Bury Depth of Fire Mains Pipe (Commercial Application)

I'd go with the head engineer's recommendation. It's obvious you don't know the requirements, if you are asking total strangers for advice.

Cheers.

Yes Lynch, don't do any due dilligence for yourself. Believe whatever other people tell you, Bahh sheap.

I assumed you have some fire hydrants to install. Check the dimensions of your hydrant accessories(spools), you might have ordered a set (elbow & spool in one) fire hydrant accessories, just like some model of CROW fire hydrant. You have a big problem there if depth of trench will not match preferred fire hydrant accessories.

Thrust restraint blocks are out dated in new construction, we use Retainer Glands. Look at MegaLug 1800 series.

Granted that concrete thrust blocks are antiquated and expensive to installed, and that MetaLug mechanical retainer glands (or it's "equivalent".....see, I don't use the word "Equal") are a great option, BUT you must first get the approval of the municipal water dept. or water authority having jurisdiction. You must first win over their minds and hearts in order to get any sort of approval for what is not the norm.

In order to even use MetaLug restraint system you had better be prepared to know the Pros & Cons of using it, let alone knowing how to design it correctly, especially when it comes to tying back into the pipe sections (like PVC C-900 and DIP pipes w/ push-on rubber gasketed joints). Otherwise you're just fooling yourself, and you're design is ripe for possible failure.

I still like concrete thrust blocks at water main and sanitary force main bends. Call me old fashion, but with any sort of mechanical restraint system you are relying solely on the "pipe monkey" down in the trench to get it right by properly tightening the restraint bolts with his handy-dandy socket & ratchet. I have yet to date (nearly 34 years in this Biz) seen any Contractor's pipe crew down in the pipe trench with any type torque wrench assuring that he achieved the required torque values on the locking bolts.....unless you bitch to the foreman or the Contractor's manage loud and clear you'll won't be assured that every bolt has been tightened properly! If you don't, then there's a fairly good chance that the fitting someday into the future will ultimately dislodge itself when there's a pressure surge or a water hammer situation say when the water dept. personnel closes a gate valve or butterfly valve too quickly. Seen it happen all too often over the years as an engineering consultant and as a City Engineer.

the locking mega-lug nuts break off at the designed torq. If you use mega lugs you must also use restraints on the bell and spigot pipe. Also if you don't have good as builts of the existing water mains you will have to pour thrust blocks. Unless submitted and approved the inspecting authority will not allow mega lugs.

Along with frost protection and uplift/thrust resistance you might want to consider possible conflicts with your other utilities as well as storm drainage. Here in SE Alaska we require a minimum 5' bury whereas further north they require much deeper bury. Since you have some flexibility with depth and alignment on water lines and much less with sewer and storm lines you might opt for deeper bury to avoid them. Be sure and maintain your horizontal separation from sewer wherever possible.

Thanks for the very informative response guys, but is there a really good reference regarding this issue. Like recommendations from NFPA or DIPRA or others? My instinct tell me that it should be buried deeper than 3 feet, since we are using push-on type D.I. Pipe and yes, we have unavoidable conflicts with other utilities, which consequently add-up 45 deg. bends- this i feared the most with out being assured that our subcontractor thoroughly installed restrained thrust blocks.

If the water in the lines will be static. It will stay that way if buried too shallow at any point along the frozen way..

If the depth of excavation is actually going to be a cause for concern ... money wise.. I can imagine it's a lot of pipe.. Which would increase the opportunity for failure.

Ask if he'll split the difference and go 4'?

As far as listening to the head engineer above all?

If any head engineer's would like to boast about their perfect track record.. I'm sure we would all love to hear about it.

...I've met a few that are perfectly cranky...

You got my point JE in Chicago. lol. Before he was a little bit cranky making such decision, but i know now he started to realize my point and well, he got his resume updated already, if something goes wrong with the mains fire line on the testing and commissioning, it really cost a lot to rework leaking pipes when the pavement had already been made. That is the worst scenario i could ever imagine, and you know, when you are on a team, a fault of one is a fault of the others. Well, he can not blame me then. But, it will be same shame for our team for that kind of decision.

