I've done a bit of this and am aware of no applicable standards. I suspect that it will come down to what the client wants, how badly they want it, and your professional judgment.

For small, individual headstones, in order of preference, I'd be inclined to:

1) Just set them right again and hope for the best.
2) Connect them to a shallow pad footing that is allowed to float with frost (frost depth in the field can be 7' here).
3) Connect them to a shallow pad footing at frost depth.
4) Connect them to a screw pile if there's access available.

For big things like statues and mausoleums, using shallow frost protected shallow foundations has proven economical.

One needs to keep in mind the nature of the facility. Too much open excavation and you risk setting a bunch of zombies free. Not cool.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

I am not aware of any minimum required depth for grave headstones in Toronto, nor would I think it would be necessary in most cases. What would typically be done, when necessary, is a shallow pad footing that floats with frost. Often there is just a base stone, no concrete. If you want to minimize movement due to frost, over-excavate more depth, perhaps 12" to 18" and place compacted, non-frost susceptible fill. Keep in mind, if you are putting a grave marker, it is disturbed fill that has been excavated and replaced so settlement may occur.

Interesting question though when I think about the stone mausoleum that was recently constructed nearby (in Toronto) (much different than a grave stone, it is likely 300 sq.ft). I should have looked at it closer during construction but would assume it was a) engineered, b) perhaps permitted, c) had footings and frost walls supporting the stone structure.

From what I have seen the person or persons that maintain the cemetery have a practice that they follow and I suspect it is by trial and error to settle on what works. Also they work with the folks that sell the head stones to set the practice there..

I would contact the head stone masons, suppliers or funeral directors.

I know the ground conditions are different what with your winters and such but this might be helpful
http://www.bramm-uk.org/userfiles/documents/4/The%...

Depth is not the issue, breadth is. Make the footing big enough to carry nicely on the (probably) weaker soil near the surface and let it float as KootK & Canuck65 say. How many brick & stone posts have you seen at the end of peoples' driveways leaning every which way even though they are on a footing below frost? You're a Canuck; forget the frost, forget wearing stilettos, & wear snowshoes.

To all who took the time to respond: Thanks you very much. Much appreciated.

To Debyloco: Your attachment is very interesting indeed. A special thanks to you. It looks though like this is a British Standard, so I am not sure that they have as severe a number of freeze cycles as we do here in Toronto. Nevertheless it is interesting and useful.

ToOldBldguy: I am not sure why you say depth is not the issue. Perhaps you are located in an area that does not see freeze-thaw cycling, ice lensing and the like, which plays havoc with foundations in unheated areas of buildings (frost heave, etc.). Where generally are you located?

Further Information:
Normally in the Toronto area, foundations for new headstones would be founded at 1.2 m depth i.e depth of frost penetration in Toronto area. My question however relates to an existing relatively old cemetery. Many of the headstones are over 100 years old, and some did not have foundations that extended to 1.2 m. Many are leaning badly and some have toppled over. Some may perhaps even have been just stuck into the ground with no separate foundation. We (a charitable organization) are trying to restore a significant number of headstones without spending excessive amounts of money, if possible. There are seemingly no local standards so this is a bit of a geotechnical/structural question of how to do it economically, but still achieve a reasonable design life. One person on the committee wants to just set them on shallow foundation (same idea as Kootk put forward), but I wonder how long it will be until noticeable movement occurs (this would be done only for the 18" high essentially flat or slightly sloping headstones, not for the higher ones). The soil is a silty clay, so I expect it is vert susceptible to frost heave, etc.

Ajk1:
What would happen if you auger drilled a couple 10-12" dia. holes, side by side, 1.2m deep and cleaned out a bit btwn. the two holes, would the soil stand on its own? Then, on top, at grade, use a simple form 16"x30"x9.25" deep for a cap, with a couple dowels in it, up into the bot. of the headstone; and fill the top form and holes in one shot of conc. Maybe fab. a couple different sized light stl. forms which are reusable, with lifting/pulling handles and dowel holders and all. These stl. forms could probably be driven down into the top soil, to proper top elev. and then cleaned out inside for pouring, but then, to also minimize cleanup (grass planting, etc.) work outside the form, when it’s removed. Finish a nice draining slope around the top of this cap to match the base size of the headstone, and grout the headstone in place.

Doing a little research, setting grave stones in concrete is a major no-no. If concrete is used for a foundation then the concrete base is slotted. The stone is then set in the slot with "Conservation Mortar" I realize, this isn't exactly the question you asked but it is terribly important to people who are invested in historic monument conservation.

Interesting Cemetery Conservation websites:
Link
Link
Link

Therefore thus saith the Lord Jehovah, Behold, I lay in Zion for a foundation a stone, a tried stone, a precious corner -'stone of sure foundation: he that believeth shall not be in haste.

