All posts by Chrys Steiakakis

About Chrys Steiakakis

Chrys Steiakakis is a practicing geotechnical engineer with more than fifteen years of experience in the field of geotechnical engineering. He earned his bachelor and master in mining engineering from the Technical University of Crete, Greece and a second master’s degree in Civil Engineering from Virginia Polytechnic Institute and State University, USA. He has been the technical director of engineering department of General Consulting ISTRIA for four years and now he is a partner and also provides his own consultancy services via Geosysta ltd. He has been involved in numerous highway, railway and mining projects. Chrys with his long term collaboration with the Technical University of Crete has participated in numerous research projects in the field of geotechnical engineering and rock mechanics and has provided self sustained seminars of geotechnical engineering in related areas for the Industry. His main field of experience covers all aspects of tunnel design, earthworks design and monitoring (slope stability, embankment in difficult ground, reinforced embankments and retaining walls), landslide investigation and mitigation, foundations for bridges and structures, risk assessment in geotechnical projects and value engineering in large projects.

Visual observations and field experience versus mathematical formulations and office work

Geotechnical information, , ,

Geotechnical Engineers, Engineering Geologists and Geoprofessionals in general are involved in evaluating and quantifying earth processes, earth materials, and human intervention on or in the earth in a way that can be used to manage geological risk and to produce safe and economical structures such as tunnels, dams, cuts etc.

In order to produce such evaluation the geoprofessional needs to understand the geology of the area, to evaluate the material properties and to analyze the problem at hand based on sound engineering principals.

Unfortunately this does not happen all of the time, either because many are focused in desk studies and numerical models without proper understanding of the actual conditions and others because they oversimplify and base their estimates solely on visual observations of the area.

The problem is that in order to effectively manage and work with models one needs to spend increased amount of time in the office studying the method and learning how to implement in a computer (not much time left for field work!). On the other hand the field is time consuming and usually far away from the office… (not much time to spent in front of a computer!).

Can we combine these two? Many people and consulting offices do, but there are others that don’t.

I will present an example where the lack of field work and understanding scree coreof the situation can produce significant errors. In figure 1 the drilling core of cemented talus is presented. The material is classified as (GP) per ASTM 2487, SPT blow counts produce refusal of penetration and anyone evaluatingscree slope this material from the office would assign the following material properties c’=0kPa and φ’>37ο, and they would design a slope with maximum inclination of about 28o in order to have a FS of about FS>1.4. The reality is that this slope is standing vertical without any stability problems as can be observed in figure 2.

It is very important for geotechnical engineers to have a real understanding of field conditions.

How easy RQD estimations are?

Geotechnical information, ,

RQD was introduced by D. U. Deere in 1964 for a quantitative description of rock mass. The RQD  is defined as the percent ratio of the sum of core pieces with higher than 10cm length to the total drill run.  Based on the percent or RQD from 0-100% the rock mass quality can be assessed. For example based on the proposal by Deere, rock mass with RQD<25% is characterized as “very poor”. If RQD is higher than 75% it is classified as “Good”.

The RQD estimation is generally easy in the field and has gained a wide popularity. There are issues that should be addressed every time such estimations are made in order to avoid misleading results. In the following some personal experience will be provided regarding this issue.

RQD should not be addressed blindly and only in relation to the length of the core sample for the following reasons:

  1. The diameter of drilling core used should be known and taken into account. In the ISRM Suggested Methods, Brown 1981 a NX (55mm) drill core is mentioned, but in recent years the diameter has significantly increased in many projects and the sample is no more 55mm but can easily be 110mm. The increased diameter has one advantage that better quality core samples can be obtained but at the same time they can include more discontinuities. It is not clear if you will obtain higher or lower RQD values without recognizing the joint system. In the first figure it is observed that the sample with smaller diameter presents more fractures (some may be due to drilling).RQD
  2. The type of drilling barrel is very important. Different quality of drilling can be succeeded with double barrel (which is suggested) or split double core barrel than single or triple core barrel. The triple core and the double split barrel usually produce similar results unless the material is very much fractured. In that case RQD values would be zero anyway.
  3. The driller’s capability may be among the most important aspects especially for rock masses that are fair and poor. In the same location, with the same equipment different drillers may produce different results. Sometimes the artificial fracturing due to drilling may be easily identified but many times they are not especially in certain types of rocks described bellow.
  4. The rock type is extremely important. Geological material wiSiltstone sandstone alteration in a folded structureth foliation and bedding can produce misleading results of natural discontinuities. Clayey like rock materials such as shale, mudstones, siltstones can produce false impressions of discontinuities that are made during drilling but appear to be natural.  In such materials especially when tectonically disturbed, they can appear as solid samples but have discontinuities that are not easily visible.  In such situation RQD estimates have to be used with great caution.
  5. Number of joint sets and orientation, especially orientation can have a profound effect on RQRQDD estimation. For example vertical or near vertical joints may produce 100% RQD in a rock mass that has a discontinuity spacing of just 11cm. This can happen even in horizontal joint sets and a have the following results of RQD=0 for horizontal joint with spacing of 9.9cm and 100% for joint spacing of 10cm!

So when evaluating RQD values,  due consideration should be given to the material type, Driller, drilling equipment, geology and structural features of the rock.

Are fast track projects related to poor engineering?

General, ,

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

Landslide triggering

Landslide, ,

Unstable soil, rock or combination of both materials, manifests in a land sliding mass when the driving forces are higher than the resisting forces. In essence a landslide forms when the shear strength providing the resisting force becomes smaller than the driving force which may be a combination of weight, external load etc. The usual conditions that trigger a landslide are the increase in water pressure which lead in a reduction of effective stress and shear strength.

