Stability analysis during rapid drawdown is an important consideration in the design of embankment dams. During rapid drawdown, the stabilizing effect of the water on the upstream face is lost, but the pore-water pressures within the embankment may remain high. As a result, the stability of the upstream face of the dam can be much reduced.

The dissipation of pore-water pressure in the embankment during rapid drawdown is largely influenced by the permeability and the storage characteristic of the embankment materials. Instead of doing a stability analysis of the embankment with an assumed piezometric line after the rapid drawdown, a rigorous approach is to model the dissipation of pore-water pressure in the embankment with SEEP/W first and then use SLOPE/W to compute the factor of safety of the embankment based on the computed pore-water pressures. SLOPE/W reads in the SEEP/W pore water pressure of all time steps automatically to compute the factor of safety versus time after the rapid drawdown. 

The following figure shows the critical slip surface and factor of safety before drawdown when the reservoir is at full supply level. The light blue region is the reservoir. The factor of safety before drawdown is 1.977.

The next figure shows the SEEP/W computed piezometric lines at different time steps after the rapid drawdown. As you can see, the piezometric surface in the embankment is dropping with time due to pore-water dissipation when the reservoir is empty.

The subsequent figure shows the critical slip surface and factor of safety of the embankment when the pore water pressure at 18 hours after rapid drawdown was used. The factor of safety is 1.144.

This last figure shows the computed factor of safety of the embankment versus time after the rapid drawdown. The factor of safety dropped quickly from 1.977 to below 1.0 shortly after the rapid drawdown and gradually increased to 1.737 after 58 days.

The advantage of this approach is that the hydraulic properties of the materials can be considered, and time can be included in the analysis. Therefore rapid drawdown is not just an instance in time, but is a process. A prerequisite is that a finite element transient seepage analysis is required, however in the design of an embankment dam, the hydraulic properties of the materials are usually available and a seepage analysis is likely necessary.

GeoStudio 2007 allows easy integration between SLOPE/W and SEEP/W, making this rigorous approach an attractive alternative.

GeoStudio 2007 Compatible with Windows^® 7

GEO-SLOPE is pleased to announce that GeoStudio 2007 is the first geotechnical modeling software to receive the "Compatible with Windows 7" logo from Microsoft.

The Compatible for Windows 7 logo indicates that GeoStudio 2007 will install reliably, run securely, and perform well on both 32-bit and 64-bit editions of Windows 7. Note that GeoStudio 2007 will also continue to run on Windows Vista, Windows XP, and Windows 2000. [read more...]

Banff Workshop

October 19-22, 2009. Banff, Alberta, Canada. Seats fill up quickly, so please register early.

Grokking GeoStudio

Check out Nate's latest blog entry that delves into sensitivity studies, probabilistic analyses, and other ways of generating large numbers of similar analyses.

We have added a new water ponding feature in all of the finite-element products, a much-requested feature after it was added to SLOPE/W.

This new feature shows the computed reservoir height dynamically moving during both the filling and drawdown of the reservoir.

To consider how this might enhance your next presentation, watch a movie of the feature in action

GeoStudio Update

Download version 7.14 of GeoStudio 2007 and review the release history for more details.

2009 European Workshop - June 1-3, 2009

We are fast approaching the Europe 2009 Geotechnical Modelling Workshop in Haarlem! There is still space available if you are considering attending this excellent training opportunity.

To join us, please complete the Registration Form or see the web site for complete details.

Peru 2009 Geotechnical Modeling Workshop

Last month we had the distinct pleasure of traveling to Lima and meeting nearly fifty engineers from Peru, Chile, Costa Rica, and Mexico at our first workshop in South America.

From our perspective the workshop was a great success and we are looking forward to cultivating the connections that were made for many years to come!

Relief wells are commonly installed on the downstream side of an earth dam or levee to control the seepage and pore-pressures. A key design requirement for a problem of this type is the required well spacing.

The plan view option in SEEP/W can be used to explore the relative effect of well spacing on the seepage and pore-pressures.

