过河拆桥

1.burn the bridge after crossing it; be ungrateful and leave one's benefactor in the lurch; cast sb. aside when he has served one's purpose; discard one's helpers after their help is made use of; kick down [away; over] the ladder; kick out sb. after his services are no longer needed; One is hardly safely across the stream when one breaks down the bridge -- ungrateful.; remove the bridge after crossing the river -- leave one in the lurch; remove the plank after crossing the bridge