Geotechnical - Foundation Design

[TXGeotech]

I have heard from several sources that a geotechnical engineering firm should not also provide structural foundation designs because of an inherent conflict of interest. I have not found any professional opinions on the topic. What are your thoughts?

 

[civilperson]

What conflict of interest do you refer to? Standard contract with Geotech firm requires footing and road section recommendations, (shallow vs. deep, controlled structural fill or soil improvement, geo-fabric uses, safe slopes for excavations, depth of piles vs. capacity, soil types and preferred use, allowable bearing capacity with given settlement), for the loads and building type specified in the scope of work as well as recommendations for construction methods. If they would provide the size and reinforcement of the footings for the given loads, then I would have to spend less time and would agree to a higher fee.

 

[VAD]

The most desired situation is for the structural and geotechnical engineer to work together on the foundation design. This scenario is realized in many larger companies that employ geotechs and structurals in house and have been established or known to be doing so.

For a company that is known to be mainly geotechnical, the liability issue is of concern if the structural foundations design is done by a staff member who is also grounded in structural design - wears two hats. You will need Professional liability insurance that endorses that you are also engaged in structural practice. In such a case you need to have someone that is experienced in this area of practice. You may also want to define your scope of work.

From a business point of view the question arises if the company is thought to be taking away work from their structural clients. This could cost you income.

There are other scenarios which I am sure others would address.

 

[emmgjld]

When my father began Geotechnical Engineering in Colorado Springs, 1956, he also was doing foundation designs for residential and small to medium commercial. I have been doing the same for these many years. In the course of a proper Geotechnical Study, the Geotech must be able to accomplish the design in order to provide an adequate study and the final report.

To me, the idea that the Geotech does only the soils work and the Structural must pick up at the concrete is a bizarre thought process. I have been amazed at how the substructure is often treated like the superstructure, many times resulting in mediocre to terrible designs. I also understand the liability issues but, I have had a lot better success when I control the design.

Much of this I do blame upon Geotechs who cannot or will not provide decent data and seem to live in a world of very conservative recommendations. I will also put a bit upon the Structurals who seem to think that a number is all they need and the actual foundation elements apparently become trivial, in their mind.

In my present practice, If I know who the Structural is, I will tailor the report to deal with how that Structural will use the provided data. For example, In the case of Expansive Soils, I have modified recommendations for the mindsets of my local areas, the Colorado Springs, the Denver and a few other localities as I have observed some rather extraordinary practices.

In many situations, such as properly proportioning footings for longterm and differential settlement, accomplishing a piled raft, designing drilled or driven piling, the Geotech should have the knowledge to properly accomplish the substructure design and the Structural may assist with the elements which will connect to the superstructure.

 

[Ron]

Many Geotechs do not do the structural foundation design due to the thought that they might infringe on a client's work (the structural engineer); and because they perceive the liability to be higher if they do both.

There is no reason that a Geotech shouldn't be able to do both.

 

[DRC1]

I agree. I have seen a lot of bad foundation designs because the Struct ships a request to a geotech who sends back a report and somewhere in between important information or concepts get lost. If you do do the design, be sure you have all the possible controlling load combinations.

 

[COEngineeer]

Is it only me or do most geotechs put higher bearing pressure and passive pressure just to cover their butt? I see more and more 60 pcf passive pressure. A lot of owners complaint about it because his foundation guy give him a high estimate due to thicker basement wall and wider footing and more reinforcement. I design the foundation based on what the numbers geotech gave me.

 

[Gokou10x]

I completely agree with the statement that all geotechs should be able to design foundation systems. I disagree with emmgjld assessment of the structural/geotech situation though. The reason why so many buildings end up with terrible foundation designs is a lack of communication between the two parties.

To put the blame largely on the shoulders of the geotech is fairly harsh. In my expierence structural engineers are so protective of their designs, the only information provided to the geotech is vague and limited. Many times, the structural engineer won't even provide load information. When loading information is provided, it's a wide range and no explanation is given as to why certian criteria are needed from an evaluation. It's a "shut up and give me my numbers" atitude.

If the structural and geotech would sit down and hash out the numbers needed and the reasons why, then perhaps the geotech wouldn't be so "conservative". Design's would be better, structures would be more econmical and owners would be happier.

 

[theCorkster]

I see the case for practising within one's area of expertise to be the solution. If you've been fortunate to practice within a small firm where the entire substructure is the practice, you'll likely have the experise. If you've practiced with larger firms that tend to prefer a stronger expertise in specific areas, you'll be exposed to facets of the structural design, but not likely to gain the expertise to perform structural design unless you decide to change desks.

With respect to "poorly" designed substructures, the real solution lies with the owner/client and the "design team" communications, regardless whether the "design team" is a single entity or not.

 

[BigH]

In the practice that I have been involved with and have seen, the geotech provides recommended (or suggested) foundation types and/or alternatives. He will provide the allowable net bearing pressures for spread footings - may give charts showing expected settlements at specific bearing pressures for various size footings (to assist the designer to match expected settlements for different size footings). He would recommend allowable loads for piles of given specifics. He does not do the reinforced concrete design of the footings (i.e., rebar and spacings). Certainly, he could do it; many have the expertise to do it but many times the footing design also impacts the superstructure (bridge) or upper floors and the like - it seems best to let the structure design be done by a single party. The geotech should be consulted (but many times isn't) on various issues as they might arise. And I agree with others, by doing so may drive some clients away. As for "conservative designs" - many times this is due to unclear concepts from the structural engineer - or that the geotech recommendations are given in a preliminary fashion but not refined as should be the case.
Hope all have had a great holidays -

 

[ergodesk]

I've noticed many companies using Eps foam in their production system's. Has anyone used EPS GeoFoam as the structure in any of your projects big or small?

StyroHome, FerroFoam, Structural Air, ThinShell Concrete.

http://ergodesk.blogspot.com/

http://ergodesk.wordpress.com/

 

[Patgeotech]

I strongly agree with all your comments and it is interesting to read the similarities. As a geotechnical engineer with a civil engineering background and having the opportunity to work in the UK and Africa, I have found that different companies have certain ways of presenting their geotech findings and one tends to adapt to the companies system, which is often governed by the level of liability the company will accept.

I have found that where the structural guys have been vague (happens a lot), as a geotech engineer one starts to lean on the conservative side in terms of bearing pressures, differential settlements, etc.

I always felt that it was a geotech's responsibility to provide as much foundation information as possible to assist the client. I 'pester' the structural guys for more information on the planned develoment. Not only did it make me feel like I had done my job to the best of my ability, but it also resulted in me getting further jobs from the same structural firm or client. Clear, concise and logical communication in a geotech report is the key.