Isaiah 28:16

Thanks for setting us straight epoxybot.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

ajk1: I'm in Niagara, I have work in Toronto basically all of the time, as well as further north & east where there's a lot more frost than TO. How can it possibly matter if the headstone is 2" higher in February than it is in August? It is not attached to any services or immovable objects. What matters is that it's perpendicular to the general earth surface & doesn't make the grieving (or simply interested) visitors feel like they should have one leg shorter than the other while they look at it. I reiterate: snowshoes are far more effective and cost efficient than stilettos (unless you're working the streets). I might also add that I've been involved with more than a few cemetery monument restorations as well as cenotaphs, art installations, & the like. Epoxybot is right about the other issues, but you were talking about foundations.

I didn't design the foundation for that interesting installation on the front lawn of Campbell House on Queen St., but I was asked to review & comment on it. The artist & his architect's concept for a foundation was based on the misconception that digging 4' deep cured all ills & nothing else mattered. The loading is severely eccentric, and as a temporary art installation it made no sense to dig the whole front lawn out to pour footings protected from frost and then rip them out in another year; I'm not sure what was done in the end but I told them the same thing I've said here. A shallow mat that loads the soil lightly and evenly is going to win hands down every time.

To dhengar: I like your idea. Very interesting. The soil should stand vertical in the drilled holes, because it is a cohesive material. A snag would be that the soil under the base would heave on freezing and lift the 16" x 30" cap together with the drilled piers. I had been thinking of something similar to what you suggest, but with a couple of helical piles under the base, but that too would be subject to frost heave under the concrete base, lifting the base and piles.

To mijowe: When Isaiah says "stone of sure foundation", does he give any details of how to accomplish that? I am sure he was not thinking in terms of frost heave, so that may not be too useful even if he did give details, much as I admire Isaiah.

To OldBldgGuy: If nature was perfectly uniform and symmetrical, then you would be right, that it may not matter that much if the top of the base is higher in summer then winter. But since soil is not uniform, the frost heave is not uniform i.e. each corner of the base may lift a different amount than another corner, so it will end up not level. Also, it never settles down exactly into the position it started in. After just a few seasons, the lack of levelness due to frost action in the cohesive soil may not be particularly noticeable, but after a number of years it will be. By 25 years, it will likely be quite noticeable. I am sure you would agree with me that if you want a base that is designed to stay level for at least 25 years or more, and the soil is clay, then the foundation should extend down to 1.2 m (Toronto area frost depth) in accordance with good engineering and construction practice in the Toronto area. If you are prepared to rebuild the base every 10 to 25 years, then the 1.2 m depth may perhaps not be essential.

You could just remove the frost susceptible material in the upper 1.2m and be done with it. For a standard headstone I feel you're putting way too much effort into this.

So, sidewalks, streets, highways, you name it, they're all completely incorrectly designed and built. They should all have foundations below frost.

We won't mention the 40 years' worth that I've seen & built & 65 years' worth that my father has seen & built of floating slab buildings that are perfectly fine. Including my 2000 sq.ft. 25 year old barn & workshop. Must be anomalies.

to OldBldgGuy - I respect your 40 years experience and your father's 65 years of experience. That 105 years trumps my 53 years experience, particularly since I have only very limited (bad) experience with shallow foundations on clay soil. I can go photograph an example and send it, if you doubt me as to what can happen with shallow foundation on clay soil.

Perhaps you can help me to be better persuaded if you can tell me:

a) whether those well-performing examples that you site had a clay soil under the foundation?

b) whether the top of slab remained level after 25 years?

c) why the building Code requires 1.2 m of frost protection for building footings that are subject to frost action, if perfectly fine performance can be achieved without going down to the depth of frost penetration?

I realize that sidewalks are replaced for may reasons, not just that they have become unlevel.
Nevertheless, when walking, I frequently look down to see the date, and I find few sidewalks are more than 20 years old. Try it and see what you find. I'd be interested. I don't think the analogy with sidewalks is necessarily apt. No one is bothered by lack of levelness of a sidewalk. Lack of levelness of a support for a headstone is not quite the same thing, as I feel it is a lack of dignity to the departed, although I may be wrong in that opinion.

To Jayrod: a few years ago there was a case locally of a headstone toppling onto a child. I am not sure that I can agree that I am "putting way too much effort" into it. This is not just one or 2 headstones. There are about 30 headstones, so in my opinion it is worth putting some effort into it, as it may save significant costs and/or achieve a longer lasting restorations and reduce life cycle costs. I understand that you hold a different opinion, and I respect and value your advice. I like your suggestion of removing the top 1.2 m of soil and filling it with a non frost susceptible material, if this turns out to be more cost effective.

To epoxybot: I notice that I forgot to thank you for the links.. So let me thank you now. Much appreciated.

I'd be interested in hearing anyone else's opinion as well.

