seismic upgrade - verifying foundation integrity

Question

We want to do a seismic retrofit on our foundation. House built in 1904. No cripple wall. Mud sill with rim joist. Foundations have a recent skim coat (that we did not do). Concrete slab.

So the question: Is there a way we can test the foundations (without doing irremediable damage) in order to test whether the foundations are reasonably solid (for a 100 year old house). For example, drill a 1/2 inch diameter hole and see if the hole maintains its shape? Install an epoxy anchor bolt and see if it holds? Thx

Answer 1

The issue with old building foundations is usually settling, which shows up as wall cracks. The underlying culprit is generally inadequate footings, if there are any. A solid foundation still cracks if it settles. Also, a solid foundation isn’t necessarily congruent with a seismic foundation. An earthquake can break any solid foundation. Foundations designed for seismic activity include flexibility, and/or the capacity to allow for some building sliding back and forth, to ride out the shock waves of an earthquake.

Compression testing (as Sam Lee mentioned) came to mind when you asked about testing see how “solid” the old foundation is. Core samples of your foundation walls are crushed under a hydraulic press. Then you know the compression strength of your concrete (if that’s what the foundation was constructed with), but I don’t think that information is particularly useful. The foundation has been holding up the house for 120 years. It is probably solid enough.

What you want to know, for seismic activity, is how well the foundation sways sideways and rides up and down – to accommodate an earthquakes P and S waves. The solidness of a foundation doesn’t have much to do with its ability to handle a seismic activity.

Answer 2

Yes, you can have old concrete tested and certified. Usually a concrete testing agency will take several samples (they’re called “cores”) and then use the average value. (Contact your local Building Code Department or your local concrete supplier for a reputable testing agency.)

Then, a structural engineer (not civil engineer) or an architect can design a structural plan.

However, a word of caution. If you don’t complete all the retrofit work, you’ll need to disclose to the “buyer” when you go to sell the property. Otherwise, you’ll be liable if the buyer ever discovers the seismic work was never completed.