The presence of a jackhammer or the evidence that one is being used in a dream signals that great change is taking place and that change is an eradication of things from the past that used to seem permanent.
Jackhammer
This incredibly noisy tool of destruction is capable of busting through very strong material in order to build something new. In this way, it symbolizes the ability to break open structures of the past that seem permanent but with great effort can be released in order to create a new set of habits, ideas, or consciousness about your life.