短语词组短语underdrainage ditch 暗沟subsurface underdrainage 地下排水subsoil underdrainage 地下排水underdrainage system 地下排水系统close underdrainage 封闭式渗沟ditch of underdrainage 地下排水沟pipe and strainer underdrainage 滤管式地下排水管渠 返回 underdrainage