The construction of a Walmart Supercenter at 160 Broadway (Route 138) is nearing completion. Walmart, which began building the 155,000-square-foot store about a year ago, plans a grand opening March 12, Christopher Buchanan, a Walmart official, said by e-mail. The facility joins an existing Supercenter at 36 Paramount Drive, to become Walmart’s second in Raynham. About 300 people will be employed at the new store, which will offer a grocery department, a garden center, and tire and lube services, in addition to its main general merchandise, according to Buchanan. He said the facility will have a number of “green” elements, including a state-of-the-art energy-management system. “We are very excited about this new store and continuing to save our Raynham-area customers money so they can live better,” Buchanan said.