and exhibits hardening or softening behavior,
depending on the over consolidations state.
Moderately over constellated to normally compressed soils
therefore exhibit accessible water pressures
due to tendency for both elastic
and plastic volumetrics training,
which is an important aspect of soft clay behavior.
Finally, for the SLOPE/W analysis,
Mohr-Coulomb material models are used
so that factors of safety can be calculated
based on the available resistance
defined by the Mohr-Coulomb criteria.
We are in are ready
for the demonstration part of this webinar.
I will open GeoStudio
and walk you through the process of defining and solving
the values analysis required
to study the Cubzac-les-Ponts example.
Here I am in GeoStudio.
The first step to any new project is to create a new file.
Let’s choose to metric letter template
and name the analysis, Cubzac-les-Ponts embankments.
I’m going to add a first 2D geometry to the project,
which will be dedicated to embankment A.
As the geometry will be shared through the values analysis,
I can define it even before I add
any specific analysis to the project.
To make sure I properly track the changes I make,
I will save the file right away.
There are many ways to draw a geometry in GeoStudio.
I already have an Excel workbook
where the coordinates of the geometry points are listed.
I will simply copy paste the X and Y columns
into the defined points window to save time.
Once this is done,
all the points needed to draw the geometry are available
to help me draw the regions
that will define the various materials
and highlight the construction sequence.
By clicking on Draw Regions,
I can easily draw the lower region where the soft clay lies.
Then the upper region where the desiccated crust is.
And finally, each of the four lifts
used to construct the embankment.
It is important here that I split the embankment
into the correct number of lifts,
even if they will share the same material properties
as they will be activated or built, if you will,
With the geometry now defined,
I can go ahead and add a SEEP/W steady-state analysis
by clicking on Defined Project, then add,
and finally choosing the steady state option
within SEEP/W analysis.
Note that I could change the analysis type to transient
if I wanted to, later on through this menu.
I will name this analysis, initial pore-water pressures.
I will take care of meshing right away
by clicking on the drum mesh properties button.
I can change their mesh layout for the whole analysis
by selecting the entire geometry,
choosing to edit the selected regions
and choosing an appropriate meshing pattern.
Quads and triangle finite elements
are generally a good choice for most use cases.
In the Elements tab, I will apply secondary nodes
as this will provide enhanced precision
for the SIGMA/W analysis to come.
Keep in mind that just as for the general geometry
that is drawn, mission priorities
will also be shared across all the finite element analysis
that use a common geometry.
Given the dimensions of the geometry,
I will specify a global finite element mesh size
of one meter.
I can now inspect the meshing
to make sure it is appropriate.
Given the triangular shape of the embankment,
I could decide to apply triangular elements
only to this part of the geometry.
I’m happy with how the meshing looks now.
As I mentioned earlier,
when discussing the numerical modeling process,
once the simple geometry has been defined,
labeled conceptualization earlier,
and the proper physics have been chosen, in this case,
as steady-state seepage analysis,
I should choose and define the appropriate constitutive laws
for the problem at hand.
To do so, I will go into Define Menu and choose materials.
Let me first define the material properties
for the desiccated crust.
The zone of the analysis with the feature both saturated
and unsaturated flow,
as the free attic surface will pass through it.
And water will seep through it
as the underlying clay consolidates
because of the weight added by the embankment construction.
For these reasons, we will use a saturated/unsaturated
material model here.
This particular model requires two input functions
to calculate water flow, the volumetric water content
and the hydraulic conductivity function.
Both of these parameters will vary
as a function of the matrix suction that develops into soil
as unsaturated flow settles in.
By clicking on the ellipses on the right,
I can define each of these functions.
I will add a new function and use a data point function,
which allows me to estimate
the volumetric water content function
using SEEP/W’s built in simple functions.
In the case of this desiccated crust,
the saturated water content is 0.3
and the material is classified as a silty clay.
By clicking edit data points,
I can view the function in semi log space
and inspect how the volumetric water content
will vary as a function of matrix suction.