Read the whole Detailed Example and follow along in GeoStudio 2007 using the data file.

Upcoming Geotechnical Workshops

GEO-SLOPE is holding a series of public geotechnical modeling workshops this spring and fall where clients from around the world can gather to learn, enhance and fine-tune their numerical modeling skills under the guidance of GEO-SLOPE personnel.

The workshops follow a similar format, teaching general numerical modeling skills as well as hands-on experience with GEO-SLOPE software. Whether you wish to be eased into the world of numerical modeling, or experiment with new types of analyses, we invite you to join us at one of the workshops.

Space is limited, so please register soon to avoid disappointment!

Hong Kong Buildings Department

SLOPE/W 2007 has recently been added to the list of Pre-accepted Geotechnical Programs for use in Hong Kong.

Please contact GEO-SLOPE or visit the Buildings Department web site for reference numbers and validity periods.

Grokking GeoStudio

Find out why long filenames can cause problems, and how you can avoid some of the common pitfalls.

GEO-SLOPE International is pleased to announce that our next Geotechnical Modelling workshop will be held 1-3 June 2009 in Haarlem, The Netherlands. Our annual public workshops are well attended events where GEO-SLOPE clients from around the world gather to learn, enhance and fine-tune their numerical modelling skills under the guidance of GEO-SLOPE personnel.

See the Europe 2009 training page for a registration form and additional details on the workshop.

Volumetric Expansion due to Excavation

SIGMA/W is commonly used to simulate the deformation and pore water pressure response of foundation soils beneath the load of a stage-constructed embankment. A less common use of SIGMA/W is the simulation these phenomenon during unloading by means of an excavation. Rapid unloading can lead to the development of negative pore water pressures around the face of the excavation.

Embankment construction problems usually involve the generation of excess pore water pressures in the foundation soils if the stratigraphic units have a low hydraulic conductivity. The rapid placement of fill creates a tendency for volumetric compression; that is to say the soil void space wants to compress, but the pore water must be expulsed from the pore space in order for this to occur, leading to excess pore water pressures. The foundation soils consolidate over time as the excess pore water pressures dissipate at a rate that is dependent on the hydraulic conductivity of the soils, and the proximity to the drainage boundaries.

Keeping this in mind, consider what happens when a low hydraulic conductivity (e.g. clay) soil is unloaded by means of an excavation. The rapid removal of the soils in the excavation creates a tendency for volumetric expansion. The soil (void space) wants to expand because of the stress relief; however, this requires that the soil imbibe, as opposed to expulse, water. In other words, water must flow from the surrounding area to the unsaturated zone around the excavation. In extreme cases—such as rapid unloading (excavation) of very low hydraulic conductivity units—it may even be possible to depress the phreatic surface and require decades for the pore water pressures to recover to positive values.

Using the View Movie command in Contour, we can show the pore water pressure response during a SIGMA/W simulation of an excavation in a very low hydraulic conductivity soil. The excavation occurs rapidly and is completed in seven lifts. The unloading causes the phreatic surface to be depressed to an elevation of about 1 metre below the base of the excavation. The subsequent recovery of the negative pore water pressures occurs over a thirty year period.

Grokking GeoStudio

Find out how using the Snap to Grid option can help you avoid costly mistakes when defining your geometry.

Merry Christmas

As the holidays approach and we draw close to the end of another year, we at GEO-SLOPE would like to take this time to express our profound sense of gratitude. We are grateful for the team that we have assembled, and for the extraordinary things that we have been able to accomplish together. We are grateful for your supportive feedback, and for the opportunity to work with you and your organization to advance the practice of geotechnical engineering.

We would like to take this opportunity to wish you a Merry Christmas and a Happy New Year!

Dig It! The Secrets of Soil at The Smithsonian

If you are looking for something to do over the holidays that will still keep you "in touch" with your work, why not visit Dig It!

