Why do you sometimes see a row of square holes dug in the street?


In his reply for this 1990 SD Classic, Cecil answers the question concerning why the holes are dug with his customary elan.

For reasons best known to himself, he fails to address the point regarding filling in these holes with cement. If the observations of David D. of Chicago are to be taken at face value I think this is worthy of comment. I say this because there is a water main running outside my house which, for some unfathomable reason, sprang a whole series of leaks several years ago. On every occasion a leak was fixed the work crew refilled the hole with soil and spread tarmac on the surface.

Is it in fact more likely that such holes in the Chicago streets of 1990 were refilled with soil and then topped out with tarmac (or with cement for a cement road)? Or were these holes really filled with cement as David D. records?

Oh, holy crap! A question I am qualified to answer!!! YEAH!
A: There are gaslines, waterlines and cables of all stripes buried under us. When new construction, or major renovation goes in, potholing must be done to visually ID what is in the ground at what depth before we dig and strike, a gas main, water main or fatally, a power cable. My company fills potholes with base rock (3/4in rocks in sand and dirt) compacts the base rock with a power compactor called a powder puff then caps the hole with cold mix, that is asphalt with an additive to keep it supple. The reason the holes are often square, we use a concrete saw (yes, even on asphalt) to give us a nice clean square.

The holes aren’t always square anymore! Sometimes we are able to/required to use a coring machine, which cuts a perfectly circular hole.

OK thanks.

I assume that all the material removed from the hole is returned to whence it came on refill. You then add the base rock and compact as described.

Only when you dig the “hard way”, that is with a shovel, the easy way is to use high pressure water pushed through a nozzle that rotates and while sucking out the detrius with a 4" high powered vacuum. Really beats the hell out of kicking a shovel…

If the square holes are at regular intervals, it could be a result of a water main rehabilitation project.

Water mains frequently become clogged with sediment and rust scaling, not unlike the way that cholesterol clogs blood vessels. Our engineering firm has pipe cross sections from towns where an eight inch water line is so congested that you can’t fit your finger into the free hole. As you can infer, this limits the flow and pressure that the line can provide.

If the old lines are considered to be structurally compromised, or if they are asbestos-cement lined (not uncommon), they are slated for removal and replacement.

However, if it is determined that the structural quality of the pipes is acceptable, towns put out bids to contractors to ream out the pipes, and to provide a cement lining. Frequently the water mains run parallel to the centerline of the road, so a square hole is dug into the pavement to access the water line. The distance between the holes is determined by the maximum reach of the pipe cleaning equipment. When this work is being performed, you will frequently see a temporary line running along the curb to provide service to homes and businesses until the work is completed and permanent service is restored. The lines are flushed to get rid of the cleaned material, but there is usually some residual material that will come out of the tap for a few days.

States and towns have their own standards as far as excavation and backfill within a public way. This is to prevent settlement and subsequent potholes. In major projects such as water or sewer or drain line replacement, the agency may require that the trench receive a temporary bituminous concrete (asphalt) patch. In the Northeast, ideally, the trench should go through one freeze thaw cycle (i.e. winter). That will aid in the compaction of the backfilled soils. The temporary patch would then be removed, and replaced with a permanent trench patch. When this is not possible, or for smaller projects, towns may require that the contractor place some depth of cement concrete before covering with bituminous concrete.

Somtimes, often times around here, the concrete is cut in such a manner to repair the road. Cracks and seams start to split and potholes form. If you take out the bad concrete and compact the ground underneath then add re-bar for strength (tying it into the surrounding concrete) and pour new concrete you just saved yourself a complete road job in a few years.