Stadium's Foundation

Hi zultekmilennia,

First of all, you need to have a plan for building a swimming pool. Also you need to consider and decide on the size of the pool and type of installation. Will it be on ground? or above ground? What kind of material you want to use or prefer? Is it concrete swimming pool lined with ceramic tile that you want? Or is it the pre-fabricated tank type of fiberglass material?

Knowing the size of the pool and the kind of material you will be able to calculate the weight of the pool and the weight of water (when the pool is considered full).

BTW, the weight of water is 62.4 lb per cubic foot. Since you already know it's volume, simply multiply it by 62.4 to get the total weight in pounds (lbs. or convert to other equivalent units, if you are using other system).

These are the main items to consider for you to be able to determine the type of supporting structures, or the foundation of the swimming pool

Regards,

Or you could use the metric system that says 1m³ of water at sea level is equal to 1 metric ton, so a pool that holds 100,000 m³ has a weight of water of 100,000 tons!

You are correct!

A cubic meter of water at sea level weighs 2,200 lbs. which is the equivalent of 1 metric ton.

So, does having the pool above ground or on the ground (excavating the site) really plays a major role in determining the type of foundation used?

So, taking into account the load at full capacity (including athletes), equipments used, and the material of the structure used, this is gonna need some heavy support.

What if the ground is unstable? Like the Petronas Twin Towers, they poured concrete in lieu of steel at the foundation as steel was unavailable at the time. Would using steel piling and raft (mat) footing be sufficient? or pile with caps would fare better at the same load?

Sorry mate, you're asking the wrong person! But I'd imagine the whole structure/ foundation would need to be quite substantial!

First, it is not advisable to plan building your structure on unstable ground for if you do so, it will be costly to make the supports and foundation to be capable of supporting the whole structure (including its occupancy use and loads it will carry).

Whatever kinds/types of piles for foundation for unstable grounds will be very costly, aside from the need of pile driving or soil boring equipment for that matter.

Site selection will be very important (critical) to have a good, stable and economical foundation.

So, now that the water's load have been resolved (with a pool width of 25m, length 50m and depth 2m, we're looking at a load of 2500 metric ton for the water alone), how do you count the live load of a stadium, at full capacity?

I'm planning on about 3000-4000, and maybe I'll put some more features into the stadium, such a stores and such. Not forgetting the machinery for the pool's maintenance, the total is about 3600 metric ton. Is that about right?

If the pool is below grade and the soil is stable, the base of the pool will usually be a concrete slab on grade. The design is not particularly demanding as the weight of water is less than the weight of soil excavated for the pool. So the net load on the soil has actually decreased as a result of building the pool.

If the pool is above grade with occupied space below it, the construction becomes much more expensive because the pool bottom must be a structural system capable of spanning between supports while carrying the entire weight of water and people. It also must remain watertight to avoid complaints from the folks below.

Given a choice, the below ground pool seems to make much more sense.

Having that in mind, I'll design the pool with the machine room beside the pool (instead of below it, which I intended at first), with the base a simple concrete slab supported by a few bored piles (maybe 7, so it'll be uniformed) and with the stands supported by columns, also with bored piles (as I'll be emphasizing strength and stability).

That sounds stable enough for the foundation. I'm using XSI mod tools to design, but its kinda limited. I'll need another software....

Hello zultekmilennia,

I would suggest that you get a geotechnical evaluation of the site before making any firm decisions regarding the design of your foundation. If the site is suitable for a slab on grade under the pool, piles should not be used. The slab should be free floating. If it wants to move, it must be free to do so. Piles would prevent that free movement. A slab without piles will float up and down as dictated by the soil. If movement is restricted by piles, the slab may crack from flexural stresses or may even fail by punching shear around each pile. Piles are simply not appropriate in this situation.

If the site is not suitable for slab on grade, you will be faced with the substantial costs of a structure, designed to carry the entire load from pile to pile. In this case, the piles could be closely spaced to preserve a modicum of economy, but it will not be an economical structure.

The stands, as you call them, or bleachers, could be supported on piles, caissons or footings designed in accordance with parameters established by a soil report. Needless to say, the bleacher structure should not be tied to the pool slab.

Without some idea as to the geotechnical conditions at the site, it is really not possible for anyone to provide specific answers to these questions.

Finally, I am not familiar with XSI mod tools. It would not have occurred to me to use any type of software to design this project. Perhaps it's not another software you need...it's another engineer!

A gallon of water weighs 8.33 lb.

US or imperial?

sorry about that... U.S gallon @ 8.33 lb. avoirdupois

I'd do it manually, but with the advent of technology, I want to sharpen my skills with computer usage. I'm planning to take a short course on Primavera next, anyways.

The land area is unstable and weak, but I haven't been informed of the soil type and condition. Its not really my project, its my uncle's.

