There is indeed a lot of violence throughout the novel, but I would argue that it is far from gratuitous. In answering this question, one needs to look at the historical time period in which the story is set. This was a time of labor unrest, in which an increasingly restless workforce ranged itself against bosses who'd previously had things their own way. Inevitably, such conflict rapidly degenerated into violence, and large-scale disturbances frequently broke out across industrialized America.
An example of one such disturbance, albeit fictionalized, is given to us in The Clearing. After Randolph makes the fateful decision to shut down the local mill, the workers don't take it lying down. They embark upon a campaign of vengeful violence, which has an intensely personal aspect to it. Though extreme, such violence isn't in any way gratuitous as it's perfectly in keeping with how feuds—and a feud is precisely what this labor dispute has become—were conducted.
In depicting violence in such graphic terms, Gautreaux is attempting to illustrate the fraught relations between the classes at that point in American history. Even today, many people still hold to the comforting myth of America as a classless society. In showing us the true nature of class relations in a capitalist society, red in tooth and claw, Gautreaux is challenging that myth in the most empathic way imaginable.