The water or pore pressures increase when heavy or prolonged rainfall occurs or when snowmelt takes place. Unfortunately these conditions cannot be controlled and a long term prediction is not possible (rainfall prediction is of a couple of days at most and the magnitude (mm/day) not easily evaluated beforehand).

130228 Landslide triggeringWater seeps in the soil/rock mass and can increase the external pressure on the backside of an unstable mass (especially in rock slopes), can increase the pore pressures in the sliding surface, and can increase the weight of the soil mass.

It is very interesting to note that although the best way to stabilize a landslide  may be by controlling the water pressures, engineers tend to ignore that and try to use more complex methods such as pile walls, ground anchors etc with questionable results. It would be great to have comments on this issue…

Future Landslides

Geotechnical information

If we look at landslides from the earth’s perspective we can define them as a condition towards stress relaxation and minimization of potential energy. The earth is trying to come to equilibrium.  Landslides are formed either from natural conditions such as erosion of slope toe, geological uplifting etc or are manmade when extensive excavation or loading is taking place in the foot or the top of a slope respectively. These are the main reasons why landslides form but the triggering mechanisms for a landslide to occur may be different.

In 130226 landslidemy opinion the most important triggering factor for a landslide to occur is the modification of groundwater or pore pressure conditions. This issue becomes more important if we consider the climate change which is producing different rainfall conditions with abrupt changes on ground water conditions.

Due to weather pattern changes, ancient, dormant or newly formed landslides will start to occur all and all more frequently. This will affect the economies and life worldwide and is something that needs to be addressed not only from geotechnical engineers and geologists but also by government officials, politicians and decision makers in general.

Landslides will become a hot topic in the near future, here are some very interesting blogs dealing with this issue:

 

http://blogs.agu.org/landslideblog/

http://arizonageology.blogspot.co.uk/

http://www.landslideblog.org/

http://science.kqed.org/quest/2012/11/08/earthquake-landslides-a-widespread-hazard/

http://ihrrblog.org/2012/07/16/stunning-images-of-four-recent-landslides/

http://slidingthought.wordpress.com/tag/bridge-of-the-gods/

Linkedin questions

Geotechnical information

Have we lost our ability to think? Have we learned that we only need to ask questions and not try to solve the problem ourselves?

In linkedin groups for geotechnical engineers and other forums I have seen (and many times replied) to questions for geotechnical problems without even the necessary information.  This is poor engineering which we should try to avoid. Many times practicing engineers or students pose questions without even try to find the answer for themselves.

I think it would be much better and more efficient if the Questioner would provide alsoengineer-thinking- his proposal. For example, instead of posting a question like “what type of shear strength parameters can I use to evaluate a soil sliding mass?” it would be much better to post: “I am evaluating a soil sliding mass which has moved xxx(mm) and I think I should use residual friction angle for the sliding surface, what is the group’s opinion?” This type of question includes thinking of the problem and a possible solution which the group can evaluate and reply if it thinks is appropriate or there are other solutions.

We should try hard to promote geotechnical engineering and increase our intelligence and experience of the subject and not try to find the easy way for someone else to solve our problem.

Why do tunnels collapse in urban areas?

General, Geotechnical information, ,

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

The passion of a Geotechnical Engineer

General

Many Geotechnical Engineers probably have not even thought about it too much, but what is that motivates many of us to practice Geotechnical Engineering? Is it the money? I don’t think so. If you compare the salaries of different engineering disciplines we are not even in the middle. If you compare with other non engineering disciplines we are so far down the list! We are under Wedding Photographers if you can believe that. Here is an article from EngineeringSalary.com regarding this issue.

So what is motivating us?
I came across two very interesting articles, the first in Geo-Strata September/October 2012 issue and the second in Ground Engineering Vol 46, No 1, January 2013. The first was the “Thoughts form the President” by Phil King in which he describes how he felt when he visited Terzaghi’s gravesite and reminisced his career as a Geotechnical Engineer. The second article was about John Burland “Towering Achievements” which describes how Prof. Burland became a Geotechnical Engineer and his career path.

Both describe with great passion their careers as Geotechnical Engineers and what more geotechnical engineering is for them.

What we do in the end is more about our passion for Geotechnical Engineering and less (much less) for material gain, salary or recognition. Our work usually is not even visible, but can you build a great structure without solid foundations?

Geotechnical information versus knowledge

General

Francis Bacon once said that knowledge is power, these words have a profound meaning but in our days where vast amount of information is available we may want to reevaluate them. Is the vast information providing knowledge or distorts it?
In our days every question one has, he just needs to type it to a search engine and in milliseconds he will find one or multiple answers. Are any of these answers correct? Is the one asking the question qualified to evaluate the answers? Will he use any answer and then find out that he has mistakenly approached a subject? Think before you use is a good advice!
This is a very difficult subject for discussion, even philosophical one can say, but the issue is that we need to pay attention to the way information is used and evolved into knowledge. We think that information should be vastly available and easily comparable in order to produce appropriate conditions for knowledge. We want to produce such a platform where geotechnical information will be provided but at the same time it could be critically evaluated from the users and in the end rated for the benefit of knowledge.

We will try hard for that…

Geotechpedia welcomes 2013

General

We would like to wish to all a happy and prosperous New Year. This year will be the starting point of our web site which will try to provide anyone involved with geotechnical engineering or geotechnical construction a vast amount of information. We will try hard to form a strong geotechnical community around geotechpedia in order to disseminate knowledge and information.

We will try to post regularly about new features in our site, technical and scientific information or opinions regarding the geotechnical field and interesting news related to geotechnical engineering. Our goal is to provide accurate and up to date information for the benefit of the geotechnical community…