While I am all about examining literature for symbols and their meanings, I'm not sure everything we read in every novel has to have some deep, hidden meaning. As an English teacher, I have heard this complaint more often than any other, and it is valid criticism. I will certainly not disagree with the interpretation presented in post #2, but I will suggest a much more mundane explanation as a possibility: Raskolnikov is in a nearly permanent state of delirium after he commits the murders, and he dug a hole bigger than he needed because he was not paying close enough attention. We know he was in a hurry to put the stolen goods somewhere other than in the wall of his apartment, and we know he barely knew what items he was burying because the murders were not really about stealing or profit. It may have just been a simple case of over-digging.
Wow. Post #2 is probably the beginning and end of this discussion.
Just to chime in though, I read the protagonist's continued mistakes as symptoms of his decline into moral and psychological fatigue.
The novel "Crime and Punishment" is an examination of the guilty conscience. For the author, guilt is the knowledge that one has done wrong and has become estranged from society and from God. From the very beginning of the novel, Raskolnikov (whose name comes from the Russian word for "schism") suffers from this separation. In murdering the pawnbroker, he seeks to prove that he is above the law. But his crime only reinforces his separation from society and from God. In Western society, a rock is a universal symbol for Jesus Christ. ( In fact, He is called "the rock" in I Corinthians 10:4). When he buries the stolen goods under a rock with a space between the rock and the goods, this reinforces the idea that he is separated from God ( the rock). The space represents the chasm that exists between Rodya and God because of Rodya's murder of the pawnbroker and her daughter.