Boring locations-Parking Stucture
Boring locations-Parking Stucture
(OP)
I am looking at a 186x120 5 or 6 story parking structure and the arch is asking for boring locations. I am think of at least 3 borings: close to NE corner, center, close SW corner. Is 3 borings reasonable for this footprint?
Thanks,
Thanks,






RE: Boring locations-Parking Stucture
I would probably recommend 4 for a project this size though I am sure many have been done as low as 2 boreholes.
The problem that I can see with your configuration is that potentially if you have a linear feature such as a dyke or former river e.t.c. then all three boreholes may coincide with the line of this.
4 boreholes can give you a reasonable 3d layout of strata e.t.c. that you can hang your hat on. Also, I expect you will be using this data for CBR e.t.c. for the ground level slab and this would help.
If you have to use 3 boreholes move the middle one off centre so you can get a good approximation of bedding planes e.t.c.
RE: Boring locations-Parking Stucture
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Yes, you might miss something. Cover that eventuality with a statement in your report such as "Subsurface conditions will vary between borings. Interpolation of conditions between boring locations should not be done by others. Interpolation for this evaluation is based on the information available at the time of the report and could change with further, more precise information."
RE: Boring locations-Parking Stucture
Thanks. I guess the 4th boring would not be not that expensive since they would already mobilized and present on site.
RE: Boring locations-Parking Stucture
RE: Boring locations-Parking Stucture
RE: Boring locations-Parking Stucture
RE: Boring locations-Parking Stucture
SPTs are cheap compared to the cost of the structure overall, drop in the bucket. And you are right, once they are mobilized there is not a huge difference between 3 or 5. I always like to pick at least one highly loaded pad footing area if you are that far ahead in your design development.
Alternatively to the throw darts at the side of a barn SPT technique, you can hire a company that can do some geophysical testing (ER, GPR) over a large swath of area that may locate anomalies that can than be drilled for further exploration. These are not prohibitively expensive either.
RE: Boring locations-Parking Stucture
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RE: Boring locations-Parking Stucture
RE: Boring locations-Parking Stucture
RE: Boring locations-Parking Stucture
RE: Boring locations-Parking Stucture
RE: Boring locations-Parking Stucture
Beat me to it! LOL
RE: Boring locations-Parking Stucture
No wonder George Costanza wanted to be an architect, not an engineer.
RE: Boring locations-Parking Stucture
www.FoundEng.com
RE: Boring locations-Parking Stucture
RE: Boring locations-Parking Stucture
Your geotechnical engineer will guide you. I was involved in 4 story parking garage few years ago and we ended up driving 16 inch square precast concrete piles about 65 ft length. We had a basement level and that helped in partially compensating the building weight. Our soils were medium dense Silty SAND and I think water table was at 15 ft+/-.
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RE: Boring locations-Parking Stucture
That being said.
"cvg (Civil/Environme) why would you dictate the boring locations to the geotech? In fact, I would not dictate the precise number of borings either. Call your favorite geotech, discuss the project with them, agree on a work plan and then rely on the recommendations they give in their proposal."
How do you, as a Structural PE expect to be treated?
I am sorry if that sounds a little hard to some.
RE: Boring locations-Parking Stucture
Is the site "new" or has there been previous structures on it in the past is another question I would find out - if there is potential for areas of fill, this might require some additional shallow borings.
Based on this, I would tailor the programme to meet my expectations. I agree that 5 borings would be prudent. The depths of the borings would be chosen to match the expectations. If there is a "great" chance that it will be spread footings, then you might go shallow borings at the corners and a deeper one in the center with the corner borings to prove the basic upper strata (which usually is the variable to be proven).
If you have sands over soft clays, for instance, you might need additional borings to confirm the sand thickness. If the sand thickness is uniform, you might be able to get away with spread foundations so that the pressure bulbs do not extend to the soft clay. However, if the sand thickness is variable, this wouldn't be an option.
If you have the potential for fills at the site - old basements that have been backfilled, etc., you may need to do additional borings to confirm the site variability. A firm I worked for in Philly always did test pits besides the borings just for this reason.
Now if you are in Europe - do you need UXO clearances?
RE: Boring locations-Parking Stucture
RE: Boring locations-Parking Stucture
The depth of borings is a function of the geology, the anticipated building loads and the probable foundation types. This actually is a very difficult question to answer without a good feeling for the geology. If I know very little about a site or area, I fall back to the borings are to be at least as deep as the total usable structure is high, including basements. This boring depth begins at the anticipated building base.
I remember a coal loadout silo in Western Colorado, encountered over 120' of a very rocky, wet & soft debris fan deposits. Never did find bottom. Broke the drill auger at 30' below the ground surface and excavated a 30' pit to facilitate the 'fishing'. Took a number of shelby samples in the soil & rock mess, which ended up being the best samples of the 6 day Drilling Follies. Eventually placed the silo on a structural fill and concrete matte. Performed well for 30 years, until removed after the mine was closed.
RE: Boring locations-Parking Stucture
Not sure if you have on grade parking outside the parking structure, but typically, we would use 2@50 ft, 3@35 ft and 1@15 ft for outside parking, if any. See attached bor. loc. map, if you have rectangular structure. We would do all the 35 ft borings first and based on the soil stratigraphy, pick the 2 deep boring locations. If you go to the City, and for some municipalities online, you can see old grading & investigation reports. Your geotechnical firm might also be able to order some aerial photos and have the engineering geologist look into existing geologic maps. There is a lot of art to this but experienced firm should be involved.
www.FoundEng.com
RE: Boring locations-Parking Stucture
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RE: Boring locations-Parking Stucture
That is exactly the way I see it and my response has always been that "this my opinion, final locations, numbers and depths are to be determined by the soils consultant".
There are a couple of architects whom I have been working with for a while, they just like to get structural engineer's opinion.
The rest of questions above are for my knowledge since we have a Gtech expert (FixedEarth) sharing his expertise.