This virtual exhibit is part of the travelling exhibition currently on display at Smithsonian's National Museum of Natural History in Washington, D.C.

Dig It! journeys just under the surface to explore the fascinating world of soil, and why it is so important for all of us understand and protect.

Grokking GeoStudio

Are you re-typing the same functions over and over again for your analysis? Read Nate's blog and find out how you can create a database of common functions.

The Henry saltwater intrusion problem is considered the benchmark analysis for testing density-dependent groundwater flow models. Originally developed in 1964, a number of authors have proposed modifications to the problem. In particular, Simpson and Clement (2004) suggested that reducing the freshwater flux rate enhances the density-dependent effects; thereby improving the worthiness of the Henry problem as a benchmark analysis.

In this detailed example, both the standard and modified Henry saltwater intrusion problems are modeled using a density-dependent CTRAN/W analysis, and the results are compared to the semi-analytical solution.

Read the whole Detailed Example and follow along in GeoStudio 2007 using the data file.

Density Dependent Flow (40 MB)

GeoStudio Technical Symposium

December 23, 2008 - Shenzhen, China.
Dr. Leonard Lam of GEO-SLOPE International will be speaking at a technical symposium in Shenzhen, organized by GEO-SLOPE's partner, CnTech Co. Ltd. The topic of his talk will be “Advanced Geotechnical Modeling with GeoStudio 2007”.

Focusing on the power of an integrated analysis, Dr. Lam will be using the GeoStudio 2007 software to illustrate, and demonstrate, the many different types of engineering problems that the software can be used to solve.

Please visit CnTech's web site for additional information and registration details.

Grokking GeoStudio

Part science and part black art, read Nate's recent blog on meshing efficiently.

Laboratory tests on stratified materials often reveal values for hydraulic conductivity that are anisotropic: different in the horizontal and vertical directions. However, anisotropic ratios from laboratory tests, when applied to field situations, can result in unrealistic solutions.

This detailed example addresses how to use the anisotropic feature in SEEP/W, and discusses the issues that can affect anisotropy.

Read the whole Detailed Example and follow along in GeoStudio 2007 using the SEEP/W data file.

Anisotropy In Seepage Analyses (931 KB)

GeoStudio 2007 - 7.13 Release

Since our last release, we have been working on several important improvements to the software. As usual, version 7.13 is a free upgrade for all GeoStudio 2007 customers, but you may be asking, "why should I bother?" Here are just a few of the key improvements that we've made:

• Spatial functions can be linearly interpolated rather than kriged.
• Improvements to contouring spatial functions make the contours more accurate.
• Spatial functions can be previewed prior to being applied to regions.
• Verify now checks for overlapping geometry lines.
• Additional control over convex angles for fully-specified slip surfaces.
• The optimized factor of safety can no longer be larger than the critical slip surface.
• Include a potential seepage face above the elevation defined with a function.
• Better default values for certain convergence parameters.
• Spring Constant vs Displacement functions are once again supported.
• VADOSE/W now supports thermosyphons.

Plus more than 120 other improvements to the software!

Visit the Downloads page to update your software and read the release history for more details.

The Annual Geotechnical Modeling Workshop in Banff

With a full conference room of eager people and a brand new format, the 8th Annual Geotechnical Modeling workshop was definitely among the best we've ever held. Nestled in the heart of the Canadian Rocky Mountains, the Banff Conference Centre was a perfect setting for attendees to learn, enhance and fine-tune their numerical modeling skills under the personal guidance of GEO-SLOPE personnel.

Many thanks to all of the attendees, and the special group of people at GEO-SLOPE who helped to make the workshop such a great success! We are looking forward to next year's workshop and will post dates and locations when they become available.

Happy Birthday!

Grokking GeoStudio celebrates its first anniversary. Well done to Nate and the readers for reaching this significant milestone in the blogosphere.

The German Society for Geotechnics has worked on establishing some benchmark problems for validating numerical analyses. One of the benchmark examples is about the construction of a tie-back wall for a deep excavation in Berlin.

