I have reviewed the posts on this forum with interest, because it seems very hard to find useful information on the web, with regard to diagnosing foundation problems, and determining rehabilitation options. This is going to be a bit of a longwinded post, but I want to give enough background.
I own a 1930's home, built on very sandy soil. I am still learning the terminology, but I believe the foundation is a "perimiter wall" foundation.
The street, that my house faces, has a substantial slope. Facing the house from the street, the right perimiter wall, perpendicular to the street, is roughly a foot higher than the opposing wall, due to the "uphill" slope. The right perimiter wall extends about a foot above the floor-slab, whereas the floor-slab intersects the left perimiter wall just about at it's top. The perimiter walls are about 12 inches at the bottom, and 8 inches wide at the top.
The soil is sandy, and there are no drainage problems at all.
With that as background, we come to the "issues". The above-grade surface of the foundation is flakey and crumbly. I can pick gravel out with my fingers. There are substantial vertical cracks in both the left and right perimiter walls that crack the walls clean through from top to bottom. The cracks appear only modestly wider at the top than at the bottom, and the house is quite level. THe crakcs look very old. The below-grade sections of foundation are in much better shape than the above-grade sections, but still chalkey. I dug out all around the house to get a good look, and you can see that the corrosion of the foundation begins above the dirt line. Efflourescence is visible on the inside of the perimiter wall.
I read, here http://www.abag.ca.gov/bayarea/eqmap.../PT10-Ch-5.PDF
that the foundation perimiter wall can be replaced in sections. This document also states "Shoring can be omitted when replacement is done in small sections at a time. The latter technique is popular for occupied structures."
Given the MASSIVE scale of a "lift and replace" job,in-situ rehabilitation is attractive.
I am considering an addition to the home, and I want to think out my options for rehabilitating, replacing, or ignoring this issue.
Any suggestions for test methods to diagnose issues with the concrete composition? Any suggestions for addressing or investigating these issues would be appreciated.