Fellow Engineers:
This is a most interesting discussion – I have only the part up through DIK of July 17 and much more may have transpired since. However, based on my reflections to that date, I would like to proffer my comments. I apologise at this time if this turns out to be a bit long. We have an interesting mix of disciplines, ideas, etc. We have structural engineers; engineers for contractors, finally a
bona fide geotech in VAD and, of course, JHeidt2543 with his usually spot-on comments. Such a mix leads to interesting discussion. One point is apparent, though – all the respondents have their own agendas. The structural types are miffed by the lack of “mandatory language” in the geotechnical/soils report and why doesn’t he prepare plans and specifications. The geotechs are miffed about the lack of understanding of their siutation – and of course, low fees. You might read some of my other offerings, say in JHeidt’s question about Factor of Safety in this Forum. I have been in the geotechnical consulting business for some 20 years at which time I moved over to actual construction of highway projects overseas (7 years now). You all want to see the dung tossed out by so-called geotechs? designers? – I’ve seen it.
As VAD rightly pointed out – the geotech usually does not have full details on the planned works – he is left to surmise, presume as to the various components that will make up the project. Does the project entail basements? - (excavations/earth pressures on walls) . . . settlement sensitive equipment? - (high speed paper machines with, say, 5mm differential settlement over 25m) . . . dynamic equipment? – (stamping presses, turbines – damping/embedment, perhaps) . . . significant tension loadings involved? (guys for stacks or towers) . . . include . . .
You get my point. I’ve been involved, as many of you have, with quite a number of projects that lacked any real detail at the time the investigation is called for. Geotechs have to surmise on many aspects. VAD is correct – this type of investigation
should be called and respected as a “preliminary investigation”. Most of our company’s old reports all had “Preliminary Soils Investigation” (or Geotechnical/Subsurface) in the reports title. We all knew, of course, that there would be no more work done on 75% of the projects until the time that foundation inspections are needed.
Given such sketchy information
at the time of the investigation , how can you expect the geotech to use “mandatory language” in his report? He is usually assuming that his allowable bearing pressure, for instance, will be based on “norm” requirements of 25mm and 15mm differential. This is, of course, not the case for high speed paper machines. Most of the time, the machinery (say turbines) has not yet been bought so the dynamic characteristics that will, of course, affect the geotech’s recommendations for, say spring constants, will not be known.
Okay – this is a fact of life in the geotechnical business. And yes, VAD, geotechnical engineers in a large degree have brought this on themselves – my old mentor called it prostituting the profession. When, in Canada, we had Golders, Geocon, EBA, Thurber, Trow, Dominion Soils, National Boring and Sounding – the “old” established firms, there was a playing field that seemed pretty well established. (sorry Quebec) Now, we have so many break-off firms, basement firms, etc. that, well, . . .
Now, to the structural types. I understand the dilemma you are in with respect to handling geotechnical information. Putting the geotech’s boreholes on the drawings – using your design time for someone else’s work. Where to put the soils report: Appendix? Make it available in Info for Bidders? Let others read it – even in the “office”? The dilemma lies, in my view with the that others, not involved in the geotechnical investigation and subsequent design, might read the report. Why is this a problem? As I’ve pointed out earlier, the geotechnical report is usually geared to a project that is not fully specified at the time of the investigation – or the project has changed since the investigation was carried out. Further, the geotechnical report includes recommendations/comments for the design and construction of the project. Do you want the contractors to read these? The geotech might suggest that piled foundations would be the most positive choice for support of the structure with, say, closed end steel tube pipe piles the appropriate choice. Still, though, given the “toys”, you could found at shallow depth after ground treatment or excavation and replace, etc. Now, you have chosen to go for piles but your designer doesn’t like closed end steel pipe piles. He wants to use slender precast concrete piles. In construction, the contractor chooses a hammer that is big and the founding till is hard – the piles show cracking, some breakage during/after driving. Problems. If the soils report containing the recommendations is in the contract – even as an exhibit – the contractor will know that the structural engineer didn’t use the recommended more robust steel pile. This may cause some consternation for the design engineer.