Part of the numerical validation program of the Society included holding an analysis competition where information about the project was made available to those wishing to model the construction and make a prediction of the wall performance. The lateral wall deflection was measured with an inclinometer and the main objective was to see if the analyst could predict the lateral wall deflection. The measured results were not made available to the analyst until the end of the competition.

SIGMA/W now has sufficient features and capabilities to simulate the construction sequence for this excavation, and obtains close agreement with the measured wall deflections.

Visit our web site for an in-depth review of the Berlin Tie-Back Wall.

Banff Geotechnical Modeling Workshop

The September workshop in Banff, Canada is almost full. Accommodations at the workshop location are limited, so if you are hoping to stay at the Banff Centre, reserve your seat now.

Remember that we have expanded the workshop to include an optional 4th day (September 18th). The format of this extra day will be flexible and will allow participants to choose from a series of concurrent specialized sessions on various topics.

Please visit the Banff Modeling Workshop page for full details.

Grokking GeoStudio

Check out the latest at the blog that dives into the details of GeoStudio, and leave a comment or question for Nate and other readers to respond to.

We have recently released a significant update to GeoStudio 2007. The version 7.1 release includes many features that had originally been slated to release with 7.00, as well as several important new features that have come about as a result of customer feedback.

As usual, 7.1 is a free upgrade for all GeoStudio 2007 users, but you may be asking, "why should I bother?"

Search Detailed Examples Online

All of our detailed examples on the Resource CD are available as searchable files for individual download from our web site. The key advantage is now you don't have to download the entire CD image, although it is still avalible if you prefer to have the complete set of examples on your own computer.

Just search online, scan the results for something of interest, and click "Open the gsz" to open it in GeoStudio. From GeoStudio you can choose File - Save As if you want to save a copy locally.

Most examples include a pdf describing the thinking behind the model. Some also include a movie generated by GeoStudio showing the computed results.

The online examples will be updated regularly, so check back often.

Banff Workshop

The upcoming workshop in Banff, Alberta, Canada is now 25% full. Register today to reserve your spot and avoid disappointment!

RSS Feed

The Direct Contact newsletter is now available as an RSS feed, which is what you are currently reading!

Nestled in the heart of the Canadian Rocky Mountains is a charming little mountain village called Banff. Just a 90 minute scenic drive or commuter shuttle from Calgary International Airport, the Banff Conference Centre is a perfect setting to learn, enhance and fine-tune your numerical modeling skills under the personal guidance of GEO-SLOPE personnel.

The annual workshop has become a very popular event and has sold out well in advance of the workshop dates for the past number of years. Many clients have returned to the workshop year after year to continually enhance their modeling skills and to experiment with new types of analyses.

This year we are expanding the workshop to include an optional fourth day (September 18th). The format of this day will be flexible and will allow participants to choose from a series of concurrent specialized sessions on various topics. Space is limited, so register soon!

Permafrost Thawing and Deformation Study

Recently there has been a large amount of interest directed towards the potential effects of global warming on permafrost regions. One important aspect of the warming trend is: “What degree of deformation may be expected if historically frozen permafrost soils start to thaw”?

This process can now be modeled by coupling TEMP/W transient results with a load/deformation SIGMA/W analysis, in which the soil properties in an elastic-plastic constitutive model are applied using an Add-In which adjusts the soil cohesion in the frozen and unfrozen zones.

Read the whole Detailed Example and follow along using the GeoStudio 2007 data file.

Permafrost Thawing and Deformation (1.39 MB)

Grokking is Rocking!

Check out Grokking GeoStudio, the unofficial blog where Nate shares his favorite 'hidden features'.

Located in a beautiful wooded valley in the heart of Shropshire stands the World's First Iron Bridge. It's fitting that the birthplace of the Industrial Revolution, which brought together innovation and engineering, will act as the setting to learn, enhance and fine-tune your numerical modeling skills under the professional guidance of GEO-SLOPE personnel.

