The clay could be making it difficult for the raspberry roots to take hold, although they're not particularly finicky about soil as long as it is well drained. Gently dig up a clump and inspect the roots. Look for lighter colored roots that show signs of new growth. Also, there should be some sign of life aboveground at this point, even if it's just a small floret of green by the base of the old twigs. If you don't see that, call the company where you got the stems and let them know.
Luke Miller, editor
Garden Ideas & Outdoor Living magazine