As suction increases, water is drawn out of the soil,
and the volumetric water content decreases.
I’m satisfied with this function and name it crust.
I finally choose this newly defined function
through the drop down menu.
In a similar way,
I will not create a hydraulic conductivity function
by clicking on the ellipses on the right
and choose a data point function type.
Again, by clicking on estimate,
I can use SEEP/W’s estimation functions,
which are quite handy,
as we don’t necessarily always have access
to proper laboratory test to define these input functions.
In this case, I will use the Van Genuchten method
and associated with the volumetric water content function
we just defined.
In the case of the crust, a saturated hydraulic conductivity
of 0.008 meter per day is suggested
by the original authors of the Cubzac-les-Ponts study.
The residual water content is 0.05
and a maximum suction of a hundred KPA is sufficient here,
given the small scale of the geometry.
Inspecting the hydraulic conductivity function generated
reveals that as metric suction increases
the hydraulic conductivity decreases,
which is what we desired.
I’m satisfied with this function and name it crust.
And finally, I choose this newly defined function
through the drop down menu.
The definition of the material model
for the desiccated crust is now completed.
I will add another material,
this time defining the underlying soft clay.
As mentioned earlier, since we expect this layer
to remain fully saturated throughout the analysis,
we can use the simple saturated only, maternal model.
The saturated hydraulic conductivity
is set at 0.001 meter per day.
And the associated saturated volumetric water content
Finally, the embankment fill material
is also submitted using a saturated only material model
We use a very high saturated hydraulic conductivity
of one meter per day to promote fast drainage
towards the lower parts of the analysis.
The saturated volumetric water content is 0.4.
Now that all the materials have been defined,
I can draw them over the various regions of the geometry,
starting from the bottom to soft clay,
then desiccated crust.
Notice here that I won’t assign the fill material just yet,
as the goal of this first analysis
is simply to establish the hydraulic conditions in the soil
prior to beginning the embarkment construction.
The last step to perform
before we can move on to solving the analysis
is to define appropriate boundary conditions.
In this case,
the boundary conditions are very straightforward.
As the piezometric level was measured
at eight meter of elevation throughout the site.
To represent this, I would go into the Define menu
and choose Boundary conditions.
I will add a new hydraulic boundary condition,
choose the water total headkind,
and define it as a constant head elevation of eight meters.
I can then name this new boundary condition
and assign it in an easy two-spot color.
Once the boundary condition has been created,
I can click on Draw Boundary Conditions
or use the dropdown menu
to apply it to the base of the geometry.
This means that a total head of eight meters
will be applied to each of the point
at the bottom of the analysis.
When launched calculations,
SEEP/W will calculate the corresponding pore-water pressures
everywhere in the domain
as to satisfy the supply boundary condition.
We are now ready to solve the analysis.
Clicking on Start will automatically save the file
and launch the calculations.
Once the analysis is marked as solved,
I can switch to the results view
and inspect the calculated results.
This is the all-important verification step
I alluded to earlier.
By clicking on Draw ISO Surface,
I can draw a continuous line
indicating where water pressure of zero KPA
is in the domain.
This is an easy way
to view where the water table is positioned.
In this case, as we desired,
the free attic surface is located in the desiccated crust.
Using the contours dropdown menu,
I can select the pressure head counter type
to view the water pressure in the entire domain.
And by selecting draw contour labels,
I can click on various contour lines
to inspect the water pressure values in the domain.
In our case, the water pressure is currently indicated
as eight meter high at the base of the analysis.
Our SEEP/W analysis then correctly represents
the initial water conditions we wanted to define.
We can move on to the other parts of the analysis.
The next part of the workflow will be to add
the SIGMA/W analysis to simulate the construction
of each embankment lift.
But before any lift can be added
on top of the existing soil deposit,
the initial stresses must be defined within the domain.
To do so, we’ll go back into the definition view,
click on Define Project
and add a SIGMA/W In-Situ analysis.
