Residential Foundation Protection While Jack-Hammering

Please appoint & consult an structural consultant to study & find solution.

Actually for most jurisdiction a geotechnical engineer would be more appropriate, or a civil trained in geotechnical engineering.

Your putting in the main line ? Call the head engineer or the county/city/town lawyer. Not you fault the rock is there and ALL CONCRETE CRACKS!!!!!!

I am the design engineer. This alignment was not the chosen route, the homeowners convinced our real estate department to put the line here. THis is a change order, and there was no time to do any borings to see if rock was present. Now I have to deal with the situation.

Get the lawyer out there!

Odd situation, installing a new sewer main to a 30-year old house. Maybe your real estate dept. needs to be the ones to soothe the owners, but I can't think a hand-held jackhammer would be powerful enough to transfer the kind of energy it would take to crack a floor or wall. A ram-hoe on a loader could, but that's a couple of orders of magnitude more powerful. In any event, photos now will document the current state so future hammer work will be covered.

I am installing water and sewer in an adjacent neighborhood that is presently on well and septic. After 35 years, the wells and septic systems have all but quit working. I had to cross this particular property to tie into an existing sewer main. No other options because of topography.

Thanks for the help.

You should take photos of the existing conditions, at least what exists now before continuing.

The cracks in the garage are probably old. It is unlikely that a medium jackhammer could be the cause of cracking in a concrete slab, even if it was right next to it. Think of what it would do to the operator if it could create enough vibration to crack an adjacent structure with a jackhammer!!

Look closely at the cracks. The presence of dirt or organic material in the crack would indicate they are not new.

There would normally be a pre-blast survey done to document the pre-existing conditions and to resolve construction claims.

There are instruments which measure the velocity of the shock wave not to exceed some value known by the geologist to be of concern to the adjacent buildings and structures.

Can you scratch the rock out with a pick fitting on a backhoe? Will the rock peel if you get a face exposed? Can you directional drill the sanitary sewer through the rock?

Is a lift station and a force main an option?

These options will not create the shock waves that can crack concrete. But they are more expensive.

You will not be able to isolate the existing concrete from energy waves if you jack hammer the rock. Before you proceed with a jackhammer, video tape all exposed concrete areas. Video tape all your progress. Get the appropriate insurance. Definitely get a lawyer. And be prepared for it to get nasty cause it will.

Check out the way of braking rocks with chemicals.

You drill holes and fill the hole with a chemical mix that swells over night and burst out the rock.

You can drill many holes and fill them all at once. Be sure to cover the rock like a blast site to prevent chips from going thru a wall or window.

Only if a lawyers agrees to this.

My qualifications: I'm a registered PE in 5 states and have about 15 years experience in heavy civil design and construction. So, for what it's worth, my suggestion would be to avoid the situation altogether. Any damage sustained (or perceived) to the existing structure could easily be blamed on you. While it is difficult to prove to anyone familiar w/ this sort of thing, your judge will likely know squat about structural or geotechnical engineering. There is also precedence for this sort of thing, I've actually been involved in cases where homeowners have sued the Army Corps and AZ Dept. of Transportation as a result of this sort of thing-and they won! These cases are not at all uncommon. But, if you decide to press forward, most municipalities will have code governing this sort of thing: you'd be looking for language pertaining to "vibration damage thresholds" or "vibration set-backs". If you live in a small town w/ no significant local government (no published standards), try your state DOT construction standards-they should be available on-line.

Contrary to what seems to be the opinion at large in this thread, it's not the damage to the concrete you need to worry about, it's the differential settlement of the soil beneath the foundation that will give you problems. The vibrations will liquefy the soils (just like an earthquake) and cause the foundation to shear in places, then it's all downhill from there. Do as you wish, but I doubt the risk is worth what you stand to be paid, especially if you don't have hefty bonding capacity for company... you might just end up buying the house....

Harmonics can cause strange things to happen. It may not be the size or magnitude of the instrument (jackhammer) being used but the sine wave frequency. I would not rule out the damage being caused by a jackhammer.