The Truth About Monopole Foundations

There is nothing scarier than digging your first monopole foundation. An augur pulls up and starts drilling a hole in the earth about five feet in diameter, and you have no idea what’s down there. Here are some ideas on what you’ll hit, and what it may mean.

Utility Lines

I’m hoping that you never forget to call to get all underground utilities located. Hitting a utility can be a very expensive problem. Or, in the case of fiber-optic phone cable, it can easily bankrupt even a moderate size company. Before you ever dig, call the one-call center for underground utilities in your market, as well as city hall to see if there are any minor utility lines that one-call does not have in their system.

I’m sorry to say that I have hit almost every utility over the years except fiber-optic cable and natural gas. Even if you get the utilities marked by the utility company, they often miss the target and you can still hit them while drilling. You often also hit utility lines that are really abandoned, but they scare you to death until you realized they are de-activated.

It’s always a good idea to stand by the edge of the hole you are drilling and look down it each time the augur pulls the drill out to throw the dirt off. You will see any utility line you have hit, or any water or other item gushing into the hole. Not that you can do much about it, but it makes you feel good when you’ve reached the bottom and not hit anything. If you are going to hit a utility line, except for a main transmission line, you will hit it in the first six feet or so. Since most monopole foundations require drilling to 15 feet or so, the pressure is off after about 1/3 of the way down.

If you hit a utility line, do not panic. First determine if the line is still an active line. Over the years, there have been millions of lines laid that have been replaced with newer, bigger ones. A 1930s water line has probably been replaced with a new, bigger one in the 1970s. If you hit a line and it is bone dry, it’s a good bet that it is no longer in service. If you hit a utility line and stuff starts pouring out, then stop digging and call the utility company. If you hit anything but fiber optic phone cable, then you will survive the hit, even though you are going to get yelled at. As long as you had the utilities mark their lines, and you do not dig where they marked, you should be O.K. on liability.

There are several utility lines that can cause extreme damage or death if you hit them, and you must be extra careful when digging near them. The first is natural gas. If you hit a natural gas line, it is very likely that it will kill the guy digging the hole, and the resulting fireball may burn down half the block. If you see gas meters in a line, and you are digging in that straight line between meters, then you need to double check your line locate. The same is true with underground electricity. If there is any question in your mind that you are clear, then don’t dig until you are 100% sure. Also look for small warning signs that may be on poles in the vicinity that you are digging that say “warning –underground gas line”. Even though you may be held innocent in the trial because you had the utilities marked, causing a major explosion and fire will tie you up in court for years, and certainly put an end to your billboard project.


Even if you don’t hit a water line, your hole may start filling with water during, or after, the digging has commenced. This can be the result of high levels of water in the soil, or an underground aquifer. Most drilling companies can handle this problem – but at an extra, significant cost. They put a steel pipe down the hole as they dig it, a process called “casing” the hole. This keeps the sides of the hole from collapsing. The water itself will not harm the drilling machine. But you can’t drill in mud unless there is pressure on the sides to contain it.

In minor cases of water, a simple solution is to order custom-crete, as opposed to concrete, to fill the hole after you put the sign’s column in. You can order this dry, and the water in the hole mixes with the concrete and soaks it up. This process works really well in the right application, but requires an experienced concrete guy to monitor the mix and the amount of water. When you consider the fact that they build bridge piers under water, you can see that your project is not that big a challenge.

Occasionally, the sides of the hole will collapse near the bottom of the hole, due to water seeping in. This normally has no negative impact on the foundation, as long as the depth does not change. You just pour the concrete anyway. Effectively, you have a bigger foundation now, shaped like a bell. Some consider this a better foundation, since you can’t really ever pull it out of the ground.


Rock is very scary, because you can feel the cost of construction skyrocket when rock is struck while digging. Again, don’t panic until you get the facts together. Sometimes, the “rock” is an old concrete slab, which can be knocked out in a few minutes with a jack-hammer. Other times, the rock is a boulder, which can be pulled out. And some rock is fairly soft, like limestone, and digging, while slower, can continue along just fine (although they are still going to bill you extra for it). The worst rock to hit is just that – solid rock. It requires a special rock cutting blade on the augur, and very time-consuming methods of drilling tiny coring holes, and then expanding them. How much more will it add to your project? Many thousands of dollars. It all depends on how far down you got before you hit rock, and far you have to dig to hit bottom.

If you are terribly concerned with the possibility of rock, you can ask neighbors who have built buildings and fences if they hit any. Or you can hire a soil sample to be done, to determine if there is rock and, if so, how deep it is under the surface. These test are expensive, so I would consider them a last resort, unless the economics of the sign are so marginal that you would not want to build it it rock is present. Other Items

There really is not much of interest in the hole normally. I always hoped for buried treasure, but never found anything of monetary value, unless you recycle old aluminum cans. I also never came across an ancient Indian burial ground, or Tutankhaman III. So the things I’ve already described pretty much sum it up.


Digging a hole is filled with uncertainty. But as long as you have had all the utility lines located, there is not much more you can proactively do except to stay close by and watch. If you see any evidence of utilities being present, even if you had a line locate performed, hold up on drilling until you get a second opinion. Unless you are scrambling to build the sign before the permit runs out, there is no reason you can’t wait one more day.

And if you hit anything, don’t panic (with the exception of fiber-optic phone cable, in which case you should just pack your bag and head for Mexico) until you get the facts. There is nothing out there that has not been hit before, and there are a million quick fixes to every eventuality.

So it will all be O.K. Dig it?

Frank Rolfe started his billboard company off of his coffee table, immediately after graduating from college. Although he had no formal training on the industry, he learned as he went, and developed his own unique systems to accomplish things, such as renting advertising space. Frank was formerly the largest private owner of billboards in Dallas/Ft. Worth, as well as a major player in the Los Angeles market.