the most possible answer is "make a hole" but you'd better tell me the context because this words sounds weird to me.

depend on what you wrote, 開洞 means to make a hole. but 開動 could means something begin to work for example 火車開動了 or means begin to eat for example 大家開動or sometime the elder in the table would say 開動, than everybody star to eat.

是洞开还是开洞？如果是开洞，那就是make a hole的意思；如果是洞开，就是像洞一样敞开着，形容开得大，而且畅通无阻。

yes