If the water lines will be static? WOW JE did you graduate from middle school?

Length and oppertunity for failure, are you serious? Split the difference and pay more to burry the pipe deeper but still in the frost zone, you should not be allowed to express your opnion.

I see there is no hope for Chicago or its morronic residents. Engineers you have met that are cranky, are so because they have to work with such a dimwitted fool.

There are codes available for the installation and other details of fire hydrants. You can refer professional bodies such as CIBSE ( U.K) ,NFPA sites to get more details.

buried depth for electrical is 36" to top of pipe for most electrical utilities here in so cal. Most water here is below frost line. check with your local city water co. and see what they have for their mains and do the same.

Would that optimum depth vary to a degree with the soil type also?, say mud to gravel, to sand to heavy clay ...

Hi,

If you are in a place where the temperature can drop to sub zero for example, Toronto, you should consider burrying the water pipes below the 'freeze line'. My understanding is that it is about 4' below the ground.

We don't know where you're located. Knowing where you're at would probably nail this issue down once and for all, especially if you are in the USA or Canada.

Question #1 for the OP:

Was a Building Permit issued for this work in question? If yes, you may want to consult with the local Building Inspector/Code Enforcement Officer and learn from him/her what the local municipal code and standards are in regard to the minimum depth of cover requirements for water mains and service lines.

If that track doesn't work, then consult the local water department that has jurisdiction over your work, especially since you are tying into one of their water mains to install the fire hydrants and it's service lateral.

Question #2: Obviously you were probably required to wet-tap the existing water main so as to install the fire hydrant service line, so EXACTLY what was the depth of the existing water main where the tap was performed? If it's greater than 3 feet of cover, then that will form a basis of your next argument with the "Head Engineer". Note: most water departments require that one of their personnel be present at the time any Contractor (or anyone else for that matter) even excavates in the vicinity of an existing water main within a public Right-Of-Way, and in your case they were most likely present for any "Wet-Tapping" of the main. Find out from the Inspector on the project site who that head of the water department is as well as who from that department witnessed the main tapping. Also, you may want to ask if anyone measured the depth of bury of the existing main, and what if any discussions were recorded in the official project Inspection/Field Observations Report in regard to minimum depth of cover requirements the water dept. employee may have talked about during his field visit.

In New England the minimum burrial depth without insultaing the main is 4.5 feet. This is due to the expected frost depth at 4-feet. What are your winters like? If your in FL than 3-ft is fine and a ductile iron pipe can withstand the HS-20 loading at that depth. Look up your frost zone, then burry the pipe a foot deeper or so. Insulation is MORE costly than an extra 2 feet of gravel backfill.

If ignorance is bliss, why aren't more people happy?

If water is moving at a velocity around 6 feet per second or more, burial depth could be at frost line. If the water is not moving, for example in a static fire line, NFPA 14 requires burial at least one foot below frost line. There is a chart of the USA within the NFPA appendix, but a much better bet is to discuss with local underground utility contractors, the local fire department authority, or local building officials. Typically, local required foundation depths will be at or below frost line, so that might be a safe reference point.

If you do not bury the pipe deep enough at the start, you will dig it up a few times (to repair frozen pipes) before deciding to bury it again at the correct depth!

Water pipes will freeze in winter at a depth of 7 feet in North Dakota if they don't have constant flow. As was mentioned by others...the Depth will depend on where these will be buried. Three feet will suffice in the warmer climates...but is far too shallow for the colder ones.

"Typical" as you describe will vary by the local climate.

I do not where this job is. The only concern is frost heave.

For this part of Canada we have had a very cold winter with several mild spells.

Most buried items that are less than three feet are moving. A lot of our roads now have speed bumps. The region is going nuts trying to keep with water main breaks.

It may cost more to go deeper, but it will be better if your in a frost zone.

Side note: About twenty years ago an engineer decided to bury a gas line above the minimum depth, in Toronto. Later, during new construction a back hoe hit it. The gas seeped thru and abandoned conduit into a building complex. Eight people died from the explosion.

Always ere on the side of caution. At least you will sleep better at night!

