Arch Coal, the second-largest U.S. coal miner, filed for Chapter 11 bankruptcy protection on Monday with a plan to cut $4.5 billion in debt from its balance sheet in the midst of a prolonged downturn in the coal industry. Arch Coal, saddled with debt since its 2011 acquisition of International Coal Group, has been suffering from a sharp drop in coal prices, stricter pollution controls, falling demand from China and increasing competition from natural gas. “Over the past several years, a confluence of economic challenges and regulatory hurdles has hobbled the coal industry,” Chief Financial Officer John Drexler said in a filing with the U.S. Bankruptcy Court in St. Louis on Monday. Shares of leading U.S. coal producer Peabody Energy Corp hit a record low on Monday and were still down 18.7 percent in afternoon, after Arch warned that 2016 pricing is expected to be weaker than initially feared.