Partition Wall Pressure Loads in Mines

[JAX91]

I am designing a fire-rated partition wall in a mine roughly 1200 feet below grade. In a normal building application, I would design for the code required 5 psf minimum (IBC 1607.13). Does anyone know if the pressure would be greater for any reason because I am 1200 feet below grade?

 

[concretemasonry]

JAX -

In a 1200 foot deep mine fire would usually come with a possible explosion and movement, so the 5 psi is minimal.

The normal fire ratings (2 hour, 3 hour, 4 hour) are for walls to prevent the escape of gasses and temperature and they are usually tested with a vertical load with a fire hose blast since the combined loadings on masonry walls can be resisted and it is cheaper to test a single wall for both loadings.

The big question is the lateral load and 5 psi is not that much, especially if there is possibility of earth movement also. Don't forget about the anchorage to Terra firma (pun intended).

Dick



Engineer and international traveler interested in construction techniques, problems and proper design.

 

[JAX91]

From what I understand, there is little to no possibility of earth movement. The corridor in which the fire wall will be placed is fully encased with 12" of concrete (designed by others). The wall is separating an MCC room from the rest of the equipment servicing the mine. The room is vented, so I think the only fire case should be from an electrical fire, which should not create an explosion. I am told I need a 3-hr fire rated wall.

 

[TDIengineer]

I can't see how atmospheric pressure would change the design of a partition. Run with your 5 psf. I am sure one of the old timer's here knows where the 5 psf came from for partitions within the code or there is a commentary discussion. It isn't a wind load...

When I have a heavily loaded partition, like with xray shielding or veneer, I always compare my seismic load Fp using the actual wall weight. For most typical interior partitions, 5 psf is greater than or approximate to Fp x self weight of the wall.

 

[77JQX]

Not a structural of HVAC guy, but I have worked underground. Have you accounted for the mine ventilation in the 5 psf figure? Usually there are some pretty substantial fans to push air around to all the potentially occupied spaces.

 

[cvg]

arc-flash can indeed cause an explosion, and the size of the explosion is related to the voltage level. you may want to check on this.

http://en.wikipedia.org/wiki/Arc_flash

 

[dik]

5 psf is not uncommon... and, for explosion 5 psi is OK depending on how far... Arcflash, although it develops a little over pressure in proximity, is not really a high pressure item, unless you are dealing with some really high voltage stuff... more common on the surface (138 kVA, etc.)... and it can be really fatal up close and personal.

Some mine materials, potash for example, 'creep' and the lateral pressures can be high... I've used foam voidform or an actual 'airspace' to minimise lateral pressures.

Dik

 

[charliealphabravo]

You guys keep switching between 5psf and 5psi. Is this intentional?

 

[miningman]

All interesting and amusing comments but the most critical questions have yet to be asked. Is this a coal mine or something else. If it is a coal mine, then the potential explosion hazardss from methane are several orders of magnitude higher than any non mining personnel can comprehend.

What EXACTLY is the wall designed to guard against. Blast within the MCC room or blasts outside the room causing damage to the electrical equipment.??

 

[JAX91]

The wall has a 3-hr fire rating to contain electrical fires inside the MCC room. Because of contractual obligations, I can't discuss what is going on in the mine. I will check with the engineers designing the mine, but I'm fairly confident blast/explosion is not an issue. Other than the blast loads, are there any other pressure loads that need to be considered because of the depth below grade? I will check on 77JQX's comment regarding the fans.

 

[TDIengineer]

OOps! 5 psi versus 5 psf.. 720x different!

What type of wall is it? Concrete.. metal stud with gypsum for your fire rating? Is it shaftwall construction because of accessibility on 1-side? If it is a metal stud wall, I would use a 6" x 16 gauge (similar to an exterior wall on a building) and use that if there is high pressure concerns. But, this isn't my area of expertise, so I should probably shut up.

 

[TDIengineer]

I meant 720 psf equivalent..for 5 psi.. that's 144x larger... sorry I was using new math.

 

[JAX91]

The wall is CMU. Although, by the time you add a door, air in/out, and cable tray, there is not a whole lot of wall left. I'm probably going to use 8" block grouted solid to get my 3-hr fire rating. This should be sufficient for a pretty decent pressure load as well.

 

[concretemasonry]

JAX -

Sounds like a good plan. That will give you a 3 HR rating. Very similar to a high security prison I was involved in - Concrete columns, post tensioned slabs (2 to 4 floors) and ground 8" CMU walls (250,000 units) vertically reinforced at 8" for security using special shapes. Anchoring the vertical rebars was a challenge when drilling into the slabs ans special block were used to allow dry packing of the top course of horizontal steel. Lots of angles, but the CMUs could easily be moved around and installed between the walls with many jogs, angles and openings.

In a mine, the logistics for block, rebar grout and mortar should not be a problem. Forming and placing concrete for walls is a much bigger problem.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[topsisu]

CVG has a good point about arc flash. A few years ago an electician was killed inside an MCC room at one of our local surface mine processing plant. An arc flash explosion was caused by an electrical fault. It damaged the concrete slab (on metal deck) roof and cracked the 8" cmu walls. The explosion had blown a hollow metal door off it's hinges and caused a black out of the site.