洞门【tunnel portal】指的是为保持洞口上方及两侧路堑边坡的稳定，在隧道洞口修建的墙式构造物。
这个洞是巢的门。
每个房间后面都有一个55加仑的鼓形炉，前面有一个门，后面有个带两个管道的烟囱洞。
Behind each chamber is a 55-gallon-drum stove with a door on the front and a chimney hole with two pipes in the back.
那两门炮用实心炮弹瞄准墙的中部轰击，为了打开一个洞，只要能造成缺口，就发起突击。
The two cannons were now discharging ball against the centre of the barrier in order to make a hole there, and, if possible, a breach for the assault.
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