Construction is underway on Dick’s Sporting Goods in what is perhaps the most visible sign of Lakeshore Mall’s $20 million-plus redevelopment efforts. Workers spent Wednesday afternoon pouring footings at what will be the 50,000-square-foot store, filling an empty space between Sears and J.C. Penney Co. and the rest of the mall. “We’re thinking the soft opening for the store will be in early October,” said Kirsten Boettcher, the mall’s marketing manager.