Method and structure for reinforcing totally-enclosed end of double-line shield tunnel

The double-line shield tunnel totally-enclosed end reinforcing method comprises the following steps that a rectangular plain underground diaphragm wall I with a closed horizontal plane is constructed on a shield starting section or receiving section, is tightly attached to a well wall on the outer side of a shield well enclosure structure, and is perpendicular to the shield tunneling direction; the depth is at least 5m lower than the bottom sideline of the shield structure or the wall bottom enters an impervious layer, the width is more than 5m larger than each of the two sides of the sideline of the shield structure, and the length is not smaller than the sum of the length of a main machine of the shield tunneling machine and the width of a ring segment; a middle separating wall is constructed in the middle of the first plain underground diaphragm wall and is parallel to the shield tunneling direction, the two ends of the middle separating wall are connected with the first plain underground diaphragm wall, a