All the discussion of the frost depth raises another question in my thinking:

Putting the fire main below the frost depth is obvious and logical - but what about the tap points or risers, how are they managed to stop them freezing up?

I have always lived in either a tropical or temperate climate that does not experience these problems, so I was wondering ......

Thanks

WAWAUS, tap points, which are known here in the NE USA as wet-tapped corporation stops. They're the connection point at the main for the service laterals conveying water to the customer.

Usually we do not use riser sections here unless the water mains are over 10 feet of bury depth. Both the corp. stops and the service laterals are keep below the frost penetration depth (and plus some more for extra measure) same as the water main.

I hope that answers your question.

I was thinking more in terms of fire hydrants.... where rapid access by the fire brigade is required in all weathers at all times of year...

Fire hydrant valves are located at the bottom of the riser, well below the frost line. The the valve stem, usually with a pentagon shaped top on it, extends down through the fire hydrant to the valve located at the bottom of the hydrant.

Hydrants also have a drain located there which is also controlled by the valve stem. In the fully closed position the drain opening allows the hydrant body to drain to the subsurface. As the hydrant is opened the supply opens and water rises to the hydrant body. Until the hydrant is fully opened both the drain is open and the supply to the hydrant body is being supplied with water. When the valve is fully opened the drain is closed. This is why whenever firefighters open a hydrant they always open it all the way, usually about twenty plus turns of the valve stem. To leave the valve in a partially open position will cause the drain hole to flush away the subsoil around the hydrant.

If you see water coming up around a hydrant body it is a good bet that the hydrant isn't open all the way or there is a leak in the hydrant below the dirt surface.

The reason for so many turns of the valve is because you have at least a 6" diameter supply at possibly in excess of 100psi, which requires a lot of force to close the valve. Also it prevents hydraulic hammer actions in the water line from occurring from the valve being opened too fast or closed too fast.

Whenever a ball valve is placed in a fire water supply pipe it usually has an operator on it that requires more than 6 complete turns to open/close it so that it is opened/closed slowly to prevent water hammer.

Good Luck, old salt

Many references, standards, and local regulations etc. discuss minimum depths for water etc. pipelines, and as noted on this thread any applicable requirements should be consulted. I noticed one of the latter local requirements on the web in an area referred to a standard and was worded, "The 2010 Edition of NFPA 24, Section 10.4.3, requires that the depth of cover for fire service main pipe be not less than 2 ½ ft. or 1 ft. below the frost line for the locality. Where frost is not a factor, the 2 ½ ft. depth of cover is required to protect the pipe from mechanical damage." [The specific standard referred to there is of course for private fire service mains.]

Thanks all you guys for very informative answers, we are actually in a temperate climate zone, no so frost are to be expected. The only thing i worry is for the push-on ductile pipes to be properly restrained and kept at depth where there should be no possibilities of joint movement. Anyway, now after seeing a lot of your reactions and advise, i realized the facts of bury depths for fire mains.

Anyway just curios, at below freeze zone its alright to locate fire mains even dry type or flooded type? Either of the two is ok? How common is dry type fire main compare to the wet/flooded type in the US. What is the most preferred type?

Wet is preferred due to faster supply time to the fire. Dry systems require the water to fill the supply pipes before there is any water to put on the fire.

Dry sprinkler systems are sometimes used for areas that are not heated. They are usually kept to a minimum due to the delayed supply of water, the higher initial cost of installation, higher maintenance costs, the need for an air compressor to maintain the system pressure and finally the higher costs of periodically testing the system (it must be drained and refilled with air).

Some systems use an anti-freeze/water solution in the exposed piping to prevent freezing. Once the head opens the solution, which is non-flammable at its concentration, flows out and is followed by water which continues to flow until the system is shut down.l

Good Luck, old salt

Not all anti-freeze solutions are non flammable. There was a recent blurb warning about use of anti-freeze that I need to dig up.

http://www.koverholt.com/2010/02/24/flammable-antifreeze-in-fire-sprinklers/

www.nfpa.org/assets/files//PDF/Research/RFAntifreezeSprinklers.pdf