2.1 million square foot distribution center investigation

[muuddfun]

I would like to know what you would do for an investigation for a large distribution center warehouse about 2.1 million square feet in size.

How many borings would you do, what type of equipment would you use, how would you structure your investigation? And how much could you charge for it? How much would your clients be willing to pay? What sampling would you collect, and what lab testing would you do? How long would it take you to do, and what would you put in a report? How much effort would it take you to write such a report?

I would like to get a feel for how much difference there is amoung all of you on something like this.

A little background to help.
You know the geology quite well. The land is flat, and the building will likely be constructed very close to the grades of the existing ground. The groundwater is shallow, the earthquake shaking is very high. Bedrock is 20,000 feet down, your geology is probably lake deposits, blow sand, and alluvial deposits. You have conducted investigations on land in the immediate vicinity, or have some data from the land close by to help with your overall understanding and comfort level of the geology etc.

What type of foundations would you consider?

 

[msucog]

your geology is much different than mine so i'd be out of my realm hazarding a guess about foundation support (even though my gut says mat foundation...likely completely wrong). but as far as subsurface explorations, a building that size would be quite expensive to explore (i won't go in to sampling, testing and all that on my post). let me estimate based on my geology being pretty sure that spread footing foundations would work. $100-150k+ would be the very low end of what my estimate would be (again thinking that the shallow foundations will be in my geology and are suitable). these borings are still spaced rather far apart so i'd might consider this exploration as the preliminary for a client i know. then after this phase is complete, go back and add borings to further evaluate critical or suspect areas. i'd also be sure to perform shear wave velocity assessments at the site to try and help get the seismic design parameters down if possible (it sounds like this possibly wouldn't help you much). but if done in a certain way, it could add information to your subsurface exploration. also, this might be a situation where knowing what the next ibc seismic hazard maps will look like might save the owner bigtime money. i'm guessing this project is slated for some time next year (maybe)...so if the owner knew in advance that if he postponed the project say 6-8 months for the revised hazard maps (which just might happen to lower the seismic parameter values) to become "official", the end result could be very positive. here's the link to the usgs website where it shows what the difference between the '08 and '02 maps might be (keep in my ibc and usgs maps are not necessarily identical--particularly in high seismic areas). or you can use the second link to read the report which has the planned maps in there.

http://earthquake.usgs.gov/research/hazmaps/products_data/2008/maps/ratio.php

http://pubs.usgs.gov/of/2008/1128/pdf/OF08-1128_v1.1.pdf

as far as subsurface conditions, if something goes wrong in one single bay of the building, the client could lose massive amounts of money since problems typically extend out several bays from a single problem bay. it may boil down to shutting down the building or having a problem renting out the space or selling the building. but if they've got the money to build a 2mil sf warehouse, they've got the money to do the exploration. besides, on top of saving them money through good engineering recommendations, it is added insurance for them. they could go get cheap recommendations that may cost them big time by the time the building is constructed.

hope this helps.

 

[fattdad]

Borings every 200 to 250 ft. If there is no real grading shown by the grading play, I'd likely go about 20 to 25 ft deep using either mud rotary or hollow-stem augers. Some may go to 100 ft at one location for IBC site class - maybe more than one. These buildings are typically light, with column loads under 200 kips (other than mezannine level areas). Floor loads can be high as well as flatness tolerance.

I'd do a CBR or two in the building area for correlation to subgrade modulus. I'd also drill in the heavy-duty pavement areas and also get a CBR or two. Each CBR will have a Proctor, so it can help during construction as well.

No clue what local issues may change my generic approach, but for many jobs I've been o.k.

f-d

¡papá gordo ain’t no madre flaca!

 

[RWF7437]

muuddfun,
shouldn't you be doing this ?

 

[howardoark]

I think I would mostly do cone penetration testing as it would be a lot cheaper. I think the Corps recommends one boring for every 2500 square feet, but you pretty much don't want to do 840 borings.

You haven't said what the floor loads are going to be. If they are large and they're laterally extensive, you may have settlement issues. If your geology is Holocene, you probably do have settlement issues. If the geology is older, then you probably don't as all that earthquake shaking will have densified the sand.

I think you should propose a phased approach - depending on floor loads and your expected vertical zone of influence, you should do some deep borings to see if you have compressible strata at depth. If you don't, I think I would do one CPT per acre scattered across the footprint and see how variable the subsurface is. I would also do a couple of geophysical lines across the footprint to see if there's some buried feature that you might have missed with the borings.

 

[muuddfun]

RWF7437, I have an idea of what I would like to do, though not of what I might be able to get signed on the dotted line. The reason I am asking is to gauge what the differences are in how each of us approaches the same problem. Also to see how things differ from region to region, because that has a large influence on our thinking and what equipment is available and the methods we rely on for testing. etc.

My problem is a real one that I realized would be a good one to use for discussion. My other problem is that in my particular neck of the woods I am up agains not one but three other geotechs who will do it for quite cheap. And they have been long established so that is what most people expect. Makes it hard to get work. Something like this is where I might be able to work my way in and get a job. Things are very very slow for everybody in my area right now.

As I first said we have data in the imeadiate area to start with so that helps. We most likely will start out slow with only a very minimal amount of work to get our foot in the door, then see if we can do a real amount of investigation after that. I would like to do CPT, some hollow stem, and then some test pits.

