Category Archives: General

Geotechpedia Online Survey Questionnaire Results

Picture1  “I like to listen. I have learned a great deal from listening carefully. Most people never listen.”                    

                                                                                                                                          Ernest Hemingway

First of all we would like to thank you all for participating in our online survey (16 June – 17 July 2016) regarding Geotechpedia’s future. As we truly value your opinion we made the first step forward for more interaction between us.

Survey Results

We managed to spread the news about Geotechpedia (34% of responses were from people visiting Geotechpedia for the first time) and at the same time we validated the fact that the majority of our users visit us on a need basis. This is logical since Geotechpedia is not a social website but a technical one and, frankly speaking, this is how we want to keep it! We are here to assist you with your queries when it comes down to geotechnical and mining engineering.

1 How oftenFurther to that, the survey results proved that publications, software and latest news sections are the most popular ones. Knowledge dissemination is our core value and we will keep striving our forces to provide you with the latest achievements in our industry.

2 Parts of Geotech

In terms of our site content we are happy to see that, as it stands at the moment, is covering most of the information our users are looking for (3.5/5) and considered to be of the highest quality (3.7/5) compared to other sites of similar content (3.7/5). However, that doesn’t mean that we are going to sit back and relax. We will keep on trying to provide you with the most recent and useful information in the industry.

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4 Information coverage 5 site content quality

6 other sitesYour overall rating for Geotechpedia (7/10) and the fact that you would be more than keen on recommending our website to a friend or colleague (3.9/5) shows that you do trust us and the results are encouraging us to keep on with the good work we believe we do.

7 overall rating 8 recommendation

Survey Demographics

Demo 1-age Demo 2 - gender Demo 3-Country

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Demo 4-Level of Education

 

 

 

 

 

Demo 5-Employment status

 

 

 

 

 

 

Participants feedback

Finally, almost half of the participants (45%) reverted back to us with some really interesting and helpful comments.

The main request refers to more technical discussion. We have to admit that during the last few months our blog wasn’t as active as we would like it to be. For that reason, we have decided to inaugurate a new feature called “Geosysta short courses”. The new feature has been already released and its main purpose is to provide you with more technical information on engineering issues (case studies will be also included) and improve the technical connection between our users and ourselves.

Further to that and based on your comments, we will try to improve the appearance of our website (our web designers have already started their brainstorming!).

Another interesting remark was regarding the absence of a monthly newsletter which will inform you for the latest additions in our website. We are happy to say that having predicted that we just recently released our monthly newsletter (http://eepurl.com/b8N02X).

Finally, we received several requests for creating a geotechnical/mining conferences, symposiums, webinars agenda. We have to admit that this kind of information would be really useful and we will try updating Geotechpedia accordingly the soonest possible.

Thank you all once more and please do not hesitate to contact us directly at contact@geotechpedia.com.

The Geotechpedia Team

DSC_0526

Geotechnical investigation data, always not enough?

 

IAEG XII congress
IAEG XII congress

This is a very controversial topic in which a straightforward answer is not possible. In this entry I would like to tackle some issues related to our own profession since we are responsiblefor the “acceptable” amount of investigation.

Recently I attended the IAEG 2014 (Engineering Geology) conference in Torino. In this conference numerous interesting topics of engineering geology and geotechnical investigation were covered. It was very interesting to note that in many cases a general conclusion was that not enough geotechnical investigation was executed prior to a geotechnical related failures.DSC_0527 geotechnical investigation

 

In conversations regarding the site investigation of a project it is very common to hear that “I would like additional investigation but the Client will not provide the funding” or that “the project finance does not allow for more or additional investigation, you have to do with what you have” etc. What do we do in such situations? We do what we have been taught as engineers to do, we overcome the problem. This means that either we accept a larger portion of liability, we either allocate the liability with statements like “additional investigation is warranted during construction” or we design very conservatively or all of the above. In any case, the design is based on limited information and it could go either way.

In many situations, due to the experience of the geotechnical designer or due to very conservative design assumptions no problems are manifested during construction or operation. But sometimes things go terribly wrong and somebody needs to take the blame, leading to long lasting litigations.

Is something wrong with the current practice? Everybody admires the great engineering attitude when nothing goes wrong and with limited investigation the project is completed. Even more, some of us proudly state “I saved so much by reducing the geotechnical investigation” but all this immediately changes when something goes wrong.