By initially selecting the precedent SEEP/W analysis,
when adding the next analysis,
I ensure that the subsequent analysis is created
as a child of the SEEP/W parent.
You can inspect this by simply noticing the L shape
that places the newly added SIGMA/W analysis underneath
the SEEP/W analysis.
You can also see that the initial
pore-water pressures analysis,
is indicated as parent to the In-Situ analysis here,
right underneath the analysis name.
For the In-Situ analysis,
we will use a gravity activation method
where gravity forces will pull downwards on the nodes
and the appropriate horizontal reactions will be calculated
based on the boundary conditions we will define.
The field below indicates that
the pore-water pressure conditions for the analysis
will be inherited from the parents, SEEP/W analysis
just as we wanted.
Notice here are how the materials
that were previously defined in SEEP/W already exist
in SIGMA/W, but the associated colors are great.
This indicates that the materials
are currently not properly defined
for the analysis we want to perform.
By clicking on Define Materials,
I can now edit these materials within SIGMA/W
and choose appropriate constitutive laws for each.
As discussed earlier, both the desiccated crust
and the fill materials will use an isotropic elastic model.
Starting with the desiccated crust,
I must input appropriate values in every field
to make sure the model is properly defined.
Following indications by the authors of the study,
the unit weight is set at 16.5 kilo newtons
per squared meter.
The effective elastic mandalas is supposed constant
at 3000 KPA.
And the effective Poisson’s ratio is set as 0.4.
The response type for this material is strain
as excess pore-water pressure
shouldn’t build up into that site layer.
We did not wish to track void ratio changes
for this material so we can leave it
as it is default at 0.5,
and it will have no influence on the soils response
given the isotropic elastic model used.
Similarly, for the embankment fill representative values
are chosen for each required field
of the isotropic elastic model.
Notice the higher value of unit weight used here,
21 kilo newtons per square meter,
which is typical for fill materials.
Finally, the soft clay material
will use the Modified Cam Clay model.
For this model, void ratio plays an important role
and must be adequately adjusted.
Based on the author’s publication,
a representative value of 2.25
is chosen for the entire clay deposit.
On site the clay was deemed slightly over consolidated.
So, an over a consolidation ratio of 1.4 is used.
Stiffness parameters for the Modified Cam Clay model
required the use of the Lambda and Kappa parameters,
which represent the slope of the normally consolidated
and rebound lines
in a one deconsolidation test respectively.
For the clay at cubzac-les-Ponts,
the following values are representatives.
An effective Poisson’s ratio of 0.4 is used again here.
The friction angle of clay is set at 30 degrees,
which correspond to a critical stress ratio of 1.2
Finally, the response type will be on drained
for this material model since we are interested
in monitoring the effect of excess pore-water pressure
buildup in the clay deposit
as the embankment is being built.
The last step to perform before solving the analysis
is to apply proper boundary conditions to the model.
In SIGMA/W, these boundary conditions
often take two different forms,
stress or force boundary conditions,
and displacement boundary conditions.
For this particular study,
there are no stresses or forces to apply on the domain.
However, we need to constrain the formations
in some part of the domain,
which corresponds to displacement boundary conditions.
we want to prevent displacements of the nodes
located at the edge of the geometry
so that they do not sway sideways once gravity is applied
or when the embankment is constructed.
Similarly, we want to prevent displacement of the node
located at the bottom of the geometry
so that gravity has something to push on
when it is activated.
Otherwise, when we are to turn on gravity,
the entire geometry would slide downward
toward the bottom of the screen.
To apply these displacement boundary conditions,
I will click on the Draw Boundary Conditions button
and assign a fixed X to the edges of the analysis.
A fixed X boundary condition
is simply a displacement boundary condition
that states that displacement in the X direction
should remain at zero for every node long,
which is boundary condition is applied.
Selecting the nodes on the edge of the geometry
will apply the chosen boundary condition.
