Tag Archives: geotechnical design cost

Geotechnical Risk Management

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In our first ever post in Geotechpedia’s blog we tried to answer the most common question among professionals in the Geotechnical engineering industry “Geotechnical Investigation data, always not enough?”. In the specific post, it has been mentioned that “some of us proudly state “I saved so much by reducing the geotechnical investigation” but all this immediately changes when something goes wrong”. We are all aware of how limited or inadequate Geotechnical Investigation (GI) can affect both a project’s schedule and budget. In the following lines, we are trying to quantify these effects, provide guidance on how to easily create a risk scoring matrix and attributed risks, typical geotechnical risks and related mitigation measures.

Cost and time effect

Back in 1748 Benjamin Franklin stated “Time is money” in his “Advice to a Young Tradesman”. This quote finds application in all business sectors and the engineering one couldn’t stand out as an exception. In every project, delays are translated into cost and as such we are going to examine the estimated cost effects of delays deriving from inadequate Geotechnical Investigation on a project’s total construction budget. The most common chart when discussing the risk management in geotechnical engineering is presented below (Figure 1). It is obvious that for low values (1% approximately) of Geotechnical Investigation cost / tender cost (adjusted values), the total increase in construction cost may vary between 2% and 98% with an average value of 15-25%. When the Geotechnical investigation budget is slightly increased (adjusted Geotechnical Investigation cost / construction tender cost values between 2 and 4%) then the total increase in the construction cost drops to a typical range of 2% to 25% with an average value of 5-10%; meaning that an increase of 1-2% on the construction tender cost for additional Geotechnical Investigation signalizes a significant drop of approximately 25 to 50% (absolute values) in the total construction cost.

Figure 1: Total increase in construction cost related to adjusted Geotechnical Investigation cost / construction tender cost (source: UK Highways Agency projects (1994))

 Typical Risk Scoring Matrix

During the tendering procedure of a project, a risk assessment needs to be undertaken in order to evaluate the geotechnical risks at an early stage and propose mitigation measures. The following table (Table 1) presents a typical and simple scoring matrix that can be used in this kind of assessments and Table 2 details the specific risks associated with geotechnical works and categorizes them into probability of occurrence and cost/time impact.

The purpose of the following matrix is to help rank the key risks on site.

Table 1 Risk scoring matrix


Scores of 1-5 are allocated to the probability and impact in order to quantify and rate the risk rating. The risk scoring matrix should be used in conjunction with the priority action table detailed below (Table 2).

Table 2 Priority action table


Typical Geotechnical Hazards and recommended mitigation measures

Successful implementation of the suggested mitigation measures will assist with managing and reducing known risks to acceptable levels.

Table 3 below presents typical risks/hazards, related impact on construction budget and proposed mitigation measures.

Table 3 Risk/hazard assessment and proposed mitigation measures

In general, Geotechnical Risk Management gains supporters through the Projects Manager’s community since experience has proved that inadequate or incomplete Geotechnical Investigation during the tendering stage can have a severe impact on a project’s schedule and overall cost. Moreover, managing geotechnical risks also helps to increase safety levels in siteworks.

Conclusions

We need to keep in mind that geotechnical risk cannot be avoided and ignored but it can be managed and mitigated.

Taking all the above into consideration it is recommended that a detailed Geotechnical Investigation program is proposed at early stages of each project, following an in-depth desk study of all available information and site walk-over surveys.

It must be highlighted that the above post and its recommendations are to be read in conjunction with site specific available information and with critical thinking. In all cases, the Designer should set strict guidance for adequate Geotechnical Investigation in line with project specifications and international standards.

Useful References

[1] BS5930:1999, British Standard Code of practice for Site Investigations

[2] EuroCode 7 – IS EN 1997-2:1997 (Part 2, Annex B3)

[3] Clayton, C.R.I. (2001) Managing geotechnical risk, Thomas Telford.

 

Is geotechnical monitoring important?

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The March / April Geo-Strata was almost entirely dedicated to the GAM (Geotechnical Asset Management) for transportation systems. It was very interesting to see how this concept is evolving in the broader field of Geotechnical Engineering and transportation infrastructures.

This Geo-Strata feature is worth reading if you are interested in the future of Asset management in relation to infrastructure projects and geotechnical involvement.

I would like to focus a bit on the issue of geotechnical monitoring. As Thompson et al (GeoStrata, 2014) very elegantly observe, we have all sorts of sensors and warning lights in our cars, which enable both us and the car dealer technicians to identify a future problem as early as possible. If treated early, this problem can be resolved at a minimum cost. If left untreated, however, it could cost us our very life or even other people’s lives should a terrible car accident occur.

Car engine sensors, or airplane sensors or even elevator sensors are mandatory and nobody really argues over whether they should be installed or not. Nobody goes to a car dealership and tries to reduce the vehicle price by arguing that he does not really need the engine sensors because he can visually check his engine once in a while…

Can you imagine an airplane company, saying that in order to reduce operating costs it will remove the black boxes?

So why is it so easy to eliminate geotechnical monitoring instruments from geotechnical projects or so difficult to persuade the owners of the importance of the use of such instruments and information?  I am sure that there is not even a single geotechnical engineer who does not have examples of struggling to enforce the use of some type of

Geotechnical Monitoring

instrument and the client arguing over its cost of installation, cost of operation or even the usefulness of such geotechnical monitoring  and instruments for the project. Even worse this argument is sometimes thrown back at the designers through a challenge such as “why should we monitor the wall? Haven’t you designed it to be safe?”

Airlines and government boards do not consider installing black boxes only in planes that are old and with mechanical problems that may have a high risk of falling out of the sky. Imagine if such practices were taking place, would our planes be as safe as they are? Would they have evolved in the way they have?

Why is it so hard to do the same in geotechnical projects? Why is geotechnical monitoring and instrument installation, warranted in critical situations, on critical structures but not on ordinary slopes or embankments etc? How is the profession going to excel in future projects when real behavior of geo-structures is so difficult to find and evaluate?

As a profession, we should try to persuade owners, government officials, policy makers etc of the significance of reliable geotechnical monitoring systems included in the majority of geotechnical works. By doing this  future works and infrastructure will become safer and costs will fall far more than we may realize. Don’t put a price tag in current projects without considering future projects…

Geotechnical engineering standard of care

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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…

How much does a geotechnical design cost?

General, Geotechnical information,

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