Maybe we should start thinking more as doctors? I don’t think anybody has gone with a medical situation and stated to the doctor that “I think you are asking too much medical testing” or “I don’t think an ultrasonic is warranted for my abdominal pain, cant you prescribe some conservative medicine that will make me better without doing all these expensive testing?” I would really like to see the face of the doctor hearing such negotiations. So why are we accepting such negotiations ?

engineering standard of care

Geotechnical engineering standard of care

November – December issue of Geo-Strata which is a published forum of the Geo-Institute of the American Society of Civil Engineers (ASCE) featured an article by Patrick C. Lucia, Chairman Emeritus of Geosyntec Consultants, titled “As I See It: Geotechnical Forensic Engineering in Defense of Geotechnical Engineers”.
In the article Patrick shares his over 25 years of experience in forensic geotechnical investigation of failures and the compliance of Geotechnical Engineers to “Standard of Care”. In his opinion the majority of failures occur due to “lack of process in conducting the geotechnical engineering practice”.

 

Unfortunately it is very difficult to standardize geotechnical engineering practice in a way that other engineering disciplines have. The difficulty of standardizing geotechnical practice is that ground is not standard. This is why geotechnical engineering is so challenging. How can you standardize an investigation in a new project? Is the text book “influence zone” depth an adequate depth to drill? Can a few centimeters thick unfavorable clay seam be found with two 30m borings in a proposed cut? Can an undisturbed or even remolded sample be acquired from that seam? Can we pursue the client to spend additional thousands of dollars when we are unsure of what lies beneath?
Pat is arguing that “when the process of engineering is properly done and properly documented, it will far reduce the number of claims and make the defense of those claims much easier.” This is true but maybe difficult, especially in a world of fast track projects and low bids. Maybe our profession needs to do much more to “standardize” proper engineering process. Firms may need to take action to “educate” potential clients and owners about the importance of a sound geotechnical investigation, peer reviewed process in ground properties evaluation and design and necessary time that is needed.
Time is a fundamental problem in geotechnical engineering profession. It is not easily understood why maybe a month is needed for a simple foundation investigation. How can you argue when you hear “we do not have such time, we need the results in a week!”, as if we control the permeability characteristics of a clay in a consolidation test!!!
These and many other issues make our profession so challenging, difficult but at the same time so rewarding, from a scientific point of view (I don’t know any billionaire geotechnical engineer). We need to practice geotechnical engineering and at the same time educate the rest of involved disciplines in its difficulties. Unfortunately probably we are not doing very well in the second part of educating…

Geosysta welcomes 2014

Geotechpedia 2014

Geotechpedia enters 2014 with the ambition to provide more geotechnical information and contribute to the geosociety with interesting and valuable publication links, software from the industry and equipment used in the sector.

Geotechpedia now has an updated look and feel more appropriate for today’s web. We hope we can make your experience more efficient and pleasurable at the same time while we save you precious time when searching for geotechnical information.

 

Register with Geotechpedia, and become a member of it’s online geotechnical community. It is very easy and safe, since it uses open ID. Geotechpedia does not request that you create yet one more password and will not store any.

 

By Registering you can rate all geotechnical information items provided in the site, you can review papers, software or equipment and you can add items in your favorite section.

Geotechpedia registered users page
Geotechpedia registered users page

Help others with your knowledge to get faster incite in our provided geotechnical information. Access your favorite items, review etc just by clicking on your user name in the top of the page

Geotechpedia and Geosysta wish you all a happy and productive new year.

Geosysta welcomes 2014
Geosysta welcomes 2014

How much does a geotechnical design cost?