Similarly, I will apply a fixed XY boundary condition
to the bottom of the geometry.
This time supports in both directions are drawn at the nodes
indicating that displacements will be permitted
at both directions during the simulation,
just as we required.
We have now probably defined a boundary conditions
for the In-Situ SIGMA/W analysis
and are ready to solve the analysis.
In the Solve Manager window,
I can untake the initial SEEP/W analysis
as I don’t want to solve it again.
Once I click on Solve, gravity is applied at the nodes
and resulting stresses are calculated.
Once calculations are completed,
I can switch into Results View and inspect the results.
I can draw contours of the total vertical stress
to view the stress distribution.
I can also plot the total vertical stress,
the effective vertical stress and the pore-water pressure
on a vertical line drawn
from the two of the future embankment.
I can view these three stress components together
by shift the king, each injured or plot-defined.
We can see here that suction develops
in the first meter of the disputed crust,
which increases the effective vertical stress
compared to the total vertical stress.
These results satisfy me,
so I can move on to constructing the embankment.
As I showed earlier,
the first embankment lift was constructed
and left in place for four days
before another lift was added.
During these four days, the accessible water pressure
that had instantly developed in the soft clay deposit
was allowed to consolidate.
To simulate this behavior,
I will add a SIGMA/W consolidation analysis
to the analysis tree.
I will go back into definition view,
and click on Define Project.
Once the In-Situ analysis is selected,
I will go into add
and choose a SIGMA/W consolidation analysis.
By having selected the In-Situ analysis
prior to adding this new analysis,
I made sure that the consolidation analysis
was a child of the In-Situ parent.
Note that the initial stress and pore-water pressure
will come from the parent analysis
as indicated by this drop down menu.
And we’ll make sure that the reset displacement and strains,
and reset state variables check boxes are checked
because I want to discard any strains
that might have arisen during the In-Situ analysis.
These strains took place in the geological history
of the soil deposit.
They have already happened
before the embankment construction began.
So I don’t want to account for them moving forward.
Next, I would go into the Time tab
and adjust the duration to four days
to reflect the construction sequence.
I will also adjust the number of calculation steps to four
so that I record the behavior everyday.
I will add the first embankment lift
by going into Draw Materials
and simply applying the fill material
to the first lift region.
When solving the analysis,
the materials weight will be activated
and the appropriate pore-water pressure response
will be generated in the on drain soft clay.
You will notice that the fixed displacement
boundary conditions that existed in the parent
In-Situ analysis already exist in this new analysis.
This is so specifically
because of the parent/child relationship
these two analysers entertain.
I could however, changed the boundary conditions
in the child and indices
without affecting the parent if needed.
And in fact, this is what I’m going to do right here.
I will add a drainage type boundary conditions
to promote drainage toward the surface
at junction of the desiccated crust and the embankment.
This way, excess pore-water pressures
that develop in the soft clay,
will be able to migrate toward the surface.
I will also add back the eight meter,
total head boundary condition to the bottom of the analysis
as this condition will still hold true
during the complete duration of the construction sequence.
Now that the materials were applied
and the boundary conditions were properly adjusted,
I can solve the analysis.
Once the computations are over, I can go into Results View
and inspect the results.
Plotting the pore-water pressure contours
highlights how accessible water pressures developed
once the first lift embankment was applied
on top of the desiccated clay.
By navigating through the calculation steps
in the steps window,
I can first select to view the pore-water pressure
before the first lift was added.
Then I can set a following days
to see the accessible water pressure.
Plotting the pore-water pressures
and multi selecting all the calculations steps
also clearly shows that pore-water pressure increased.
The red line indicates the starting pore-water pressure.
If time was allowed to tend toward infinity,
the pore-water pressure profile
would fall back on the red line
and these dissipated pour water pressures
would translate into consolidation deformations,
but instead of allowing the pore-water pressure
to dissipate further,
another leaf of embankment will be added
on the fifth day of construction.
