MELBOURNE, Australia — China is expanding its submarine base on the edge of the South China Sea, with satellite photos showing it’s building two new piers. The imagery of the Yulin naval base on the southern tip of China’s Hainan Island taken by Maxar Technologies on July 31 and published on Google Earth shows the structure for two new piers under construction, adding to the four existing piers at the site. The new piers are being built to the north and south of the existing piers, connected to