Several miners were trapped in the collapsed tunnel for over a day before rescue teams reached them.

were 是 be 动词的过去式复数形式，在这里构成被动语态，表示"被..."的状态。 trapped 是动词 trap 的过去分词形式，trap 本意是"设陷阱捕捉"，引申为"困住、使陷入困境"。在这里与 were 一起构成被动语态，表示"被困住"的状态。