To add the second lift,
I will proceed just as I did for the first lift.
returning into definition view, clicking on Define Project
and adding a SIGMA/W consolidation analysis
as a child of the first stage of construction.
This time, I don’t want to check the reset displacement
and strain and reset state variable check boxes
As I want to keep accounting
for the added strains produced by the construction sequence.
In the Time tab, I will adjust the duration to two days
and a number of steps to two
to properly reflect the construction sequence.
As you’ll recall, the second embankment lift was added
and maintained in place for two days
before the third lift was placed.
By going into Draw Materials, I can add the second lift.
The boundary conditions remain exactly the same as before
for this analysis as we are simply adding more weight
to the embankment.
I can go ahead and solve this analysis
and inspect the additional accessible water pressures
that were generated as this new lift was placed
on top of the first one.
Let me go ahead and quickly add the third and fourth lifts
to the embankment using the exact same procedure.
Both lifts were constructed in a single day
before the next lift was placed.
Inspecting the results after the fourth lift has been built,
shows how excess pore-water pressures
have continued to build up in the soft clay layer.
By plotting the effective vertical stress profile
we can see how the effective stresses are being reduced
by the increasing excess pore-water.
This will affect sheer resistance that can be mobilized
and will result in large deformations being generated.
Let us look at these right now.
I will begin by plotting surface settlement
which correspond to vertical displacement
in the wide Y direction along the embankment
at the top of the desiccated crust layer.
As expected settlements are smaller
toward the left side of the embankment,
as the height is smaller.
And toward the middle of settlements reach 80.5 centimeters.
Another interesting deformation plot to look at
is the lateral displacement at the toe of the embankment.
The toe of the embankment itself moved toward the right
by more than 17 centimeters.
Another way to appreciate these deformations
is to overlay XY displacement vectors
on top of the geometry.
To do this, I click on the Draw Vectors button
and toggle and on the XY displacement vectors.
We can now see how the entire right side of the embankment
deforms in a circular motion toward the right side.
Seeing this deformation pattern,
one wonders if stability of the embankment
is currently compromised.
To verify this, let us add a SLOPE/W stability analysis
to this analysis tree.
As before, to add this new analysis,
I will go back into definitions view
and click on the Define Project.
I will add a SLOPE/W, SIGMA/W stress analysis.
This type of analysis will use the stresses
passed along by the parent’s SIGMA/W analysis
and perform stability analysis based on these stresses.
Compared to a traditional SLOPE/W limit equilibrium,
the finite element slope stability analysis
doesn’t need to iterate to find enters life stresses
that will ensure the factor of safety
is the same in all the slices.
Instead as the stresses are known
the resistance is directly compared to the substation
and factor of safety is locally computed in every slice.
The overall safety factor for a slip surface
is determined by integrating the share resistance
and mobilized chair along the entire slip surface.
The slip surface direction of movement
will be from left to right,
and I will use the entry and exit method
to generate the trials grip surfaces.
I will also toggle on the slip surface optimization option.
As we define the slope stability analysis,
notice how the materials are now grayed out.
This again, indicates that our materials
are not properly defined for the analysis.
By going into Define Materials,
I can see no resistance model is currently used.
The SIGMA/W material models differ
from what we need for stability analysis.
So I must make sure to properly define the materials
Every material we have,
we’ll use a Mohr-Coulomb material model.
The soft clay will use equation of zero KPA
and a fictional angle of 30 degrees.
And notice that the unit weight was already defined here
as we had defined it previously in the SIGMA/W analysis.
The embankment field will use zero cohesion
and a fictional of 35 degrees.
An finally, the desiccated crust
will use a zero cohesion,
as well as a friction angle of 30 degrees.
Before solving the analysis
I need to define where to slip surface
entry and exit points will be.
This layout that I’ve just drawn will produce 10 increments
of entry and exit points as well as 10 radiuses
to be studied for each pair of entry and exit points.
Once I hit the Start button,
all the trials slip surfaces are analyzed
and a critical slip surface is shown.
