For the time travel lovers, I am looking for a book of short stories where one of the stories is about a crew of scientists that travels in time into the future and learns that a disaster has taken place way in the future and they try to determine what really happened and when that happened. As a consequence of this disaster humans have taken an appearance very different from ours--more like monsters in appearance but they are very peaceful in nature and have the disturbing habit of burying themselves alive. They don't speak any of the languages we know today and the scientists. while trying to unbury all the creatures, also try to learn their language in order to communicate and get more information of what happened and when that took place. In the end they manage to communicate with one of the creature and she tells the scientists of two disasters that have taken place.
That's "The Failed Men" by Brian Aldiss. It's collected in "Man in his Time".
EDIT: I didn't realize the answer needed more detail, since the story matches so well in every detail I'm sure that's the one. Time travelers go to the future and try to help a race of humans who look rather monstrous but are very gentle and unresisting and who have an odd urge to bury themselves alive. The travelers don't understand this apparently suicidal impulse, and even when they manage to translate their language, they only know the words, and can't understand the meaning behind their actions.