The trees on one's grave have grown large enough to be embraced, implying that the person has been dead for a very long time. It can also be used as a harsh or sarcastic remark to suggest someone is about to die or should have died.
那个老项目的负责人已经退休多年了，恐怕他那时的计划如今墓木已拱，不合时宜了。
The person in charge of that old project retired many years ago; I'm afraid his plans from back then are now completely outdated, like trees on a tomb that have long grown large.
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