But he told me to give it a try and show him the results. I'm doing a lot of research (dusted out all my old books) and learning along the way. I've thought out the design, but I'm still inexperience in foundation types. That's why I needed some help. Maybe a general idea of what kind of foundation used in weak and unstable areas point me in the right area. I can do the research myself.

The land area is unstable and weak, but I haven't been informed of the soil type and condition. Its not really my project, its my uncle's.

How unstable...how weak...and to what depth? How can you or anyone else make an intelligent decision respecting foundation type when you have no understanding of the soil conditions on the site.

The soil may be too unstable and too weak to use footings or even piles. Perhaps the best thing to do is to abandon the site in favor of a more suitable location. Perhaps your uncle expects too much of you or perhaps he is pulling your leg.

The total weight isn't really what you want to know, but it's nice to know. You want to know the pressure exerted by the water at a certain point. The pressure is the unit weight times the depth, so at the deep end of 12 ', the pressure is 62.4x12=748.8 pounds per square foot. That's a pretty light loading, really, most soils will handle that pretty well.

Yeah, I kinda had that feeling at first. I've only done menial tasks up until now (still haven't got my degree) but I'll push him for more details. Maybe in a few days, I'll be more well informed of the situation.

He won't really use my design, but maybe this'll land me a recommendation from him, which kinda helps when I finally graduate.

By excavating the site for the pool to be below grade, it'll definitely be better and even though it'll exert pressure onto the sides as well, the load can really be ignored as it is insignificant. At least that's what I concluded after some minor research.

I asked my uncle why didn't he just changed the site, he said that the client gave him the site, and told him to build the pool there. In this business, its either you can or they'll give the project to someone else. In other words, make it work or just find another job. Talk about a cutthroat field.

Anyways, I've left out the type of foundation to the side and focused on the superstructure. Is there a need to add any kind of special structure like a baseplate under the pool, so that in case of any movement, the entire pool will move instead of individual sections, causing cracks to appear?

When the client gave your uncle the site, he should have given him the soil report too. It is essential before any design can be done. It is better the job be given to someone else than to continue under idiotic conditions. In the end, clients like this don't pay anyway, so what have you lost?

You cannot focus on the superstructure. The pool doesn't have a superstructure. It is all foundation. I don't know what you mean when you refer to a baseplate under the pool.

Ignore the baseplate part. It was my dumb attempt at design innovation. I'm still trying to get the soil report from the engineer in charge. I called him up (his sister, actually, but that's another story) and he'll see what he can do. Don't know what that means..

Anyways, anybody got any reference picture for the foundation design? I'm stuck a little here. I need maybe a cross-section diagram of the stands (and the pool too, if that's not too much to ask).

You need to figure out what the soil bearing capacity is. Then calculate the load. Finally, design a foundation that will distribute the load such that the capacity of the soil to support the structure will not be exceeded.

If the soil does not have sufficient bearing capacity, you may need to drive piles down to firm ground below. A pool must be designed to resist buoyancy forces when empty. You will need to find the high water table.

Be sure to provide safety factors and design to meet any building codes within the jurisdiction.

btw, if you use two different kinds of foundation (I'm assuming raft and piles) you need to figure out how to connect the slabs between the two parts in order for it not to effect the advantage of using a buoyancy raft.

I'm not really experienced in this matter, so maybe a more veteran member of the forum can help.

You must have a soil report. To be able to adequately design a foundation for a swimming pool you will need the following:

• ground water levels (buoyancy when the swimmimg pool is empty)
• type of soil to at least a depth of 2m below slab level for a raft foundation
• type of soil to at least the base of a pad foundation
• type of soil to at least the depth of the pile (generally between 6m and 12m depending on the type of soil encountered)

The soil report is commisioned and paid for by the client but the specification for the soil report is prepared by the engineer. You will need to stipulate the type of loading that you think will be put onto the different types of foundation (it is worthwhile investing in a good foundation book: Tomlinson is the best in my view - google "tomlinson foundations"). you should ask for recommendations as to the type of foundation that is most suitable.

You can get a hold of the local geotechnical map to get an initial idea of the type of soil. You can also ask the local building authority as to what type of soils are encountered in the area and what specific problems are often encountered. these should be highlighted in your specification.

One specific problem of swimming pools is the buoyancy of the empty pool. The soil you have removed needs to be anchored down to the ground. I have already designed a house with piles simply to be able to anchor the basement down due to buoyancy. Another solution is to make the base slab thicker. It depends on the amount of buoyancy that you have to design for. Ground water levels are important for this.

Is the soil clay? will it present expansion problems in dry/wet conditions? Clay soils expand and contract depending on the water content.

There is alot to do and understand. It really is worthwhile buying Tomlinson as it will serve you all your working life.

Tomlinson, huh? Maybe I'll get around to buying it. It'll be helpful for my work and less taxing than going to the public library all the time.

Thanks.