M and Q represent the bending moment and shear force, respectively.

M Q 分别代表剪切力。

Under the action of the bending moment, as shown in Figure 7, the upper part of the lining segment bears tension, and the lower part bears pressure.

在用下，如图 7 所示，衬砌段上部承拉力，下部承压力。

Then, the bending moment M and the shearing force are 0 at both ends, and they are determined, respectively, as follows: By solving (1)–(3), the external load q(x) at the existing tunnel position caused by the surcharge can be obtained.

然后，两端 M 剪力均为 0，分别确定如下：通过求解 （1）–（3），可以得到由附加物引起现有隧道位置外部载荷 q（x）。