(1) The milk passes right through the channel,only to get a little thicker and sweeter.
(2) He turned up the driveway,only to find his way blocked.
这两句都是非谓语动词作结果状语,常放在 only 或 never 之后.
第一句是预期的结果,to get the milk thicker and sweeter （令牛奶更浓更甜） 是目的.
第二句是与预期愿望相反或意料之外的结果,turned up the driveway的意思是把车开上车道,不料发现路已被堵.