With the price of gas another solution may be worth considering.
I recall reading a few years ago of a drilling contractor recovering
commercial quantities of natural gas in old garbage dumps. This
happened in the province of Ontario, in Canada.
H. D. Richardson
Nicholas Blackburn wrote:
> A thick mat slab should be feasible, although maybe not practical. A mat
> slab will be stiff enough that you can activate whatever area you need to
> resist overturning forces (with a suitable allowable bearing pressure). For
> instance if the footing was 40' long x 10' wide x by 3' thick (30cubic
> feet/foot along the length) assuming 150pcf for the concrete you would get
> 4.5k per foot dead load.
> A 3' or more thick mat slab will also allow adequate development of the
> anchors. I might also thicken up the edges to provide additional resistance
> to sliding unless the slab becomes enormously thick. I am assuming that the
> critical overturning direction is across the short direction of the system,
> so it may be impractical to just thicken up the footing (and widen it as
> necessary to control bearing pressure) to add dead load (overturning
> resistance). This being the case, you may be stuck with some form of pier.
> Will the pier option really take longer to install if you are only
> installing six?
> Nicholas Blackburn, PE
> -----Original Message-----
> From: Robert Valorio [mailto:geotex1(--nospam--at)yahoo.com]
> Sent: Tuesday, January 30, 2001 10:42 AM
> To: seaint(--nospam--at)seaint.org
> Subject: Slab Foundation Possible?
> I am looking for some help on a foundation for an
> enclosed, skid-mounted landfill flare unit (i.e.,
> burns off the methane from garbage degradation).
> Anyway, the unit is self-contained because it is
> mounted on a 40ft long x 8.5ft wide trailer skid and
> will be delivered to the site and set upon a prepared
> foundation. After which, a 40ft tall (ground level to
> tip of stack) flare stack will be bolted on. So, what
> we have is a long narrow footprint with a tall chimney
> that can produce a large overturning moment due to
> wind loads.
> >From the flare manufacturer, wind design was for 100
> mph winds, exposure C, and I = 1.05, which is
> reasonable for the site and unit. The manufacturer
> also provided loads at the bearing for the foundation
> design. There are six bearing points in two rows of
> three (either side along the length of the skid). So,
> without a picture to show, here's how they're
> positioned: picturing a rectangle 40ft x 8.5ft, one
> bearing is positioned at each corner of the rectangle
> and the two intermediate bearings are placed 8ft from
> the end of the skid along the same line as the other
> bearings. (Note, all descriptions imply centerline
> dimensions.) Loading from the manufacturer is as
> At one set of end bearings and the intermediate
> bearings 8 ft from them:
> Wind Shear = 4kips
> Download = 12.6kips
> Uplift = 5.58kips
> The bearings at the opposite end are:
> Wind Shear = 2.1kips
> Download = 6.6kips
> Uplift = 0kips
> Now the dilema, foundations for these units are
> normally cookbook for me. For this loading, and
> typical soil conditions encountered, I've always used
> drilled or poured piers beneath each bearing point.
> However, this particular installation, the owner is
> strongly pushing a foundation slab of some sort. I
> have no experience with designing a slab to handle
> this sort of equipment and it's loads, which the
> overturning potential 'feels' too great to me for a
> slab given the narrowness of the footprint (Note, no
> guywires will be installed either to further support
> the stack). Can anyone offer me some advice for design
> or at least persuading the owner not to go with a
> slab? I've searched through ACI, PCA, and Corps of
> Engineers literature, but nothing has given me any
> level of comfort for this kind of design. I was told
> to buy Ringo and Anderson's book, "Designing Floor
> Slabs on Grade: Step-By-Step Procedures, Sample
> Solutions, and Commentary," which will arrive
> tomorrow. However, the owner is pushing for a fast
> turnaround, so I'm limited on where I can seek out
> further advice. The manufacturer cannot help as they
> want no liability for the foundation design. I've been
> reading the mail list for sometime, but this is my
> first post and I really could use the guidance of
> those of you who are more experienced than I.
> Thanks in advance!
> Rob Valorio, PE
> Cherry Hill, NJ
> P.S. - Also, if it helps in your response, the
> foundation soils are ideal being a virgin deposit of a
> very dense gravelly sand with a high modulus of
> subgrade reaction.