Q.: We are concerned about future settlement of a low-rise building. It doesn't seem practical to take the foundation all the way to bedrock. The soil is sufficiently compressible so that settlement is certain. What is a good method of stabilizing the elevation?

A.: Prestressed rock anchors have been used for this purpose. Anchors into the rock or soil are attached to the foundation and post-tensioned. The post-tensioning forces are of the same magnitude as the future design load. This compresses whatever layer or layers of soil might otherwise permit settlement of the structure.