Msucog, I have read the open file report and in most of our area it will help out in reducing the shaking we design for, but it will not make to much difference in this area. The ground will liquefy, there is no doubt about that, the only question is how much settlement, and how badly I will loose bearing capacity. I would like to think I could make a mat slab or raft foundation system work, I don't know how it would do over so large an area with the liquefaction. I don't know what the floor loads will be, or anyting really beyond the fact that it is some kind of distribution wearhouse, of which there are many all over around here. So probobly heavy forklift traffic and large stacks unloaded from the containers as they come in from asia, then redistributed to the rest of the country. I might have to put it on piles or do some ground improvements, but that gets expensive fast. The problem I have with piles is the downdrag from the liquefaction adds up so fast. Any body have any thoughts on that? I will probobly try to push a seismic CPT to 100 feet at least very near the beginning to see what we have down there. The sediments are fairly young fairly deep. They were laid down as part of a lake bed many time over the years. The lake would fill, then dry out, then fill again etc. It has created many layers of interbedded sands, silts, and clays. Even if the liquefaction settlement is not that much because the water i lower in any area, then the dry sand settlements will do me in as well.

Fattdad, Even though I am in California, we don't do CBR's around here, how well do they work? How deep of an influence do they provide you info. As I understand it you are using about a 1 foot square plate to test the subgrade in the field? Is that correct. Around here practicaly all pavement design is done by the R-Value test, so we kind of miss out on the actual field testing of the subgrade, usually have to infer that from the drilling data. Do you have good correlations between SPT and CBR? or is that not very practical. Mostly I have just been looking at NAVFAC to get subgrade modulus, but for more critical work sometimes I would like to do something more. How much does it cost to do a CBR test?

 

[msucog]

it sounds like you've definitely got a tough situation to get you foot in the door but still provide the client "real" recommendations while keeping your neck out of the litigattion noose.

this sounds like a very challenging project to say the least. i leave the discussion to those of you more familiar with these conditions.

one thing you might consider is using ReMi in conjunction with your exploration to assess the shear wave velocities. since it can evaluate conditions very deep from the surface, you might realize some cost savings while obtaining information about the deeper conditions across the building pad. also, for seismic assessment the 100' depth should really extend deeper for such conditions. i see folks argue this both ways but my interpretation of the language is that it should extend deeper for these type conditions.

 

[muuddfun]

Msucog
I am not familiar with the term ReMi, can you please explain more? Thanks

 

[msucog]

search "ReMi" or "refraction microtremor" on here since there's a few threads i mentioned/discussed it and posted links. you can also search the web to find several papers on the subject. it is used to evaluate shear wave velocity and can see just about as deep as you could possibly want depending on your setup. it's setup is very similar to refraction work but it is not the same (it is also similar to the older, well known seismic shear wave analysis methods). i've had great luck using it along with borings. in particular, i think it is good to use prior to drilling to help pinpoint problem areas so that borings can be placed more effectively. the basic data analysis is fairly straightforward but the more complex analysis does take some expertise.

http://www.optimsoftware.com

is probably the best place to send you.

 

[Mickney]

Suggestions:

Set up a systematic grid pattern. If the borings or subsurface profile remains pretty consistent, then begin to widen your pattern.

On jobs where competition is tight, I have given at-cost pricing for the geotechnical work provided a guarantee is given for the materials testing (where most of the money is made for my firm). This requires good conversation and rapport with the owner and their team. Also, do you know any of the other players (structural, civil, architect) who could get your foot in the door?

 

[fattdad]

re: CBR testing - we do it in the laboratory with a remolded sample prepared to 95 percent relative compaction (Standard Proctor). After the sample is prepared, we soak it for 4 days and then use the piston to measure the load to acheive 0.1-in penetration (per the ASTM method). The CBR can then be used for AASHTO pavement design the CBR can be correlated to subgrade modulus (for use in industrial slab design) and the Proctor can be useful during construction.

Don't really think I'd like to make a correlation between SPT and CBR.

Don't really like to do this sort of design without a site-specific CBR test (they're just not that hard to do).

Don't like making a wider grid if things look consistent - here's where the body is buried: During construction the contractor turns the site to mud, the geotechnical testing firm looks to the data and sees that the "soft" ground is in an area where the borings are spaced at 400 ft rather then the other area where the borings are at 200 ft. The contractor claims the borings missed it and you're off to a pi$$ing contest. I think there's value to setting a program and being consistent. If anything looked to be really that consistent, I'd maybe make alternating borings 10 footers and keeping the others are the more conventional 15 to 20 ft (depending on the overall grading plan).

I would widen the boring spacing if there was dilatometer or cone data also in the field program. I would not do just in-situ testing (i.e., were samples are not recovered).

f-d

¡papá gordo ain’t no madre flaca!

 

[muuddfun]

Thanks fattdad

 

[civilperson]

50 borings with two each to 150' depth and the remainder at 25'. If no great variation is found then deem sufficient, other wise fill in gaps at the change locations. Drilled piers at columns and grade beams at perimeters are usually cost effective due to high production rates after mobilization cost is distributed over the large number needed.

 

[Ron]

The original post seems a whole lot like a homework problem. I'm surprised this post has been around this long without red flagging.