特长隧道的埋深常达到百米甚至千米以上,成为特长超深隧道。本文根据这类隧道在含水层中的埋 置深度大、初期涌水以弹性释水为主及围岩渗透系数随深度增加而递减等特点，将隧道概化为补给边界附近隧道最大涌水量的计算模型。 适当简化后，该模型与现有的部分模型相吻合。

The thickness of overburden of extra-long tunnels often amounts to hundreds of meters，even goes beyond 1000 m. Here， an extra~long tunnel whose thickness exceeds 500 mis called extra~U)ng tunnel with superthick overburden. Their depth in aquifers is big and the initial discharge mainly comes from elastic yield. Moreover，the permeability of wall rock gets ofter poorer and poorer with depth. In view of the above aspects， the tunnels are formularized as the wells near boundaries， and the calculation model for maximum discharge rate is got by way of method of images. Having been simplified properly， the model tallies basically with part of the existing relative models.