Similarly, most soils reports give a compaction level for fill and the type of fill – say well graded sand and gravel compacted to 95% modified Proctor dry density or higher. The specs, borrowed from another project, indicates that the fill will be compacted to 98% modified Proctor dry density – and the type of fill isn’t defined. Now, if you say on your drawings that the contractor is to follow the soils report – what to do? There is a conflict in the report and on the drawings/specifications. Is it not a tad bit embarrassing to have 95% in the soils report and 98% on the drawings or in the specifications – or
vice versa . As the receptor of various other design professionals (electrical, mechanical, etc.) and normally charged with the putting out the project specifications, for uniformity the specs should be written – surely edited – by a single agency.
Now to the contractors. Why do you want to see how the allowable bearing pressure was derived? Sure, you want to know the soils to be encountered (for digging to footing level, e.g., boulders in the deposits), you want to know if your construction methodology may cause disturbance and you need a mud mat (blinding concrete). But, how the designer chose his footing size and the assumptions he used, etc. is not immediately of your concern, really – unless of course, you want this information for subsequent claims.
Given the above, I propose the following for consideration:
1. Have the geotechnical engineer prepare two reports. The first report is the
factual report. This report gives facts – undisputable. Includes geological setting, site description, soil strata encountered (including topsoil, pavement layers, etc.), groundwater conditions at the time of the investigation (perched levels, general levels, etc.), borehole logs with laboratory testing information included (liquid and plastic limits, natural water contents, undrained shear strengths). Include other lab data such as e-log p curves, grain size distributions, etc. Include chemical testing that may affect concrete. Borehole location plan. Keep it factual – no interpretation. The second report, is the
interpretive report. This report will put forth the engineering discussion for the design and construction of the project for the designer’s use – recommended (primary and/or alternative) foundation type, estimated settlements, suggested fill details, lateral earth pressures, etc.
INSIST on the two report system.
2. Include the factual report in your contract documents – either on the drawings or as “Information for Bidders”. The facts are given – all parties will know the soils encountered, the groundwater levels, the laboratory test results.
3. Keep interpretive report for your files. Some of the recommendations/comments may not have been followed if the design is like many I have seen. This report is a guidance report for the designer and does not HAVE to be seen by the contractor. Of course, the structural drawings should state the basic information used in design – you can glean this from the interpretive report or state what you, as the designer, finally chose to use.
4. Advise the geotechnical consultant of any changes in the nature of the project – it may be an adjustment in the building footprint from one part of site to another. I suggest that as the design proceeds, you call him in for an early review of your schemes so that he may comment and advise. If he needs to change his recommendations/comments, this is the time to do it – not after the contract has been let.
5. Consider letting the geotechnical engineer help develop the project specifications for earthwork construction. He will feel more like a team member and the structural engineer may feel better about staying within their expertise. In earthworks – say for highways – standard specifications do not always work. It will force the designer to put together project oriented plans and specification.
6. Let the geotechnical engineer review the final design and specifications to ensure that it is consistent with his understanding – for that is the basis of his recommendations/comments.
7. We, as a geotechnical company, on building of tailings dams (owner build) did put together specifications and drawings – but these projects are 90% geotech oriented.
8. Geotechnical engineers are not too expensive – pay for them now or pay more later.
9. Geotechnical engineers do take the heat for liability – they probably have the highest liability insurance premiums of all (for their level of remuneration).
The points above for consideration are typical of larger projects but should be viewed with the intention of including these in all reports. Of course, the more complex the geotechnical problems, the more the geotech should become involved.
Thanks for permitting me to take your time so I could put forth my views. Snaps ![[cook]](/data/assets/smilies/cook.gif "[cook] [cook]")
to all comments to date.
