... lying indoor, tunnel, underground and canal. Unable to bear external mechanical pulling force and pressure during lay.YJYYJLYCu, Al ... tunnel, underground and canal. Able to bear external mechanical forces, but unable to bear large pulling force. YJY23YJLY23Cu, Al core ... water and large difference of level, able to bear external mechanical pressure and moderate pulling force. YJY33YJLY33Cu, Al core ...