护坦的排水结构有以下三种型式:(1)明排水型式。为了防止排水孔孔口发生气蚀现象,它仅适用于水流流速小于15米/秒的护坦。此外,在多沙河流上也不宜采用此种型式;(2)暗排水型式。此种型式不受流速及挟沙量的限制;(3)封闭排水型式。此种型式也不受上述条件的限制,但在下述两种情况下,采用此种排水方式更为经济。消力池内没有隔水墙,采用此种排水型式的消力池护坦对隔墙的稳定有利;消力池水跃跃首在各级流量下,上、下游摆动范围很大,采用此种排水方式可以减薄摆动范围内的护坦厚度。岩基上护坦抗浮稳定设计常凭经验确定,我国、苏联、日本、美国等国家均未形成规 Protector drainage structure has the following three types: (1) Clear drainage type. To prevent cavitation in the drain hole, it is only suitable for shields with a flow rate of less than 15 m / s. In addition, this type should not be used on the rivers of the Dousha River. (2) Dark drainage type. This type is not subject to flow rate and sediment discharge restrictions; (3) closed drainage type. This type is not subject to the above conditions, but in the following two cases, the use of such drainage is more economical. There is no wall in the stilling pool, and the use of this type of drainage tank is beneficial to the stability of the wall. The still water in the stilling pool is at the first flow rate at all levels and has a large swing range in the upper and lower reaches. Way to reduce the swing range of the shield thickness. On the rock-based shield anti-floating stability design often determined by experience, China, the Soviet Union, Japan, the United States and other countries did not form a regulation