The UK workshop has become a very popular event and has sold out well in advance as many clients have returned to the workshop year after year.

This year you can attend for a full three-day session or a shortened session with reduced content for two days. The two-day workshop will focus on SLOPE/W with introductory sessions on both SEEP/W and SIGMA/W. More advanced SEEP/W, SIGMA/W and introductory QUAKE/W sessions will be included on the third day.

Register Today!

Predicting Climate-Ground Interactions with VADOSE/W Basic

Landfill and mine waste cap design has typically been based on regulated design criteria, simple water balance modeling (e.g., HELP model), or semi-rigorous finite element or finite difference modeling (e.g., UNSAT-H, HYDRUS). These latter two models are rigorous from a seepage solution standpoint, but are limited in their ability to accurately predict the climate-ground interactions. VADOSE/W has been commercially available for seven years in a two-dimensional formulation but is now available in a one-dimensional Basic Edition formulation at a significantly reduced cost. VADOSE/W is unique in its formulation in that actual evaporation from a ground surface is based on the stress state in the soil; in particular the temperature and relative humidity and matric suction at the soil-climate interface.

Read the whole Detailed Example and follow along in GeoStudio 2007 using the VADOSE/W data file.

VADOSE/W Basic Tutorial (836 KB)

Grokking GeoStudio

Functions don't have to be frustrating or mysterious. Read Nate's recent blog entry on Editing Functions in GeoStudio 2007.

The release of GeoStudio 2007 included the concept of conducting multiple analyses within a single project file. While this powerful new feature has opened up countless new possibilities for constructing your numerical models, it can be a little intimidating at first.

The key benefit of this new feature is that you can carry out parallel analyses that do not depend on each other in a single file. This ability enhances the numerical modeling process by encouraging you to experiment with different techniques and allowing you to vary many different parameters and easily compare results. Experimenting will help you to gain confidence and achieve a better understanding of what can be modeled with the software in future projects. To utilize the software effectively, it is helpful to know what can be changed for a specific analysis, and when the changes will affect all the analyses contained within the project file.

As a start, you may wish to begin by reading about global vs analysis objects in the Grokking GeoStudio blog.

GEO-SLOPE Now A Microsoft Gold Certified Partner

We are pleased to announce that GEO-SLOPE has achieved Gold Certified Partner status. As a Gold Certified Partner we have secured premier access to Microsoft that will enable us to build our expertise, and bring to you, our customers, continued excellence in our software applications and support resources.

This detailed example uses AIR/W to illustrate how the process of axis translation is used in pressure plates to measure the water content function, and how this can be modeled in GeoStudio 2007.

The volumetric water content function describes the capability of the soil to store and release water under changes in negative pore-water pressure or matric suctions.

Since water cavitates at relatively small negative pressures, there is a limit to the amount of negative pressure that can be applied to a soil in order to measure the volumetric water content function. With the axis translation technique, a soil sample is placed in a pressure plate apparatus and positive air pressure is applied to push water out of the soil sample as an alternative method to using negative pressures to suck the water out.

Some of the GeoStudio 2007 features that this detailed example highlights include: air pressure and water pressure coupling (Ua-Uw), water balance in a drying / wetting soil sample, and verification with known solutions.

Read the whole Detailed Example and follow along in GeoStudio 2007 using the AIR/W data file:

     Pressure plate cell wetting and drying (3.96 MB)

Merry Christmas!

As the holidays approach and we draw close to the end of another year, we at GEO-SLOPE would like to take this time to express our profound sense of gratitude. We are grateful for the team that we have assembled, and for the extraordinary things that we have been able to accomplish together. We are grateful for your supportive feedback, and for the opportunity to work with you and your organization to advance the practice of geotechnical engineering.

We would like to take this opportunity to wish you a Merry Christmas and a Happy New Year!

Grokking GeoStudio

Nate's blog has been exploring 'selection' the last few weeks. Get some tips on selecting objects, selecting in lists, and selecting data in graphs.