The slip surface reaches into the soft clay layer
where excess pore-water pressure had built
during the embankment construction.
The minimum factor of safety is computed as 1.09.
And from this slip surface SLOPE/W calculated
and optimized slip surface,
where the fact of safety was decreased further down to 1.03,
by optimizing the sleep surface geometry.
At this stage of the embankment construction sequence,
the stability is marginal.
This correctly reflects the situation described
in the case study,
as the embankment failed on the ninth day of construction.
By plotting the sheer resistance and the sheer marbleized
along the slip surface, I can see how both of these vary.
For the slices that are located
toward the top of the embankment,
their share mobilized is generally higher than resistance
and conversely, toward the toe of the embankment.
This type of plot neatly shows where resistance is too low
along the slip surface.
This concludes the analysis
for the first embankment geometry.
This embankment was built quickly
so that the embankment would fail.
We saw that the excess pore-water pressure
that developed in the soft clay layer
during the embankment construction was sufficient
to bring the overall factor of safety close to one,
indicating that the stability was marginal.
The second embankment was constructed more slowly,
and to a lesser height than embankment A.
Since the geometry of the second embankment is different,
I will need to create as distinct geometry.
I can do this within the same file
to keep both analysis together
and easily use the same materials and boundary conditions
that I have already defined.
To the new geometry, I will go into definition view,
.click on Define Project,
select the first element of the overall hierarchy
and add the 2D geometry.
Let us call this one embankment B.
Similar to how I worked for the first embankment geometry
I will go into defined points to paste the geometry points
I already had on hand from an Excel file.
I will finish defining the geometry by drawing the regions
corresponding to the materials that will be used later on.
Notice here, as we saw earlier,
we take advantage of the symmetry of the geometry
by only drawing half of the embankment.
I will now create the SEEP/W analysis
to initiate the water and seepage conditions in the domain
and also build the embankment lifts using SIGMA/W
just like I did for the first embankment.
The steps are mostly identical.
So I will speed up the process in the interest time.
Here, I adjust the mesh size and shape.
I draw the materials to the regions.
The materials are the same as for embankment A.
A I now apply the total head hydraulic boundary conditions
at the bottom of the domain, and solve.
I now create the In-Situ SIGMA/W analysis
to initiate the stresses.
I applied a fixed displacement boundary conditions
to the bottom and sides.
And notice here that I applied the fixed X
boundary condition to the entire left side of the geometry.
Even the lift regions that are currently empty.
These will not affect the In-Situ analysis,
but will affect the next SIGMA/W consolidation analysis.
I could have drawn each portion
when the lifts are individually placed,
but this saves a bit of time.
I now solve the analysis
and verify that distresses are appropriate.
Next I add the first lift of the embankment
using a SIGMA/W consolidation analysis.
I apply the material to the first lift
and apply the hydrate boundary conditions
just as I did previously.
I will add the remaining lifts
as separated SIGMA/W consolidation analyses
and inspect the results.
Plotting the pore-water pressure
under the central line of embankment
shows that the load created
by the construction of the embankment
created excess pore-water pressure.
The red line is the profile of the pore-water pressure
before the construction began.
I can also plot the surface settlement
along the entire length of the geometry
at the top of the desiccated crust.
Settlements are currently reaching
a maximum of 8.7 centimeters under the embankment.
We can also see an uplift near the embankment toe
reaching about 4.5 centimeters.
Finally, literal displacements
show that the toe of the embankment
is moving toward the right, which can also be seen
by drawing the XY displacement vectors.
At this point, it is interesting to perform
a stability analysis to verify how impactful
this slower construction sequence
and lesser embankment height was
compared to the embankment.
Again, I add a SLOPE/W stress-based stability analysis
at the tail of the analysis tree.
This time, the factor of safety is around 1.5,
which is quite a lot higher than previously,
and would not suggest stability issues.
This result aligns with what we expected.
The last analysis we will perform here
is a dissipation analysis.