I am sure that many geotechnical designers have either been asked this question or have had to answer it internally in order to price a project. After the offer has been prepared, comes the negotiation phase, where the owner of the project starts asking questions about the “high” price (in his opinion) or about a different offer he has had which was half that price!
I would like to point out some aspects that come into play in this negotiating tango between the Consultant and the Owner and some pitfalls that can come about with relation to this issue.
In geotechnical engineering a design is never “easy” or “simple” and this is because the ground is inherently variable, anisotropic and with minor details that cannot be easily assessed but nevertheless can have a detrimental effect during construction. Do we forget this, many times in our practice?
Pizza
So how do you go about performing a geotechnical design? A geotechnical investigation is executed initially with a predefined number of boreholes, usually less than we would like and a selective number of field and laboratory tests are executed. This investigation may be based on prior experience of the area but often it is not. The depth and location are governed with minimum information and mostly based on the structure to be constructed. Then with the geotechnical information gathered and evaluated the subsurface is formulated and the geotechnical design is executed, based on some form of standard (Eurocode, LRFD etc).
So the question now becomes “how many man hours will your engineers work determining the price you will ask for?” So in an effort to reduce the cost of design, the limited geotechnical investigation parameters are used with some partial factors of safety and the calculations are executed with nice software for bearing capacity or slope stability etc and the design is completed, on time, satisfying the standards and everybody is comfortable over the outcome. So how many man hours does such a procedure require? Don’t you think you should reduce your offer?
This is a recipe for disaster. In order to cut the cost of design, many things that should have been evaluated are not, inexperienced engineers work in the office with the software that they know so well but at the same time they may completely lose touch with the actual conditions or the geotechnical details that will actually control the performance of the project.
The cost of performing a geotechnical design is not merely the man hours spent doing some mainstream calculations but the time and experience that has been devoted to evaluate the most probable conditions and the most unfavorable conceivable deviations from these conditions and how they will affect the proposed project. This is not an easy task; it needs great experience (shouldn’t this be paid?) and many hours of thinking, sketching, performing simple hand or computer calculations, revisiting the site and the site investigation information etc. But this cannot be easily measured or quantified and produced as a cost estimate. So how can two Consultants compete when one routinely executes such practices and the other doesn’t? Sometimes luck favors the bold so the second consultant could have the same track record as the first one. And if a failure or excessive deformation etc happens then it is easy to blame it on “the unforeseen geological conditions”. No harm done! Just the budget and time of the project may significantly increase, maybe increase orders of magnitude in relation to the reduction that was achieved with the negotiation of the geotechnical design fees or with the selection of the geotechnical consultant with the lowest bid.

Factor of safety and probability of failure, E. Hoek  - Practical Rock Slope Engineering
So Geotechnical Designers should advertise in more detail what they actually do, advertise the experience and expertise they pose in house and the way they tackle a geotechnical design. They may need to make the owner aware of what is at stake with an improper geotechnical design even if it meets all available standards.

Owners should take a step back and think; is the lower bid the best way to go? Is the reduced price that was achieved after hours of negotiations worth the risk of an improper geotechnical design? What is the gain of a reduced cost of design in relation to the actual cost of construction? Never forget that you get what you pay for and this in geotechnical design can really have a significant cost!

Shanghai building foundation failure, http://activerain.com/blogsview/1524118/nashville-building-inspection-foundation-failure-what-is-wrong-with-this-picture-3-2-10

The Mohr – Coulomb strength criterion

This is something that all geotechnical engineers should know but it is surprising how many do not! Just a brief overview of how the Mohr – Coulomb strength criterion came about.

The Mohr – Coulomb criterion is the outcome of inspiration of two great men, Otto Mohr born on 1835 and passed away on 1918 and Charles-Augustin de Coulomb born on 1736 and passed away on 1806.

The two men never coexisted but their brilliant minds contributed significantly in the scientific knowledge. The combination of two hypotheses gave us the Mohr – Coulomb failure surface.

Chronologically,  Coulomb was involved in military defense works (how much knowledge have we gained due to war!) trying to built higher walls for the French. In order to investigate why taller walls than usual were failing and try to built them to stand, he wanted to understand the lateral earth pressure against retaining walls and the shear strength of soils. He devised a shear strength test and observed (at that time, with his tests) that soil shear strength was composed of one parameter that was stress – independent named cohesion (c) and one that was stress – dependent, similar to friction of sliding solid bodies named angle of internal friction (φ). Probably he executed shear strength tests and found for different normal stresses (σ) different shear stresses (τ). By plotting these data on a (τ-σ) diagram he obtained the straight line denoted by the equation τ=c+σ.tan(φ) as can be seen in the next figure.

Coulomb failure surface

Mohr (1900) proposed a criterion for the failure of materials on a plane which has a unique function with the normal stress on that plane of failure. The equation for that was τ=f(σ) where τ is the shear strength and σ the normal stress on the plane.  With the use of the Mohr circles which is a two dimensional graphical representation of the state of stress at a point and the circumference of the circle is the locus of points that represent the state of stress on individual planes the Mohr failure envelope was proposed. The Mohr envelope was a line tangent to the maximum possible circles at different stresses and no circle could have part of it above that tangent curved line. (figure 2).

Mohr failure envelope

It is not known (Holtz et al, 1981) who first combined both theories but combining the Mohr failure criterion with the Coulomb equation gave a straight line tangent (to most of the Mohr circles) and the Mohr – Coulomb strength criterion was born (figure 3).

Mohr - Coulomb failure criterion

Holtz R. D., Kovacs W. D., (1981). “An Introduction to Geotechnical Engineering”, Prentice Hall.

Geotechpedia reached over 3000 free publication links on geotechnical engineering!

Our database is a continually growing database of assorted geotechnical engineering information. Everyone interested in geotechnical engineering i.e. students, professionals, academics, can browse in geotechpedia’s free publications.

