Horizontal Directional Drilling (HDD) caused distress?

[dylansdad]

A utility subcontractor was installing a casing under an existing building using HDD and drilling mud. As soon as "breakthrough" was achieved, the occupants of the building noticed a loud popping sound. Some of the interior sheetrock walls cracked (slightly) and there appeared a noticeable (on one wall only) stair stepped crack in the brick veneer wall. The crack was wider at the top (near the frieze board) than at the bottom. The crack exists not only at the mortar joints, but in some cases through the brick itself. Some interior rolling files would not roll as easily. This happened approximately one week ago, and the building seems to have "settled" down. The rolling files stay put now and doors close tighter. The conduit is approximately 3-4 feet below the building and is 10" diameter. The building is of concrete slab on grade construction with a turned down edge beam. My question is could the pressure induced from this drilling operation have caused a "lift-up" of the exterior edge beam? By all appearances this is what happened.

 

[dik]

Some questions/ramblings:
What is HDD? Is the process fully sleeved to prevent the pressure from escaping? What pressure is the HDD and drilling mud injected at? Can the sleeved area be inspected by cutting out a portion of SOG? Was there an existing condition report undertaken? Were the cracks reviewed to confirm that they are recent? Often cracking has been around for several decades, before people realize something is cracked.

If there was a leakage of HDD and drilling mud and even a small pressure 5 psi is equivalent to 700 psf... and can cause some real issues. If the system is closed, it's a matter of determining if leakage has allowed HDD and mud to lift the grade beam. Was there a void underneath the grade beam.

Dik

 

[dylansdad]

dik,
You asked some of the same questions that I had asked the prime contractor. HDD also known as horizontal directional drilling involves the advancement of a casing behind rotary cutting heads and drilling mud. There are no sleeves involved. The electrical contractor told me that he had seen asphalt pavement "rise" and then settle down in similar parking lot work. I do not know the pressures involved and there were no "existing" condition reports available. This major veneer crack was simultaneous with the punching through of the cuting head on the opposing side. I hope that I have answered the majority of your questions, and I do not know if there was a void underneath the grade beam or not. Thank you for your time.

 

[GeoPaveTraffic]

In short, yes the HDD could have raised the building. It could also lead to settlement of the building in time. Placing a 10" HDD only 3 to 4 feet below a slab on grade building...generally sounds like a bad idea to me.

I would say that the contractor has some interior remolding to do.

 

[dylansdad]

Guys,
Thanks for the replies. This work is part of an expansion project for this building. The brick veneer wall that cracked was coming out anyway. When we excavate for the new grade beam for the addition, we can investigate this matter more in depth.

 

[dik]

Was the foundation beam 4' deep and did he cut through the bottom of it?

Dik

 

[dylansdad]

Dik,
The foundation edge beam bottom is approximately 2' below the floor slab, and I have been corrected that the conduits are approximately 6' below the floor slab.

 

[dik]

I think it will have to wait until you get a chance to look at the areas damaged... you can possible tell which areas may have been uplifted... any idea of the pressure?