In a sense, a dissipation analysis
is just a standard consolidation analysis,
but in which no additional load is added.
The goal is simply to let time pass
as excess pore-water pressure dissipates
and the soil consolidates.
To perform this analysis,
I will add another SIGMA/W consolidation analysis
to the analysis tree.
Notice that when going into Definition View
and then define project,
I will select stage six of construction
as this is the parent to which I want to add a child,
not the slope stability analysis.
In the Time tab, I will adjust the duration to 2000 days
and I will increase the number of steps to 50.
To make sure I have enough resolution in the earlier stages
of the analysis where pore-water pressure
will vary more quickly,
I will toogle the steps in to increase exponentially
and adjust the initial increment size to one day.
Finally, I will save the analysis results every 10 steps
as recording all the calculation steps
will provide more data than I really need,
including fewer safe steps will accelerate computations.
In the window on the right,
I can see the time increments as well as the safe points
that will be recorded.
I can now solve the dissipation analysis.
There are no further steps to take care of
as the boundary conditions are remained the same as before.
Once the analysis is solved,
I can, once again, inspect the results.
Plotting the pore-water pressure underneath the embankment
shows how the excess pore-water pressure
that had been generated by the embankment construction
has now mostly been dissipated after 2000 days.
The excess pore-water pressure dissipation we see
is synonymous with soil consolidation.
Plotting the surface settlement during these 5.5 years
or 2000 days reveals that vertical deformation
in the middle of the embankment
went from 11 centimeters to almost 55 centimeters.
This is the direct result of the consolidation
of the soft clay that took place
as excessive pore-water pressure were being dissipated.
This concludes the demonstration portion of the webinar.
In the interest of time, I have not shown comparison plots
between the simulated results in GeoStudio
and results from the original Cubzac-les-Ponts study.
Interested users should download the website example,
which contains both the GeoStudio file for you to review,
as well as a PDF with detailed comments
about the case study.
So this concludes the October edition
of our GeoStudio Tech Talk webinars series.
The webinar focused on GeoStudio Core,
the group of products featuring SLOPE/W, SEEP/W,
We saw how each product fulfills its own role
through an integrated solution approach.
We also reviewed how a thorough numerical modeling process
should be conducted.
And six important steps were laid out.
Conceptualizing a complex problem
into a manageable, simple model.
Choosing the appropriate physics
that should be taken into account.
Choosing and prioritizing the appropriate
constitutive of laws that correctly represent the soils
we want to model.
Applying boundary conditions
to drive the analysis or impose appropriate constraints.
Resolving the analysis
once the model is correctly defined
and interpreting the results.
And finally verifying the results
to make sure they appropriately represent
what we intended to model.
Each of these steps requires reflection
and might bring us to reconsider some choices
we made earlier in the modeling process.
We have also discussed what parent-child relationships are
and how the help structure a practical hierarchy
within analysis tree.
The final part of the webinar was dedicated to building
the Cubzac-les-Ponts example,
where to construction sequence of two embankment
built on soft clay is simulated
using the GeoStudio Core products.
We saw both the failure of embankment A
and the longterm behavior of embankment B
could be simulated appropriately in GeoStudio.
Don’t forget that you can download the example
from our website
if you want to give this workload a try by yourself.
If you’d like some new features and capabilities
added in GeoStudio Core, don’t hesitate to make suggestions
by submitting support requests.
Finally, don’t forget that GeoStudio learning content
is available for free through Seequence website.
We offer a three courses,
part of our learning management system.
GeoStudio basics, SLOPE/W fundamentals,
and SEEP/W fundamentals.
Head over to seequent.com,
create your Seequent ID using your company email address
and take advantage of these incredible
learning resources for free.
We have now reached the end of this webinar.
A recording of the webinar will be available to view online.
Please take the time to complete the short survey
that appears on your screen
so we know what types of webinars
you are interested in attending in the future.
Thank you very much for joining us
and have a great rest of your day.