I have watched them setting head stones in WI (fair amount of freeze/thaw).
If it is a slender stone (few inches thick) then the typically dig ~12" wide x 18-24" deep, just to prevent leaning too much.
For larger stones they would make the footing 6" wider than the base of the monument x 24" + whatever they feel fits the height, taller ones they go deeper.
As has been said, no one really cares if they rise or settle a bit, it is resisting overturning that matters.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

If you would like to look into how things are typically done in Toronto, I would suggest you contact Mt. Pleasant Cemetery. I say this only because a few years ago I was brought in to provide an engineering opinion on a grave stone (not the foundation, only the gravestone) for a family and Mt. Pleasant was responding with a) their written standards and drawings, and b) their engineers opinion. I think there is likely a wealth of information that you may obtain from a large operation such as Mt. Pleasant.

ok, thanks. Much appreciated.

Canuck65 - Would you happen to have a contact person at Mt. Pleasant Cemetery that I can contact who would be willing to talk to me about this?

Ed - do you know if the 2 foot deep foundations that you observed were on a granular soil, or a cohesive soil?

I do not have a specific contact person, I was working through a memorial stone company who were the main point of contact and all the info I was provided was heavily censored as it was for a very high profile, confidential, 6 figure $$ gravesite.

to Canuck65 - ok, I understand.

Many places in WI you are digging into piles of gravel with a bit a clay, this is all glacial till.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

To Edstainless - ok, that may explain their success. The gravel will be relatively free draining relative to clay and less frost susceptible. Thanks for your help. Much appreciated.

ajk1
Dad & I overlap, we can't take credit for the cumulative total of years. The Ontario & National building codes do not require 1.2m frost cover. That's a prescriptive number for soil used for Part 9 in place of engineering judgement and design (and it actually says 1.2m "unless local experience says it should be otherwise"). An engineer should be able to distinguish between when the prescriptive number is convenient, economical, or necessary; when a material other than soil is appropriate (insulation?); and when neither is necessary or appropriate. If one can't, that's fine, they can defer to someone who can. There are a multitude of configurations and circumstances, and appropriate design details for them. Clay, sand, gravel, peat, rock; they all require different considerations. That doesn't mean one has to default to the non-engineered approach. It might seem impossible but I have a 1500 sq.ft. unheated barn attached to a 700 sq.ft. heated workshop on a continuous reinforced concrete slab on grade. The barn sits on a 2' high 2-wythe kneewall of block & brick bearing a heavy timber structure, and the workshop is of typical stick framing sitting directly on the slab with a 2' high brick skirt to deflect splash from the roof. There's plumbing in the workshop. There isn't a crack in the masonry & nothing but shrinkage cracks in the slab, it's more than 20 years old (I dismantled & relocated the 175 yr. old barn), and it's founded on clay, but it's properly designed, drained, and insulated. I've designed and built countless heated & unheated structures on reinforced slabs including a 6000 sq ft church with 54' span scissor trusses and 100% masonry exterior cladding (built 2010, no drywall cracks in 2015), a 6000 sq.ft. unheated pre-engineered steel building for Ontario Hydro (25 years ago) and within the last 2 months 3 pre-engineered steel buildings >7500 sq.ft. both heated and unheated. I've also seen plenty of designs from other engineers for similar buildings (contractors love to shop), with very little deviation from what I would recommend. Just because one hasn't managed to do it oneself, it doesn't mean it can't be done.

To OldBldgGuy:

Thank you for the very detailed and clear response. Your experience and information seems to prove the rule that I made up for myself some years ago, namely that the more certain that I am that I am right, the more likely it is that I am wrong! Well I came on this forum to learn, and you have been a good teacher. You have provided persuasive information that it does work, in clay soil, and that it has continued to work over a significantly long period of time. Thank you again for your counsel and patience. Much appreciated.

To OldBldgGuy:

Just a bit of follow-up.
I notice that you say that it's insulated. Do you mean that it is insulated under the slab? If so, then I am not at all surprised that it has been successful. I have done that successfully too, and is not that uncommon to do so. However to put insulation under a headstone foundation would mean having to extend it about 1.2 m beyond the headstone foundation, all sides. It is something I had considered before posting the question, but that has some practical considerations. Also, it may not be that practical to put underslab drainage for a headstone foundation. Or is there no insulation under the slab in your unheated building?

Sorry if I wasn't clear. I meant that some shallow foundations are insulated to replace the soil frost cover, and some are not, and the trick is knowing when either is appropriate or necessary. Considering what seasonal movement might do to something is key, and considering how you have to recover from the movement or mitigate any potential differential movement is also crucial. For instance, in most cases seasonal movement of a monument is inconsequential but differential movement is critical. That's where you want to be sure that the snowshoes are big enough to always keep you upright, without being so big you can't afford to buy them and you can't wear them. Knowing what kind of snow you're walking on is pretty important too.

To OldBldgGuy - OK, now I understand and I am in general agreement with you. Thanks.