soils problem

huangyhg

soils problem
i have a job where that is on poor soils.  this was revealed during the geotechnical investigation.  3 small buildings are going to be placed on this site.  the geotechnical engineer recommended timber piles or pif to remedy the problem under 2 of the 3 buildings (building #3 can be placed on virgin soil supported by spread footings).  the contractor did not like the price of these solutions so he contacted a company that specializes in rammed aggregate piers (rap).  this company came in and did further testing under these 2 buildings and designed their rap based off of my loads.  construction of the rap's is now under construction for building #1
we are in the process of designing building #2 of which the contractor is still unhappy about paying to remedy this soil problem.  i have just received an email from a 3rd geotechnical engineer (if you count the rap contractor as geotech #2) stating that he has reviewed the testing borings of the other two and concluded that the building can be supported by virgin soil on spread footings.
being responsible for the design of the spread footing and building... should i be concerned with the fact that the contractor is "shopping" the geotechnical report around to see who would give him the best results?  where would my responsibility end?  

check out our whitepaper library.
first, i am not sure why the contractor is doing this. are you working for the owner or the contractor? if these alternate foundation systems are cheaper, the owner should be getting a credit for this alternate. by the way, who is approving these changes? to answer your question, you need to write a letter to your client telling him that you had the geotechnical report prepared for your work and that if some one else is designing the foundations they have the responsibility for that work,including the appropriateness of the geotechnical report, and that you revoke your seal for that portion of the work. send the letter certified mail and touch base with your client to be sure they got it. i would also ask him what is going on. i would also talk to your lawyer and e&o agent. if this is going to continue, you may ask if you want to stay involved in this project.
     if you follow the recommendations of a licensed and insured geotech, then any failures may be paid for by the liability insurance of the geotech.  request a copy of the policy with your project named as included in the coverage.
     rammed aggregate piers are extremely competent if no drilling is done to produce the hole.  the surrounding soil is densified and the allowable loads are derived with generous safety factors.
i think this is a tough one.
i certainly think you should be concerned. i'm not really sure  who would end up liable if the foundation system were to fail.
but i say this is tough because i know from experience that some geotech companies tend to operate so far on the side of conservative that they essentially do not have to do any work. geotech by nature is uncertain, but the higher the factor of safety they use, the less work they have to do.
it is impossible to tell whether the first company was not doing its job and simply being overly conservative, or whether the last company will be proven to be criminally negligible.
tough call.
drc1
i'm sorry,i should have mentioned that the owner is very unhappy that he bought a poor site and is driving these changes (he seems to be taking it out on everyone).  in a weird situation i am providing engineering services for a steel fabricator who is providing design build services to the contractor.
sounds like someone has a tiger by the tail. i think my sugestion of disavowing responsiility for work you did not design still stands. it oes not have to be confrontational. the  ownwer asked for your ideas and in the end went with someone else's. no big deal. but i would make certian that you do not have  the responsibility for that design.
take 5 geotechs - get 4 reccomendations for we are all prisoners of our own experience.  sounds like you have a site where spread foundations mayfff"> work.  a more positive solution to the problem, though, is with the rammed earth and still more positive is the piled foundations.  how much 'risk' is the owner willing to take to get the least cost?  if spread footings are used and they do fail (i.e., from settlement point of view - not implying shear failure), will the owner be happy with the time consumed by legal avenues, remediation works, lost revenue from his rentals (presuming this is the case), extra interest for the construction loans?  or would he be happier with a more positve solution where the worries are minimal?  always a question to pose.  and, for what cost savings?  the legalities/responsibilities i'll leave to drc1 and others.
cheap is cheap...expecially when the contractor is pushing the buggy. i don't think the contractor should be doing the shopping around unless they are responsible for whole package. i suggest you consult your legal team and be aggresive at safing up your position in the project. if it goes to crap, you'll be in the middle of it all.
and i've seen plenty of project where the owner went with the cheap geotech and the geotech gave the easy answer of "put it on piles" where spread footings would have worked assuming that the appropriate sampling, testing and analysis were performed. this also assumes that they were actually looking at all aspects of the issue (doesn't do any good to have a foundation good for 6,000psf if the darn thing settles 5 inches...as with soils here, settlement is typically the controlling factor).  
you should do due dillegence and ask why the other geotechs are more conservative.  what specific issues do they have with going to spreads.  ie.. why recommend piles, geo-piers over spreads?  is their response open to opinion.  have they provided soils testing/ calcs backing up their report.  they are losing out on this contract, have them fight for it.  expose the inconsistencies.  if the spread footing geotech didn't consider something this should bring it to light.
i think teguci is right. have the other geotech firms explain themselves. this could bring to light some important information.
keep in mind that there's lots of different ways to resolve geotechnical issues. if the client insists on spending $5k for a subsurface, that likely doesn't include the testing and analysis required to justify using spreads on a marginal site. if the client opens their check book, then that opens up the paths that they can take. for example, if a client wants to spend $5k on a normal site, i'll drill a few holes and give them 2-3ksf bearing pressure as long as nothing looks ugly to me. if they want to spend another $5k ($10k total), then i might run some consols and triaxials, perform a settlement analysis and get them 4ksf. if they want to drop $50k on the same site, then they can likely find a wide variety of solutions. and as the sophostication of analysis/recommendations goes up, the construction costs will go up and they (owner) typically lower their overall risks (but some other headaches can show up on the construction end). for small projects, it's almost a given that the cost of all the extras won't pay for itself. on larger projects or on projects where the client insists on a particular route, then the proposal becomes more in depth, the associated dollar figure increases and the end result is an "improved" recommendation. in other words, the client essentially has to make a decision about their own personal safety factor versus costs. and lets not forget that some firms may prostitute themselves and/or volunteer their time on this one particular project to get their foot in the door with the client.
one of the things one has to watch out for is letting the contractors lead the project off in to dangerous territory.
and let's also not forget that soils are by far the most complicated "animal" of all the construction materials. you could have two different geotechs look at a site and come to different (but likely somewhat similar) solutions...just take this discussion board for example: you can post a rather straight forward question about a situation on the geotech pages and you'll see a wide range of opinions that all sort of trend toward a similar answer...you also sometimes have the "out in left field" responses...and sometimes thinking outside of the text book can be the most beneficial approach to a project. so i'm not exactly sure anyone necessarily has any explaining to do...sometimes, the more sophisticated approaches may be out of the expertise of a particular firm. there again, it never hurts to ask.