衬砌是沿隧道开挖周边修筑的永久性支护结构物 ,国内采用的衬砌类型主要有下列几种。·整体式衬砌———用模筑混凝土或砌体施作的衬砌。该衬砌内轮廓形状、尺寸与截面厚度 ,百余年来虽经多次改变 ,但至今在山岭铁路隧道中仍占主导地位。·装配式衬砌———由预制构件在隧道内 Lining is a permanent support structure built around the excavation of the tunnel. Lining types used in China mainly include the following types. Monolithic lining - lining made of concrete or masonry. Although the shape, size and cross-sectional thickness of the inner lining of the lining have changed several times over the past hundred years, the lining of the tunnel still occupies the leading position in the mountain railway. Assembled lining - prefabricated components in the tunnel