Taking into account the demands of geotechnical engineering, updating information is the crucial goal for us. We are proving this by continually increasing the number of free publication links.

fireworks-

Geotechpedia team is now pleased to announce that the number of free publication links that disseminate geotechnical knowledge is over 3000!

This means that Geotechpedia has cataloged over 3000 geotechnical publications in the database, including published papers, manuals, reports, dissertations etc.

 

Each publication is presented in Geotechpedia with its title, author, author’s organization, location, publication type, publication reference, tags, a small description summary and of course the link.

In our effort to provide professionals in geotechnical engineering with everything they need, the database includes catalogued geotechnical software and also geotechnical equipment.

Geotechpedia is the most integral and extensive geotechnical tool on line for everyone interested in geotechnical engineering! We will be happy to receiving your feedback concerning this project. Feel free to contact us and leave your comments!

Are fast track projects related to poor engineering?

To130301 bridgeday I was reading on the digital wire of ENR.com about the costly mistake of the highway 520 Bridge Pontoons. Cracks start to appear and the long term durability is questioned. The article states that “the state chose to design the pontoons itself on a fast track (rather than delegate that responsibility to contractors) as a strategy to attract lower bids…”. In my mind came also the article from International Business Times about the problems and collapses of new Chinese infrastructure. Is this new fast track project approach responsible for poor engineering?

Is the time pressure and the lowest budget to blame for serious engineering mistakes? The challenging economic environment is pressing away from serious engineering judgment and step by step design and construction, to all at once. Designs are constructed from automated drawings with serious mistakes before the calculations have been completed. Thinking time, quality control and checking are practically omitted even though this is not admitted. Is this the way to go? Should we stop and rethink and try to persuade decision makers and money driven decisions that in the end you are not saving money?

Additional information regarding the fix of the bridge pontoons can be found here

Collapsed Tunnel in Central Japan Fully Reopens

An expressway tunnel in central Japan whose ceiling collapsed in December, killing nine, became fully operational Friday after a 68-day hiatus, its operator Central Nippon Expressway Co. said.

The nearly 5-kilometer-long Sasago Tunnel in Yamanashi Prefecture became fully usable again ahead of the previously targeted reopening date later this month as restoration work was hastened ahead of the upcoming long weekend when traffic is expected to increase.

The Ministry of Land, Infrastructure, Transport and Tourism gave its go-ahead on the grounds that all safety issues have been cleared.

Some bereaved relatives of the victims are taking issue, however, with the road operator’s policy to prioritize the tunnel reopening before the cause of the fatal accident has been fully clarified.

The tunnel restarted partial operation on Dec. 29 after tunnel collapse with half of the lanes reopened to traffic.

source: http://enr.construction.com

Tunnel collapse can happen for a number of reasons such as: inadequate ground investigation, shallow ground conditions, inadequate support measures, cost optimization, inexperienced contractors, inadequate supervision, delays of excavation and support erection.

tunnel collapse

 

Why do tunnels collapse in urban areas?

In recent history numerous headlines present tunnel collapses in major cities. One can ask why so many failures? I would like to provide some insight regarding this issue.

The following reasons can produce a single cause or combined effect that can result in ground tunnel collapse during tunnel construction in urban areas:

  • Inadequate ground investigation due to condense building construction.
  • Continuous differentiation of shallow ground conditions due to manmade structures, faulty utilities seeping fresh water, sewage or storm water etc. Especially in shallow ground the mechanical properties of the soil may have been modified from one building block to another.
  • Inadequate support method of excavation. Especially in difficult and complex ground condition with mixed face conditions (strong rock and soft soil are encountered on the tunnel face).
  • Cost optimization of excavation and support. This can lead to reduced support measures or higher advance rates of excavation to meet deadlines and follow inappropriate scheduling.
  • Cost optimization with selection of inappropriate tunnel boring machine (TBM) that can accommodate most of the encountered conditions but not all.
  • Inexperienced contractors and design engineers with local conditions, especially for international projects.
  • Inadequate supervision of construction works.
  • Delays of excavation and support erection due to unforeseen conditions such as archeological discoveries, union strikes etc.

These are the most usual conditions (many other may exist) that can produce tunnel collapses. Unfortunately most of them are related to cost reduction or cost optimization. This is especially true in low bit contracts for investigation, design or construction.

Usually after a tunnel collapse has been formed and its causes are evaluated, it is found that

it could have easily been avoided. The most interesting outcome is that the cost of repairs usually is far more that the cost required for a better initial investigation, or design or construction!

tunnel collapse